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NANO-SILVER MANUFACTURE PATENTS






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MASS PRODUCTION METHOD OF NANO SILVER
US2006278534 // WO2006135128


Colloidal Nanosilver Solution and Method for Making the Same
US2003185889 //  AU2003225460


STABILIZED SILVER NANOPARTICLE COMPOSITION
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Silver Powder and Method of Preparing the Same
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Reactive, Monodispersed Surface Modified Silver Nanoparticle
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SILVER NANOPARTICLE AND PRODUCTION METHOD THEREFOR
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PRODUCTION METHOD OF SILVER NANOPARTICLE...
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METHODS OF CONTROLLING NANOPARTICLE GROWTH
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Ag NANOPARTICLE, METHOD FOR PRODUCING...
JP2006118010


SILVER NANOPARTICLE AND PRODUCTION METHOD THEREFOR
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PLASMA SYNTHESIS OF METAL OXIDE NANOPARTICLE
JP2005132716


Silver Comprising Nanoparticles and Related Nanotechnology
US2005008861


Synthesis Metal Nanoparticle
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Nanoprisms and Method of Making Them
US7135054


METHOD FOR MANUFACTURING SILVER NANOPARTICLE
JP2003253311


METHOD FOR PRODUCING METAL NANOPARTICLES
WO2008003522



MASS PRODUCTION METHOD OF NANO SILVER...
US2006278534
WO2006135128

Abstract --- Disclosed herein are a method of mass-producing nanosilver, a method of manufacturing nanosilver-coated antibacterial fiber, and antibacterial fiber manufactured thereby. Nanosilver having a size of 5 nm or less can be produced on a mass scale by applying an electric field of 10,000 to 300,000 volts (DC) across two Ag electrode plates equipped in a water electrolysis system and allowing only a microcurrent to flow between the electrode plates. The nanosilver-coated, antibacterial fiber is manufactured by applying a aqeous solution of the nanosilver to the surface of the synthetic fibers, adsorbing the nanosilver onto the cloth using a process selected from the group consisting of thermal fixation, high frequency radiation, bubbling, and combinations thereof; and conducting a post-finishing at 160 to 200 DEG C. And thus, an antibacterial fiber manufactured thereby may be a fundamental solution to the synthetic fiber's problems, that is, poor perspiration functionality and the generation of statistic electricity.
 
BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates to a method for producing nanosilver on a large scale, a method of manufacturing nanosilver-adsorbed fiber, and antibacterial fiber manufactured thereby. More particularly, the present invention relates to the method for producing nanosilver on a large scale having a size of 5 nm or lower by allowing only a minute electric current to flow between two opposite silver electrodes in the presence of a high voltage in a water electrolysis system, a method of manufacturing nanosilver-adsorbed fiber by taking advantage of the better applicability of smaller silver particles, and an antibacterial fiber manufactured thereby.

[0003] 2. Description of the Prior Art

[0004] A variety of microbes are found in large quantities in daily living environments. Particularly, they grow and proliferate on clothes and form flora even on the skin. The microbes degrade fibers or digest nutrients in sweat or contaminants, producing bad odors or causing great damage to the health of humans.

[0005] WHO reports that microbial contamination corresponds to about 30% of the mortality in the world. Unfortunately, current scientific technologies fall short of sufficiently controlling harmful microbes.

[0006] Therefore, it is intensively researched to develop antimicrobial/germicidal agents or products that are satisfied with harmless to human bodies and have improved functionality.

[0007] As representative example of the antimicrobial agents, it is known that silver can absolutely suppress almost all single cell pathogens. Because of such antimicrobial activity, silver has been used long and widely in antimicrobial fields, for example, tableware, such as bowls, spoons, chopsticks, etc., and herbal medicines such as silver-coated pills.

[0008] As for the antibacterial function of silver, it is reportedly based on the activity of suppressing certain enzymatic reactions essential for the metabolism of pathogens, thus killing them.

[0009] Particularly in association with nano technology, silver in a nano state exhibits more powerful antibacterial and germicidal activity. Many research results report that silver in a nano state can kill as many as 650 kinds of bacteria and other microbes and show powerful suppression against fungi.

[0010] In addition, the smaller silver particles are, the more powerful antibacterial/germicidal activity, because silver becomes to the increase in surface area.

[0011] According to experimental data, silver powders show 99.9% antibacterial and germicidal efficiency over a variety of bacteria, including enterobacteria, Staphylococcus aureus, Salmonella, Vibrio, shigella, Pneumococcus, typoid, and even MRSA (methicillin resistant Staphylococcus aureus). That means that almost no bacteria can survive 5 minutes or longer in contact with nanosilver.

[0012] While having tenfold more potent suppression against bacteria than the conventional chloride-based agent, a nanosilver does not damage human bodies at all. Therefore it is expected to be a useful therapeutic agent against various inflammations. In addition, taking advantage of nanosilver, various functional products having antibacterial and deodorizing activities are on the market.

[0013] In the fiber and textile industries, accordingly, it is key point to produce nanosilver having such excellent effects on a large scale and to effectively intercalate the nanosilver into fibers.

[0014] In past three decades, synthetic fibers have been used in a wide range of fields of human life as complements to or substitutes for natural fibers and even as materials that are functionally superior to natural fibers. During this period, synthetic fibers for clothes have been developed towards practicality, comfort, and other functionalities. Furthermore, it has been actively researched to environment- and body-friendly synthetic fibers in recent. In a persistent effort to develop synthetic fibers that satisfy the above request, the antibacterial activity of nanosilver is applied to fibers.

[0015] Conventionally, nanosilver has been extracted using a physical method, such as liquid phase reduction, grinding, etc., or an electrolytic method. The electrolytic method is conducted under low temperature and voltage that silver having 99.9% of contents is added to distilled water, and then the silver-containing compounds are electrolyzed and carried to electrophoresis through the (+) and (-) of each molecule, results in collecting nanosilver.

[0016] On the other hand, as a representative method to intercalate nanosilver into fibers, synthetic fibers are manufactured by mixing nanosilver with raw synthetic fiber materials before the synthetic fibers are spun. However, the fibers, which are synthesized in the above mentioned method, is poor in antibacterial or germicidal activity because most silver is deeply intercalated into synthetic fibers while only a small amount of silver is exposed on the surfaces of synthetic fibers.

[0017] Alternatively, antibacterial agents, such as silver, silver oxide, nanosilver etc., are coated onto synthetic fibers. However, the antibacterial agents have poor adhesive strength with synthetic fibers; therefore the synthetic fibers are inferior to washing durability.

[0018] Leading to the present invention, intensive and thorough research, conducted by the present inventors, on antibacterial fibers and cloth resulted in the finding that nanosilver must be exposed in a larger amount on the surface of synthetic fibers, rather than be embedded within them, in order to maximize the germicidal or antibacterial effect of silver. The smaller the synthetic fibers are, the more powerful antibacterial/germicidal activities are. Also, In order to obtain the smaller nanosilver, it is designed that the mass production of nanosilver is generated by keeping up with minute electronic current between the two Ag electrodes in water electrolysis system to high voltage.

SUMMARY OF THE INVENTION

[0019] It is an aspect of the present invention to provide a method for producing nanosilver on a large scale.

[0020] It is another aspect of the present invention to provide a method for manufacturing nanosilver-adsorbed fiber that nanosilver is intensively adsorbed on surface of synthetic fibers.

[0021] It is another aspect of the present invention to provide an antibacterial fiber manufactured thereby.

[0022] In an exemplary embodiment of the present invention, a method for producing nanosilver on a large scale is provided. More practically, the nanosilver on a large scale is generated by controlling a minutely electronic current between the two Ag electrodes in water electrolysis system, while a voltage of 10,000300,000 is applied to two Ag electrodes.

[0023] An object of the invention is to provide a nanosilver on a large scale, preferably comprising; loading water so as to immerse the two Ag electrode plates in the water electrolysis system, applying voltage of 10,000300,000 to two Ag electrodes, moving the circuit breaker upwards or downwards relative to the voltage, and thus controlling minutely electric current between the two Ag electrodes. The water electrolysis system preferably comprises: a water reservoir provided with a water inlet valve for introducing water thereinto and a water outlet valve for draining the water therefrom; the two Ag electrode plates connected to a DC+ electric power source and a DC- electric power source respectively, the two Ag electrodes being provided on respective opposite sides of the water reservoir; a circuit breaker for dividing the water reservoir into two sections, and being provided in a middle of the water reservoir; and a groove for the circuit breaker, being formed in a middle portion of the water reservoir.

[0024] The particle size of the nanosilver is preferably from 1 to 5 nm.

[0025] Another object of the invention is to provide a method for manufacturing nanosilver-adsorbed fiber where nanosilver is intensively adsorbed on the surface of synthetic fibers. More practically, the preferred method comprises; preparing aqueous solution containing the nanosilver on a large scale; scouring and washing synthetic fibers; applying the aqueous solution containing the nanosilver to the surface of the synthetic fibers; adsorbing the nanosilver onto the synthetic fibers using a process selected from the group consisting of thermal fixation, high frequency radiation, bubbling, and combinations thereof; and conducting post-finishing at 160 to 200[deg.] C.

[0026] The latter preferred method may further comprise a dyeing step before the post-finishing.

[0027] Preferably, the thermal fixation is carried out at a temperature from 150 to 230[deg.] C.

[0028] The aqueous solution containing the nanosilver is preferably in an amount of 10 to 100 ppm of the nanosilver.

[0029] The step of applying the aqueous solution containing the nanosilver to the surface of the synthetic fibers is preferable to conducting a process selected from the group consisting of spraying, coating, and dipping.

[0030] In accordance with a further aspect of a preferred form of the present invention, an antibacterial fiber manufactured thereby, in which antibacterial fiber has the nanosilver has adsorbed thereon in an amount of 0.01 to 0.1 g per 100 g of synthetic fibers

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows a device for preparing the aqueous solution containing the nanosilver in accordance with the present invention,

[0032] FIG. 2 shows the particle distribution prepared in the presence of a high voltage in the aqueous solution containing the nanosilver according to the present invention, and

[0033] FIG. 3 shows the particle distribution prepared in the presence of a low voltage in the aqueous solution containing the nanosilver according to conventional method.



DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, the present invention is described in detail.

[0035] First, a method for producing nanosilver on a large scale is described according to an exemplary embodiment of the present invention. The method for producing nanosilver on a large scale is provided, based on the electrolysis of water in which, while high voltage, namely 10,000300,000 V, is applied to two Ag electrodes (104, 105), the nanosilver on a large scale are generated by keeping up with minute electric current between the two electrodes by controlling the height of the circuit breaker.

[0036] FIG. 1 shows a device for preparing the aqueous solution containing the nanosilver in accordance with the present invention.

[0037] More practically, the method for producing nanosilver on a large scale by using a water electrolysis system comprises:

loading water so as to immerse the two Ag electrodes;
applying voltage of 10,000300,000 to two Ag electrodes;
moving the circuit breaker upwards or downwards with the voltage, and thus controlling minutely electric current between the two Ag electrodes.

[0041] The water electrolysis system comprises,

[0042] a water reservoir (101) provided with a water inlet valve (102) for introducing water thereinto and a water outlet (103) valve for draining the water therefrom;

[0043] the two Ag electrode plates (104, 105) connected to a DC+ electric power source and a DC- electric power source respectively, the two Ag electrode plates being provided on respective opposite sides of the water reservoir (101);

[0044] a circuit breaker (107) for dividing the water reservoir (101) into two sections, being located of a middle of the water reservoir (101); and

[0045] a groove (106) formed by the circuit breaker(107).

[0046] It will be readily understood by those skilled in the art that the water reservoir, the water inlet valve, the water outlet valve, and the circuit breaker are all electrically insulated.

[0047] Generally, it was widely acknowledged that an electric current rises in proportion to voltage, in accordance with the following Formula 1. When low voltage is applied, electric current can be controlled using circuits, diodes and the like. However when high voltage is applied, current control is generally impossible.
Voltage(V)=Current(I)*Resistance(R) [Formula 1]

[0048] Therefore, the present invention is characterized that while a high voltage, 10,000300,000 V, is applied to electrolysis system, the electric current control is possible in high voltage. When the high voltage is applied, it is accomplished that the circuit breaker (107) installed at a middle portion of the water reservoir (101) is moved upwards or downwards to allow only minute electric current between the two electrodes. So, the nanosilver on a large scale is generated.

[0049] In more detail, when the circuit breaker (107) is absent, electric current flowing through the water reservoir with a certain voltage follows Formula 1. The other side, the circuit breaker (107) is controlled by [1/2] the height of the water reservoir (101), the electric current flows on the decrease until [1/2].

[0050] Thus, while high voltage, 10,000300,000 V is applied to two Ag electrodes, the nanosilver on a large scale is generated by keeping up with minute electric current between the two electrodes by controlling the height of the circuit breaker.

[0051] The electric current control is conducted until the nanosilver size becomes 5 nm or less and preferably 1 to 5 nm. When exceeding 5 nm in size, nanosilver particles lose the property of being easily adsorbed, characteristic of nanosilver, which is generated, because their surface area is decreased. In addition, if the electric current amount is not controlled to the high voltage, silver ions are not isolated to produce nano particles, but silver plating occurs.

[0052] FIG. 2 shows the particle distribution prepared in the presence of a high voltage in the aqueous solution containing the nanosilver according to the present invention. The particle distribution is observed using scanning electron microscopy. FIG. 2 shows that the nanosilver having a size of 5 nm or less is uniformly distributed. However, FIG. 3 shows the particle distribution prepared in the presence of a low voltage in the aqueous solution containing the nanosilver according to conventional method. FIG. 3 shows that the particles are non-uniformly distributed, with particle aggregations found therein.

[0053] In addition, the nanosilver prepared according to the exemplary embodiment of the present invention is in a nanosilver solution state so that the nanosilver particles are uniformly distributed, and the nanosilver can be uniformly and readily coated or adsorbed on synthetic fibers.

[0054] Another exemplary embodiment of the present invention is related to a method manufacturing nanosilver-adsorbed fiber. The method is comprised of; preparing aqueous solution containing the nanosilver synthesized on a large scale; scouring and washing synthetic fibers; applying the aqueous solution containing the nanosilver to the surface of the synthetic fibers; adsorbing the nanosilver onto the synthetic fibers using a process selected from the group consisting of thermal fixation, high frequency radiation, bubbling, and combinations thereof; and conducting post-finishing at 160 to 200[deg.] C.

[0055] The method may further comprise a dyeing step before the post-finishing.

[0056] The nanosilver-adsorbed fiber may be carried out on general cloth types, for example, leather, natural fibers, and synthetic fibers, and preferably with synthetic fibers.

[0057] The term "synthetic fiber" as used herein means generic fiber made from raw chemical materials, such as polyester, nylon, acryl, etc. Preferably, synthetic fiber has smooth surface such that the nanosilver can be easily adsorbed thereon, in contrast with natural fibers consisting of warp and weft. In the case of natural fibers, nanosilver is deeply intercalated into natural fibers, thus antimicrobial activity is poor. The application of the aqueous solution containing the nanosilver to the surface of synthetic fibers may be carried out using a spraying method, a coating method, or a dipping method followed by coating using a knife or a roll knife.

[0058] The antibacterial fiber is preferably adsorbed with nanosilver in an amount of 0.01 to 0.1 g per 100 g of synthetic fibers. According to the exemplary embodiment of the present invention, large amounts of nanosilver can be adsorbed on the synthetic fibers in comparison to conventional methods. When the amount of the nanosilver adsorbed on the synthetic fiber is less than 0.01 g, the synthetic fibers have insufficient antibacterial activity. On the other hand, if the amount of the nanosilver adsorbed on the synthetic fibers is more than 0.1 g, the cost for excessively increases relative to the improvement of antibacterial effects.

[0059] The adsorption of the nanosilver onto the surface of synthetic fibers may be achieved using various processes. An example among preferred processes is a thermal fixation process at 150 to 230[deg.] C. The thermal fixation process makes the cloth flexible. Here, when the temperature during the process is below 150[deg.] C., the surface of raw fiber becomes too flexible. On the other hand, when the temperature during the process is higher than 230[deg.] C., the surface of raw fiber becomes too stiff. Thermal fixation process is needed to be carried out under about 2 atm.

[0060] Another process for the adsorption of the nanosilver onto the surface of the synthetic fibers uses high-frequency radiation. The high-frequency radiation process uses an ultrasonic wave frequency that exceeds the upper limit of the range of audio frequencies (16 to 16000 Hz). Generally, ultrasonic waves may be generated by applying an ultrasonic signal produced in an electric circuit to an ultrasonic oscillator. The irradiation of ultrasonic waves onto the nanosilver solution produces innumerable fine voids. The innumerable fine voids are helpful in adsorbing the nanosilver onto the surface of synthetic fibers.

[0061] Another process for the adsorption of the nanosilver onto the surface of the synthetic fibers may be accomplished through bubbling. In this process, nanosilver particles, ionized by electrolysis, are oscillated leftwards and rightwards, upwards and downwards, or backwards and forwards by the bubbling. The oscillation of the nanosilver particles activates mobility, which is accelerated in the presence of a voltage, so that the nanosilver particles are uniformly distributed over the synthetic fibers. To carry out the above process using the bubbling, the target synthetic fibers are immersed in a separate inner vessel placed inside the water reservoir which has a plurality of openings through which bubbles are generated at a lower portion of the water reservoir.

[0062] Next, post-finishing is conducted, in which the synthetic fibers having nanosilver adsorbed thereon are ironed at 160 to 200[deg.] C.

[0063] In addition, a dyeing process may be further conducted before the post-finishing. In the dyeing process, the nanosilver-adsorbed fiber may be dyed at about 130[deg.] C. for 3 to 5 hours with a mixture of a dye and a dispersant.

[0064] An antibacterial fiber prepared according to the exemplary embodiment of the present invention includes nanosilver adsorbed thereon in an amount from 0.01 to 0.1 g per 100 g of the synthetic fibers. The synthetic fibers have excellent antibacterial activity because the nanosilver particles are intensively adsorbed on the surface thereon.

[0065] The antibacterial fiber is semi-permanently maintained washing durability, since the antibacterial fiber was manufactured by easily adsorptive properties of the nanosilver itself. Test results for washing durability of the antibacterial fiber made of nanosilver-adsorbed fiber reveals that the nanosilver remained thereon even after 50 washes.

[0066] In addition, the nanosilver is intensively adsorbed onto the surface of the synthetic fibers. Therefore, the antibacterial fiber according to the exemplary embodiment of the present invention is excellent to antibacterial activity, and simultaneously can prevent poor perspiration functionality and the generation of static electricity.

[0067] A better understanding of the present invention may be obtained in light of the following examples, which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE 1

[0068] Step 1: Preparation of Aqueous Solution Containing the Nanosilver

[0069] As shown in FIG. 1, the device for preparing aqueous solution containing the nanosilver comprises a water reservoir (101), provided with a water inlet valve (102) for introducing water thereinto and a water outlet (103) valve for draining the water therefrom; the two Ag electrodes (104, 105) connected to a DC+ electric power source and a DC- electric power source respectively, the two Ag electrodes being provided on respective opposite sides of the water reservoir (101); a circuit breaker (107) for dividing the water reservoir (101) into two sections, being located of a middle of the water reservoir (101); and a groove (106) being formed owing to the circuit breaker (107).

[0070] In this device, water was loaded on the water reservoir (101) with the level of immersing the two Ag electrodes (104, 105). Next, 30,000 V was applied across the two Ag electrodes in the water electrolysis system. The mass production of nanosilver was generated by keeping up with minute electric current between the two electrodes by controlling the height of the circuit breaker (107) to the water reservoir (101).

[0071] The nanosilver thus prepared was proven to have a size of 5 nm or less, with uniform particle distribution as measured using a scanning electron microscope (Model LEICA-STEROSCAN440) in FITI Testing & Research Institute of Korea (FIG. 2).

[0072] Step 2: Preparation of Antibacterial Fiber

[0073] Synthetic fibers were washed with water and scoured at a maximum temperature of 125[deg.] C. so that the synthetic fibers were made clean and neat.

[0074] Thereafter, the synthetic fibers were immersed in aqueous solution containing the nanosilver. Here, the temperature of the aqueous solution containing the nanosilver for the adsorption process was maintained at 230[deg.] C. under a pressure of about 2 atm, so that the nanosilver was thermally fixed on the surface of the synthetic fibers. In order to ensure the thermal fixation of the nanosilver onto the synthetic fibers, ultrasonication was conducted and bubbles were generated to accelerate the mobility of the nanosilver particles.

[0075] Afterwards, a dye and a dispersant were mixed in acetic acid and the synthetic fibers were dyed at 130[deg.] C. for 3 to 5 hours, followed by post-finishing in which the cloth was pressed at 200[deg.] C.

EXAMPLE 2

[0076] An antibacterial fiber was manufactured in a same manner to that of Example 1, with the exception that the circuit breaker (107) was controlled to cause the size of nanosilver to be 5 rn or less in the presence of 300,000 volts (DC+, DC-) in Step 1 of Example 1.

COMPARATIVE EXAMPLE 1

[0077] The same procedure as in Example 1 was performed, with the exception that 220 volts (DC+, DC-) was applied in Step 1.

[0078] As seen in FIG. 3, the nanosilver prepared in Comparative Example 1 was observed to aggregate together, with a non-uniform particle distribution under a SEM (model: LEICA-STEROSCAN440) in FITI Testing & Research Institute of Korea.

[0079] While this invention has been described in connection with certain exemplary embodiments and examples, it is to be understood that the present invention is not limited to the disclosed embodiments and examples, but, on the contrary, is intended to cover various modifications included within the spirit and scope of the appended claims and equivalents thereof.

[0080] As described hereinbefore, the present invention provides a method for producing nanosilver on a large scale by applying a high voltage in water electrolysis, and an antibacterial fiber having intensively nanosilver adsorbed thereon. Furthermore, the nanosilver adsorbed cloth is free of the problems possessed by general synthetic fibers, that is, poor perspiration functionality and high static electricity generation, and as well, shows potent suppression against a broad range of bacteria and microbes.



Colloidal Nanosilver Solution and Method for Making the Same
TW250969B


Also published as: WO03080231 //    US2003185889 //  AU2003225460

Abstract --- The present invention provides a nanosilver composition which contains nanosilver particles having diameters between 1 nm and 100 nm. The silver content in the nanosilver composition is between 0.001% to 0.4% by weight. The nanosilver composition also contains a stabilizing agent which includes, but is not limited to, starch or its derivative, cellulose or its derivative, polymer or copolymer of acrylate or acrylate derivative, polyvinyl pyrrolidone, alginic acid, and xantham gum. The present invention also provides a method for making the nanosilver composition. The nanosilver composition prepared by this method does not contain any toxic substances

FIELD OF THE INVENTION

[0001] The present invention relates to a colloidal nanosilver solution containing nanosilver particles with sizes ranged from 1 to 100 nm in diameter. The silver content in the colloidal nanosilver solution is about 0.001% to 0.4% by weight. The colloidal nanosilver solution also contains a gelling agent which includes, but is not limited to, starch or its derivatives, cellulose or its derivative, polymer or copolymer of acrylate or acrylate derivative, polyvinyl pyrrolidone, alginic acid, and xanthogenated gel. The colloidal nanosilver solution is characterized by not containing toxic or impure substances and is suitable for use in sanitation, disinfection, or as antimicrobial agent for treatment of patients. The present invention also relates to a method for making the colloidal nanosilver solution by interacting silver oxide first with ammonia water then with hydrazine hydrate.

DESCRIPTION OF THE RELATED ART

[0002] It has been known for centuries that silver possesses germicidal properties and has been employed as germicide before modern antibiotics were developed. During those days, users would shave silver particles into their drinking water, or submerge whole silver pieces in the drinking water, for the purpose of ingesting silver by drinking the water. Even after the onset of modem antibiotics era, silver remains to be used as antimicrobial agent, particularly because microorganisms treated by silver do not acquire resistance to the metals, while the conventional antibiotics often induce the formation of antibiotic-resistant microorganisms.

[0003] Silver is a safe and effective antimicrobial metal. In the late eighteenth century, western scientists confirmed that silver, which had been used in oriental medicine for centuries, was an effective antibacterial agent. Scientists also knew that the human body fluid is colloidal. Therefore, colloidal silver had been used for antibacterial purposes in the human body. By the early nineteenth century, colloidal silver was considered the best antibacterial agent until the discovery of the antibiotics. Due to the potency and revenue-driven advantages of antibiotics, the antibiotics gradually substituted colloidal silver as the main choice for antibacterial agent. However, thirty years into the discovery of the antibiotics, scientists began to discover that antibiotics induced the development of antibiotic-resistant bacterial strains which significantly affected the efficiency of antibiotics. Therefore, since 1870s, silver has again been recognized as a preferred antibacterial use, particularly due to its non-toxic and non-induction of bacterial-resistant characteristics.

[0004] There are many reasons why administering silver suspended in solution (e.g., colloidal silver) would enhance an individual's health. It is possible that such a solution operates to inhibit the growth of bacteria, fungi, viruses, and other unwanted organisms, as well as eradicating such existing bacteria, fungi, viruses, and other organisms. It is also possible that a solution of silver can have an anti-inflammatory effect, sufficient to reduce symptoms of asthma. Silver in solution might also act in a similar fashion to a homeopathic remedy.

[0005] There have been numerous attempts to produce silver-based solutions, including colloidal silver. However, many of the silver-based products fail to maintain the silver particles in suspension, either because the silver solution is not a true colloid or because it is otherwise unstable. When the suspension of the silver particles fails, the particles fall to the bottom of the solution, thereby reducing the solution's concentration of silver and rendering it less effective.

[0006] In the invention to be presented in the following sections, a colloidal nanosilver solution will be disclosed. The colloidal nanosilver solution of the present invention can maintain the colloidal nanosilver particles in suspension for a long period of time. It also has the advantages of not containing toxic or impure substances so that it is particularly suitable for medicinal and healthcare use.

SUMMARY OF THE INVENTION

[0007] The present invention provides a colloidal nanosilver solution containing nanosilver particles with sizes ranged between 1 nm and 100 nm in diameter, the silver content in the colloidal nanosilver solution is about 0.00% to 0.4% by weight.

[0008] The colloidal nanosilver solution also comprises a gelling agent, which is starch or its derivative, cellulose or its derivative, polymer or copolymer of acrylate or acrylate derivative, polyvinyl pyrrolidone, alginic acid, or xanthogenated gel. Examples of starch derivative include, but are not limited to, sodium carboxymethyl starch, hydroxyethyl starch, and pregelatinized starch. Examples of cellulose derivative include, but are not limited to, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose. An example of polymer or copolymer of acrylate derivative is carbomer, which is a carboxy vinyl polymer. Carbomer generally are high molecular weight ("MW") polymers (MW above 1,000,000). Carbomer is commercially available. B. F. Goodrich Company currently sells carbomer using the tradename of Carbopol. Carbopol 934P has a MW of about 3,000,000 and Carbopol 940 is about 4,000,000. The preferred Carbopol is Carbopol 934P. The preferred concentration of the gelling agent is at about 0.2 to 5% by weight of the total solution.

[0009] The colloidal nanosilver solution has antimicrobial activity, particularly for inhibiting growth of bacteria, fungi, or chlamydia. Examples of microorganisms which can be inhibited by the colloidal nanosilver solution include, but are not limited to, Escherichia coli, Methicillin resistant Staphylococcus aureus, Chlamydia trachomatis, Providencia stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative bacillus, Staphylococcus aureus, Candida albicans, Bacillus cloacae, Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B, Citrobacter, and Salmonella paratyphi C.

[0010] The present invention also provides a method for making the colloidal nanosilver solution. The method includes the following steps: (1) dissolving silver oxide (Ag2O) in ammonia water (NH3.H2O) to form a solution containing silver ammino ion [Ag(NH<3>)<+>]; (2) dissolving a gelling agent in water to form a gelling medium; (3) mixing the silver ammino ion-containing solution with the gelling medium to form a colloidal nanosilver ammino ion-containing solution; and (4) mixing the colloidal nanosilver ammino ion-containing solution with hydrazine hydrate (NH2NH2.H2O) to form the colloidal nanosilver solution. The ammonia water used in step (1) is preferred to be at a concentration of 28% by weight. Also, the silver oxide and the ammonium water in step (1) is preferred to be at a ratio of about 1:7 to about 1:10 (w/v). In addition, the silver oxide and the hydrazine hydrate in step (4) is preferred to be at a ratio of about 1:0.087 to about 1:0.26 (w/v).

[0011] It is preferred that the colloidal nanosilver ammino ion-containing solution is mixed with hydrazine hydrate (NH2NH2.H2O) at about 0 to 45[deg.] C. for about 0.5 to 2 hours. Also, after the formation of the colloidal nanosilver solution, it is preferred to let the colloidal nanosilver solution be in contact with air for about 0.5 to 5 hours.

[0012] The colloidal nanosilver solution can be used as an antibacterial or antifingal agent for treatment of patients with bum and scald-related skin infection, wound-related skin infection, dermal or mucosal bacterial or fungal infection, surgery cut infection, vaginitis, and acne-related infection, by applying or spraying the solution onto the wounds. It can also be used as a disinfectant or sanitary agent to clean areas in need of disinfection or sanitation.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention provides a colloidal nanosilver solution which contains nanosilver particles having diameters with sizes ranged between 1 nm and 100 nm. A colloid is a gelatinous or mucinous dispersion medium that consists of particles which are larger than an ordinary crystalloid molecule, but are not large enough to settle out under the influence of gravity. These particles normally range in size from 1 to 100 nm. There are generally two kinds of colloids: (1) Suspension colloids (suspensoids), in which the dispersion medium consists of particles that are insoluble, such as a metal, and the dispersion medium may be gaseous, liquid, or solid. (2) Emulsion colloids (emulsoids), in which the dispersion medium is usually water and the disperse phase consists of highly complex organic substances, such as starch or glue, which absorb much water, swell, and become uniformly distributed throughout the dispersion medium. The suspension colloids tend to be less stable than the emulsion colloids. The colloidal nanosilver solution of the present invention is a hybrid of both the suspension and the emulsion colloids.

[0014] The colloidal nanosilver solution of the present invention is further characterized by its non-toxic and purity nature, as well as its stability. The silver content in the colloidal solution is between 0.001% to 0.4% by weight. It is also stable at room temperature (about 25[deg.] C. or 77[deg.] F.) for at least 110 days. Because of these characteristics, the colloidal nanosilver solution is particularly suitable for use in healthcare related matters such as sanitization and disinfection.

[0015] The colloidal nanosilver solution of the present invention can be used in sanitary products, which include, but are not limited to, solutions for cleansing agents for clothing, women hygiene, acne or pimples, and soaking solution for tooth brush. It can also be used in healthcare products, which include, but are not limited to, treating patients with all kinds of injuries and/or burns, bacterial and fungal infections (including gynecological infections such as vaginitis), gastrointestinal bacterial infection, and sexually transmitted diseases. In addition, the colloidal nanosilver solution of the present invention can be used in industrial products, which include, but are not limited to, food preservatives especially for fruits and vegetables, drinking water disinfectants, paper and construction filling materials preservation (especially to prevent mold formation).

[0016] The colloidal nanosilver solution of the present invention possesses a broad spectrum of antibacterial and antifungal ability. It can kill and suppress growth of bacteria and fungi, such as Escherichia coli, Methicillin resistant Staphylococcus aureus, Chlamydia trachomatis, Providencia stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative bacillus, Staphylococcus aureus, Candida albicans, Bacillus cloacae, Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B, Citrobacter, and Salmonella paratyphi C.

[0017] The antibacterial and antifungal activity of the colloidal nanosilver solution of the present invention has advantage over the conventional antibiotics in killing and suppressing bacterial growth, as it does not induce drug-related resistance in the bacterial or fungal strains.

[0018] Conventionally, a colloidal silver solution is prepared by reducing silver nitrate (AgNO3) to metallic silver with reducing agent such as glucose, ascorbic acid, hydrazine hydrate, hydrazine sulfate, and formaldehyde. The term "colloidal silver solution" as used in this context refers to a colloidal solution containing silver particles where the sizes of the silver particles are not necessarily within the nanometer range in the "colloidal nanosilver solution" as described in the present invention.

[0019] Under this preparation method, other than silver, oxidized products of the reducing agents, which are possibly toxic, are generated. The presence of these oxidized products not only affect the purity of the colloidal silver solution but also make the colloidal silver solution unsuitable for use in healthcare related industry due to its toxicity. Also, although the oxidized products of the reducing agents can be removed from the colloidal silver solution by conventional methods, such as dialysis, the method of dialysis involves excessive steps which not only is time-consuming but also adds more difficulties and expenses to the industrial-scale manufacturing process.

[0020] To avoid producing unwanted toxic products, at least two methods are disclosed which produce a colloidal silver solution containing harmless side products from the reducing agents. For example:

[0021] (1) Reacting silver oxide (Ag2O) with hydrogen gas to form metallic silver and water:
Ag2O+H2->2Ag+H2O

[0022] (2) Reacting silver oxide (Ag2O) with hydrazine hydrate (NH2NH2.H2O) to form metallic silver, nitrogen gas, and water.
2Ag2O+NH2NH2.H2O->4Ag+N2+3H2O

[0023] Because the above reactions produce metallic silver, nitrogen gas, and water, which are non-toxic in nature so that no additional steps are necessary for removing the unwanted toxic products, theoretically, they should be suitable for the production of colloidal silver solution. However, the reactions as shown above are not practical in manufacturing industrial-scale colloidal nanosilver solution. For example, in the reaction as described in (1), which requires the silver oxide to interact with hydrogen gas, a multiphase reaction is involved which make it very difficult to carry out. See V. Kohlschuetter Strassburg (Z. Elektrochem., 14, 49-63. CA: 2: 1379-1380). When the silver oxide and hydrogen are sealed in a glass tube and reacted at 18[deg.] C. or lower, the reduction reaction takes place very slowly. On the other hand, if the reaction is carried out at 60[deg.] C. or lower, the hydrogen gas is discharged into the saturated silver oxide solution, which results in yielding a colloidal silver solution with silver particles partially in suspension and partially precipitated. A colloidal silver solution prepared in this way is not suitable for use in sanitation or healthcare products due to precipitation of silver.

[0024] Also, in the reaction as described in (2) above, the interaction of silver oxide with hydrazine hydrate in water is limited by the low solubility of the silver oxide in water. See J. Voigt et al. (Z. Anorg. Allgem. Chem. 164, 409-419, CA21:3512). Therefore, in order to obtain a soluble silver oxide solution, the silver content of the silver oxide solution must be no more than 0.001% by weight. Using such a diluted silver oxide solution as starting material, the resulting silver content in the colloidal silver solution is too low to be effective for sanitation or healthcare use.

[0025] The present invention provides a method for making a colloidal nanosilver solution which is distinctively different from the prior art methods. Based on this method, a colloidal nanosilver solution which contains high silver concentration (i.e., containing 0.001% to 0.4% by weight of silver), high stability in the colloidal state (i.e., stable at room temperature for no less than 110 days), and no toxic substances, is formed.

[0026] The method for preparing the colloidal nanosilver solution of the present invention contains the following reactive steps:

[0027] (1) Dissolution of Silver Oxide in Ammonia Water (N3.H2O).

[0028] Silver oxide (Ag2O) is dissolved in concentrated ammonia water (NH3.H2O) to obtain a silver ammino oxide [Ag(NH3)<+>]2O solution where the silver ion is in the form of silver ammino ion [Ag(NH3)<+>] in as follows:

Ag2O+2NH3.H2O->[Ag(NH3)<+>]2O+2H2O

[0029] The concentrated ammonia water is preferred to be about 28%. The preferred ratio of silver oxide and ammonium water is at about 1:7 to about 1:10, w/v. This procedure has the advantage of increasing the solubility and concentration of silver in the solution.

[0030] (2) Dissolution of Gelling Agent in Water to Form a Gelling Medium.

[0031] A gelling medium is provided by dissolving a gelling agent in water. This gelling medium serves as a protective gel/colloid mechanism for keeping the nanosilver particles suspended in the colloidal nanosilver solution and preventing the nanosilver particles from aggregating with each other to form bigger pellets and precipitate. Preferably, the concentration of the gelling agent is between 0.2% to 5% by weight.

[0032] The gelling agent can be a synthetic or natural polymer or a combination thereof, which can be readily dissolved in water. Examples of the gelling agent include, but are not limited to, starch or starch derivatives, cellulose or cellulose derivatives, polymer or copolymer of acrylate or acrylate derivatives, polyvinyl pyrrolidone (PVP), alginic acid, and xanthogenated gel. The starch derivatives include, but are not limited to, sodium carboxymethyl starch, hydroxyethyl starch, and pre-gelatinized starch. The cellulose derivatives include, but are not limited to, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose. The polymer or copolymer of acrylate or acrylate derivative is preferred to be Carbomer.

[0033] Carbomer is a polymer of acrylic acid (or a carboxy vinyl polymer). It is currently sold under the tradename of Carbopol by B. F. Goodrich Company. The preferred carboxy vinyl polymer is a high molecular weight (preferably MW above 1,000,000; and most favorably MW above 3,000,000) polymer, such as Carbopol 934P which has a molecular weight of about 3,000,000.

[0034] Carbopol is the trademark of B. F. Goodrich Company's carboxy vinyl polymers, which generally are high molecular weight ("MW") polymers (MW above 1,000,000). Specifically, Carbopol 934P has a MW of about 3,000,000 and Carbopol 940 is about 4,000,000. The preferred Carbopol is Carbopol 934P.

[0035] (3) Mixing Silver Ammino Oxide Solution with the Gelling Medium.

[0036] The silver ammino oxide [Ag(NH3)<+>]2O solution is thoroughly mixed with the gelling medium to form a uniformly dispersed silver ammino oxide-gelling solution to be used for the next reaction. The silver ammino oxide-gelling medium is preferred to be controlled at about 0[deg.] to 45[deg.] C.

[0037] (4) Reaction of Silver Ammino Ion with Hydrazine Hydrate.

[0038] The silver ammino ion is further interacted with hydrazine hydrate in the presence of oxygen gas to form metallic silver, nitrogen gas, and water as follows:
[Ag(NH3)<+>]2O+NH2NH2.H2O+2O2->2Ag(metallic)+2 N2+6H2O

[0039] The preferred temperature for the above reaction is at about 0[deg.] C.-45[deg.] C. The reaction is preferred to be conducted in about 0.5 to 2 hours. The silver ammino oxide and hydrazine hydrate are preferred to be at a ratio of 1:0.087 to 1:0.26 by weight. The nanosilver particles prepared by the reactive steps (1)-(4) have diameter of 1 nm to 100 nm.

[0040] Because hydrazine hydrate is toxic, after the completion of step (4), the colloidal nanosilver solution is preferred to be kept in the presence of air for additional 0.5 to 5 hours so that the residue of hydrazine hydrate in the final colloidal nanosilver solution can be decomposed into nitrogen and water by the following oxidative reaction:
NH2NH2.H2O+O2->N2+3H2O

[0041] The resulting nitrogen gas and water are non-toxic so that no removal of the side products is necessary.

[0042] Moreover, the present invention provides a method for making the colloidal nanosilver solution of high silver concentration, high stability in the gel state, and no toxic ingredients. The above mentioned problems associated with the reaction are solved in the present invention: the solubility of silver oxide and final concentration of silver in the colloidal solution are improved, the colloidal nanosilver is stabilized as the gel state in the solution, and the toxic reactant, hydrous ammonia, is carefully removed from the colloidal nanosilver solution by further decomposition reaction with oxygen in the air. The colloidal nanosilver solution of the present invention is suitable for healthcare purposes and serves as an effective antimicrobial agent.

[0043] The following examples are illustrative, but not limiting the scope of the present invention. Reasonable variations, such as those occur to reasonable artisan, can be made herein without departing from the scope of the present invention.

EXAMPLE 1

Preparation of the Colloidal Nanosilver Solution of the Present Invention

[0044] The colloidal solution containing nanosilver particles of the present invention was prepared according to the following steps:

[0045] 1. 60 g of sodium carboxymethyl starch 60 g was dissolved in 1600 ml of distilled water. The dissolved sodium carboxymethyl starch solution was added to a 5000 ml flask. The flask was heated to and maintained at 70[deg.] C. until the solution became gelatinized. The gelatinized solution was cooled down to room temperature.

[0046] 2. 3 g of silver oxide was added to and mixed with 22 ml of 28% ammonia water to form a silver ammino oxide (i.e., [Ag(NH3)<+>]2O)-solution.

[0047] 3. The silver ammino oxide solution was then mixed thoroughly with the gelatinized solution of (2) to form a silver ammino oxide-gelling medium.

[0048] 4. 0.5 g of 80% hydrazine hydrate was mixed with and dissolved in 200 ml of distilled water to form a hydrazine hydrate solution.

[0049] 5. The hydrazine hydrate solution was added to the flask containing silver ammino oxide-gelling medium. An additional 115 ml of distilled water was then added to and mixed with the rest of the solution. The solution was then reacted at room temperature for 1.5 hours under seal. The flask was then opened to allow the reactants to be in touch with air for additional 3.0 hours.

EXAMPLE 2

Preparation of the Colloidal Nanosilver Solution of the Present Invention

[0050] The colloidal solution containing nanosilver particles of the present invention was prepared according to the following steps.

[0051] 1. 1600 ml of distilled water was added to a 5000 ml flask and heated to and maintained at 70[deg.] C.

[0052] 2. 50 g of methyl cellulose was gradually added to the flask containing the heated distilled water. After thorough mixing of the methyl cellulose with the distilled water, the temperature of the solution was gradually reduced to around 30[deg.] C. until a gelatinized solution was formed.

[0053] 3. 3 g of silver oxide was added to and mixed with 22 ml of 28% ammonia water to form a silver ammino oxide solution.

[0054] 4. The silver ammino oxide solution was then added to and mixed with the gelatinized solution to form a silver ammino oxide-gelling medium.

[0055] 5. 0.6 g of 80% hydrazine hydrate was dissolved in 200 ml of distilled water to form a hydrazine hydrate solution.

[0056] 6. The hydrazine hydrate solution was then added to the flask containing silver ammino oxide-gelling medium. An additional 125 ml of distilled water was then added to and mixed with the rest of the solution. The solution was then reacted at room temperature for 1 hour under seal. The flask was then opened to allow the reactants to be in touch with air for additional 4.0 hours.

EXAMPLE 3

Preparation of the Colloidal Nanosilver Solution of the Present Invention

[0057] The colloidal solution containing nanosilver particles of the present invention was prepared according to the following steps.

[0058] 1. 1600 ml of distilled water was added to a 5000 ml flask and heated to and maintained at 70[deg.] C.

[0059] 2. 4.5 g of carboxypropyl methyl cellulose was gradually added to the flask containing the heated distilled water. After thorough mixing of the carboxypropyl methyl cellulose with the distilled water, the temperature of the solution was gradually reduced to around 30[deg.] C. until a gelatinized solution was formed.

[0060] 3. 4.5 g of silver oxide was added to and mixed with 33 ml of 28% ammonia water to form a silver ammino oxide solution.

[0061] 4. The silver ammino oxide solution was then added to and mixed with the gelatinized solution to form a silver ammino oxide-gelling medium.

[0062] 5. 1 g of 80% hydrazine hydrate was dissolved in 260 ml distilled water to form a hydrazine hydrate solution.

[0063] 6. The hydrazine hydrate solution was added to the silver ammino oxide-gelling medium and 76 ml of distilled water was further added to and mixed with the rest of the solution. The flask was then sealed and kept at room temperature for about 1 hour.

[0064] 7. The flask was then unsealed to allow the solution to be in touch with air for 4 hours to obtain the colloidal nanosilver solution of the present invention.

EXAMPLE 4

Preparation of the Colloidal Nanosilver Solution of the Present Invention

[0065] The colloidal solution containing nanosilver particles of the present invention was prepared according to the following steps.

[0066] 1. 1600 ml of distilled water was added to a 5000 ml flask.

[0067] 2. 1 g of polyvinylpyrrolidone (PVP) was gradually added into the flask at room temperature and dissolved therein to form a gelatinized solution.

[0068] 3. 6 g of silver oxide was dissolved in 44 ml of 28% ammonia water to form a silver ammino oxide solution.

[0069] 4. The silver ammino oxide solution of step (3) was add to and thoroughly mixed with the gelatinized solution of (2) to form a silver ammino oxide-gelling medium.

[0070] 5. 1.5 g of 80% hydrazine hydrate was dissolved in 270 ml of distilled water to form a hydrazine hydrate solution.

[0071] 6. The hydrazine hydrate solution was then mixed with the silver ammino oxide-gelling medium of (4) in the flask with 73 ml of additional distilled water added to and mixed into the rest of the solution. The flask was sealed and kept at 30[deg.] C. for 1.5 hours.

[0072] 7. The flask was unsealed to allow the solution to be in touch with air for 5 hours to obtain the colloidal nanosilver solution of the present invention.

EXAMPLE 5

Examination of the Dimension and Stability of the Colloidal Nanosilver Solution

[0073] I. Purpose:

[0074] The colloidal solution containing nanosilver particles of the present invention was examined for the dimension of the nanosilver particles and stability of the colloidal nanosilver solution over time (days) in terms of suspension by electron microscopy.

[0075] II. Method:

[0076] In accordance with the standard procedures for JY/T011-1996 transmission electron microscope, JEM-100CXII transmission electron microscope was used under the testing conditions of accelerating voltage at 80 KV and resolution at 0.34 nm. The colloidal nanosilver solutions produced by Examples 1-4 of the present invention were observed for the size and distribution of the nanosilver particles therein. Aliquots of the samples from Examples 1-4 were taken out from the solutions either being freshly made or after being stored at room temperature for 110 days.

[0077] III. Results:

[0078] For the freshly made colloidal nanosilver samples, the diameters of all the silver particles contained therein were below 35 nm, among which, most particles (37%) had a diameter of 15 nm.

[0079] For the colloidal solution stored after 110 days, the diameters of all the silver particles contained therein were kept below 35 nm, among which, most particles (38%) had a diameter of 15 nm.

[0080] IV. Conclusion:

[0081] The colloidal solution of the present invention containing nanosilver particles which had a size range of 1 nm to 100 nm and was very stable after storage of 110 days at room temperature. There was no visible increase in size of the silver particles contained therein and no precipitation of silver particles. The colloidal solution of the present invention was stable for further processing and adopted for use, storage, and transportation.

EXAMPLE 6

Antimicrobial Activity of the Colloidal Nanosilver Solution of the Present Invention

[0082] I. Purpose:

[0083] The colloidal solution of the present invention was tested for the antimicrobial ability.

[0084] II. Method:

[0085] Microbial strains tested were Escherichia coli, Methicillin resistant Staphylococcus aureus, Chlamydia trachomatis, Providencia stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative bacillus, Staphylococcus aureus, Candida albicans (ATCC 10231), Bacillus cloacae, Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B, Citrobacter, and Salmonella paratyphi C. These strains were either isolated from clinical cases or purchased as standard strains from Chinese Biological Products Testing and Standardizing Institute.

[0086] A typical example of the test, as illustrated by Candida albicans (ATCC 10231), was as follows:

[0087] Colloidal nanosilver solutions of examples 1-4 (each contains a concentration of 1370 [mu]g/ml of silver) were tested for its antifungal activity against Candida albicans. The colloidal nanosilver solutions were diluted in distilled water to make the final concentrations of 137 [mu]g/ml, 68.5 [mu]g/ml, 45.7 [mu]g/ml, 34.2 [mu]g/ml, and 27.4 [mu]g/ml. In the control group, no colloidal nanosilver solution was added. Candida albicans was added to each tested and control groups, respectively, and the viability of the fungus in each group was examined 2 minutes after incubation with the colloidal nanosilver solutions of examples 1-4.

[0088] Typically, due to the resilience of Candida Albicans, a higher concentration of disinfectant is required to kill or suppress the growth of Candida albicans than for killing bacteria such as Staphylococcus aureus and Escherichia coli.

[0089] III. Results:

[0090] There was an average of 99.99% killing rate (1.78*10<6 >cfu/mu) for all of the colloidal nanosilver solution tested (Examples 1-4) after 2 minutes of incubation. Among the same example, the most diluted sample demonstrated about the same fungicidal activity as the least diluted one.

[0091] IV. Conclusion:

[0092] The colloidal solution containing nanosilver particles of the present invention was effective as antimicrobial agent even at a diluted concentration of 27.4 [mu]g/ml of silver.



STABILIZED SILVER NANOPARTICLE COMPOSITION
US7270694

Abstract --- A composition comprising a liquid and a plurality of silver-containing nanoparticles with a stabilizer, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an organic solvent wherein the hydrazine compound is a hydrocarbyl hydrazine, a hydrocarbyl hydrazine salt, a hydrazide, a carbazate, a sulfonohydrazide, or a mixture thereof and wherein the stabilizer includes an organoamine.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] Yiliang Wu et al., U.S. application Ser. No. 10/733,136 filed Dec. 11, 2003, titled "NANOPARTICLE DEPOSITION PROCESS."

BACKGROUND OF THE INVENTION

[0003] Fabrication of electronic circuit elements using liquid deposition techniques is of profound interest as such techniques provide potentially low-cost alternatives to conventional mainstream amorphous silicon technologies for electronic applications such as thin film transistors (TFTs), light-emitting diodes (LEDs), RFID tags, photovoltaics, etc. However the deposition and/or patterning of functional electrodes, pixel pads, and conductive traces, lines and tracks which meet the conductivity, processing, and cost requirements for practical applications have been a great challenge. Silver is of particular interest as conductive elements for electronic devices because silver is much lower in cost than gold and it possesses much better environmental stability than copper. There is therefore a critical need, addressed by embodiments of the present invention, for lower cost methods for preparing liquid processable, stable silver-containing nanoparticle compositions that are suitable for fabricating electrically conductive elements of electronic devices.

[0004] The following documents provide background information:

[0005] Pozarnsky et al., U.S. Pat. No. 6,688,494.

[0006] Lee et al., U.S. Pat. No. 6,572,673 discloses hydrazide as a reducing agent at for example column 1, lines 52-53.

[0007] Heath et al., U.S. Pat. No. 6,103,868.

[0008] Wilcoxon, U.S. Pat. No. 5,147,841 discloses hydrazine as a reducing agent at for example column 4, line 44.

[0009] G. Blanchet and J. Rodgers, "Printed Techniques for Plastic Electronics", Journal of Imaging Science and Technology, Vol. 47, No. 4, pp. 296-303 (July/August 2003).

[0010] P. Buffat and J-P. Borel, "Size effect on the melting temperature of gold particles", Physical Review A, Vol., 13, No. 6, pp. 2287-2298 (June 1976).

[0011] C. Hayashi, "Ultrafine Particles", J. Vacuum Sci. Technol. A, Vol. 5, No. 4, pp. 1375-1384 (July/August 1987).

[0012] S. B. Fuller, E. J. Wilhelm, and J. M. Jacobson, "Ink-Jet Printed Nanoparticle Microelectromechanical Systems", Journal of Microelectromechanical Systems, Vol. 11, No. 1, pp. 54-60 (February 2002).

[0013] X. Z. Lin, X. Teng, and H. Yang, "Direct Synthesis of Narrowly Dispersed Silver Nanoparticles Using a Single-Source Precursor", Langmuir, Vol. 19, pp. 10081-10085 (published on web Nov. 1, 2003).

[0014] H. Hiramatsu and F. E. Osterloh, "A Simple Large-Scale Synthesis of Nearly Monodisperse Gold and Silver Nanoparticles with Adjustable Sizes and with Exchangeable Surfactants", Chem. Mater., Vol. 16, No. 13, pp. 2509-2511 (Jun. 29, 2004; published on web May 28, 2004).

SUMMARY OF THE DISCLOSURE

[0015] In embodiments, there is provided a process comprising: reacting a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent, to form a plurality of silver-containing nanoparticles with molecules of the stabilizer on the surface of the silver-containing nanoparticles.

[0016] In further embodiments, there is provided a process comprising:

(a) reacting a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent, to form a plurality of silver-containing nanoparticles with molecules of the stabilizer on the surface of the silver-containing nanoparticles;

(b) isolating the plurality of silver-containing nanoparticles with the molecules of the stabilizer on the surface of the silver-containing nanoparticles; and

(c) preparing a composition including a liquid and the plurality of silver-containing nanoparticles with molecules of the stabilizer on the surface of the silver-containing nanoparticles.

[0020] In other embodiments, there is provided a process comprising:

(a) depositing a composition comprising a liquid and a plurality of silver-containing nanoparticles with a stabilizer on a substrate by a liquid deposition technique to form a deposited composition, wherein the silver-containing nanoparticles are obtained by reacting a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent; and

(b) heating the deposited composition to form an electrically conductive layer comprising silver.

[0023] There is further provided in embodiments, a composition comprising a liquid and a plurality of silver-containing nanoparticles with a stabilizer, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent.

[0024] In additional embodiments, there is provided an electronic device comprising in any suitable sequence:

a substrate;

an optional insulating layer or an optional semiconductor layer, or both the optional insulating layer and the optional semiconductor layer; and
an electrically conductive element of the electronic device, wherein the electrically conductive element comprises annealed silver-containing nanoparticles, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent.

[0028] In more embodiments, there is provided a thin film transistor circuit comprising an array of thin film transistors including electrodes, connecting conductive lines and conductive pads, wherein the electrodes, the connecting conductive lines, or the conductive pads, or a combination of any two or all of the electrodes, the connecting conductive lines and the conductive pads comprise annealed silver-containing nanoparticles, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent.

[0029] In yet other embodiments, there is provided a thin film transistor comprising:

(a) an insulating layer;
(b) a gate electrode;
(c) a semiconductor layer;
(d) a source electrode; and
(e) a drain electrode,

wherein the insulating layer, the gate electrode, the semiconductor layer, the source electrode, and the drain electrode are in any sequence as long as the gate electrode and the semiconductor layer both contact the insulating layer, and the source electrode and the drain electrode both contact the semiconductor layer, and
wherein at least one of the source electrode, the drain electrode, and the gate electrode comprises annealed silver-containing nanoparticles, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other aspects of the present invention will become apparent as the following description proceeds and upon reference to the following figures which represent exemplary embodiments:

[0038] FIG. 1 represents a first embodiment of a thin film transistor wherein the conductive layers were made using the present silver-containing nanoparticles.

[0039] FIG. 2 represents a second embodiment of a thin film transistor wherein the conductive layers were made using the present silver-containing nanoparticles.

[0040] FIG. 3 represents a third embodiment of a thin film transistor wherein the conductive layers were made using the present silver-containing nanoparticles.

[0041] FIG. 4 represents a fourth embodiment of a thin film transistor wherein the conductive layers were made using the present silver-containing nanoparticles.



[0042] Unless otherwise noted, the same reference numeral in different Figures refers to the same or similar feature.

DETAILED DESCRIPTION

[0043] Suitable silver compounds include organic and inorganic silver compounds. In embodiments, the silver compounds include silver acetate, silver carbonate, silver nitrate, silver perchlorate, silver phosphate, silver trifluoroacetate, silver benzoate, silver lactate, and the like, or mixtures thereof in any suitable ratio.

[0044] The reducing agent for the silver compounds includes a hydrazine compound. The hydrazine compound includes hydrazine and any suitable derivatives (substituted at one or both nitrogen atoms where each nitrogen atom can be substituted one or two times with the same or different substituent), as well as salts and hydrates of hydrazine and salts and hydrates of the hydrazine derivatives. It is understood that the exemplary compounds described herein for the hydrazine compound also include the hydrate form where applicable. For example, the compound "hydrazine" includes hydrazine hydrate and hydrazine not in hydrated form. Exemplary examples of the hydrazine compound are as follows:

[0045] Hydrazine (H2HNH2);

[0046] Hydrazine salt such as for example hydrazine acid tartrate, hydrazine monohydrobromide, hydrazine monohydrochloride, hydrazine dichloride, hydrazine monooxalate, and hydrazine sulfate.

[0047] Hydrocarbyl hydrazine (e.g., RNHNH2 and RNHNHR and RRNNH2) where one nitrogen atom is mono- or di-substituted with R, and the other nitrogen atom is optionally mono- or di-substituted with R, where each R is an independently selected hydrocarbon group such as methyl ethyl, propyl, butyl, hydroxyethyl, phenyl, benzyl, tolyl, bromophenyl, chloropehnyl, nitrophenyl, xylyl, and the like. Illustrative examples of hydrocarbyl hydrazine include for example, methylhydrazine, tert-butylhydrazine, 2-hydroxyethylhydrazine, benzylhydrazine, phenylhydrazine, tolylhydrazine, bromophenylhydrazine, chlorophenylhydrazine, nitrophenylhydrazine, 1,1-dimethylhydrazine, 1,1-diphenylhydrazine, 1,2-diethylhydrazine, and 1,2-diphenylhydrazine.

[0048] Hydrocarbyl hydrazine salt (which is a salt of the hydrocarbyl hydrazine described herein) such as for example methylhydrazine hydrochloride, phenylhydrazine hydrochloride, benzylhydrazine oxalate, butylhydrazine hydrochloride, butylhydrazine oxalate salt, and propylhydrazine oxalate salt.

[0049] Hydrazide (e.g., RC(O)NHNH2 and RC(O)NHNHR' and RC(O)NHNHC(O)R) where one or both nitrogen atoms are substituted by an acyl group of formula RC(O), where each R is independently selected from hydrogen and a hydrocarbon group, and one or both nitrogen atoms are optionally mono- or di-substituted with R', where each R' is an independently selected hydrocarbon group. Illustrative examples of hydrazide are for example, formic hydrazide, acethydrazide, benzhydrazide, adipic acid dihydrazide, carbohydrazide, butanohydrazide, hexanoic hydrazide, octanoic hydrazide, oxamic acid hydrazide, maleic hydrazide, N-methylhydrazinecarboxamide, and semicarbazide.

[0050] Carbazate (or hydrazinocarboxylate) (e.g., ROC(O)NHNHR' and ROC(O)NHNH2 and ROC(O)NHNHC(O)OR) where one or both nitrogen atoms are substituted by an ester group of formula ROC(O), where each R is independently selected from hydrogen and a hydrocarbon group, and one or both nitrogen atoms are optionally mono- or di-substituted with R', where each R' is an independently selected hydrocarbon group. Illustrative examples of carbazate are for example, methyl carbazate (methyl hydrazinocarboxylate), ethyl carbazate, butyl carbazate, benzyl carbazate, and 2-hydroxyethyl carbazate.

[0051] Sulfonohydrazide (e.g., RSO2NHNH2, RSO2NHNHR', and RSO2NHNHSO2R) where one or both nitrogen atoms are substituted by a sulfonyl group of formula RSO2, where each R is independently selected from hydrogen and a hydrocarbon group, and one or both nitrogen atoms are optionally mono- or di-substituted with R', where each R' is an independently selected hydrocarbon group. lullustraive examples of sulfonohydrazide are for example, methanesulfonohydrazide, benzenesulfonohydrazine, 2,4,6-trimethylbenzenesulfonohydrazide, and p-toluenesulfonohydrazide.

[0052] Other exemplary hydrazine compounds are for example hydrazine acetate, aminoguanidine, thiosemicarbazide, methyl hydrazinecarbimidothiolate, and thiocarbohydrazide.

[0053] Unless otherwise indicated, in identifying the substituents for R and R' of the various hydrazine compounds, the phrase "hydrocarbon group" encompasses both unsubstituted hydrocarbon groups and substituted hydrocarbon groups. Unsubstituted hydrocarbon groups may be for example a straight chain alkyl group, a branched alkyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group. Exemplary alkyl groups include for example methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, cyclopentyl, cyclohexyl, cycloheptyl, and isomeric forms thereof. Substituted hydrocarbon groups may be the unsubstituted hydrocarbon groups described herein which are substituted one, two or more times with for example a halogen (chlorine, bromine, fluorine, and iodine), nitro, cyano, an alkoxy group (e.g., methoxyl, ethoxyl, and propoxy), or a mixture thereof. In embodiments, the hydrocarbon group may be optionally substituted alkyl and optionally substituted aryl.

[0054] In embodiments, the hydrazine compound is other than a hydrazine and a hydrazine salt; in other embodiments, the hydrazine compound is other than a hydrazide; and in further embodiments, the hydrazine compound is other than a hydrazine, a hydrazine salt, and a hydrazide.

[0055] One, two, three or more reducing agents may be used. In embodiments where two or more reducing agents are used, each reducing agent may be present at any suitable weight ratio or molar ratio such as for example from about 99(first reducing agent):1(second reducing agent) to about 1(first reducing agent):99(second reducing agent). The amount of reducing agent used in the embodiments of the present invention is for example about 0.25 molar equivalent or more per mole of silver compound.

[0056] Any suitable stabilizer may be used which has the function of minimizing or preventing the silver-containing nanoparticles from aggregation in a liquid and optionally providing the solubility or dispersibility of silver-containing nanoparticles in a liquid. In addition, the stabilizer is thermally removable which means that the stabilizer can be caused to dissociate from the silver-containing nanoparticle surface under certain conditions such as through heating. The heating may be accomplished to a certain temperature such as for example below about 250 degree C., or below about 200 degree C., under normal atmospheric conditions or at a reduced pressure of for example from several mbars to about 10<-3 > mbar. The thermal dissociation of the stabilizer from the silver-containing nanoparticles at a temperature such as for example lower than about 250 degree C. may result in the evaporation of the stabilizer or decomposition of the stabilizer into gaseous forms.

[0057] In embodiments, the stabilizer may be an organic stabilizer. The term "organic" in "organic stabilizer" refers to the presence of carbon atom(s), but the organic stabilizer may include one or more non-metal heteroatoms such as nitrogen, oxygen, sulfur, silicon, halogen, and the like. Exemplary organic stabilizers include for instance thiol and its derivatives, amine and its derivatives, carboxylic acid and its carboxylate derivatives, polyethylene glycols, and other organic surfactants. In embodiments, the organic stabilizer is selected from the group consisting of a thiol such as for example butanethiol, pentanethiol, hexanethiol, heptanethiol, octanethiol, decanethiol, and dodecanethiol; an amine such as for example ethylamine, propylamine, butylamine, penylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, and dodecylamine; a dithiol such as for example 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol; a diamine such as for example ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane; a mixture of a thiol and a dithiol; and a mixture of an amine and a diamine. Organic stabilizers containing a pyridine derivative (e.g., dodecyl pyridine) and/or organophosphine that can stabilize silver-containing nanoparticles are also included as a stabilizer in embodiments of the present invention.

[0058] In embodiments, the stabilizer is an organoamine such as for example butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, hexadecylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminononane, diaminodecane, diaminooctane, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, methylpropylamine, ethylpropylamine, propylbutylamine, ethylbutylamine, ethylpentylamine, propylpentylamine, butylpentylamine, tributylamine, trihexylamine, and the like, or mixtures thereof.

[0059] One, two, three or more stabilizers may be used. In embodiments where two or more stabilizers are used, each stabilizer may be present at any suitable weight ratio or molar ratio such as for example from about 99(first stabilizer): 1(second stabilizer) to about 1(first stabilizer):99(second stabilizer). The amount of the stabilizer used is for example about 1 or more molar equivalents per mole of silver compound, or about 2 or more molar equivalents per mole of silver compound, or about 10 or more molar equivalents per mole of silver compound, or about 25 or more molar equivalents per mole of silver compound.

[0060] In embodiments, the silver-containing nanoparticles may form a chemical bond with the stabilizer. The chemical names of the stabilizer provided herein are before formation of any chemical bond with the silver-containing nanoparticles. It is noted that the nature of the stabilizer may change with the formation of a chemical bond, but for convenience the chemical name prior to formation of the chemical bond is used.

[0061] The attractive force between the silver-containing nanoparticles and the stabilizer can be a chemical bond and/or physical attachment. The chemical bond can take the form of for example covalent bonding, hydrogen bonding, coordination complex bonding, or ionic bonding, or a mixture of different chemical bondings. The physical attachment can take the form of for example van der Waals' forces or dipole-dipole interaction, or a mixture of different physical attachments.

[0062] The extent of the coverage of stabilizer on the surface of the silver-containing nanoparticles can vary for example from partial to full coverage depending for instance on the capability of the stabilizer to stabilize the silver-containing nanoparticles in the solvent. Of course, there is variability as well in the extent of coverage of the stabilizer among the individual silver-containing nanoparticles.
[0063] Any suitable solvent can be used for the reaction mixture including for example organic solvents and/or water. The organic solvents include for example hydrocarbon solvents such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, mesitylene, and the like; alcohols such as methanol, ethanol, propanol, butanol, pentanol and the like; tetrahydrofuran; chlorobenzene; dichlorobenzene; trichlorobenzene; nitrobenzene; cyanobenzene; acetonitrile; and mixtures thereof. One, two, three or more solvents may be used. In embodiments where two or more solvents are used, each solvent may be present at any suitable volume ratio or molar ratio such as for example from about 99(first solvent): 1(second solvent) to about I(first solvent):99(second solvent).

[0064] The reaction of the silver compound with the reducing agent is carried out at a suitable temperature of for example from about -50[deg.] C. to about 200[deg.] C., or from about 0[deg.] C. to about 150[deg.] C., particularly at a temperature ranging for example from about 20[deg.] C. to about 120[deg.] C.

[0065] The silver-containing nanoparticles have a particle size of for example less than about 100 nm, less than about 50 nm, less than about 25 nm, or less than about 10 nm. The particle size is defined herein as the average diameter of silver-containing particle core, excluding the stabilizer, as determined by transmission electron microscopy ("TEM"). Generally, a plurality of particle sizes may exist in the silver-containing nanoparticles obtained from the preparation. In embodiments, the existence of different sized silver-containing nanoparticles is acceptable.

[0066] In embodiments, the silver-containing nanoparticles are composed of elemental silver or a silver composite. Besides silver, the silver composite includes either or both of (i) one or more other metals and (ii) one or more non-metals. Suitable other metals include for example Al, Au, Pt, Pd, Cu, Co, Cr, In, and Ni, particularly the transition metals for example Au, Pt, Pd, Cu, Cr, Ni, and mixtures thereof. Exemplary metal composites are Au-Ag, Ag-Cu, Au-Ag-Cu, and Au-Ag-Pd. Suitable non-metals in the metal composite include for example Si, C, and Ge. The various components of the silver composite may be present in an amount ranging for example from about 0.01% to about 99.9% by weight, particularly from about 10% to about 90% by weight. In embodiments, the silver composite is a metal alloy composed of silver and one, two or more other metals, with silver comprising for example at least about 20% of the nanoparticles by weight, particularly greater than about 50% of the nanoparticles by weight. Unless otherwise noted, the weight percentages recited herein for the components of the silver-containing nanoparticles do not include the stabilizer.

[0067] Silver-containing nanoparticles composed of a silver composite can be made for example by using a mixture of (i) a silver compound (or compounds) and (ii) another metal salt (or salts) or another non-metal (or non-metals) in the reaction.

[0068] The preparation of silver-containing nanoparticle compositions, which are suitable for the preparation of conductive elements for electronic applications can be carried out using all or some of the following procedures: (i) addition of a scavenger to the final reaction mixture from the preparation of silver-containing nanoparticles to destroy excess reducing agent; (ii) concentrating the reaction mixture by removing solvent; (iii) adding the concentrated reaction mixture to a non-solvent (or vice versa) to precipitate the silver-containing nanoparticles; (iv) collecting the silver-containing nanoparticles by filtration or centrifugation to result in isolated silver-containing nanoparticles (with the stabilizer molecules on the surface of the silver-containing nanoparticles); (v) dissolving or dispersing (assisted by for example ultrasonic and/or mechanical stirring) the isolated silver-containing nanoparticles (with molecules of the stabilizer on the surface of the silver-containing nanoparticles) in an appropriate liquid.

[0069] Silver-containing nanoparticle compositions can also be made by mixing silver-containing nanoparticles with other metal or non-metal nanoparticles.

[0070] In embodiments, it may be possible to form a silver-containing nanoparticle composition (with stabilizer molecules on the surface of the silver-containing nanoparticles) suitable for forming conductive elements for electronic applications without the need for the above described procedures to isolate the silver-containing nanoparticles from the reaction mixture. In such embodiments, the reaction mixture (optionally augmented with another liquid which may be the same or different from the solvent used in the reaction mixture) may be considered the silver-containing nanoparticle composition.

[0071] The scavengers that can be used to destroy excess reducing agent include for example ketone, aldehyde, carboxylic acid, or a mixture thereof. Specific exemplary scavengers include acetone, butanone, pentanone, formaldehyde, acetaldehyde, acetic acid, and the like, or a mixture thereof.

[0072] Suitable non-solvents that can be used for the precipitation of silver-containing nanoparticles include any liquids that are mixable with the reaction solvent or solvents for the preparation of silver-containing nanoparticles.

[0073] The liquid that can be used to disperse or dissolve silver-containing nanoparticles to form a silver-containing nanoparticle composition includes organic liquids or water. The organic liquids include for example hydrocarbon solvents such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, mesitylene, and the like; alcohols such as methanol, ethanol, propanol, butanol and the like; tetrahydrofuran; chlorobenzene; dichlorobenzene; trichlorobenzene; nitrobenzene; cyanobenzene; acetonitrile; and mixtures thereof. One, two, three or more liquids may be used. In embodiments where two or more solvents are used, each solvent may be present at any suitable volume ratio or molar ratio such as for example from about 99(first liquid): 1(second liquid) to about 1(first liquid):99(second liquid).

[0074] Exemplary amounts of the components of the silver-containing nanoparticle composition are as follows. The silver-containing nanoparticles and the stabilizer are present in an amount ranging for example from about 0.3% to about 90% by weight, or from about 1% to about 70% by weight, the balance being the other components of the composition such as the liquid.

[0075] In embodiments, the stabilizer present in the silver-containing nanoparticle composition originated from the reaction mixture for the preparation of silver-containing nanoparticles; no stabilizer is added subsequently for the formation of the silver-containing nanoparticles. In other embodiments, the same or different stabilizer may be added subsequently for the formation of the silver-containing nanoparticles in an amount ranging for example from about 0.3% to about 70% by weight based on the weight of the silver-containing nanoparticle composition.

[0076] The silver-containing nanoparticle composition has a stability (that is, the time period where there is minimal precipitation or aggregation of the silver-containing nanoparticles) of for example at least about 3 hours, or from about 3 hours to about 1 month, from about 1 day to about 3 months, from about 1 day to about 6 months, from about 1 week to over 1 year.

[0077] The fabrication of an electrically conductive element from the silver-containing nanoparticle composition ("composition") can be carried out by depositing the composition on a substrate using a liquid deposition technique at any suitable time prior to or subsequent to the formation of other optional layer or layers on the substrate. Thus, liquid deposition of the composition on the substrate can occur either on a substrate or on a substrate already containing layered material (e.g., a semiconductor layer and/or an insulating layer).

[0078] The phrase "liquid deposition technique" refers to deposition of a composition using a liquid process such as liquid coating or printing, where the liquid is a solution or a dispersion. The silver-containing nanoparticle composition may be referred to as an ink when printing is used. Illustrative liquid coating processes include for example spin coating, blade coating, rod coating, dip coating, and the like. Illustrative printing techniques include for example lithography or offset printing, gravure, flexography, screen printing, stencil printing, inkjet printing, stamping (such as microcontact printing), and the like. Liquid deposition deposits a layer of the composition having a thickness ranging from about 5 nanometers to about 5 millimeters, preferably from about 10 nanometers to about 1000 micrometers. The deposited silver-containing nanoparticle composition at this stage may or may not exhibit appreciable electrical conductivity.

[0079] As used herein, the term "heating" encompasses any technique(s) that can impart sufficient energy to the heated material to cause the desired result such as thermal heating (e.g., a hot plate, an oven, and
a burner), infra-red ("IR") radiation, microwave radiation, or UV radiation, or a combination thereof.

[0080] Heating the deposited composition at a temperature of for example below about 250[deg.] C., or below about 200[deg.] C. or about 150[deg.] C., causes the silver-containing nanoparticles to form an electrically conductive layer which is suitable for use as an electrically conductive element in electronic devices. The heating temperature preferably is one that does not cause adverse changes in the properties of previously deposited layer(s) or the substrate (whether single layer substrate or multilayer substrate). The heating is performed for a time ranging from for example about 1 second to about 10 hours, particularly from about 10 seconds to about 1 hour. The heating is performed in air, in an inert atmosphere for example under nitrogen or argon, or in a reducing atmosphere for example under nitrogen containing from about 1 to about 20 percent by volume hydrogen. The heating is performed under normal atmospheric conditions or at a reduced pressure of for example from several mbars to about 10<-3 > mbar.

[0081] Heating produces a number of effects. Prior to heating, the layer of the deposited silver-containing nanoparticles may be electrically insulating or with very low electrical conductivity, but heating results in an electrically conductive layer composed of annealed silver-containing nanoparticles which increases the conductivity. In embodiments, the annealed silver-containing nanoparticles may be coalesced or partially coalesced silver-containing nanoparticles. In embodiments, it may be possible that in the annealed silver-containing nanoparticles, the silver-containing nanoparticles achieve sufficient particle-to-particle contact to form the electrically conductive layer without coalescence.

[0082] Heating may cause separation of the stabilizer and the liquid from the silver-containing nanoparticles in the sense that the stabilizer and the liquid are generally not incorporated into the electrically conductive layer but if present are in residual quantities. In embodiments, heating may decompose a portion of the stabilizer to produce "decomposed stabilizer." Heating may also cause separation of the decomposed stabilizer such that the decomposed stabilizer generally is not incorporated into the electrically conductive layer, but if present is in a residual amount. Separation of the stabilizer, the liquid, and the decomposed stabilizer from the silver-containing nanoparticles may lead to enhanced electrical conductivity of the resulting electrically conductive layer since the presence of these components may reduce the extent of silver-containing nanoparticle to silver-containing nanoparticle contact or coalescence. Separation may occur in any manner such as for example a change in state of matter from a solid or liquid to a gas, e.g., volatilization.

[0083] In embodiments, one or more of the stabilizer, decomposed stabilizer, and the liquid is absent from the electrically conductive layer. In embodiments, a residual amount of one or more of the stabilizer,
decomposed stabilizer, and the liquid may be present in the electrically conductive layer, where the residual amount does not appreciably affect the conductivity of the electrically conductive layer. In embodiments, the residual amount of one or more of the stabilizer, decomposed stabilizer, and the liquid may decrease the conductivity of the electrically conductive layer but the resulting conductivity is still within the useful range for the intended electronic device. The residual amount of each component may independently range for example of up to about 5% by weight, or less than about 0.5% by weight based on the weight of the electrically conductive layer, depending on the process conditions such as heating temperature and time. When heating causes separation of the stabilizer and/or decomposed stabilizer from the silver-containing nanoparticles, the attractive force between the separated stabilizer/decomposed stabilizer and the silver-containing nanoparticles is severed or diminished. Other techniques such as exposure to UV radiation, microwave radiation, or IR radiation may be used or combined with thermal heating to accelerate the separation of the liquid and the stabilizer (and/or the decomposed stabilizer) from the silver-containing nanoparticles.

[0084] In embodiments, after heating, the resulting electrically conductive layer has a thickness ranging for example from about 5 nanometers to about 5 millimeters, preferably from about 10 nanometers to about 1000 micrometers.

[0085] The conductivity of the resulting silver-containing element produced by heating the deposited silver-containing nanoparticle composition is for example more than about 0.1 Siemens/centimeter ("S/cm"), more than about 100 S/cm, more than about 500 S/cm, more than about 2,000 S/cm, more than about 5,000 S/cm, more than about 10,000 S/cm, and more than about 20,000 S/cm as measured by four-probe method.

[0086] The resulting conductive elements can be used as conductive electrodes, conductive pads, conductive traces, conductive lines, conductive tracks, and the like in electronic devices. The phrase "electronic device" refers to macro-, micro- and nano-electronic devices such as thin film transistor, organic light emitting diodes, RFID tags, photovoltaic, and other electronic devices which require conductive elements or components.

[0087] In embodiments, the advantages of the present chemical method for preparing silver-containing nanoparticles are one or more of the following: (i) single phase synthesis (where the silver compound, the stabilizer, and the solvent form a single phase) without the need for a surfactant; (ii) short reaction time; (iii) low reaction temperatures of below about 100[deg.] C.; (iv) uniform particle size and narrow particle size distribution; (v) stable silver-containing nanoparticle composition which can be easily processed by liquid deposition techniques; (vi) relatively inexpensive starting materials; and (vii) suitable for large-scale production that would significantly lower the cost of silver-containing nanoparticles.

[0088] In embodiments, the silver-containing nanoparticle composition can be used in for example, but not limited to, fabricating conductive components such as source and drain electrodes in thin film transistor ("TFT").

[0089] In FIG. 1, there is schematically illustrated a TFT configuration 10 comprised of a heavily n-doped silicon wafer 18 which acts as both a substrate and a gate electrode, a thermally grown silicon oxide insulating layer 14 on top of which are deposited two metal contacts, source electrode 20 and drain electrode 22. Over and between the metal contacts 20 and 22 is an organic semiconductor layer 12.

[0090] FIG. 2 schematically illustrates another TFT configuration 30 comprised of a substrate 36, a gate electrode 38, a source electrode 40 and a drain electrode 42, an insulating layer 34, and an organic semiconductor layer 32.

[0091] FIG. 3 schematically illustrates a further TFT configuration 50 comprised of a heavily n-doped silicon wafer 56 which acts as both a substrate and a gate electrode, a thermally grown silicon oxide insulating layer 54, and an organic semiconductor layer 52, on top of which are deposited a source electrode 60 and a drain electrode 62.

[0092] FIG. 4 schematically illustrates an additional TFT configuration 70 comprised of substrate 76, a gate electrode 78, a source electrode 80, a drain electrode 82, an organic semiconductor layer 72, and an insulating layer 74.

[0093] The substrate may be composed of for instance silicon, glass plate, plastic film or sheet. For structurally flexible devices, plastic substrate, such as for example polyester, polycarbonate, polyimide sheets and the like may be used. The thickness of the substrate may be from amount 10 micrometers to over 10 millimeters with an exemplary thickness being from about 50 micrometers to about 2 millimeters, especially for a flexible plastic substrate and from about 0.4 to about 10 millimeters for a rigid substrate such as glass or silicon.

[0094] The gate electrode, the source electrode, and the drain electrode are fabricated by embodiments of the present invention. The thickness of the gate electrode layer ranges for example from about 10 to about 2000 nm. Typical thicknesses of source and drain electrodes are, for example, from about 40 nm to about 1 micrometer with the more specific thickness being about 60 to about 400 nm.

[0095] The insulating layer generally can be an inorganic material film or an organic polymer film. Illustrative examples of inorganic materials suitable as the insulating layer include silicon oxide, silicon nitride, aluminum oxide, barium titanate, barium zirconium titanate and the like; illustrative examples of organic polymers for the insulating layer include polyesters, polycarbonates, poly(vinyl phenol), polyimides, polystyrene, poly(methacrylate)s, poly(acrylate)s, epoxy resin and the like. The thickness of the insulating layer is, for example from about 10 nm to about 500 nm depending on the dielectric constant of the dielectric material used. An exemplary thickness of the insulating layer is from about 100 nm to about 500 nm. The insulating layer may have a conductivity that is for example less than about 10<-12 > S/cm.

[0096] Situated, for example, between and in contact with the insulating layer and the source/drain electrodes is the semiconductor layer wherein the thickness of the semiconductor layer is generally, for example, about 10 nm to about 1 micrometer, or about 40 to about 100 nm. Any semiconductor material may be used to form this layer. Exemplary semiconductor materials include regioregular polythiophene, oligthiophene, pentacene, and the semiconductor polymers disclosed in Beng Ong et al., U.S. patent application Publication No. US 2003/0160230 A1; Beng Ong et al., U.S. patent application Publication No. US 2003/0160234 A1; Beng Ong et al., U.S. patent application Publication No. US 2003/0136958 A1; and "Organic Thin Film Transistors for Large Area Electronics" by C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater., Vol. 12, No. 2, pp. 99-117 (2002), the disclosures of which are totally incorporated herein by reference. Any suitable technique may be used to form the semiconductor layer. One such method is to apply a vacuum of about 10<-5 > to 10<-7 > torr to a chamber containing a substrate and a source vessel that holds the compound in powdered form. Heat the vessel until the compound sublimes onto the substrate. The semiconductor layer can also generally be fabricated by solution processes such as spin coating, casting, screen printing, stamping, or jet printing of a solution or dispersion of the semiconductor.

[0097] The insulating layer, the gate electrode, the semiconductor layer, the source electrode, and the drain electrode are formed in any sequence, particularly where in embodiments the gate electrode and the semiconductor layer both contact the insulating layer, and the source electrode and the drain electrode both contact the semiconductor layer. The phrase "in any sequence" includes sequential and simultaneous formation. For example, the source electrode and the drain electrode can be formed simultaneously or sequentially. The composition, fabrication, and operation of thin film transistors are described in Bao et al., U.S. Pat. No. 6,107,117, the disclosure of which is totally incorporated herein by reference.

[0098] The invention will now be described in detail with respect to specific exemplary embodiments thereof, it being understood that these examples are intended to be illustrative only and the invention is not intended to be limited to the materials, conditions, or process parameters recited herein. All percentages and parts are by weight unless otherwise indicated. Room temperature refers to a temperature ranging for example from about 20 to about 25 degrees C.

EXAMPLE 1

[0099] Silver acetate (0.167 g, 1 mmol) and 1-dodecylamine (3.71 g, 20 mmol) were first dissolved in toluene (100 mL) by heating at 60[deg.] C. until silver acetate was dissolved. To this solution was added a solution of phenylhydrazine (0.43 g, 4 mmol) in toluene (50 mL) with vigorous stirring over a period of 10 min. The resulting reaction mixture was stirred at 60[deg.] C. for 1 hr before cooling down to room temperature. Subsequently, acetone (10 mL) was added to the reaction mixture to destroy excess phenylhydrazine. Solvent removal from the reaction mixture gave a residue which was added to stirring methanol (100 mL) to precipitate the crude silver nanoparticle products. The crude silver nanoparticle product was isolated by centrifugation, washed with acetone twice, and air-dried. It was then dispersed in cyclohexane (2 mL) to form a dispersion of silver nanoparticles in cyclohexane (with molecules of the 1-dodecylamine stabilizer on the surface of the silver nanoparticles). This dispersion was suitable for fabricating conductive elements for electronic devices.

[0100] To form a conductive thin film for conductivity measurement, the dispersion of silver nanoparticles in cyclohexane (with the 1-dodecylamine stabilizer) was spin-coated on a glass substrate to form a brownish thin film. The latter was heated on a hot plate at about 120[deg.] C. under ambient conditions, a shiny silver film formed immediately upon heating. The thin-film conductivity of the resulting silver film was about 23,000 S/cm as calculated from the measurements using the conventional four-probe technique.

EXAMPLE 2

[0101] Silver acetate (0.167 g, 1 mmol) and 1-hexadecylamine (4.83 g, 20 mmol) were first dissolved in toluene (100 mL) by heating at 60[deg.] C. until silver acetate was dissolved. To this solution was added a solution of phenylhydrazine (0.43 g, 4 mmol) in toluene (50 mL) with vigorous stirring over a period of 10 min. The resulting reaction mixture was stirred at 60[deg.] C. for 1 hr before cooling down to room temperature. Subsequently, acetone (10 mL) was added to the reaction mixture to destroy excess phenylhydrazine. Solvent removal from the reaction mixture gave a residue which was added to stirring methanol (100 mL) to precipitate the crude silver nanoparticle product. The crude silver nanoparticle product was isolated by centrifugation, washed with acetone twice, and air-dried. It was the dispersed in cyclohexane (2 mL) to form a dispersion of silver nanoparticles in cyclohexane (with molecules of the 1-hexadecylamine stabilizer on the surface of the silver nanoparticles). This dispersion was suitable for fabricating conductive elements for electronic devices.

[0102] To form a conductive thin film for conductivity measurement, the dispersion of silver nanoparticles in cyclohexane (with the 1-hexadecylamine stabilizer) was spin-coated on a glass substrate to form a brownish thin film. The latter was heated on a hot plate at about 160[deg.] C. under ambient conditions, a shiny silver film formed immediately upon heating. The thin-film conductivity of the silver film was about 26,000 S/cm as calculated from the measurements using the conventional four-probe technique.

EXAMPLE 3

[0103] Silver acetate (0.167 g, 1 mmol) and 1-dodecylamine (3.71 g, 20 mmol) were first dissolved in toluene (100 mL) by heating at 60[deg.] C. until silver acetate was dissolved. To this solution was added a solution of benzoic hydrazide (benzoylhydrazine) (0.54 g, 4 mmol) in toluene (50 mL) with vigorous stirring over a period of 10 min. The resulting reaction mixture was stirred at 60[deg.] C. for 1 hr before cooling down to room temperature. Subsequently, acetone (10 mL) was added to the reaction mixture to destroy excess benzoic hydrazide. Solvent removal from the reaction mixture gave a residue which was added to methanol (100 mL) with stirring to precipitate crude silver nanoparticle product. The crude silver nanoparticle product was isolated by centrifugation, washed with acetone twice, and air-dried. It was dispersed in cyclohexane (2 mL) to form a dispersion of silver nanoparticles in cyclohexane (with molecules of the 1-dodecylamine stabilizer on the surface of the silver nanoparticles). This dispersion was suitable for fabricating conductive elements for electronic devices.

[0104] To form a conductive thin film for conductivity measurement, the dispersion of silver nanoparticles in cyclohexane (with the 1-dodecylamine stabilizer) was spin-coated on a glass substrate, and the resulting brownish film was heated on a hot plate at about 120[deg.] C. for 1.5 hr under ambient conditions, The thin-film conductivity of the resulting silver film was about 15,000 S/cm as calculated from the measurements using the conventional four-probe technique.

EXAMPLE 4

[0105] A bottom-contact thin film transistor, as schematically shown by FIG. 1, was chosen to illustrate the use of silver-containing nanoparticle composition as the conductive electrodes of a thin-film transistor. The experimental device was fabricated under ambient conditions, and comprised of an n-doped silicon wafer with a thermally grown silicon oxide layer of a thickness of about 110 nm thereon. The wafer functioned as the gate electrode while the silicon oxide layer acted as the insulating layer and had a capacitance of about 30 nF/cm<2 > (nanofarads/square centimeter), as measured using a capacitor meter. The silicon wafer was first cleaned with oxygen/argon plasma, isopropanol, air dried, and then immersed in a 0.1 M solution of octyltrichlorosilane in toluene for about 20 min at 60[deg.] C. Subsequently, the wafer was washed with toluene, isopropanol and air-dried.

[0106] Stencil printing was used to deposit the silver-containing nanoparticle composition on the modified wafer substrate. A stainless stencil with a thickness of 13 [mu]m was positioned on top of the wafer. A dispersion of silver-containing nanoparticle composition of Example 1 in cyclohexane (30 wt %) was then painted through the electrode features of the stencil with a fine paint brush. After drying at room temperature for 1-5 min, the stencil was removed. The printed silver-containing nanoparticle elements were heated at 120[deg.] C. on a hotplate under ambient conditions. This resulted in the formation of shiny silver electrodes. Subsequently, a semiconductor layer was deposited on the electroded substrate using the polythiophene semiconductor of the following Formula:
[0107]
EMI1.0

[0108] where n is a number of from about 5 to about 5,000. This polythiophene and its preparation are described in Beng Ong et al., U.S. patent application Publication No. US 2003/0160230 A1, the disclosure of which is totally incorporated herein by reference. The semiconductor polythiophene layer of about 30 nm to about 100 nm in thickness was deposited on top of the device by spin coating of the polythiophene in dichlorobenzene solution at a speed of 1,000 rpm for about 100 seconds, and dried in vacuo at 80[deg.] C. for 20 hr, followed by annealing in a vacuum oven at 120-140[deg.] C. for 10-30 min to induce high structural orders of the semiconductor.

[0109] The evaluation of field-effect transistor performance was accomplished in a black box at ambient conditions using a Keithley 4200 SCS semiconductor characterization system. The carrier mobility, [mu], was calculated from the data in the saturated regime (gate voltage, VG<source-drain voltage, VSD) accordingly to equation (1)
ISD=Ci[mu](W/2L)(VG-VT)<2 > (1)
where ISD is the drain current at the saturated regime, W and L are, respectively, the semiconductor channel width and length, Ci is the capacitance per unit area of the insulating layer, and VG and VT are, respectively, the gate voltage and threshold voltage. VT of the device was determined from the relationship between the square root of ISD at the saturated regime and VG of the device by extrapolating the measured data to ISD=0. An important property for the thin film transistor is its current on/off ratio, which is the ratio of the saturation source-drain current in accumulation regime over the current in depletion regime.

[0110] The inventive device prepared in this manner showed very good output and transfer characteristics. The output characteristics showed no noticeable contact resistance, very good saturation behaviour, clear saturation currents which are quadratic to the gate bias. The device turned on at around zero gate voltage with a sharp subthreshold slope. Mobility was calculated to be 0.08 cm<2> /V.s, and the current on/off ratio was about 10<6> -10<7> . The performance of the inventive device was essentially the same as that of a conventional bottom-contact TFT with vacuum deposited silver electrodes.



Silver Powder and Method of Preparing the Same
US7776442

Abstract --- To obtain a silver nanoparticle powder suitable for a wiring material for forming a fine circuit pattern, particularly for a wiring formation material through inkjet method. The silver nanopowder has an average particle size (DTEM) below 30 nm, aspect ratio below 1.5, crystal particle diameter (Dx) by X ray under 30 nm, single crystalline degree [(DTEM)]/(Dx) under 5.0, and CV value [=100 x standard deviation (sigma)/number average particle size [(DTEM)] under 40%, measured by TEM observation, the surface of the powder being covered with an organic protective agent with molecular weight 100 to 400. The nanopowder is obtained by reducing silver salt at temperature of 85 to 150 DEG C in the co-existence of the organic protective agent within the alcohol of boiling point 85 to 150 DEG C.

TECHNICAL FIELD

The present invention relates to a particulate powder of silver, particularly to a nanoparticle powder of silver that is a suitable material for forming interconnects of fine circuit patterns, especially for forming interconnects by the ink-jet method, and a method of manufacturing the powder. The particulate powder of silver of the present invention is a suitable material for forming interconnects on LSI substrates, and electrodes and interconnects of flat panel displays (FPDs), and for filling in fine trenches, via holes and contact holes. It is also suitable for use as a coloring material for automobile paints and the like. Moreover, its low impurity and toxicity levels make it useful as a carrier for adsorbing biochemical substances and the like in the fields of medical treatment, diagnostics and biotechnology.

BACKGROUND ART

When the size of solid substance particles reaches the ultrafine nanometer order (called "nanoparticles" in the following), the specific surface area of the particles becomes very great, so that, even though they are solids, their interface with a gas or liquid becomes extremely large. Their surface characteristics therefore strongly affect the properties of the solid substance.
It is known that the melting point of metal nanoparticles is dramatically reduced from that in the bulk state. In comparison with conventional micrometer-order particles, therefore, metal nanoparticles offer not only fine interconnect formation capability but also other features such as low-temperature sinter capability. Owing to the low resistance and excellent weatherability of silver nanoparticles, and also their low price compared with other noble metal nanoparticles, silver nanoparticles are seen as metal nanoparticles with particular promise as the next-generation material for fine interconnects.

Known methods of manufacturing nanometer-order particles (nanoparticles) of silver are broadly divided into vapor phase methods and liquid phase methods. Vapor phase methods are ordinarily methods that conduct deposition in a gas. Patent Document 1 describes a method of vaporizing silver in a helium or other inert gas atmosphere, under a reduced pressure of around 0.5 torr. Patent Document 2 teaches a liquid phase method for obtaining a silver colloid by reducing silver ions in an aqueous phase using an amine and transferring the obtained silver deposition phase to an organic solvent phase (polymeric dispersant). Patent Document 3 describes a method in which a reducing agent (alkali metal borohydride or ammonium borohydride) is used to reduce a silver halide in a solvent in the presence of a thiol type protective agent.

Patent Document 1: JP 2001-35255A
Patent Document 2: JP 11-319538 A
Patent Document 3: JP 2003-253311A

Problems to be Overcome by the Invention

The silver particles obtained by the vapor phase method of Patent Document 1 are 10 nm or less in diameter and have good dispersibility in solvent. However, the technology requires a special apparatus. This makes it difficult to synthesize large quantities of silver nanoparticles for industrial use. In contrast, the liquid phase method is basically suitable for large-volume synthesis but has a problem in that the metal nanoparticles in the liquid have a strong tendency to agglomerate, making it difficult to obtain a monodispersed nanoparticle powder. In most cases, citric acid is used as the dispersant when manufacturing metal nanoparticles, and the metal ion concentration in the liquid is usually very low as 10 mmole/L (0.01 mole/L) or lower. This is a barrier to its industrial application.

Although the foregoing method of Patent Document 2 achieves synthesis of stably dispersed silver nanoparticles by using a high metal ion concentration of 0.1 mole/L or greater and a high reaction mixture concentration, it suppresses agglomeration by using a polymeric dispersant having a high number average molecular weight of several tens of thousands. The use of a dispersant of high molecular weight is not a problem when the silver nanoparticles are to be used as a coloring material, but when the particles are to be used in circuit fabrication applications, a firing temperature that is equal to or higher than the polymer boiling point is required and, in addition, pores readily form in the interconnects after the firing, so that problems of high resistance and breakage arise, making the particles not altogether suitable for fine interconnect applications.

The foregoing method of Patent Document 3 conducts the reaction at a relatively high reactant concentration of 0.1 mole/L or greater and disperses the obtained silver particles of 10 nm or less using a dispersant. As a suitable dispersant, Patent Document 3 proposes a thiol type dispersant, which can be readily vaporized by low-temperature firing at the time of interconnect formation because it has a low molecular weight of around 200. However, the thiol type surfactant contains sulfur (S), and sulfur causes corrosion of interconnects and other electronic components, making it an unsuitable element for interconnect formation applications. The method is therefore not suitable for interconnect formation applications.

Therefore, an object of the present invention is to overcome such problems by providing a nanoparticle powder of silver suitable for fine interconnect formation applications, and a liquid dispersion thereof, at low cost and in large quantities. Moreover, since monodispersion of spherical silver nanoparticles of uniform diameter is preferable, another object is to provide a liquid dispersion of such silver particles.

Means for Solving the Problems

In accordance with, the present invention, which was accomplished for achieving the foregoing objects, there is provided a particulate powder of silver having an average particle diameter measured by TEM observation (DTEM) of 30 nm or less, an aspect ratio of less than 1.5, an X-ray crystallite size (Dx) of 30 nm or less, a degree of single crystal grain {(DTEM)/(Dx)} of 5.0 or less, and a CV value {100*standard deviation ([sigma])/number average diameter (DTEM)} of less than 40%, which particulate powder of silver has adhered to the surface of the particles thereof an organic protective agent (typically an amino compound, particularly a primary amine) having a molecular weight of 100 to 400. The present invention further provides a liquid dispersion of silver particles obtained by dispersing such particulate powder of silver in an organic solvent, which liquid dispersion of silver particles has an average particle diameter (D50) measured by the dynamic light-scattering method of 100 nm or less and a degree of dispersion {(D50)/(DTEM)} of 5.0 or less. As can be seen in the photograph of FIG. 1, the silver particles of the present invention are spheres of uniform diameter. In a liquid dispersion, they are monodispersed with the individual particles spaced at regular intervals. Further, as a method of manufacturing such a particulate powder of silver, the present invention provides a method of manufacturing a particulate powder of silver coated with an organic protective agent, wherein a silver salt (typically silver nitrate) is subjected to reduction treatment at a temperature of 85 to 150[deg.] C. in an alcohol having a boiling point of 85 to 150[deg.] C. and in the co-presence of an organic protective agent (typically an amino compound, particularly a primary amine, having a molecular weight of 100 to 400). The alcohol is desirably one or a mixture of two or more of isobutanol, n-butanol, s-butanol, and t-butanol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission electron microscope (TEM) photograph of a nanoparticle powder of silver of the present invention.

FIG. 2 is a transmission electron microscope (TEM) photograph of the nanoparticle powder of silver of the present invention taken at a different magnification from that of FIG. 1.



The present inventor conducted numerous experiments to manufacture nanoparticle powder of silver by the liquid phase method and found it was possible to obtain a powder composed of spherical silver nanoparticles of uniform particle diameter by subjecting a silver salt to reduction treatment at a temperature of 85 to 150[deg.] C. in an alcohol having a boiling point of 85 to 150[deg.] C. (while refluxing vaporized alcohol to the liquid phase) and in the co-presence of an amino compound having a molecular weight of 100 to 400. This nanoparticle powder of silver disperses well in a dispersant because it is in a condition of having the organic protective agent adhered to its surface. It is therefore a suitable material for forming interconnects of fine circuit patterns, especially for forming interconnects by the ink-jet method. The characteristic features of the invention particulate silver powder are explained individually below.

TEM Particle Diameter (DTEM)

The average particle diameter (DTEM) of the invention silver particles measured by TEM (transmission electron microscope) observation is 30 nm or less. It is determined by measuring the diameters of 300 discrete, non-overlapping particles observed in a 600000*TEM image and calculating the average thereof. The aspect ratio and CV value are determined from the same observational results.

Aspect Ratio

The aspect ratio (ratio of long diameter/short diameter) of the particulate silver powder of this invention is less than 1.5, preferably less than 1.2, and more preferably less than 1.1. The particles in the photograph of FIG. 1 are substantially spherical and have an (average) aspect ratio of less than 1.05. They are therefore ideal for interconnect formation applications. If the aspect ratio exceeds 1.5, particle packing is degraded when the particle liquid dispersion is applied to a substrate and dried, which may cause pores to occur during firing, increasing the resistance and possibly giving rise to interconnect breakage.

CV Value

The CV value is an index of particle diameter variation; a smaller CV value indicates more uniform particle diameter. CV value is expressed as: CV value=100*standard deviation ([sigma])/number average diameter. The CV value of the particulate silver powder of the present invention is less than 40%, preferably less than 25%, more preferably 15%. A nanoparticle silver powder having a CV value of less than 40% is ideal for interconnect applications. If the CV value is 40% or greater, then, similarly to the foregoing, particle packing is inferior, so that pores occurring during firing may increase the resistance and give rise to interconnect breakage.

X-Ray Crystallite Size (Dx)

The crystallite size of the silver nanoparticles of this invention is less than 30 nm. The Scherrer relationship can be used to find the crystallite size of the particulate silver powder from the results of x-ray diffraction measurement. In this specification, the crystallite size is therefore called the X-ray crystallite size (Dx). It is determined as follows.

The Scherrer relationship is expressed by the general equation:
D=K.[lambda]/[beta] Cos [theta],

where K is Scherrer constant, D is crystallite size, [lambda] is wavelength of the x-ray used for the measurement, [beta] is half-value width of the x-ray diffraction peak, and [theta] is Bragg angle of the diffraction line.
If 0.94 is used as the value of K and a Cu X-ray tube is used, the equation can be rewritten as:
D=0.94*1.5405/[beta] Cos [theta].

Degree of Single Crystal Grain

Degree of single crystal grain is represented by the ratio of TEM particle diameter to X-ray crystallite size {(DTEM)/(Dx)}. The degree of single crystal grain approximately corresponds to the number of crystals per particle. The higher the value of the degree of single crystal grain, the greater is the number of crystallites, which called the particle to be composed of multiple crystals. The degree of single crystal grain of the invention silver particles is 5.0 or less, preferably 3.0 or less, more preferably 1.0 or less. Grain boundaries within the particles are therefore few. Electrical resistance rises with increasing number of grain boundaries present. In the invention particulate silver powder, the value of the degree of single crystal grain is low, which gives it low resistance and makes it suitable for use in conductors.

Average Particle Diameter by the Dynamic Light-Scattering Method

The invention liquid dispersion obtained by mixing the particulate silver powder and the organic solvent has an average particle diameter (D50) by the dynamic light-scattering method of 60 nm or less and the degree of dispersion {(D50)/(DTEM)} is 5.0 or less. The silver particles of this invention readily disperse in the organic solvent (dispersion medium) and can remain in a stable dispersed state in the dispersion medium. The dynamic light-scattering method can be used to assess the state of dispersion of the silver particles in the dispersion medium, and also to calculate the average particle diameter. The principle of the method is as follows. In a liquid, the translational, rotational and other forms of Brownian movement of particles having a diameter in the range of around 1 nm to 5 [mu]m ordinarily changes the location and orientation of the particles from instant to instant. When a laser beam is projected onto the particles and the scattered light that emerges is detected, there are observed fluctuations in the scattered light intensity that are attributable to the Brownian movement. By measuring the time dependence of the scattered light intensity, it is possible to determine the velocity of the Brownian movement (diffusion coefficient) of the particles and also to learn the size of the particles. If the average diameter of the particles in the dispersion medium measured utilizing this principle is close to the average particle diameter obtained by TEM observation, this means that the particles in the liquid are individually dispersed (not attached to each other or agglomerated). In other words, the particles in the dispersion medium are spaced apart from each other and thus in a state that enables them to move independently. The average particle diameter of the nanoparticle silver powder in the invention liquid dispersion determined by carrying out the dynamic light-scattering method thereon is on a level not much different from the average particle diameter found by TEM observation. More specifically, the average particle diameter of the invention liquid dispersion measured by the dynamic light-scattering method is 60 nm or less, preferably 30 nm or less, and more preferably 20 nm or less, which is not very different from the average particle diameter by TEM observation. This means that a monodispersed state is achieved and indicates that the present invention is capable of providing a liquid dispersion in which the nanoparticles of the silver powder are independently dispersed. Still, even when the particles are completely monodispersed in the dispersion medium, cases arise in which measurement error or the like causes differences to arise with respect to the average particle diameter obtained by TEM observation. For example, the concentration of the liquid dispersion during the measurement must be suitable for the performance and the scattered light detection system of the measurement apparatus, and errors occur if the concentration does not ensure transmission of enough light. Moreover, the signal obtained when measuring nanometer-order particles is so feeble that contaminants and dust come to have a strong effect that may cause errors. Care is therefore necessary regarding pretreatment of samples and the cleanliness of the measurement environment. The laser beam source used for nanometer-order particle measurement should have an output power of 100 mW or greater so as to ensure adequate scattered light intensity. In addition, it is known that when the dispersion medium is adsorbed on the particles, the adsorbed dispersion medium layer has an effect that works to increase particle diameter even when the particles are completely dispersed. This effect becomes particularly manifest when particle diameter falls below 10 nm. So it can be assumed that good dispersion is maintained even if the dispersed particles do not have exactly the same degree of dispersion as the value found by the TEM observation, provided that the degree of dispersion (D50)/(DTEM) is 5.0 or less, preferably 3.0 or less.

Manufacturing Method

The particulate silver powder of the present invention can be manufactured by subjecting a silver salt to reduction treatment at a temperature of 85 to 150[deg.] C. in an alcohol having a boiling point of 85 to 150[deg.] C. and in the co-presence of an organic protective agent. The alcohol used in the present invention as a solvent/reducing agent is required to have a boiling point of 85 to 150[deg.] C. but is not otherwise particularly limited. An alcohol having a boiling point below 85[deg.] C. does not readily enable a reaction temperature of 85[deg.] C. or higher without using a special reactor such as an autoclave. Preferred alcohols include one or a mixture of two or more of isobutanol, n-butanol, s-butanol, and t-butanol. A silver salt is used that is soluble in alcohol. Silver nitrate is preferable from the viewpoint of low price and security of supply. As the organic protective agent, there is preferably used a metal coordination compound of a molecular weight of 100 to 400 that has coordinating capability towards silver. Use of a compound having no or only weak coordinating capability toward silver is undesirable from the viewpoint of practicability, because a large amount of protective agent would be needed to produce silver nanoparticles of 30 nm or smaller. An amino compound is suitable as the organic protective agent constituted of a metal coordination compound. Viewed generally, metal coordination compounds include isonitrile compounds, sulfur compounds, amino compounds, and fatty acids having a carboxyl group. However, a sulfur compound would degrade the reliability of electronic components because it would cause corrosion owing to the sulfur it contains. When silver nitrate is the starting material, a fatty acid or the like generates fatty acid silver and isonitrile compounds are problematic because they are toxic. This invention uses an amino compound having a molecular weight of 100 to 400 as the organic protective agent. Among amino compounds, a primary amine is preferable. A secondary amine or tertiary amine would itself operate as a reducing agent, which would cause an inconvenience in a case where an alcohol is already in use as a reducing agent, because the resulting presence of two types of reducing agent would complicate control of the reduction rate and the like. An amino compound having a molecular weight of less than 100 has low agglomeration suppressing effect. One with a molecular weight exceeding 400 has strong agglomeration suppressing effect but also has a high boiling point. If a particulate powder of silver whose particle surfaces are coated therewith should be used as a material for forming interconnects, the amino compound would act as a sinter inhibitor during firing. The resistance of the interconnects would therefore become high, possibly to the point of impairing conductivity. Since this is undesirable, it is best to use an amino compound having a molecular weight of 100-400.

At a reaction temperature under 85[deg.] C., the silver nanoparticle yield is extremely low. On the other hand, a reaction temperature exceeding 150[deg.] C. is undesirable because no additional yield improvement is observed but coarsening of the silver particles by sintering becomes pronounced. The reduction of the silver ions by alcohol is therefore best conducted with the temperature maintained between 85 and 150[deg.] C., but with the reaction being carried out while using an apparatus equipped with a reflux condenser to return vaporized alcohol to the liquid phase. The silver salt concentration of the reaction mixture is preferably made 50 mmole/L or greater. A lower concentration than this increases cost and is therefore not suitable from the industrial viewpoint. Upon completion of the reaction, the slurry obtained is centrifuged to separate solid from liquid. The resulting sediment is added with a dispersion medium such as ethanol and dispersed therein using an ultrasonic disperser. The dispersion is again centrifuged and the sediment is again added with ethanol and dispersed with the ultrasonic disperser. This process of [solid-liquid separation->dispersion] is repeated three times, whereafter the supernatant is discarded and the sediment dried to obtain the particulate powder of silver of the present invention. As the dispersion medium (organic solvent) for dispersing the invention particulate silver powder can be used an ordinary non-polar solvent or a low-polarity solvent such as hexane, toluene, kerosene, decane, dodecane or tetradecane. The liquid dispersion obtained is then centrifuged to remove coarse particles and agglomerated particles. Next, only the supernatant is collected as a sample to be subjected to TEM, x-ray, particle size distribution and other measurements. The nanoparticle powder obtained is dried in a vacuum drier (for 12 hours at 200[deg.] C., for example), whereafter the dry product can be assayed for silver purity using the gravimetric method (upon dissolution in nitric acid followed by addition of HCl to prepare a silver chloride precipitate) to measure purity from the weight thereof. The purity of the particulate powder of silver of the present invention is 95% or greater.

WORKING EXAMPLES

Example 1

Isobutanol (reagent grade from of Wako Pure Chemical Industries, Ltd.), 200 mL, used as a solvent/reducing agent, was added with 132.74 mL of oleyl amine (Wako Pure Chemical Industries, Ltd.) and 13.727 g of silver nitrate crystal, and the mixture was stirred with a magnetic stirrer at room temperature to dissolve the silver nitrate. The solution was transferred to a container equipped with a reflux condenser which was then placed in an oil bath. The solution was stirred with a magnetic stirrer at 200 rpm and heated while nitrogen gas used as an inert gas was blown into the container at the rate of 400 mL/min. Refluxing was continued for 5 hours at 100[deg.] C. to complete the reaction. The temperature increase rate to 100[deg.] C. was 2[deg.] C./min. After the reaction, the slurry was subjected to solid-liquid separation and washing by the procedure set out below:

1. The slurry following the reaction was centrifuged at 5000 rpm for 60 minutes in a CF7D2 centrifuge made by Hitachi Koki Co., Ltd. to separate solid from liquid, and the supernatant was discarded.

2. The sediment was added with ethanol and dispersed using an ultrasonic disperser.

3. Steps 1 and 2 were repeated 3 times.

4. Step 1 was performed and the supernatant was discarded to obtain a sediment.

The pasty sediment obtained in Step 4 was prepared for evaluation as follows:

a) For the measurement of particle size distribution by TEM observation and dynamic light-scattering, the sediment was added with and dispersed in kerosene, the liquid dispersion was centrifuged to sediment coarse particles and agglomerated particles, and the sediment was removed to obtain a liquid dispersion. Evaluation was carried out on the liquid dispersion .

b) For the x-ray diffraction and crystallite size measurement, the liquid dispersion removed of coarse particles and agglomerated particles prepared in a) was concentrated to a paste that was coated onto a non-reflective substrate and analyzed with an x-ray diffractometer.

c) For determining Ag purity and yield, the sediment was dried in a vacuum drier for 12 hours at 200[deg.] C. and the weight of the dried product was measured. More specifically, the Ag purity of the dried product was measured by the gravimetric method (method of dissolving the dried product in nitric acid, adding HCl to the solution to prepare a silver chloride precipitate, and measuring the purity from the weight thereof). Yield was calculated as {(dried product actually obtained after reaction)/(silver amount calculated from added silver nitrate)}*100(%) per batch.

The results of the measurements were TEM average particle diameter: 6.6 nm, aspect ratio: 1.1, CV value: 10.5%, crystallite size (Dx): 8.7 nm, and degree of single crystal grain (DTEM/Dx): 0.76. Only peaks attributable to silver were observed in the x-ray diffraction results. D50 measured by the dynamic light-scattering method (Microtrack UPA) was 26.6 nm. D50/DTEM was 4.0. Silver purity was 96.8% and silver yield was 93.1%.
FIGS. 1 and 2 are TEM photographs of the nanoparticle silver powder of this Example (photographs for determining TEM average particle diameter and the like). In these photographs, spherical silver nanoparticles are observed to be well dispersed at regular intervals. Although a very small number of overlapped particles are observed, the measurements of average particle diameter (DTEM), aspect ratio and CV value were made with respect to completely dispersed particles.

Comparative Example 1

Example 1 was repeated except that propanol was used as the solvent/reducing agent and the reaction temperature was made 80[deg.] C. The results showed the silver yield to be a very low 1.1%, and while only peaks attributable to silver were observed in the sediment by x-ray diffraction, Dx was 15.9 nm. Measurements other than the x-ray diffraction analysis were impossible to carry out because the amount of sample was too small.

Comparative Example 2

Example 1 was repeated except that ethanol was used as the solvent/reducing agent and the reaction temperature was made 75[deg.] C. The results showed the silver yield to be a very low 0.9%, and while only peaks attributable to silver were observed in the sediment by x-ray diffraction, Dx was 25.4 nm. Measurements other than the x-ray diffraction analysis were impossible to carry out because the amount of sample was too small.

As can be seen from the Comparative Examples, silver yield was extremely low and productivity poor both when using an alcohol having a boiling point of 85[deg.] C. or lower and when making the reaction temperature lower than 80[deg.] C.



Chemical Preparation Method of Ag Nanoparticle
CN1994633

Abstract --- The invention relates to a method for preparing silver nanometer particles, wherein it is characterized in that: it uses silver nitrate or silver perchlorate as initial reactant; uses sodium oleate or linolic acid sodium as surface activator; mixing them at free ratio; uses toluene, dimethylbenzene, and sub dichlorobenzene or chloroform reaction medium; in organic phase, obtaining silver nanometer particles. The invention has simple control, without preparing forward element and organic solvent with high boiling point, with low cost. The inventive silver nanometer particles can be dispersed in non-polar medium and polar medium.

DESCRIPTION

The invention belongs to the chemical solution synthesis method, particularly relates to a process for the preparation of chemical Silver nanoparticles.

[0003] BACKGROUND:

[0004] As the silver nanoparticles can produce features in the visible or near-infrared absorption peaks. Within ten years time, studies on silver nanomaterials in the world has attracted wide attention. Currently Silver nanoparticles have been in preparation  of organic / inorganic hybrid nano-emitting devices, nano-biosensors and has
Antibacterial function of polymer materials show good prospects.

[0005] Depending on the chemical environment in which silver nanoparticles, their preparation methods can be separated into an organic phase, the aqueous phase And two-phase reaction of the three categories. The first method is mainly used as a reducing agent sodium borohydride, in particular surfactant The agent molecules at room temperature (or temperature) conditions, the chemical reaction of silver nanoparticles, Although the reaction can be completed successfully at room temperature, but due to the strong reducing action of sodium borohydride, so that the anti- Should be difficult to control, and this is for the preparation of different morphologies and sizes of silver nanoparticles is a Lee factor. The second method uses special reaction precursor in the presence of a surfactant under high temperature, taken With an organic amine such as a reducing agent under high temperature conditions, the silver nanoparticles prepared synthetically. This method has the The main problem is the need of preparing the precursor complex, and to use as high-boiling organic solven The reaction medium, so that the further application is limited. The third method of preparation used in the process Phase transfer catalyst, the silver ions from the aqueous phase to the organic phase shift, and then add sodium borohydride reducing agent, In the preparation of silver nanoparticles in the organic phase, although this method in the preparation process of metallic silver nanoparticles The still widely used, but the method in the preparation process requires a lot of expensive phase transfer catalysis Agent, thereby increasing the cost of raw materials.

[0006] SUMMARY OF THE INVENTION:

[0007] The purpose of the invention: The present invention provides a method for preparing chemical silver nanoparticles, whose aim is to solve the current Some production methods difficult to control the reaction, is desired to prepare the precursor complex structure and has a high boiling point As the reaction solvent in the presence of medium and large and the production cost aspects.

[0008] Technical Solution: The present invention is  achieved by the following technical solutions:

[0009] A chemical method for preparing silver nano-particles, characterized in that: selection of silver nitrate, silver perchlorate or A silver acetate as the starting reactant, linoleic acid or sodium oleate as a surface active agent, than any Examples mixed in toluene, xylene, dichlorobenzene, chloroform Pro as reaction medium, the organic phase obtained silver nano M particles.

[0010] Select the silver nitrate as the starting reactant, the surfactant selection oleate; choose toluene as a reaction Media.

[0011] Molar ratio of the starting reactant silver nitrate sodium oleate surfactant is 10:1 to 1:10; starting reaction On silver nitrate concentration in the reaction medium in the range between 1.0-50mmol / L.

[0012] The solution was slowly warmed the reaction temperature is controlled within the range of 80-200 ℃, the electromagnetic stirring of the reaction conditions, The reaction time is 1 to 2 hours at constant temperature, the crude product obtained in the above reaction was centrifuged, The supernatant was discarded, washed with acetone and the precipitate with deionized water 2-3 times and then at 40 ℃ conditions,The precipitate was dried in vacuo for 12 hours to obtain a surfactant of sodium oleate as a nano silver coating agents for Particles.

[0013] The obtained silver oleate modified nanoparticles can be well dispersed in both the non-polar medium, but also Preferably dispersed in a polar medium.

[0014] Advantages and effects: The invention uses silver nitrate as a starting reactant, sodium oleate as a surfactant, pass Controlling the reaction temperature and reaction time, the silver nanoparticles prepared by the. Studies in recent years show that: oil Acid molecule (or oleic acid ion) of semiconductor and metal nanoparticles having a good surface modification.  Such amphiphilic organic molecule can provide a good environment for chemical limited nanoparticles self-assembled from To form a three-dimensional or two-dimensional ordered structures of nanoparticles. Further, sodium oleate surface is a common industrial Active agents, cheap, abundant source. Therefore, in the present invention, we use oil as a reaction over sodium Process surfactant.

[0015] Looking to the present invention, a method for preparing a chemical nano-silver particles. Through the use of silver nitrate, oleate Sodium basic chemical raw materials as reactants at different reaction temperatures, reaction time and concentration of The following piece, by using cheap and easy to get the basic chemical raw materials, the organic phase was prepared silver nanoparticles. In the process of the present invention, the surface active agent is sodium oleate play a dual role: on one hand it is a silver nanoparticle Provides a good growth restricted chemical environment, which can make the size of silver nanoparticles get better control System; hand it also plays a role of a reducing agent to the starting reactant silver nitrate was reduced to nano M silver particles. And because the specific nature of the surfactant sodium oleate so that the obtained silver nanoparticles Both dispersed particles is preferably in toluene, chloroform and other non-polar medium can be well dispersed in water, Ethanol and other polar media. This is further application of nano silver material has important significance.

[0016] Brief Description:

[0017] Figure 1 of the present invention prior to centrifugation of silver nanoparticles in toluene in the UV - visible absorption spectra of sample Measured according to schematic;

[0018] 2 is a UV drawings centrifuged silver nanoparticles in toluene - visible absorption spectra of sample Measured according to schematic;

[0019] 3 is a drawing of UV centrifuged silver nanoparticles in water - visible absorption spectroscopy Based schematic;

[0020] 4 is a UV drawings centrifuged silver nanoparticles in ethanol - visible absorption spectra of sample Measured according to schematic;

[0021] 5 is a UV drawings centrifuged silver nanoparticles in chloroform - visible absorption spectra of sample Measured according to schematic;

[0022] Figure 6 of the invention, a transmission  electron micrograph of the silver nanoparticles.



[0023] Specific Embodiment:

[0024] By the present invention, selection of silver nitrate, silver perchlorate or silver acetate, as a starting reactant, oil
Linoleic acid or sodium as a surfactant, an arbitrary mixing ratio, toluene, xylene, dichlorobenzene or Pro Chloroform as the reaction medium in the organic phase obtained silver nanoparticles. But under different reaction conditions to give Silver nanoparticles have characteristic absorption peaks are somewhat different, but the above method is able to achieve complete The purpose of the invention.

[0025] Example 1:

[0026] The oil 122mg sodium, 34mg of silver nitrate, 20ml toluene was added to a 250ml three-necked reaction flask Inner temperature was slowly increased to 80 ℃, the electromagnetic stirring at constant temperature for 1 hour, You can get a yellow meter gold particles containing silver hydrosol. The crude product was subjected to centrifugation of the reaction Separation, the supernatant was discarded, washed with acetone and the precipitate with deionized water 2-3 times, and then the condition 40 ℃ Next, the precipitate was vacuum dried for 12 hours to obtain a surfactant of sodium oleate as a parcel Agent nano-silver particles. The resulting silver nanoparticles can be well dispersed in toluene, chloroform and other non-polar medium Interstitium to be well dispersed in water, ethanol and the like polar media. UV - visible spectroscopy knot Results showed that the silver nanoparticles on the non-polar and polar dispersion system, at 420-430nm Department can To produce significant nanosilver has characteristic absorption peaks.

[0027] Example 2:

[0028] The sodium oleate 61mg, 17mg of silver nitrate, 20ml toluene was added to a 250ml three-necked reaction flask, The temperature was slowly increased to 90 ℃, the electromagnetic stirring at constant temperature for 1 hour, to M to obtain a yellow gold particles containing silver hydrosol. The crude product obtained in the above reaction were centrifuged Away, the supernatant was discarded, washed with acetone and deionized water sediment 2-3 times, 40 ℃, then, The precipitate was dried in vacuo for 12 hours to obtain a surfactant agent, sodium oleate as the parcelNano-silver particles. The resulting silver nanoparticles can be well dispersed in toluene, chloroform and other non-polar medium, Can be well dispersed in water, ethanol and other polar media. UV - visible spectroscopy results show Silver nanoparticles in the non-polar and polar dispersing system, at 420-430nm can be generated out of the Nanosilver has significant characteristic absorption peaks.

[0029] Example 3:

[0030] Linoleic acid sodium 31mg, 10mg silver perchlorate, 20ml of xylene was added to the anti-necked 250ml Should the bottle, the temperature was slowly raised to 120 ℃, the electromagnetic stirring at constant temperature for 2 hours the reaction When you can get a yellow meter gold particles containing silver hydrosol. The crude product was subjected to the above reaction Centrifugation, the supernatant was discarded, washed with acetone and the precipitate with deionized water 2-3 times, then 40 Under ℃, the precipitate was vacuum dried for 12 hours to obtain a surfactant as sodium oleate Nano silver particles wrapped agent. The resulting silver nanoparticles can be well dispersed in the non-toluene, chloroform and the like Polar media, can be well dispersed in water, ethanol and other polar media. UV - visible spectroscopy measurements The results show that a given silver nanoparticles in the non-polar and polar dispersing system, in 420-430nm may be generated at the silver nanoparticles having a distinct characteristic absorption peaks.

[0031] Example 4:

[0032] The 16mg sodium oleate, 5mg silver acetate, 20ml Pro-dichlorobenzene was added to a 250ml three-necked reaction Flask, the temperature was slowly raised to 180 ℃, the constant reaction temperature for 1 hour to obtain silver-containing yellow Water sol-meter gold particles. The crude product was centrifuged, the supernatant was discarded, washed with acetone and deionized The precipitate was washed with water 2-3 times, and then at 40 ℃ conditions, precipitate was dried for 12 hours to give Of sodium oleate as a surfactant coating agents for nano silver particles. The silver nanoparticles can be obtained preferably Dispersed in toluene, chloroform and other non-polar medium can be well dispersed in water, ethanol and the like polar medium The. UV - visible spectroscopy results indicate that silver nanoparticles on the non-polar and sub-polar Bulk system, at 420-430nm in produce silver nanoparticles has significant characteristic absorption peaks.

[0033] 1,2,3,4,5 show drawings of the present invention prior to centrifugation of silver nanoparticles in toluene UV - visible absorption spectroscopy based diagram centrifuged silver nanoparticles in toluene UV - Visible absorption spectroscopy based diagram centrifuged silver nanoparticles in water by UV - visible absorption Closing the spectral detector according to a schematic, centrifuged silver nanoparticles in ethanol UV - visible light absorption Schematic spectrum detection based on centrifugal separation after UV silver nanoparticles in chloroform - visible absorption spectroscopy Schematic basis.
Among them, a, b, c, d, e, f represent a reference curve for the reaction time 5min, 10min, 15min, 20min, 25min, 30min before centrifugation UV silver nanoparticles in toluene
- Visible absorption spectra; in Figure 2 in a, b, c, d, e, f represent the reaction time curve 5min, 10min, 15min, 20min, 25min, 30min curve obtained after centrifugation silver
Nanoparticles in toluene UV - Vis absorption spectrum. Figure 6 of the present invention through the silver nanoparticles Transmission electron microscope.

[0034] Conclusion: The experiments show that the initial selection of reactant silver nitrate, sodium oleate as a surface active agent, Toluene as the reaction medium, the organic phase obtained in the silver nanoparticles. Under different reaction conditions that silverUV nanoparticles - visible absorption spectrum in the 420-430nm range has exhibited the characteristics of nano-silver
Absorption peaks. Sodium oleate and the resulting silver nanoparticles modified preferably either dispersed in toluene, chloroform and the like
Non-polar medium can be well dispersed in water, ethanol and other polar media.



Reactive, Monodispersed Surface Modified Silver Nanoparticle
CN1966586    

Abstract --- The invention disclosed a reactable mono dispersal surface silver nanometer bead as well as the preparing method, which belongs to the nanometer material and it's preparing technology domain. The product in the invention has a general formula of (I), of which X1 refers to halogen, X2 refers to unsaturated hydrocarbon, n=4-22, m=4-22. The preparing procedure includes the following steps: dissolving the dialkyl dithio-phosphoric acid with the general formula of (II) in the organic solvent; adding the previous solution into the sodium borohydride solution at 0-5DEG C; adding soluble silver salt solution; extracting with organic solution after reaction; vacuum distillating to get the product. The product in the invention can be dispersed stably in non-pole or low-pole solvents, it can be dispersed in the polar solvent in the form of similar dissolving which has enlarged the utilizing scope of nanometer bead. The preparing procedure has the advantage of simple operation, low cost and high yield, it is applicable to large-scale production.

[0001] Technical field

[0002] The present invention relates to a reaction monodisperse silver nanoparticles surface modified its preparation method, which belongs to the field of nano-materials and their preparation techniques.

[0003] BACKGROUND

[0004] Metal nanoparticles because of its size effect has many unique optical, electrical, magnetic, and catalytic properties caused extensive study of people, and because of the problem solving nanoparticles dispersed rise of surface modification chemistry has become a hot research. Silver nanoparticles also because itself has optical, electrical and catalytic properties by researchers from the attention, a lot of reports about the surface modification of silver nano materials. Are generally used as monofunctional organic modifier, such as: mercaptans, cetyl trimethyl ammonium bromide, PVP and PVA and so on.
Such modifiers solves the problem reunion silver nanoparticles were prepared silver nanoparticles can be dispersed, and some have been industrialized, but there are still inadequate in many applications.
In recent years, functional nanomaterials become the focus of attention, functional nanomaterials containing material itself features and functional surface modification agent for silver nanoparticles functionalized surface modifier is a relatively new and very promising subject.

[0005] SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide a reaction surface modified monodisperse silver nanoparticles and a preparation method.

[0007] Object of the present invention is achieved by the following technical solutions:

[0008] The reaction may be one kind of monodispersed silver nanoparticles surface modified, the substances of the formula:

[0010] Wherein, in the formula X1, X2 is a halogen, an unsaturated hydrocarbon, n is 4 ~ 22, m is 4 to 22.

[0011] The reaction may be mono-dispersed silver nanoparticles surface modified method for preparing the formula

[0012] Dialkyl dithiophosphate in an organic solvent;

[0013] At a temperature of 0-5 ℃, take dialkyl dithiophosphate was added to the aqueous solution of sodium borohydride, the reaction was added an aqueous solution of a soluble silver salt after the reaction was extracted with an organic solvent, distillation under reduced pressure, and drying to obtain the product ; formula X1, X2 is a halogen, an unsaturated hydrocarbon group, n is 4 ~ 22, m is 4 to 22.

[0014] Molar ratio of the soluble silver salt and a dialkyl dithiophosphate is from 0.75 to 4.5, a soluble silver salt and a molar ratio of sodium boron hydride is 1:3 to 8.

[0015] The value of n and m are equal.

[0016] X1 and X2 are the same substituents.

[0017] Concentration of the soluble silver salt is 1.0 × 10-3mol / L ~ 2.0 × 10-2mol / L, the concentration of sodium borohydride is 4.0 × 10-3mol / L ~ 8.0 × 10-2mol / L, dialkyl phosphoric acid in an organic solvent concentration in the 12.5mol / L ~ 1.0 × 102mol / L.

[0018] Said organic solvent is an alcohol, toluene, chloroform, petroleum ether.

[0019] The present invention addresses previously prepared nanoparticles by modifying agent is inert, and should not participate in the reaction, the halogen-containing unsaturated hydrocarbons such bifunctional dithiophosphate compound as the modifying agent was prepared to the reaction surface-modified silver nanoparticles may be formed between the phosphorothioate group of silver nanoparticles chemically modified, a halogen, an unsaturated hydrocarbon such functional groups such as quaternary amination can occur, addition reaction with other substances, and the reaction of silver nanoparticles formed after bond appearance and modifiers between silver nanoparticles together unchanged. Thus, long-term stability of the product can not only dispersed in non-polar or weakly polar solvent, and the reaction can be re-dissolved form can be dispersed in a class type of a polar solvent, broadens the scope of application of the nanoparticles.

[0020] Compared with the existing technology of silver nano particles, the preparation method has the raw materials cheap and easy to get, easy operation, low cost, high yield and other characteristics suitable for large-scale industrial production. The preparation of the silver nano-particle size uniform, the dispersion of less than 5%. The kind of silver nanoparticles is stable in air, can be stably dispersed in the benzene, toluene, chloroform, petroleum ether and other organic solvents, which have a wide range of industrial applications.

[0021] Brief Description

[0022] Figure 1 is an example of embodiment of a UV-visible absorption spectrum;

[0023] Example 2 is an embodiment of an infrared absorption spectrum;

[0024] Figure 3 is a transmission electron micrograph of the embodiment of Example 1;

[0025] Figure 4 is a transmission electron micrograph of Example 2;

[0026] Figure 5 is a transmission electron micrograph of Example 3;

[0027] Figure 6 is a transmission electron micrograph of Example 4;

[0028] Figure 7 is a transmission electron micrograph of Example 5.



[0029] Infrared spectra using Nicolet Avatar360 infrared spectrometer (Nicolet American company), the nanoparticle black viscous material obtained by the modified potassium bromide crystal coated on the test; transmission electron microscopy using JEM 100CX-II-type transmission electron microscopy (TEM, JEOL Ltd., Japan, the acceleration voltage 100KV), the silver nanoparticles prepared by the modified dispersion in toluene, 2 to 3 drops of the sprayed drops of carbon copper grid test after drying; UV - visible absorption spectrum of the test used is Heλios a UV - visible absorption spectroscopy (UK UNICAM company), the sample was dispersed in chloroform was added to the quartz tank for testing.

[0030] Embodiment

[0031] Example 1 was weighed (excess 10%) 1.2400g of phosphorus pentasulfide in a three-necked flask, toluene was added and stirred.
At room temperature was added dropwise a toluene solution containing 5.0110g (0.02mol) of ω-bromo alcohols XI, after completion of the dropwise addition, heating to reflux until the reaction mixture became clear (without the use of lead acetate paper sulfide That is considered complete gas evolution) After the reaction was filtered to remove unreacted phosphorus pentasulfide, and then the solvent was distilled toluene was distilled under reduced pressure to give a pale yellow mucus is ω-bromo-undecyl-bis dithiophosphate.

[0032] Under ice-cooling, sodium boron hydride solution prepared 40mmol 250mL / L of a methanol solution containing 10mL 0.125mol double ω-bromo-undecyl dithiophosphoric acid and stirred fifteen minutes, then added dropwise with good Silver nitrate solution 250mL 10mmol / L, the dropwise addition was complete, 200mL of chloroform, 4.0g of sodium dihydrogen phosphate to prevent the emulsion was stirred and extracted, the organic phase was separated, washed with water 2-3 times.
Solvent recovery by distillation with chloroform under reduced pressure, washed with acetone and dried to give brown solid, a pair of ω-bromo-undecyl two phosphorothioate silver nanoparticles.

[0033] 1, ω-bromo-UV double undecyl two phosphorothioate silver nanoparticles a visible (UV-vis) absorption spectrum, there are two lines in the strong absorption at 200nm which Absorption of ω-bromo-bis modifier absorbed undecyl dithiophosphoric acid, and a strong absorption at 420nm corresponding to the surface of the nanoparticle plasmon resonance absorption.

[0034] Fig, infrared silver nanoparticles prepared two absorption spectra, it can be seen with the IR spectra of the organic modifier compared to only SH and P = S absorption peak disappeared, with the SPS For absorption peak. Indicate the presence of organic modifiers in the silver nanoparticles prepared by phosphorus and sulfur functional groups bonded with silver nanoparticles. C-Br functional group peaks evident also prove the existence of reactive functional groups of the prepared silver nano powder.

[0035] Figure 3, for the implementation of ω-bromo-bis TEM prepared in Example 1, two phosphorothioate undecyl silver nanoparticles can be seen from FIG samples prepared spherical particles without agglomeration.

[0036] Example 2 weighed (excess 10%) 1.2400g of phosphorus pentasulfide in a three-necked flask, toluene was added and stirred. At room temperature was added dropwise a toluene solution of a polymerization inhibitor comprising 3.4000g (0.02mol) of ω-undecenyl alcohol amount, and after the completion of the dropwise addition, heating to reflux until the reaction mixture became clear (lead acetate Hydrogen sulfide gas evolution test strip that is considered non-completion of the reaction) and then filtered to remove unreacted phosphorus pentasulfide, and then the solvent was distilled toluene was distilled under reduced pressure to give a pale yellow mucus is eleven pairs of ω-alkenyl dithiophosphate.

[0037] Under ice conditions, the preparation of sodium borohydride 40mmol 250mL / L, the ω-bis dithiophosphate undecenyl methanol 10mL 0.25mol stirred fifteen minutes, then added dropwise with good 10mmol / L silver nitrate solution 250mL, addition was complete, 200mL of chloroform was added, 4.0g sodium dihydrogen phosphate to prevent the emulsion was stirred and extracted, the organic phase was separated, washed with water 2-3 times. Solvent recovery by distillation with chloroform under reduced pressure, washed with acetone and dried to give dark brown viscous liquid is eleven pairs of ω-alkenyl two phosphorothioate silver nanoparticles.

[0038] Figure 4 shows, in Example 2 bis Preparation of ω-alkenyl eleven dithiophosphoric acid modified transmission electron micrograph of silver nanoparticles. Can be seen, the nanoparticles prepared in uniform size with no agglomeration, the average particle diameter of 10nm.

[0039] Example 3 weighed 2.4800g (10% excess) of phosphorus pentasulfide in a three-necked flask, toluene was added and stirred. At room temperature was added dropwise a toluene solution containing 4.3200g (0.04mol) of ω-chloro-tetraalkyl alcohol after completion of the dropwise addition, heating to reflux until the reaction mixture became clear (without the use of lead acetate paper sulfide i.e., hydrogen release reaction is considered complete) and then filtered to remove unreacted phosphorus pentasulfide, and then the solvent was distilled toluene was distilled under reduced pressure to give a pale yellow mucus is four pairs of ω-chloro alkyl dithiophosphate.

[0040] Under ice-cooling, sodium boron hydride solution prepared 40mmol 250mL / L of a methanol solution containing 10mL two ω-chloro 0.125mol tetraalkyl dithiophosphoric acid and stirred fifteen minutes, then added dropwise with good 10mmol / 250mL L silver nitrate solution, the addition was complete, 200mL of chloroform was added, 4.0g sodium dihydrogen phosphate to prevent the emulsion was stirred and extracted, the organic phase was separated, washed with water 2-3 times. Solvent recovery by distillation with chloroform under reduced pressure, washed with acetone and dried to give brown solid, a pair of ω-chloro-tetraalkyl two phosphorothioate silver nanoparticles.

[0041] Figure 5 shows a transmission electron micrograph of Example IV bis ω-alkyl dithiophosphoric acid chloride prepared three silver-modified nanoparticles. Can be seen, the nanoparticle size distribution is wide prepared without agglomeration, the average particle size of 8nm.

[0042] Example 4 Weigh (excess 10%) 1.2400g of phosphorus pentasulfide in a three-necked flask, toluene was added and stirred. At room temperature was added dropwise a toluene solution of a polymerization inhibitor comprising 3.3800g (0.02mol) of ω-alkynyl alcohol XI amount of the dropwise addition, the temperature was raised to reflux until the reaction mixture became clear (lead acetate Hydrogen sulfide gas evolution test strip that is considered non-completion of the reaction) and then filtered to remove unreacted phosphorus pentasulfide, and then toluene was distilled under reduced pressure and the solvent was evaporated to give a colorless viscous UNDECYNE is ω-bis dithiophosphoric acid.

[0043] Under ice-cooling, sodium boron hydride solution prepared 40mmol 250mL / L, the ω-bis sixteen alkynyl dithiophosphate containing 0.125mol 10mL methanol and stirred for fifteen minutes and then added dropwise with good 10mmol / 250mL L silver nitrate solution, the addition was complete, 200mL of chloroform was added, 4.0g sodium dihydrogen phosphate to prevent the emulsion was stirred and extracted, the organic phase was separated, washed with water 2-3 times. Solvent recovery by distillation with chloroform under reduced pressure, washed with acetone and dried to give brown solid, a ω-bis sixteen two phosphorothioate alkynyl silver nanoparticles.

[0044] Figure 6 is a transmission electron micrograph of Example alkynyl sixteen ω-bis dithiophosphate 4 Modified prepared silver nanoparticles. Can be seen, the nanoparticles prepared in uniform size with no agglomeration, the average particle diameter of 6nm.

[0045] Example 5 weighed 2.2270g of phosphorus pentasulfide in a three-necked flask, toluene was added and stirred. At room temperature was added dropwise 5.0110g (0.02mol) ω-bromo alcohols XI (0.02mol) of toluene solution of ω-chloro-cetyl alcohol containing 2.7200g, after completion of the dropwise addition, heating to reflux until the reaction the mixture became clear (without the use of lead acetate paper release hydrogen sulfide gas that is considered complete reaction) then filtered to remove unreacted phosphorus pentasulfide, and then the solvent was distilled toluene was distilled under reduced pressure to give a pale yellow mucus is ω-bromo ten an ω-chloro-alkyl and mixed alkyl substituted six dialkyl dithiophosphate.

[0046] Under ice-cooling, sodium boron hydride solution prepared 40mmol 250mL / L of a methanol solution containing the ω-bromo 0.125mol undecyl and ω-chloro-hexadecyl dialkyl substituted mixed acid 10mL, stirred for fifteen minutes and then added dropwise with good 10mmol / 250mL L silver nitrate solution, the addition was complete, 200mL of chloroform was added, 4.0g sodium dihydrogen phosphate to prevent the emulsion was stirred and extracted, the organic phase was separated, washed with water 2-3 times. Solvent recovery by distillation with chloroform under reduced pressure, washed with acetone and dried to give brown solid, a ω-ω-bromo-undecyl, and mixed alkyl-substituted chloro six dialkyl phosphorothioate silver nanoparticles.

[0047] Figure 7, for the implementation of ω-bromo-prepared in Example 5 and ω-chloro-undecyl mixed hexadecyl dialkyl substituted phosphorothioate silver nanoparticles transmission electron micrograph.
Can be seen, the nanoparticles prepared in uniform size with no agglomeration, the average particle diameter of 6nm.



SILVER NANOPARTICLE AND PRODUCTION METHOD THEREFOR
JP2007063580

Abstract --- PROBLEM TO BE SOLVED: To provide silver nanoparticles having more excellent dispersibility and superior dispersibility in water and/or a water-soluble organic solvent. SOLUTION: A method for producing the silver nanoparticles includes the step of heat-treating a starting material containing (1) an amine compound, (2) a silver salt and (3) a polycyclic hydrocarbon compound having a carboxyl group.

DESCRIPTION

[0001]The present invention relates to a method of manufacturing the same and silver nanoparticles.

[0002] With the increasing expectations for silver nanoparticle paste capable of forming a fine conductive circuit, the research and development has also been carried out in various fields.
In recent years, with the demand for miniaturization of circuit formation, the development of the silver nanoparticle paste, which can accommodate not only screen printing but also the ink jet system are also being requested.
In order to meet these needs, that silver nanoparticles are excellent in dispersibility in organic solvents, and the like are essential.

[0003] However, since the prior art, it is not possible to introduce only linear carboxylic acids and aliphatic amines having a long chain alkyl group as the organic protective layer, the type of the solvent for dispersing the silver nanoparticles or the constraint is a limit to the dispersion concentration some. WO2004/012884

[0004] Accordingly, a primary object of the present invention is to provide silver nanoparticles having excellent dispersibility and more. Further, the present invention is also to provide silver nanoparticles having excellent dispersibility in water-soluble organic solvent and / or water.

[0005] As a result of extensive research in view of the problems of the prior art, and found that it is possible to achieve the above object by employing the method specified, the present inventors have accomplished the present invention.

[0006] That is, the present invention relates to a method for producing silver nanoparticles below.

1. A method of producing silver nanoparticles, and characterized in that it comprises a step of heat-treating a starting material containing a polycyclic hydrocarbon compound having (1) an amine compound, and (2) silver and (3) a carboxyl group manufacturing how to.

2. Containing the solvent in the starting material, the method according to the claim 1.

3. Is silver carbonate silver salt method as claimed in any of the claim 1.

4. Amine compound method as described comprises at least one, in any one of 1 to 3 above, wherein the morpholines and alkanolamines.

5. Amine compound, at least one of the following (1) to (3); (. Wherein, R1 is an aryl group or an alkyl group which may have a substituent group) (1) R1NH2, (2) R1R2NH However (, R1 ~ R2 represents an aryl group or an alkyl group which may be the same or different, which may have a substituent group.
R1 ~ R2 may also be connected to the ring. (3) R1R2R3N where (, R1 ~ R3 represents an alkyl group or an aryl group which may be the same or different, which may have a substituent group).
R1 ~ R3 and may be connected to the ring. The production method according to a), to any one of the claim.

6. Cholic acid, deoxycholic acid, dehydrocholic acid, chenodeoxycholic acid, 12 wherein the polycyclic hydrocarbon compound, - oxo chenodeoxycholic acid, glycocholate, colanic acid, lithocholic acid, hyodeoxycholic acid, ursodeoxycholic acid, apocholic is at least one acid, taurocholic acid, abietic acid, glycyrrhizic acid and glycyrrhizic acid, the method according to any one of items 1 to 5 above, wherein.

7. Silver nanoparticles obtained by the method according to any one of items 1 to 6 above, wherein.

8. A coating film-forming composition comprising silver nanoparticles according to the claim 7 and the solvent.

9. Conductive circuit forming composition comprising silver nanoparticles according to the claim 7 and a solvent.

10. Decorative layer forming composition comprising silver nanoparticles according to the claim 7 and a solvent.

11. Plating replacement composition comprising silver nanoparticles according to the claim 7 and a solvent.

12. The solvent is at least one water-soluble organic solvent and water, composition according to any 8-11 above, wherein the noise.

13. Method is used as an ink composition according to the claim 12, forming a coating on a substrate by an ink jet printer.




[0007] With the manufacturing method of the present invention, from the use of starting materials comprising specific components, it is possible to efficiently produce silver nanoparticles having excellent dispersibility. Therefore, it can be suitably used as a printing ink screen printing, by an inkjet method or the like. In particular, since it is excellent in dispersibility in water and a water-soluble organic solvent and / or silver nanoparticles obtained by the production method of the present invention may also be used in the form of an aqueous composition.

[0008]A process for producing silver nanoparticles, the production method of the present invention, heat treatment of the starting material containing a polycyclic hydrocarbon compound having (1) an amine compound, and (2) silver and (3) a carboxyl group and characterized in that it comprises a step.

[0009] Amine compounds amine compound may be not particularly limited, and an amine of the various. In the present invention, it is preferable to use at least one of morpholines and alkanolamines is desirable at least. In the case of using the morpholines, it is possible to produce silver nanoparticles having excellent water dispersibility or more alkanolamines. As the alkanolamines, for example ethanolamine, diethanolamine, triethanolamine, propanol amine, N, N-di - it is possible to increase the (2-hydroxyethyl) glycine and the like. The morpholines, it is possible to increase the derivative thereof, or morpholine. Among these, the use of at least one ethanolamine, diethanolamine, morpholine and triethanolamine is preferable.

[0010] The morpholines and other alkanolamines, it is possible to use primary amines of various secondary amine, a tertiary amine.

[0011] For example, at least one of the following (1) to (3); (. Wherein, R1 is an aryl group or an alkyl group which may have a substituent group) (1) R1NH2, (2) R1R2NH (where , R1 ~ R2 represents an aryl group or an alkyl group which may be the same or different, which may have a substituent group.
R1 ~ R2 may be connected in a ring. (3) R1R2R3N where (, R1 ~ R3 represents an alkyl group or an aryl group which may be the same or different, which may have a substituent group).
R1 ~ R3 may be connected to the ring. It can be preferably used).

[0012] It can be the amount of the amine compound, may be suitably selected depending on the type of the amine compound used. In general, 1 to 20 mol and 1 to 10 mol, particularly preferably the amount of silver 1 mol of the silver salt described later.

[0013] The Ginshioginshio, it may be appropriately selected from organic or inorganic acid salts of silver. Fatty acid silver, silver acetate, silver benzoate, silver citrate, silver carbonate, silver oxide, silver sulfate, silver nitrate, silver tetrafluoroborate, silver hexafluorophosphate, silver hexafluoroantimonate, silver trifluoromethanesulfonate, it is possible to increase the silver trifluoroacetate and the like. Among these, in particular, can be preferably used silver carbonate (Ag2CO3).

[0014] Polycyclic hydrocarbon compounds having a polycyclic hydrocarbon compounds carboxyl group having a carboxyl group, may be those having a carboxyl group of one or more polycyclic hydrocarbon compounds. Further, the carboxyl group may be bonded via a hydrocarbon group, or may be bonded directly to a hydrocarbon ring.

In particular, the present invention, cholic acid, deoxycholic acid, dehydrocholic acid, chenodeoxycholic acid, 12 - oxo chenodeoxycholic acid, glycocholate, colanic acid, lithocholic acid, hyodeoxycholic acid, ursodeoxycholic acid, apocholic acid, taurocholic The use of at least one acid, abietic acid, glycyrrhizic acid and glycyrrhetinic acid. These may be those known or commercially available.

[0015] The amount of these compounds is generally 1 to 5 moles, and 1 to 3 mol, particularly preferably the amount of silver 1 mol of the silver salt of the.

[0016] The solvent present invention, it is preferable to use a solvent. Type of solvent is not particularly limited, the use of at least one alcohol and water is desirable. The alcohol may be, for example, methanol, ethanol, propanol, isopropanol, ethylene glycol, propylene glycol and the like. In particular, it is more preferred to use water and / or ethanol.

[0017] The amount of solvent used may be appropriately set within a range that is 40 to 99 wt% starting material in general.

[0018] May be either heat such as heating without limitation, for example, in 1) oil bath, 2) microwave heat treatment heat treatment method. In addition, I can also be when the solvent is included in the starting material is heat-treated heated to reflux, by microwave heating or the like.

[0019] The heat treatment is carried out organic component to contain 1 to 65 wt% of silver nanoparticles to be obtained is desirable. This can be controlled by heat treatment temperature, treatment time and adjust the atmosphere or the like.

[0020] The heat treatment temperature may be appropriately determined in accordance with the type of amine compound solvent used, silver, or polycyclic hydrocarbon compound. In particular, it is possible 200 ℃ will be appropriately set within a range of 50 ~ 100 ℃ particular.

[0021] The heat treatment time, the composition of the starting materials used, it may be appropriately determined depending on the heat treatment temperature and the like, usually 0. 5-10 hours, preferably 0. May be 5 to 3 hours. It is possible by heat treatment temperature and time, and also controls the particle size. In general, there is a tendency for the longer reaction time, the greater the particle size also, as the reaction temperature is high.

[0022] But also the case where the solvent is contained in (the starting material in the heat treatment atmosphere. ) Is not particularly limited. For example, the atmosphere, and may be either an inert gas atmosphere, a reducing atmosphere or a vacuum secondary. If an inert gas atmosphere, for example, may be used an inert gas such as nitrogen, carbon dioxide, argon, or helium.

[0023] After the heat treatment is completed, purification is carried out as needed. Purification method may be employed the known purification processes. For example, it can be used reprecipitation, filtration, washing, centrifugation, membrane purification, solvent extraction and the like.

[0024] Silver nanoparticles present invention includes silver nanoparticles obtained by the method described above.

[0025] Silver content in the particles, due to particle diameters of the particles use of the end product obtained, 60 to 99% by weight, to 70 to 99% by weight, particularly preferably normally. In the present invention, even at high content of 80 wt% or more, and that there is excellent in dispersibility in organic solvents and the like.

[0026] In general, the organic component is an organic component derived from the amine compound and / or polycyclic hydrocarbon compound. It is possible due to the presence of organic components, to achieve improvement in dispersion stability of the silver nanoparticles.

[0027] The average particle size of the silver nanoparticles can be appropriately set within the range of about 1 ~ 100nm Normally, it 1 ~ 50nm in particular, is 1 ~ 20nm and more preferably.

[0028] The shape of the silver nanoparticles are not particularly limited. It may be either a spherical, rod-shaped, wire-like, polygonal, polyhedral, irregular shape or the like.

[0029] The electronic materials (printed circuit, a conductive material, electrode material, bonding material, etc.), (a magnetic recording medium, electromagnetic wave absorber, electromagnetic wave resonator, etc.), the catalyst material a magnetic material silver nanoparticles of the present invention (fast reaction catalyst , a variety of sensors, etc.), (far infrared material, composite film-forming material, etc.), (brazing material, sintering aids, coating material, etc.), ceramics for decoration materials, medical materials, such as ceramics, metal material structure material It is possible to use a wide range of applications. In particular, it can be suitably used as the conductive circuit formation.

[0030] Silver nanoparticles may also be used in unmodified form, but can also be used in admixture with a solvent. That is, it can be suitably used as a coating film-forming composition comprising a solvent and silver nanoparticles. Because it contains an organic component as described above, even at high content of silver, the silver nanoparticles of the present invention may exhibit high dispersion stability to solvents, and a solubilized state. As the solvent, for example, addition of the terpene solvent, it is possible to use an organic solvent such as acetone, benzene, toluene, hexane, diethyl ether and kerosene.
In particular, the present invention can also be suitably used as a solvent (aqueous solvent) at least one water-soluble organic solvent and water. The water-soluble organic solvent is not limited as long as they are water-soluble.

In the present invention, water-soluble organic solvent may be preferably used at least one of its derivatives and polyhydric alcohols and monohydric water-soluble alcohol. For example, it is possible to increase the derivative thereof or a polyhydric alcohol monohydric alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol diethyl ether, glycerol, glycerol glycidyl ether. For example, in the manufacturing method described above, a silver-halide silver carbonate, amine compound in the case of using each of the glycyrrhizic acid or cholic acid alkanolamines, polycyclic hydrocarbon compounds and morpholines / or water or an aqueous solvent (water it is possible to provide silver nanoparticles having excellent dispersibility than the mixed solution) and a water-soluble organic solvent with.

[0031] Further, the present invention can also be used as a paste by mixing a paste of agents known.

[0032] Film-forming composition as described above can be used, for example, suitably conductive circuit-forming composition, the decorative layer forming composition, as the plating replacement composition or the like.

[0033] In particular, a coating film forming composition is also suitable as an ink for screen printing is used, the inkjet method or the like. In particular, the composition can be suitably used as an inkjet ink. Especially, the film-forming aqueous composition using an aqueous solvent as the solvent is advantageous. The film-forming aqueous composition of 1) the present invention, that the high surface tension with water is suitable for injection of a small amount of ink, a solvent-based ink 2) Conventionally, the reason for the head of an ink jet printer If A plastic head whereas degraded by a solvent, the film-forming aqueous composition of the present invention, points etc. can avoid problems caused by such solvents, and the like. Thus, it can be used as an ink (water-based compositions, particularly) the composition to form a coating preferably on a substrate by an ink jet printer.

[0034] When used as a plating alternative compositions of the present invention composition, for example, to form a coating film formed from the plating alternative composition for the portion for forming a film, it is forcibly dried or air-dried as necessary By, followed by heat treatment at 50 ~ 350 ℃ about atmosphere, it is possible to obtain a metal film equivalent plating film plating method according to the conventional (wet plating method). That is, in the present invention compositions, it is possible without passing through the wet plating method, is formed in an environment dry metallization equivalent to (film) plating. Thus, it is possible to avoid waste water treatment by wet plating, safety issues, and the like. Further, the wet plating methods such as electroless plating and electroplating, and while being carried by immersing the workpiece all the plating solution strongly alkaline or strongly acidic, in the case of using the plating alternative composition it is possible to form a film only the desired area. Further, in the case of forming a metal film by the present invention compositions, it is possible to obtain a film exhibiting metallic luster gold, silver, blue silver, etc. just to dry the coating. Therefore, the present invention composition can be suitably used a surface decoration (surface modification).

[0035] In the case of forming a conductive circuit (conductive) or the like using silver nanoparticles, after forming on the substrate a predetermined circuit pattern by using, for example, a film-forming composition exemplified above, it may be heat-treated. The heat treatment, 100 ~ 600 ℃ usually, may be in the range of 150 ~ 350 ℃, preferably.

[0036] Below by way of its examples, it is more clearly the place to be a feature of the present invention. However, the present invention is not limited to the scope of the examples.

[0037] The measurement of physical properties in each example was performed as follows. The identification of (1) qualitative analysis metal components was carried out by powder X-ray diffraction analysis method using intense X-ray diffraction apparatus "Rigaku RINT 2500" a (manufactured by Rigaku Corporation).
Measure (2) the average particle diameter transmission electron microscope (TEM) "JEM1200EX" by (JEOL Ltd.), to obtain the arithmetic mean of the diameters of 200 particles randomly selected, and the average particle size to have the value . Was determined by using the content of the thermal analyzer (3) metal component "SSC/5200" a (Seiko Instruments Inc.), and TG / DTA analysis.
The check of the analysis of organic components (4) organic components and the like, were performed using GC / MS "Hewlett-Packard 6890 GC system" (Gas chromatography mass spectrometry) apparatus (Hewlett-Packard).

[0038] From ethanolamine and cholic acid and 1 silver carbonate example ethanol preparation of silver nanoparticles (1. Where in addition (24.40g, a 400mmol) ethanolamine (27.58g, and 100mmol) (81.71g, 200mmol), silver carbonate cholic acid in 5L), was heated under reflux for 3 hours with stirring, brown solution was obtained were.
By then allowed to cool to room temperature, was added acetone (3L), and allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a blue powder.
The powder was dispersed stably in any of ethanol, propanol or isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0039] The silver content is preferably 69% from the TG / DTA was confirmed. Silver nanoparticles from TEM observation photograph of Figure 1, the resulting 3 average particle diameter spherical.
Distribution 5 ± 0.59nm, the particle size was 1.1nm ~ 4.8nm. Since the peak of the organic matter derived from cholic acid and (m / z = 61) ethanolamine from the GC / MS was observed to be a particle that is protected with an organic material used was confirmed that the silver nanoparticles.

[0040] (149mg, 1mmol) and triethanolamine (276mg, 1mmol) and (82mg, 0.2mmol), silver carbonate cholic acid ethanol preparation of silver nanoparticles (5ml) and triethanolamine and cholic acid and 2 silver carbonate Example place and the mixture was heated under reflux for 3 hours with stirring, deep yellow solution was obtained.
After cooling to room temperature, was added acetone (5ml), and allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a brown powder.
Silver content was 75% higher than TG / DTA.

[0041] Morpholine (2.76g, 10mmol) and (3.48g, 40mmol (8.18g, 20mmol), silver carbonate cholic acid water preparation of silver nanoparticles (28.75g) from morpholine and cholic acid and three silver carbonate Example was added) 2 with stirring. Where it was heated under reflux for 5 hours, red-brown solution was obtained After cooling to room temperature, was added methanol (60ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a powder having a metallic luster blue-green. The powder was dispersed stably in water. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0042] Silver nanoparticles from TEM observation photograph of Figure 2, the resulting 7 average particle diameter spherical. Distribution 9 ± 4.1nm, the particle size was 2.4nm ~ 21.1nm. Silver content was 38% from TG / DTA.

[0043] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (1) in ethanol (7ml) Preparation of silver nanoparticles from amine two types of calls and acid and 4 silver carbonate Example and where was added (259mg, 2mmol) octyl amine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained. After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0044] Silver nanoparticles from TEM observation photograph of Figure 3, the resulting 7 average particle diameter spherical. Distribution 6 ± 2.0nm, the particle size was 2.8nm ~ 12.5nm.

[0045] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (2) in ethanol (7ml) Preparation of silver nanoparticles from two types of amine and cholic acid and 5 silver carbonate Example and where was added (483mg, 2mmol) and di-octylamine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained. After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0046] Silver nanoparticles from TEM observation photograph of Figure 4, the resulting 6 average particle diameter spherical. Distribution 0 ± 1.3nm, the particle size was 2.5nm ~ 9.1nm.

[0047] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (3) in ethanol (7ml) Preparation of silver nanoparticles from amine two types of calls and acid and 6 silver carbonate Example and where was added (707mg, 2mmol) and tri-octylamine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained. After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0048] Silver nanoparticles from TEM observation photograph of Figure 5, the resulting 11 average particle diameter spherical. Distribution 5 ± 4.3nm, the particle size was 2.9nm ~ 22.6nm.

[0049] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (4) in ethanol (7ml) Preparation of silver nanoparticles from two types of amine and cholic acid and 7 silver carbonate Example and 2 - where was added (259mg, 2mmol) and ethylhexyl amine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained. After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0050] Silver nanoparticles from TEM observation photograph of Figure 6, the resulting 16 average particle diameter spherical. Distribution 7 ± 1.9nm, the particle size was 9.0nm ~ 23.3nm.

[0051] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (5) in ethanol (7ml) Preparation of silver nanoparticles from amine two types of calls and acid and 8 silver carbonate Example and bis - where was added (483mg, 2mmol) and (2-ethylhexyl) amine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained.
After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol, In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0052] Silver nanoparticles from TEM observation photograph of Figure 7, the resulting 5 average particle diameter spherical. Distribution 6 ± 1.4nm, the particle size was 2.1nm ~ 9.0nm.

[0053] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid (6) in ethanol (7ml) Preparation of silver nanoparticles from amine two types of calls and acid as in Example 9 silver carbonate and tris - where was added (707mg, 2mmol) and (2-ethylhexyl) amine, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained.
After addition of acetone (10ml) was cooled to room temperature and allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder.
The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0054] Silver nanoparticles from TEM photograph observation of Figure 8, the resulting 10 average particle diameter spherical. Distribution 6 ± 2.4nm, the particle size was 5.4nm ~ 17.4nm.

[0055] (276mg, 1mmol) (818mg, 2mmol), silver carbonate, ethanol amine (122mg, 2mmol) cholic acid preparation ethanol of silver nanoparticles (7ml) from N-methylpyrrolidone and ethanolamine and cholic acid and 10 silver carbonate Example and where was added (198mg, 2mmol) and N-methylpyrrolidone, and the mixture was heated under reflux for 1 hour with stirring, the red-brown solution was obtained.
After cooling to room temperature, was added acetone (10ml), allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a red-brown powder. The powder was dispersed stably in either ethanol, propanol and isopropanol. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0056] Silver nanoparticles from TEM observation photograph of Figure 9, the resulting 5 average particle diameter spherical. Distribution 2 ± 0.88nm, the particle size was 3.5nm ~ 10.0nm.

[0057] In addition (122mg, 2mmol) ethanol amine (276mg, 1mmol) and (412mg, 0.5mmol), silver carbonate glycyrrhizic acid water preparation of silver nanoparticles (5ml) and from ethanolamine and glycyrrhizic acid and 11 silver carbonate example, it was heated under reflux for 1 hour while stirring, red-brown solution was obtained. After cooling to room temperature, was added methanol (5ml), and allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a green powder. The powder was dispersed stably in water. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0058] Silver nanoparticles from TEM observation photograph of Figure 10, the resulting 4 average particle diameter spherical. Distribution 6 ± 1.6nm, the particle size was 2.1nm ~ 12.8nm.

[0059] Added (174mg, 2mmol) and morpholine (276mg, 1mmol) and (412mg, 0.5mmol), silver carbonate glycyrrhizic acid preparation water of the silver nanoparticles (5ml), was stirred morpholine and glycyrrhizic acid 12 silver carbonate Example it was heated to reflux for 1 hour while, red-brown solution was obtained. After cooling to room temperature, was added methanol (5ml), and allowed to stand, it was filtered with a Kiriyama funnel, and dried under reduced pressure to give a green powder having a metallic luster. The powder was dispersed stably in water. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0060] Silver content was 92% higher than TG / DTA. Silver nanoparticles from TEM observation photograph of Figure 11, the resulting 12 average particle diameter spherical. Distribution 0 ± 3.5nm, the particle size was 4.0nm ~ 25.0nm. Since the peak pattern of metallic silver was observed from the XRD of Figure 12, it was found to be the silver nanoparticles.

[0061] Put in a necked flask 4 (64.3g, 0.233mol) the preparation of silver carbonate silver nanoparticles from N-methylpyrrolidone and abietic acid and 13 silver carbonate example, (125g, 0.966mol) octylamine followed have made. Further, it is heated in an oil bath in addition (15.0g, 0.050mol) and abietic acid (41.3g, 0.416mol) and N-methylpyrrolidone was heated at 90 ℃. After the reaction, the reaction mixture was cooled to 70 ℃, washed with methanol (100ml × 3), was filtered with a Kiriyama funnel as a solid silver nanoparticles. Yield 49.0g. The resulting particles could be dispersed in toluene. In other words, I have confirmed that that is a (almost transparent) solubilized state.

[0062] Silver content was 96% from TG / DTA. Since the peak pattern of metallic silver was observed from the XRD of Figure 13, it was found to be the silver nanoparticles. Since the peak of the organic matter derived from abietic acid or (m / z = 99) N-methyl-pyrrolidone from the GC / MS was observed, the silver nanoparticles was found to be a particle that is protected with an organic material used .

[0063] Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 1 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 3 (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 4 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 5 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 6 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 7 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 8 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 9 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 10 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 11 is a (image). Shows the results of observation by transmission electron microscopy (TEM) of silver nanoparticles obtained in Example 12 is a (image). Is a graph showing the results of (XRD) X-ray diffraction analysis of the silver nanoparticles obtained in Example 12.
Is a graph showing the results of (XRD) X-ray diffraction analysis of the silver nanoparticles obtained in Example 13.



PRODUCTION METHOD OF SILVER NANOPARTICLE, SILVER NANOPARTICLE AND APPLICATION THEREOF
JP2006328472       

Abstract --- PROBLEM TO BE SOLVED: To provide a method of producing silver nanoparticles (average grain size 1 to 20 mm) for a silver paste having a good specific resistance of a hardening film at a high yield by a chemical reduction process. SOLUTION: More than stoichiometerically excessive ammonia water is added to an aqueous silver nitrate solution to form a silver complex and the silver nanoparticles are produced by reduction with an aqueous formalin solution at >=0.90 in the ratio of the solvent and water at temperature 20 to 40[deg.]C in a methyl ethyl ketone solvent containing >=2% polymer dispersant.





METHODS OF CONTROLLING NANOPARTICLE GROWTH
US7033415

Also published as: WO2004089813 // EP1613787 // KR20060080865

Abstract --- The invention provides new types of plasmon-driven growth mechanism for silver nanostructures involving the fusion of triangular nanoprisms. This mechanism, which is plasmon excitation-driven and highly cooperative, produces bimodal particle size distributions. In these methods, the growth process can be selectively switched between bimodal and unimodal distributions using dual beam illumination of the nanoparticles. This type of cooperative photo-control over nanostructure growth enables synthesis of monodisperse nanoprisms with a preselected edge length in the 30-120 nm range simply by using one beam to turn off bimodal growth and the other (varied over the 450-700 nm range) for controlling particle size.

FIELD OF THE INVENTION

[0003] The invention resides in the field of nanoparticles and specifically in methods of forming silver nanoprisms of varying sizes.

BACKGROUND OF THE INVENTION

[0004] Nanoclusters are an important class of materials that are having a major impact in a diverse range of applications, including chem- and biodetection, catalysis, optics, and data storage. The use of such particles dates back to the middle ages, and the scientific study of them has spanned over a century. These nanostructures are typically made from molecular precursors, and there are now a wide variety of compositions, sizes, and even shapes available. Because of their unusual and potentially useful optical properties, nanoprism structures in particular have been a recent synthetic target of many research groups. We recently reported a high yield photosynthetic method for the preparation of triangular nanoprisms from silver nanospheres. For many nanoparticle syntheses, an Ostwald ripening mechanism, where large clusters grow at the expense of smaller ones, is used to describe and model the growth processes. This type of ripening typically results in unimodal particle growth. Thus, method of controlling the growth and ultimate dimensions of such structures is desired. Such a method will necessarily fall outside of the known Ostwald ripening mechanisms.

SUMMARY OF THE INVENTION

[0005] The present invention provides a method of forming nanoprisms by exposing silver particles to a wavelength of light between about 400 nm and about 700 nm for a period of less than about 60 hours. The nanoprisms formed have a bimodal size distribution. Preferably, the silver particles are present in a colloid containing a reducing agent, a stabilizing agent and a surfactant. If the colloid contains a stabilizing agent and a surfactant, the ratio of the stabilizing agent to the surfactant is preferably about 0.3:1. The nanoparticle starting materials have a diameter between 0.2 nm and about 15 nm. The nanoprisms formed are single crystalline and have a {111} crystal face on a base plane of the nanoprism and a {110} crystal face on a side plane of the nanoprism and display plasmon bands having [lambda]max at 640 nm and 1065 nm, 340 nm and 470 nm.

[0006] Another embodiment of the present invention provides a method of forming a nanoprism by exposing silver nanoparticles to a primary and a secondary wavelength of light such that one of the primary and secondary wavelengths of light excites quadrupole plasmon resonance in the silver particles. In this embodiment, one of the primary and secondary wavelengths of light coincides with the out-of-plane quadrupole resonances of the silver nanoprisms. In a preferred embodiment of this method, the secondary wavelength of light is about 340 nm and the primary wavelength of light is in the range of about 450 nm and about 700 nm.

[0007] By adjusting the primary wavelength of light used in these embodiments of the present invention, the edge length of the nanoprisms produced can be controlled. When the secondary wavelength of light is about 340 nm and the primary wavelength of light is in the range of about 450 nm and about 700 nm, the nanoprisms produced have an edge length of between about 31 nm and about 45 nm. Alternatively, if the primary wavelength of light is in the range of about 470 nm and about 510 nm, the nanoprisms have an edge length between about 53 nm and about 57 nm. Alternatively, if the primary wavelength of light is in the range of about 500 nm and about 540 nm, the nanoprisms have an edge length between about 53 nm and about 71 nm. Alternatively, if the primary wavelength of light is in the range of about 530 nm and about 570 nm, the nanoprisms have an edge length between about 64 nm and about 80 nm.

[0008] Alternatively, if the primary wavelength of light is in the range of about 580 nm and about 620 nm, the nanoprisms have an edge length between about 84 nm and about 106 nm. Alternatively, if the primary wavelength of light is in the range of about 650 nm and about 690 nm, the nanoprisms have an edge length between about 106 nm and about 134 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1(A) shows a transmission electron microscopy (TEM) image of a sample of silver nanoprisms formed using single beam excitation (550+-20 nm) and the inset shows the histograms used to characterize the size distribution as bimodal. FIGS. 1(B) and (C) are TEM images of nanoprism stacks showing the two different sized nanoprisms having nearly identical thicknesses (9.8+-1.0 nm).

[0010] FIG. 2(A) shows the time evolution of ultra violet-visible-near infra red (UV-VIS-NIR) spectra of a silver colloid (4.8+-1.1 nm spheres) under single beam excitation (550+-20 nm). In the graph, curve 1 is the initial colloid, curve 2 is at a time of 10 h, curve 3 is at a time of 15 h, curve 4 is at a time of 19 h, curve 5 is at a time of 24 h, curve 6 is at a time of 55 h. FIG. 2(B) is the theoretical modeling of the optical spectra of two different sized nanoprisms (edge length of Type 1=70 nm, Type 2=150 nm, thickness=10 nm).

[0011] FIG. 3(A) is a schematic depicting dual beam excitation (primary: 550+-20 nm, secondary: 450+-5 nm). FIG. 3(B) is the UV-VIS-NIR spectrum of a silver colloid. FIG. 3(C) is a TEM image of the final silver nanoprisms (average edge length 70+-8 nm, thickness 10+-1 nm, images of prism stacks not shown). The inset shows a histogram characterizing the distribution as unimodal.

[0012] FIG. 4(A) Shows the optical spectra for six different sized nanoprisms (edge length: 38+-7 nm, 50+-7 nm, 62+-9 nm, 72+-8 nm, 95+-11 nm, and 120+-14 nm) prepared by varying the primary excitation wavelength (central wavelength at 450, 490, 520, 550, 600, and 670 nm, respectively, width=40 nm) coupled with a secondary wavelength (340 nm, width=10 nm). (B) The edge lengths are plotted as a function of the primary excitation wavelength. FIG. 4(C)-(E) show TEM images of silver nanoprisms with respective average edge lengths of 38+-7 nm, 62+-9 nm, and 120+-14 nm.

[0013] FIG. 5(A) shows UV-VIS-NIR spectra of a silver colloid before (dash line) and after (solid line) excitation with a 532.8 nm laser beam (Nd:YAG, approximately 0.2 W). FIG. 5(B) is a TEM image of the resulting nanoprisms after laser induced conversion shows a bimodal size distribution.

[0014] FIG. 6 is a schematic of the proposed mechanism for bimodal growth in which an edge-selective particle fusion mechanism where four Type 1 nanoprisms come together in step-wise fashion to form a Type 2 nanoprism.

[0015] FIG. 7(A) is a TEM image showing dimer and trimer intermediate species depicted in FIG. 6. FIGS. 7(B) and (C) are theoretical modeling of the optical spectra of the dimmer and timer species.

[0016] FIG. 8 Shows the optical spectrum of a silver colloid after dual beam 550 nm/395-nm excitation. 395-nm corresponds to the dipole plasmon of silver nanospheres. Such a coupled bean excitation pattern does not effect a unimodal growth process.

[0017] FIG. 9 shows the emission spectrum of a fluorescent tube.

[0018] FIG. 10(A) is a scheme depicting two possible nanoprism growth routes when spherical silver particles (4.8+-1.1 nm) are added to an existing colloid of nanoprisms (edge length of 38+-7 nm). (B) The UV-VIS-NIR spectrum of the colloid after the silver nanospheres described in (A) have been completely converted into nanoprisms (top line) is almost identical to the spectrum for the 38 nm stating prisms (bottom line).



DETAILED DESCRIPTION OF THE INVENTION

[0019] The invention provides a method of controlling the growth and size of nanoprisms formed from a metal colloid by excitation of surface plasmons. This method provides control over nanoparticle growth allowing the synthesis of monodisperse samples of nanoprisms having a desired edge length simply by controlling the excitation wavelength of a narrow band light source. Exposure to a light source having the correct excitation wavelength causes plasmon excitation on the surface of the metal nanoparticles. When a single beam (e.g. 550+/-20 nm) was used, it has been surprisingly found that the suspension of nanoprisms formed consists of two different size distributions, of which the smaller (designated as Type 1) and the larger nanoprisms (designated Type 2) have average edge lengths in the range of about 55 nm to about 85 nm and about 130 nm to about 170 nm, respectively (FIG. 1A).

[0020] These nanoprisms form stacks, and therefore, edge views allow precise determination of the nanoprism thickness (FIG. 1B-C). Although the average edge lengths for the Type 1 and Type 2 nanoprisms are significantly different, their thicknesses are almost identical between about 8 nm and about 11 nm. Both types of nanoprisms are single crystalline with face-centered cubic (fcc) structures. The {111} crystal face forms the top/base plane of the nanoprism, and three {110} crystal faces form the side planes.

[0021] During the formation reaction, the plasmon band at approximately 395 nm associated with the spherical silver particles disappears while two new strong bands having [lambda]max at 640 nm and 1065 nm associated with the Type 1 and Type 2 nanoprisms, respectively, appear. The band for the Type 1 prisms is initially centered at [lambda]max=680 nm and gradually blue shifts to [lambda]max=640 nm. This blue shifting correlates with the tip sharpness of the nanoprism features as rounding is known to lead to blue-shifting. The second strong band at [lambda]max=1065 nm is assigned to Type 2 particles. As shown by curve 6 in FIG. 2A, two other weak resonances having [lambda]max at 340 nm and 470 nm are observed in addition to the two strong surface plasmon bands.

[0022] Theoretical modeling using a finite element-based method known as the discrete dipole approximation (DDA) shows plasmon bands that reproduce the experimentally observed spectrum. For example, by comparing FIG. 2(B) and curve 6 of FIG. 2(A), unambiguous peak assignments can be provided. The first three peaks in the spectrum of the colloid containing both Type 1 and Type 2 particles, 340 nm (out-of-plane quadrupole resonance), 470 nm (in-plane quadrupole resonance) and 640 nm (in-plane dipole resonance), result from the Type 1 nanoprisms. In the case of the Type 2 nanoprisms, only the strong dipole resonance at 1065 nm is clearly observed. FIG. 2(B) shows that quadrupole resonances, which occur at 340 nm and 600 nm in the solution of the Type 2 nanoprisms, are overlapped with plasmon bands from the Type 1 nanoprisms. These time-dependent optical spectra are consistent with a bimodal process rather than the unimodal growth processes expected for the conventional Ostwald ripening of the prior art.

[0023] The nanoprisms are composed of silver present in the silver colloid starting material. Any silver salt can be used to form the silver nanoparticles. Preferably, the silver salt is AgNO3, CH3CO2Ag, AgClO4, Ag2SO4 or combinations of these silver salts. The silver nanoparticles used to obtain the silver nanoprisms are less than about 15 nm in diameter and preferably less than about 10 nm in diameter. More preferably, the silver nanoparticles are between about 2 nm and about 6 nm in diameter. Most preferably, the silver nanoparticles are about 4.8 nm in diameter.

[0024] The colloidal silver suspension that forms the starting material can be formed by any means to contain silver nanoparticles falling within the desired size range. Many methods of forming a silver colloid are known in the art and generally all include different forms of agitation to produce the colloidal particles. The colloidal suspension may also include other chemicals that do not participate in the reaction forming the nanoprisms. For example, reducing agents, suspending agents, surface acting agents, particle stabilizing agents and the like can be used in formation of the suspension without adversely affecting the formation of the nanoprisims in the methods of the present invention. The colloid can be easily prepared using the methods described by Cao et al. (Cao, Y. W.; Jin, R.; Mirkin, C. A. J. Am. Chem. Soc. 123, 7961 (2001)) which includes vigorous stirring in the presence of sodium borohydride followed by the addition of Bis (p-sulfonatophenyl) phenylphosphine dihydrate dipotassium (BSPP) and additional stirring. Surfactants used to form the suspension of nanospheres may vary widely in concentration without affecting the extent of the conversion of nanospheres to nanoprisms. However, the reaction rate is affected by surfactant and provides an additional means of controlling the conversion reaction based on the conversion rate. Preferably, trisodium citrate is present as a surfactant in the suspension of silver nanospheres and bis(p-sulfonatophenyl) phenylphosphine dihydrate (BSPP) is added to the suspension as a particle stabilizing agent. Although the nanoprisms are formed over the entire range of surfactant concentration, the rate of the conversion reaction decreases as a function of increasing the ratio of BSPP to citrate over a range of about 0.01 to about 1. The most rapid conversion rate is obtained at a BSPP to citrate ratio of 0.3:1. Thus, the reaction rate may be optimized by varying the surfactant concentration and the ratio of the surfactant to a stabilizing agent added to the suspension.

[0025] The light source used to produce the nanoprisms having a bimodal size distribution must possess a wavelength that generates the plasmon excitation resulting in nanoprism formation and growth. The excitation wavelength is between about 400 nm and about 700 nm. Preferably the excitation wavelength is between about 530 nm and 570 nm. More preferably, the excitation wavelength is about 550 nm. However, the bimodal growth of the nanoprisms is not caused by the wavelength dispersity of the excitation beam. For example, when a monochromatic laser beam having a wavelength of 532.8 nm (the second harmonic of a Nd:YAG laser) is used to photolyze the silver colloids, bimodal growth is still observed. Preferably, a narrow band light source is used to irradiate the silver colloid. A 150 watt xenon lamp having a light output of about 12 watts with an optical bandpass filter having a center wavelength of 550 nm and a width of 40 nm is suitable for use in the methods of the present invention although one of skill in he art will recognize that many suitable light sources producing a light having a wavelength within the desired range are available for use in the methods of the present invention. The colloid is exposed to the light for a period of time that is dependent upon the intensity of the light used. The exposure time is usually less than about 100 hours and typically the exposure time is about 60 hours.

[0026] Without intending to be bound by any single theory, it is believed that the observed bimodal growth process results from an edge-selective particle fusion mechanism wherein four smaller, Type 1, nanoprisms come together in step-wise fashion to form a larger, Type 2, nanoprism as depicted in the shaded region of FIG. 6. Several observations are consistent with this mechanism. First, bimodal growth results in Type 1 and Type 2 prisms where four of the former prisms can fit together to form a prism with dimensions (cumulative edge length=140+-17 nm) that compare well with the latter (150+-16 nm). Second, edge selective growth occurs with no apparent change in nanostructure thickness in going from the Type 1 to Type 2 nanoprisms. Third, as shown in FIG. 2(A), detailed time-dependent UV-VIS-NIR measurements show that the onset of the growth of the band at 1065 nm (assigned to Type 2) is significantly delayed in comparison with the growth of the band at 640 nm (assigned to Type 1) indicating that the fusion of nanoprisms occurs only after Type 1 nanoprisms accumulate. Fourth, as shown in FIG. 7, dimer and trimer intermediates (depicted as 2 and 3, respectively, in FIG. 6) are observed during the early stages of Type 2 nanoprism growth. Electrodynamics calculations for the possible intermediate species in the fusion growth process show that the dimer and trimer intermediates have plasmon excitations close to 600 and 1065 nm meaning that Type 1 nanoprisms and the dimmer/trimer intermediates can all absorb at 600 nm. This leads to the excited state needed for particle fusion. However, Type 2 nanoprisms do not absorb at that wavelength, which is why these nanoprisms represent the end of the nanoparticle growth path.

[0027] This edge- and crystal face-selective (side={110} lattice planes) fusion growth is unusual, especially in view of the many other possible products that could arise from oligomerization of the Type 1 nanoprisms depicted in FIG. 6 outside of the shaded region. If these forms exist, they must be in a fast equilibrium with the main growth route (shaded in Scheme 1), since they are not observed by TEM. While methods of fusing spherical nanoparticles into nanowire structures (CdTe or PbSe) after removal of surface ligands, as well as other examples involving spherical particle fusion, are known in the art, the methods of the present invention are the only methods that use photochemistry to effect the edge- and crystal face-selective particle fusion process.

[0028] The bimodal growth appears to contradict previous results in which unimodal nanoprism growth was observed when visible light from a conventional fluorescent tube was used as the excitation source (co-pending U.S. patent application Ser. No. 10/256,875; Publication No. 20030136223 A1). However, by careful analysis of the optical properties of these nanostructures and the effects of photolysis on them, surface plasmon cooperativity has been identified in the photochemistry of silver nanoprisms. As shown schematically in FIG. 3(A), excitation of a solution of silver nanoparticles at two wavelengths, 550+-20 nm (primary) and 450+-5 nm (secondary) (I550:I450=2:1, FIG. 3A) completely inhibits the formation of Type 2 nanoprisms. This treatment results in the exclusive formation of the smaller, Type 1, nanoprisms. By varying the wavelength of the secondary beam, a 550-nm/340-nm coupled beam, in which the 340-nm light coincides with the out-of-plane quadrupole resonances of the Type 1 and Type 2 nanoprisms, can also inhibit the growth of Type 2 nanoprisms. As shown in FIG. 8 however, in the cases of 550-nm/395-nm, 550-nm/610-nm, and 550-nm/650-nm coupled beams, in which the secondary wavelengths fall within the dipole resonances of the silver nanospheres (395 nm) and Type 1 nanoprisms (610 and 650 nm), respectively, bimodal growth is observed. Thus only secondary wavelengths that can excite quadrupole plasmon modes can inhibit bimodal growth. It is this photo-cooperativity that leads to the results observed with a fluorescent tube as the excitation source. Interestingly, the emission spectrum of a fluorescent tube, shown in FIG. 9, exhibits bands at 546-nm and 440-nm and has the appropriate intensity ratio (100%:40%) to effect photosynthetic cooperativity and hence unimodal growth. Consistent with this conclusion, when a 550+-20 nm band filter is used with a fluorescent tube to effect the photosynthetic conversion, bimodal growth is observed.

[0029] Thus, in a preferred embodiment of the present invention, the silver colloid starting material is exposed to light of two different wavelengths to produce dual beam excitation and unimodal growth. Using this method, bimodal growth can be selectively turned off with one fixed secondary beam allowing the formation of nanoprisms having a desired edge length, through a unimodal growth process. This type of cooperative photo-control over nanoparticle growth results in the synthesis of relatively monodisperse samples of nanoprisms with a desired edge length in the range of about 30 nm to about 120 nm simply by controlling the excitation wavelength of the primary beam. Therefore, this embodiment provides the first methods of controlling particle size and shape using light as a directing element. By varying the primary light source between the wavelength of about 450 nm and about 700 nm, with a fixed secondary beam corresponding to the out-of-plane quadrupole plasmon excitation unimodal growth results to generate a solution of nanoprisms of a desired average size.

[0030] Using this method, it is possible to synthesize nanoprisms with in-plane dipole plasmon resonances with edge lengths ranging from about 30 nm to about 120 nm. The average edge lengths of the resulting nanoprisms correlate well with the wavelength of the primary excitation source in which a longer primary excitation wavelength produces larger particles with in-plane dipole plasmons (the red-most peak in each spectrum) that are red-shifted with respect to the excitation wavelength. For example, when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 430 nm and about 470 nm and the nanoprisms have an edge length between about 31 nm and about 45 nm; when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 470 nm and about 510 nm the nanoprisms have an edge length between about 53 nm and about 57 nm; when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 500 nm and about 540 nm, the nanoprisms have an edge length between about 53 nm and about 71 nm; when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 530 nm and about 570 nm, the nanoprisms have an edge length between about 64 nm and about 80 nm; when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 580 nm and about 620 nm, the nanoprisms have an edge length between about 84 nm and about 106 nm; and when the secondary wavelength of light is fixed at 340 nm and the primary wavelength of light is between about 650 nm and about 690 nm, the nanoprisms have an edge length between about 106 nm and about 134 nm. This type of growth is not necessarily a result of particle fusion.

[0031] Another feature of using wavelength to control the size of the nanoprisms formed is that, as shown in FIG. 10, subsequent addition of silver spherical nanoparticles to the nanoprism colloid does not lead to enlargement of the nanoprism but instead the added particles grow into nanoprisms similar in size to those present as determined by the excitation wavelength. This result is in contrast with conventional thermal strategies for controlling particle sizes, in which addition of precursors typically leads to larger particles. Therefore, the methods of the present invention represent fundamentally new ways of controlling particle size through wavelength modulation.

[0032] The particle size control observed here is not a result of photothermal (or optical "burning") effects as those effects have been invoked in other studies involving intense pulse laser irradiation of metal nanostructures. By comparison, the light source used to effect nanoparticle conversion by the methods of the present invention is very weak, having a beam power of less than about 0.2 watts. According to the equation, [Delta]T=[Delta]H/Cp where, [Delta]H is the absorbed photon energy, and Cp is the heat capacity of silver (0.235 J.K<-1> .g<-1> ), single 550 nm photon absorption by a Type 1 prism can only lead to a negligible increase in temperature and the cumulative experimentally-determined temperature increase after 50 hours of photolysis (550+-20 nm) was less than 10[deg.] C. Thus, photo-induced thermal effects are not responsible for the particle growth and size control in the methods of the present invention.

[0033] Surface plasmons are typically studied as physical properties of metal nanostructures rather than chemical tools that provide control over growth and ultimate particle dimensions. The methods of the present invention take advantage of plasmon excitation in the nanoprism growth process, both for Type 1 particles which grow from the initially produced colloidal particles to a size that depends on the dipole plasmon wavelength, and for Type 2 particles whose growth also requires dipole plasmon excitation, but is inhibited by quadrupole plasmon excitation. Without intending to be bound by any one theory, it is believed that plasmon excitation leads to ligand dissociation at the particle edges, whereby the local fields are the most intense, allowing the Type 1 particles to grow through the addition of silver atoms or clusters and the Type 2 particles to form by particle fusion. The results presented in the following examples are consistent with a fundamentally new type of particle growth and size control that is light initiated and driven, highly cooperative, and surface plasmon directed.

EXAMPLES

Example 1

[0034] This example illustrates one method of making silver colloids suitable for use in the methods of the present invention. AgNO3 (99.998%) and NaBH4 (99%) were obtained from Aldrich, and bis (p-sulfonatophenyl) phenylphosphine dihydrate dipotassium (BSPP) was purchased from Strem Chemicals, Inc. All H2O was purified by a Barnstead Nanopure H2O purification system (resistance=18.1 M[Omega].cm). 100 mL of nanopure H2O, 1 mL of 30 mM trisodium citrate, and 2 mL of 5 mM AgNO3 solution were mixed in a 250 mL three neck flask. The flask was immersed in an ice bath, and the solution was bubbled with argon under constant stirring for approximately 30 minutes. 1 mL of 50 mM aqueous NaBH4 (ice-cold, freshly made) was quickly injected into the solution under vigorous stirring. The clear solution immediately turned light yellow. The reaction was allowed to proceed for approximately 15 min, and 1 mL of 5 mM BSPP solution and a 0.5 mL aliquot of NaBH4 were added to the solution in a dropwise fashion. The colloids were left overnight stirring in the dark. Transmission electron microscopy (TEM) analyses show that the as-prepared particles have an average diameter of 4.8+-1.1 nm.

Example 2

[0035] This example illustrates the production of a nanoprism suspensions by the photo-initiated plasmon excitation means of the present invention. A xenon lamp (Novalight system, 150 W, light output approximately 12 W, Photon Technology, Inc.) was utilized as the light source for the photosynthetic experiments. Optical band filters (diameter=25 mm, band width=10 nm or 40 nm) were obtained from Intor, Inc. The photoconversion of nanospheres to nanoprisms was performed in a glass flask or quartz cell. The quartz cell was only used in double beam experiments when light less than 400 nm was introduced. The silver colloid was sealed in the reactor wrapped with aluminum foil. For the single beam excitation experiment, the 550+-20 nm beam (green, approximately 100,000 Lux, measured with a digital light meter, Model LM-1, Family Defense Products) was introduced to the silver colloids through a hole (ca. 20 mm in diameter) on the aluminum wrap. The distance between the reactor and the light output window was approximately 8 cm. For the double beam excitation experiment, two holes (approximately 20 mm in diameter) were made in the aluminum wrap, and two beams (the 550+-20 nm primary beam and a wavelength-varied secondary beam with FWHM approximately 10 nm) from two Xe lamps were simultaneously introduced to the silver colloid, with the beams forming a 90[deg.] angle. The silver colloids were exposed to the light sources for about 50 hours (variable with light intensity). To control the silver nanoprism size (edge length), a primary beam (450, 490, 520, 550, 600 and 670 nm, respectively, width=40 nm) coupled with a secondary beam (450 nm or 340 nm, width=10 nm) was used to photolyse the silver colloid. For the laser excitation experiment, the laser beam (532.8 nm, CW, light output approximately 0.2 W, Nd:YAG) was directly introduced to the reactor containing the silver colloid.

[0036] TEM imaging of the nanoprims was performed with a 200 kV Hitachi H8100. Approximately 400 particles were used for the particle size statistical analyses. High-resolution TEM imaging was carried out with a 200 kV field-emission Hitachi HF 2000 electron microscope equipped with a Gatan Imaging System. UV-VIS-NIR spectroscopic measurements of colloids were performed with a Cary 500 spectrometer. The emission spectrum of a fluorescent tube (white daylight type, Philips TLD 36 W/865 or General Electric 40 W) was measured with a HP 8453 diode array spectrophotometer, and is given in arbitrary units for the 250-800 nm range.

Example 3

[0037] This example provides a sample calculation of the temperature rise in the silver nanoparticles exposed to 550+-20 nm beam excitation. The parameters for the silver colloid:

[0038] 100 mL of silver colloid (silver atomic concentration=0.1 mM);

[0039] The volume of a Type 1 prism (edge length=70 nm, thickness=10 nm): 2.1*10<-17 > cm<3> ;

[0040] The mass of a Type 1 prism=2.1*10<-17 > (cm<3> )*10.5 (g/cm<3> )=2.2*10<-16 > g;

[0041] The number of Type 1 prisms in 100 mL of colloid=4.8*10<12> ;

[0042] The energy of a 550-nm photon=1240 (eV.nm)/550 (nm)=2.25 eV=3.6*10<-9 > J

[0043] The 550-nm beam power approximately 0.2 Watt;

[0044] The 550-nm photon flux=0.2 (J/s)/3.6*10<-19 > (J/photon)=5.6*10<17 > photons/sec;

[0045] Bulk silver specific heat capacity=0.235 J/g/K (CRC Handbook of Chemistry and Physics, 83<rd > ed., London, New York)

[0046] The heat capacity of a Type 1 prism=0.235 (J/g/K)*2.2*10<-16 > (g/particle)=5.2*10<-17 > J/K.

[0047] In the calculation, it is assumed that the absorbed photon energy is rapidly equilibrated among the conduction electrons, resulting in hot electron gas. The hot electrons equilibrate with the phonons on a time scale of a few picoseconds, which leads to a temperature increase in the s silver lattice. The temperature increase of silver particles under 550+-20 nm beam excitation can be estimated by the equation [Delta]T=[Delta]H/Cp, where, [Delta]H is the total absorbed energy, and Cp is the heat capacity for silver nanoparticles (assumed to be the bulk value Cp=235 J/(KgK)). If one photon is absorbed by a Type 1 nanoprism, then [Delta]T, the photon energy/heat capacity is 0.007 K.

[0048] In a second calculation, we assume that the beam energy (beam power=0.2 W, measured by a light meter) is 100% absorbed (for estimation of maximum temperature increase), and that there is a 1 picosecond time scale for heat transfer from the surface plasmon excited state to the silver lattice, and during this time there is no heat dissipation to the surroundings. In this case, [Delta]H=0.2 (W)*1*10<-12 > (s), Cp=0.235 (JK<-1> g<-1> )*0.1 (L)*0.1*10<-3> (molL<-1> )*108(gmol<-1> ), thus, [Delta]T is approximately equal to 10<-9 > K.

[0049] Once the electrons and lattice have reached equilibrium, the heat is finally dissipated into the surroundings (water and air) by phonon-phonon couplings. Energy "storing" by the silver lattice as temperature increases is negligible because the photon flux in these methods is extremely low, and the silver lattice can efficiently dissipate heat to the surroundings. In addition, multiple photon absorption is statistically negligible due to the extremely low photon flux.

Example 4

[0050] This example demonstrates the production and characterization of a suspension of nanoprims having a bimodal size distribution by the methods of the present invention. Colloidal silver nanoparticles (diameter 4.8+-1.1 nm) were irradiated with a narrow band light source (using a 150 W xenon lamp (light output approximately 12 W) with an optical bandpass filter; center wavelength=550 nm, width=40 nm) for approximately 50 h. TEM shows that the colloid formed consists of two different size distributions of nanoprisms (FIG. 1A and inset), of which the smaller and the larger particles have average edge lengths of 70+-12 nm and 150+-16 nm, respectively. The thicknesses of both size nanoprisms are almost identical at 9.8+-1.0 nm (FIGS. 1B and C). High-resolution TEM studies reveal that the {111} crystal face forms the top/base plane of the nanoprism, and three {110} crystal faces form the side planes of both sizes of nanoprisms. The growth process was been monitored by UV-VIS-NIR spectroscopy (FIG. 2A). Disappearance of the plasmon band (at 395 nm) during the reaction is associated with the spherical silver particles and formation of two new strong bands (at 640 nm and 1065 nm, respectively) associated with the Type 1 and Type 2 nanoprisms, respectively. The band for the Type 1 prisms is initially centered at [lambda]max=680 nm and gradually blue shifts to [lambda]max=640 nm. The second strong band at [lambda]max=1065 nm is assigned to Type 2 particles. In addition to the two strong surface plasmon bands, two other weak resonances are observed at 340 and 470 nm, respectively (FIG. 2A curve 6).

Example 5

[0051] This example demonstrates the use of dual beam plasmon excitation to form silver nanoprisms of a discrete size. Silver nanoparticles (4.8+-1.1 nm) were excited at two wavelengths, 550+-20 nm (primary) and 450+-5 nm (secondary) (I550:I450=2:1, FIG. 3A). Double-beam excitation at these wavelengths results in exclusive formation of the smaller Type 1 nanoprisms (72+-8 nm), as evidenced by UV-VIS-NIR spectra and TEM analysis (FIGS. 3B and C). A 550-nm/340-nm coupled beam, in which the 340-nm light coincides with the out-of-plane quadrupole resonances of the Type 1 and Type 2 nanoprisms, also inhibits the growth of Type 2 nanoprisms and the final UV-VIS-NIR spectrum is very similar to the spectrum obtained from the two beam 550-nm/450-nm experiment. However, in the cases of 550-nm/395-nm, 550-nm/610-nm, and 550-nm/650-nm coupled beams, in which the secondary wavelengths fall within the dipole resonances of the silver nanospheres (395 nm) and Type 1 nanoprisms (610 and 650 nm), respectively, bimodal growth is observed (FIG. 8).

Example 6

[0052] This example demonstrates a way of controlling nanoprism size and shape using light as a directing element. The silver colloid was exposed to a primary light source (450-700 nm) with a fixed secondary beam (340 nm, corresponding to out-of-plane quadrupole plasmon excitation). Silver nanoprisms with six different average edge lengths (38+-7 nm, 50+-7 nm, 62+-9 nm, 72+-8 nm, 95+-11 nm, and 120+-14 nm) but similar particle thickness (10+-1 nm) were synthesized from colloidal particles (4.8+-1.1 nm) using primary excitation wavelengths of 450+-20 nm, 490+-20 nm, 520+-20 nm, 550+-20 nm, 600+-20 nm, and 670+-20 nm, respectively. The average edge lengths of the resulting nanoprisms correlate well with the wavelength of the primary excitation source (FIG. 4B), which shows that a longer primary excitation wavelength produces larger particles with in-plane dipole plasmons (the red-most peak in each spectrum) that are red-shifted with respect to the excitation wavelength (FIG. 4A).


Ag NANOPARTICLE, METHOD FOR PRODUCING THE SAME AND DISPERSED SOLUTION OF Ag NANOPARTICLE
JP2006118010

Abstract --- PROBLEM TO BE SOLVED: To provide Ag nanoparticles easily redispersed even if a dispersed solution of Ag nanoparticles is dried and hardened or is made into a state close thereto by a method of concentration or the like, and from which a dispersing agent can be removed by a simple operation, and to obtain a dispersed solution comprising the Ag nanoparticles. SOLUTION: The Ag nanoparticles with a particle diameter of 1 to 20 nm comprising the ammine complex of silver nitrate as a dispersing agent can be obtained by mixing silver nitrate, a reducing agent which does not show reducibility in an organic solvent and alkylamine in an organic solvent.

DESCRIPTION

[0001] Redispersion is easy even if the state or near dryness by a method such as concentrated dispersion solution of Ag nanoparticles, and moreover, the present invention, the Ag and nanoparticles can be removed in a simple operation dispersant providing a dispersion solution containing Ag nanoparticles.

[0002] Recently, with the miniaturization of various electronic devices, lighter, and higher performance, improved characteristics are required for materials used in electronic components.

[0003] In particular, metallic nanoparticles as compared to ceramic substrates, such as heat-resistant glass, as the material of the circuit wiring to a resin substrate having a low melting point, electrical conductivity similar to that of a metal bulk as possible can be obtained by sintering at a low temperature process But it has been requested. It is said that since the melting point of the particles is reduced particle diameter is the size of several nanometers, Ag nanoparticles and is promising as a low temperature sintering material among metals. Further, Ag nanoparticles having a uniform shape are monodisperse, can be expected to use the nanocrystal material having a high performance pigment, a three-dimensional structure or two-dimensional.

[0004] However, in case of using such a circuit wiring of various electronic components is actually a process for preparing a low cost Ag nanoparticles in large quantities are required. Methods of synthesizing Ag nanoparticles having a particle diameter of several nanometers which is been many reports until now, mass, and, it was as hard to say the method excellent in industrial productivity at low cost. I was considered to be in the efficiency of the purification process and subsequent reaction concentration when preparing the Ag nanoparticle this cause.

[0005] Conventionally, (Patent Documents 1 to 3) method by reducing an aqueous solution containing a silver salt, obtained colloidal silver is known.

[0006] Furthermore, (Patent Documents 4 to 6) the method for producing colloidal silver particles in high concentration using a polymeric pigment dispersant have been proposed. By using the polymeric pigment dispersant, a colloidal solution of a concentrated silver fine silver particles of 93% or higher are obtained after concentration.

[0007] Usually, in the case of synthesizing nanoparticles by a wet process, it is necessary to purify the work of removing the excess dispersing agent and the reducing agent after the reaction. It is said that conventional, recrystallization, ultrafiltration, and centrifugal separation method is performed as the refining operation, the recrystallization is desirable as a method of purifying large quantities of nanoparticles.

[0008] Excess dispersant and a reducing agent dissolved therein by is weakly agglomerated nano-particles by adding to the reaction mixture in which the nanoparticles are dispersed poor solvent nanoparticles are hardly dispersed, filtered and decanted recrystallization method The method is to remove the solution, purifying the nanoparticles.

[0009] This method is the simple, but to dispersants needed to re-dispersion of the nanoparticles or is removed with a weak excess dispersant adsorption force to the nanoparticle dispersions, aggregation of nanoparticles with each other, such as too strong in some cases the cause is not redisperse. Further, when re-dispersed into a good solvent to the next step, you should have sufficiently removed the poor solvent used for the above, the dispersion stability of the nanoparticles is exacerbated in the case of high concentration of nanoparticles in particular. Therefore, a technique is distilled off as much as possible the anti-solvent under vacuum or atmospheric pressure in order to remove the poor solvent is taken. In some cases re-dispersibility is poor by making the state close to dryness and dryness at this time. This is because the particles tend to aggregate strongly the drying time had to be done carefully over the addition of the good solvent to remove the poor solvent, a state wet with a solvent always.

[0010] Thus, in the case of synthesizing nanoparticles by wet process, especially, the more manageable in the redispersion step or purification step, i.e. nanoparticles with excellent handling properties has been required. Efficiency of purification also increases the handling property is good, it is possible to obtain nanoparticles at low cost.

[0011] On the other hand, it can be said to be re-dispersed easily even when a state close to dryness and dryness are possible, nanoparticles are synthesized using a polymeric dispersant, and has excellent handling properties. However, there remains a problem in that it is necessary to use ultrafiltration during purification Further, when the adsorption force between the nanoparticles and the dispersant is strong in many cases when the polymer dispersant, converted to a dispersant Suit can be difficult to such particles. Further, the electric resistance is intimidated by the polymer dispersant is not removed by heating at the time of firing is concerned in the case of using the material of the conductive paste.

[0012] 11-319538 JP-JP-2003-103158 2002-121606 Patent Publication No. 11-80647 JP 7-76710 JP 1-104338 JP 1-104337 JP-A-Hei

[0013] An Ag nanoparticles having a particle size of several nanometers, redispersion is easy even after the state or near dryness concentrated solution containing dispersed Ag nanoparticles, moreover, in order to replace the dispersant dispersion solution containing the Ag nanoparticles and Ag nanoparticles can be removed by a simple operation dispersant is where it is most required currently, it has not yet been obtained.

[0014] That is, in the manufacturing method 3 described, since it is the reaction of an aqueous solution, the particle size obtain fine particles of several nanometers in size is difficult to Patent Document 1 supra.

[0015] The production method according to 6, since it is the reaction of an aqueous solution, to obtain fine particles of several nanometers in size is difficult to Patent Document 4 supra. Further, the polymeric pigment dispersant is excellent in dispersibility, but a special purification system of fine nanoparticles colloidal solution, and ultrafiltration concentration step is required. Further, when using the conductive ink or conductive paste, high temperature is required in order to decompose the polymeric pigment dispersant, problem still remains as a low-temperature sintering property.

[0016] In the method of 7 Patent Document, it is not generated by the thermal decomposition method using a raw material acetylacetonate salts of the metal the metal particles to the dispersant alkyl amine, in this case, must be heated to decompose there is a problem in productivity because it requires special raw materials and can be omitted. Further, it requires a special vacuum equipment such as a gas evaporation method for the production of silver particles to the dispersing agent alkylamine in the prior art.

[0017] Therefore, in the present invention, redispersion is easy even after the state or near dryness solution concentrated Ag nanoparticles are dispersed, that is excellent in handling properties of the nanoparticles, the substitution of dispersant desired It is a technical object to provide an optimal combination of dispersant Ag nanoparticles can remove the dispersing agent easily to.

[0018] The technical problems can be achieved by the present invention as follows.

[0019] That is, the present invention is an Ag nanoparticles 1 ~ 20nm average particle diameter containing ammine complexes of silver nitrate.

[0020] Also, in an organic solvent, the present invention is a method for producing the Ag nanoparticles, which comprises admixing an alkyl amine and a reducing agent does not exhibit reducing ability of silver nitrate, in an organic solvent.

[0021] Further, the present invention is a dispersion liquid, characterized in that together with the Ag nanoparticles, is contained as a dispersant ammine complexes of silver nitrate in an organic solvent.

[0022] Redispersion and also is easy, Ag nanoparticles according to the present invention can be removed in a simple operation dispersants even after the state or near dryness concentrated dispersion solution.

[0023] Is as follows: In detail the configuration of the present invention.

[0024] By ammine complexes of silver nitrate is present, excellent dispersibility, moreover, Ag nanoparticles according to the present invention can be removed in a simple operation.

[0025] The abundance of silver nitrate ammine complex of Ag nanoparticles according to the present invention, 10 ~ 30wt% is preferred. Problem of dispersion stability becomes poor in case of less than 10wt%, resulting in up the viscosity of the solution when it exceeds 30wt% results. More preferably 20 ~ 28wt%. In addition, I was calculated from alkyl amine component scattered by (calorimetry) TG is abundance of ammine complexes of silver nitrate.

[0026] The average particle size of the Ag nanoparticles according to the present invention is 1 ~ 20nm. In the process of the present invention, can be obtained on an industrial scale Ag nanoparticles less than 1nm is difficult. In the case of more than 20nm, it is not practical there is a problem with low-temperature sintering properties when applied to a conductive paste or the like. Preferably from 1 ~ 15nm, and more preferably 1 ~ 10nm.

[0027] The concentration of Ag nanoparticles in the dispersion of Ag nanoparticles according to the present invention, it is sufficient to variously changed depending on the application, it contains 10 ~ 80wt% of Ag nanoparticles in an organic solvent is preferred. As the organic solvent, is not limited as long as the dispersed Ag nanoparticles is stable, for example, toluene, terpineol, hexane, tetradecanoic like.

[0028] Next, I described a method for manufacturing the dispersion solution of Ag nanoparticles and Ag nanoparticles according to the present invention.

[0029] Silver nitrate is preferably a silver raw material in the present invention.

[0030] Reducing agent in the present invention is a reducing agent having no reducing ability in an organic solvent, preferably formic acid ascorbic acid, ascorbic acid derivatives, isoascorbic acid, isoascorbic derivatives. In the case of using sodium borohydride as a reducing agent, can not be obtained particles of interest of the present invention aggregate and formation of large particles occurs.

Further, for dissolving in a small moisture can be produced industrially manage the water content of the organic solvent used is required, it is difficult to sodium borohydride.

[0031] The alkyl amines of the present invention can be made basic liquid to be able to form an ammine complex coordinated with silver ion as silver nitrate, to promote the reduction reaction, and further, it is an ammine complex of silver nitrate is not particularly limited as long as it can be dispersed stably in an organic solvent Ag nanoparticles adhered, but considering coordinating to silver ions of silver nitrate and dispersion stability of Ag nanoparticles in organic solvent Then, the primary alkyl amine of long chain.

[0032] The amount of the reducing agent, may be any amount sufficient to reduce the silver nitrate, silver nitrate, preferably the ratio of the reducing agent is 1:1 to 1:2 molar ratio. In the case of a large amount than the above range, there is no meaning to be added more than necessary because the effect is saturated amount of the reducing agent.

[0033] The addition amount of the alkyl amine, necessary amount of a combination of the required amount to the amount required to basic humoral to promote the reduction reaction, as a dispersing agent to adhere to the Ag nanoparticles as a nitrate ammine complex is the ratio of alkyl amine nitrate 1:1 molar ratio. 1 to 1:2. 1 is preferred. In the case of a large amount than the above range, there is no meaning to be added more than necessary because the effect is saturated alkyl amine.

[0034] Order of addition of silver nitrate and alkyl amine and a reducing agent is not particularly limited as long as it is well mixed.

[0035] As long as the silver salt, an alkyl amine and a reducing agent are mixed thoroughly, mixing and stirring means is not particularly limited.

[0036] The mixing and stirring time, it is not necessary to heat particular, may be performed at room temperature.

[0037] Reaction solution at first, it is a clear, colorless solution white crystals of iso-ascorbic acid or ascorbic acid and silver nitrate is dispersed, but exhibits a yellow color characteristic of the Ag nanoparticles with stirring time, further, yellow to blackish ( it is solution of a thick yellow).

[0038] In the case of using formic acid in the reducing agent, a method of dropping the formic acid in the mixed solution of the alkylamine nitrate advance. Including the reaction solution is clear, colorless solution of silver nitrate is dispersed, but a yellow color characteristic of the silver particles together with the stirring time, and further, it is a solution of (thick yellow) yellow blackish.

[0039] When poured into a mixed solution of methanol and water or a large amount of acetone to the resulting reaction solution, precipitate Ag nanoparticles are weakly aggregated results. Was removed by decantation and the supernatant, again, the addition of a mixed solvent of water and methanol or acetone. Repeat this operation, to remove the alkyl amine or excess of silver nitrate reduction reaction after.

Remove the precipitate of Ag nanoparticles weakly agglomerated, and the solvent is removed sufficiently due to a rotary evaporator and re-dispersed into an organic solvent such as toluene or hexane again after being dried. Can be prepared Ag nanoparticle dispersion solution of the desired concentration by weight by adding a solvent according to the weight of the solid content of Ag which is generated at this time.

[0040] When preparing the Ag nanoparticles by wet synthesis method as described above, the Ag ammine complex composed the raw material also acts as a dispersing agent was estimated from the experimental facts below.

[0041] The resultant mixture is agglomerated precipitated with methanol Ag nanoparticles produced by (i) the wet synthesis method, and repeatedly washed with methanol, it was attempted to redispersion in toluene and concentrated to dryness after the aggregation of Ag nanoparticles thing was easily re-dispersed. After coagulated precipitated with methanol Ag nanoparticles prepared by (ii) the wet synthesis method, it was washed with water and aggregate, washed with methanol, and dried well was subsequently redispersed in toluene after dryness place, I was easily re-dispersed. After coagulated precipitated with methanol Ag nanoparticles prepared by (iii) the wet synthesis method, it was washed with an aqueous solution of sodium chloride agglomerates. Subsequently, in step four, when the post (remove the salt with water) which was washed with water, and thoroughly dried, it was attempted to redispersion in toluene and concentrated to dryness after the precipitate formed re-dispersion is deteriorated.

Furthermore, when washed with formic acid and methanol and the precipitate washed, and rated on the weight of the organic component by thermal analysis, organic significantly compared to (a state of the (i), of (ii)) before cleaning component had weight loss (Figure 1). After coagulated precipitated with methanol Ag nanoparticles prepared by (iv) the wet synthesis method, it was washed with an aqueous solution of sodium chloride agglomerates. When the post (remove salt by using a large amount of water), which was subsequently washed with water, water was removed from the system during while adding toluene so as not to dryness, and tried to re-dispersed in toluene and re-dispersed easily .

[0042] When preparing the Ag nanoparticles by wet synthesis method described above, the experimental fact shows that the material that reacts with chloride ions has a role as a dispersant. In the Ag nanoparticles according to the present invention, substances that react with the chloride ions are Ag ions, it is understood to be a nitrate ammine complex since dissolved in toluene. Silver nitrate ammine complex is the silver chloride by chloride ion, alkyl amines attached to the Ag nanoparticles, Ag nanoparticles (Condition (iv)) dispersed in toluene as a dispersion agent. Re-dispersibility becomes worse when there dispersant only alkylamine, and the state or near dryness dispersion solution results (Condition (iii)) that precipitate may form. alkyl amines are removed by washing with a mixture solution of methanol added as a solvent for cleaning and formic acid added to remove the salt and alkylamine, the aggregates were washed with aqueous sodium chloride solution to the alkyl amine is liberated It can be seen from it that the organic component is reduced by thermal analysis ((i), Condition (iii)).

[0043] Thus, when prepared the Ag nanoparticles by a wet process described above, by ammine complex nitrate acts as a dispersing agent, is combined with the Ag nanoparticles ammine complex nitrate, and taken to dryness and the solvent was removed it is found to be excellent in re-dispersibility. (Condition (iv)) and can be easily decomposed while maintaining the dispersion stability of the chloride ion ammine complexes of silver nitrate are additional dispersant, dispersants another desired alkyl amine that acts as a dispersant I also becomes possible to convert.



[0044] A representative embodiment of the present invention is as follows.

[0045] The average particle size of the Ag nanoparticles was observed with a transmission electron microscope (500,000-fold), and the average value was calculated by measuring the particle diameters of 100 particles.

[0046] UV using a Shimadzu UV-3150 Ag nanoparticles, - measuring the visible absorption spectra were confirmed to be the Ag nanoparticles.

[0047] I have weighed the (8.3g) of silver nitrate (4.0g), ascorbic acid <Agnanoryushibunsanyoekinoseizo> beaker: Example 1. Take the (12.6g) oleylamine in a separate beaker, I was dissolved in hexane (50mL). I was stirred at room temperature for 2 hours added to the beaker previous hexane solution. The color of the solution had a yellow color blackish. Then, acetone, methanol - to aggregate precipitate the Ag nanoparticles using aqueous mixed solution was removed by decantation and the supernatant, were washed and excess alkyl amine and salts. After drying, to give a solid 2.5g were weighed on a rotary evaporator. Organic component was 20wt% of solid content. To obtain a Ag nanoparticle dispersion solution of about 30wt% by the addition (4.2g) in hexane.

[0048] When preparing a hexane solution diluted sufficiently Ag nanoparticle dispersion solution obtained here, it was observed particle state with a transmission electron microscope, the average particle size of the Ag nanoparticles were 8nm. Further, ultraviolet same solution - was measured visible absorption spectrum, a peak is observed at 416nm, Ag nanoparticles are generated was confirmed.

[0049] I have weighed the (3.1g) of silver nitrate (2.0g), ascorbic acid 2 beaker example. Take the (4.3g) dodecylamine in a separate beaker, I was dissolved in toluene (50mL).

I was stirred at room temperature for 2 hours added to a beaker of previously toluene solution. The color of the solution had a yellow color blackish. Acetone, methanol - to aggregate precipitate the Ag nanoparticles using aqueous mixed solution was removed by decantation and the supernatant was washed away and excess alkyl amine and salts. After drying, to give a solid 1.2g were weighed on a rotary evaporator. The organic component was 16wt% of solid content. To obtain a Ag nanoparticle dispersion solution of about 50wt% by the addition (0.8g) in toluene.

[0050] When preparing a hexane solution diluted sufficiently Ag nanoparticle dispersion solution obtained here, it was observed particle state with a transmission electron microscope, the average particle size of the Ag nanoparticles were 8nm. Further, ultraviolet same solution - was measured visible absorption spectrum, a peak is observed at 416nm, Ag nanoparticles are generated was confirmed.

[0051] Take the (31.5g) oleylamine and silver nitrate (10g) in a beaker Example 3 was added and stirred toluene (100mL). Dark yellow solution was obtained is gradually added (the dispersed state without being dissolved) was added formic acid (4.1g) and toluene (50mL) to this solution. After 3 hours, allowed to agglomerate precipitated Ag nanoparticles was poured into methanol and the reaction solution was removed by decantation and the supernatant was washed away and excess alkyl amine and salts. Ag solid content of the aggregates was about 5g. Aggregates were easily re-dispersed in toluene. It was observed particles with a transmission electron microscope was diluted a portion of the solution was re-distributed.

[0052] When preparing a hexane solution diluted sufficiently Ag nanoparticle dispersion solution obtained here, it was observed particle state with a transmission electron microscope, the average particle size of the Ag nanoparticles were 8nm. Further, ultraviolet same solution - was measured visible absorption spectrum, a peak is observed at 416nm, Ag nanoparticles are generated was confirmed.

[0053] I have weighed the (218g) silver nitrate (140g), iso-ascorbic acid to 4 beaker example. Take (441g) oleylamine to a separate beaker, I was dissolved in toluene (1000mL). I was stirred at room temperature for 2 hours added to a beaker of previously toluene solution. The color of the solution had a yellow color blackish. Acetone, methanol - to aggregate precipitate the Ag nanoparticles using aqueous mixed solution was removed by decantation and the supernatant was washed away and excess alkyl amine and salts. After drying, to give a solid 77g was weighed on a rotary evaporator. The organic component was 21wt% of solid content. To obtain a Ag nanoparticle dispersion solution of about 50wt% by the addition (44.7g) in toluene. I was subjected to thermal analysis of Ag nano-particle dispersion solution was obtained. (Upper part of Figure 1) shows the results of TG in FIG. and alkyl amine which is considered 65.7wt% solids after the toluene solvent was evaporated, and the residue after heating up to 500 ℃ or more is 55wt%, 10.7wt% of this difference has been liberated from the ammine complex of silver nitrate I thought to correspond to the nitrate ion portion of the silver nitrate from. It is considered that the silver ions to be reduced to Ag burning organic content of the silver nitrate ammine complex by heating, by converting the molecular weight ratio of the organic components of the Ag-amine complexes, and Ag to about 23wt% relative to Ag nanoparticles I will be included amine complex.

[0054] When preparing a hexane solution diluted sufficiently Ag nanoparticle dispersion solution obtained here, it was observed particle state with a transmission electron microscope, the average particle size of the Ag nanoparticles were 8nm. Further, ultraviolet same solution - was measured visible absorption spectrum, a peak is observed at 416nm, Ag nanoparticles are generated was confirmed.

[0055] Synthesis of Comparative Example Ag nanoparticles was carried out in the same manner as in Example. Was coagulated precipitated by adding a large amount of methanol to the Ag nanoparticle dispersion solution was prepared using oleylamine. Subsequently, to remove the methanol by decantation, was added aqueous sodium chloride solution, and was stirred vigorously for 1 h. After removing the aqueous sodium chloride solution, and then washed five times with pure water, under reduced pressure to dryness by rotary evaporation. We tried to re-dispersed in toluene was added, but was redispersed in part, but was still aggregated without redispersed in part.

[0056] Purification process is facilitated by the excellent handling properties redistribution of ease even after a state or near dryness by concentration Ag nanoparticle dispersion solution and Ag nanoparticles in the present invention, moreover, the dispersant is easy to operate In it is possible to remove.

[0057] Thermal analysis measurement results of Ag nanoparticles obtained in Example 4. Upper measurement results of Ag nanoparticles obtained in Example 4. The bottom measurement results washed with aqueous sodium chloride solution Ag nanoparticles obtained in Example 4.


SILVER NANOPARTICLE AND PRODUCTION METHOD THEREFOR
JP2006045655

Abstract --- PROBLEM TO BE SOLVED: To provide a silver nanoparticle which is used for a raw material of a conductive paste for electronics industry or the like, and is superior in dispersibility, and to provide a production method therefor. SOLUTION: In a process for obtaining the silver particle by reducing a silver nitrate solution with ferrous sulfate under the presence of sodium citrate, and collecting the formed silver nanoparticle, the method for producing the silver nanoparticle includes charging the silver nitrate solution in a short while of 10 seconds or shorter, when charging the silver nitrate solution into the mixed solution of ferrous sulfate and citric acid soda. The silver nanoparticles produced with the method are spherical particles having uniform diameters of 20 nm or smaller by average.



DESCRIPTION

[0001] The present invention relates to a process for producing silver nanoparticles with excellent particle size (referred to as silver nanoparticles) silver nano-sized particles, the dispersibility as a raw material for the electronics industry conductive paste or the like.

[0002] Recently, high performance of electronic devices has progressed, smaller density of electronic devices has been demanded along with this, for the silver powder as a raw material for a paste material for forming electrode, or the like wiring, dispersible fine good thing there is a demand.

[0003] As a method for producing fine metal particles, a wet process using a vapor phase method such as spray pyrolysis CVD or reducing chemical reaction is known in general, nanoparticles prepared by wet conventional aggregation Because the sex is strong, monodisperse particles are difficult to obtain, and silver particles of high purity aggregation less have been produced by vapor phase method is more.

On the other hand, fine metal particles obtained by the vapor phase method is excellent monodispersity, but there is a problem that the particle size control is difficult manufacturing cost is high.

Therefore, a wet production method is excellent in dispersibility of the fine metal particles have been attempted.

[0004] As the wet production method for a silver fine powder, to form a silver carbonate with sodium carbonate or, to form a silver oxide by adding sodium hydroxide to the silver salt solution such as (a) nitrate, and reduced with hydrazine to this How to have been known, but the aggregated particles with amorphous Most silver particles obtained by this method. Therefore, a method for producing a silver fine powder by reducing silver amine complex, or (ii) a silver salt, and precipitate the silver is added to the silver nitrate solution such as a reducing agent solution prepared by the alkaline sulfite and the organic reducing agent, it by drying to recover, and a method for producing a silver fine powder by reducing method for producing a spherical silver powder monodisperse and dendritic submicron (Patent Document 1), silver ammonia complex or (c) silver In a method for producing a spherical silver particles having good dispersibility by using a sulfite and hydroquinone as a reducing agent, is reacted at a liquid temperature of 25 ~ 60 ℃ is known (Patent Document 2). However, there is a problem that variation in particle size is large silver particles obtained by the production method thereof.

[0005] As a wet method of controlling the particle size of the silver particles, citric acid method using as a protective agent, sodium citrate when reducing the silver nitrate is known. Specifically, for example, were mixed under stirring nitric acid solution in a mixed solution of ferrous sulfate and (e) sodium citrate, and to produce silver particles by the reaction of 5 ~ 50 ℃, was recovered and were uniformly mixed by adding the aqueous ferrous sulfate solution with stirring method of the silver colloidal solution is dispersed in the medium Te (Patent Document 3), and (f) sodium citrate aqueous silver nitrate solution with vigorous stirring this are known (Patent Document 4) a method for producing a silver colloid by adding. No. 3429958 Patent Publication No. 8-134513 Patent No. 4-59904 JP JP

[0006] When the reaction of ferrous sulfate solution and silver nitrate solution, a method for producing silver nanoparticles by the citrate conventional methods of intense both and charged over a relatively long time of several minutes the silver nitrate solution I have mixed under stirring. For example, we have mixed in a strength under 1000rpm or more in the above method (f), which is a severe condition considerably on production equipment. Moreover, the particle size of the silver particles obtained are not uniform.

[0007] The present invention is intended to solve the above problems in the conventional manufacturing method, without the need for vigorous agitation during the population of silver nitrate solution, the particle size is efficiently produced uniform silver nanoparticles by mild production conditions to provide a method, silver nanoparticles produced by this method.

[0008] According to the present invention, a method of manufacturing silver nanoparticles composed of the following configuration is provided.In the presence of sodium citrate, in the method of reduction by ferrous sulfate, obtaining silver nanoparticles by recovering silver particles formed, a mixed solution of sodium citrate and ferrous sulfate (1) silver nitrate solution method for producing silver nanoparticles, characterized in that when introducing the silver nitrate solution, is carried out in a short time of 10 seconds the introduction of the silver nitrate solution. Particle size of the average particle size of 20nm or less, the title compound was prepared by the method described in (2) above (1) uniform spherical silver nanoparticles.

[0009] I Figure 1 shows the flow of a manufacturing method according to the present invention [detailed description]. As shown, in the presence of sodium citrate, in the method of reduction by ferrous sulfate, obtaining silver nanoparticles by recovering silver particles formed, the manufacturing method of the present invention, (II) sulfate, silver nitrate solution It is a manufacturing method of the silver nanoparticles is characterized in that when introducing a silver nitrate solution in a mixed solution of sodium citrate and ferrous, is carried out in a short time of 10 seconds the introduction of the silver nitrate solution.

[0010] A method of reducing the silver by adding a reducing agent to a solution of silver nitrate to produce silver nanoparticles by recovering the particles formed, using ferrous sulfate as the reducing agent, the use of sodium citrate as a protective agent. It may be used as a mixture thereof in advance.

[0011] Concentration of silver nitrate solution is suitably 1 ~ 200g / L. It is difficult to handle must be many amount of sodium citrate as a protective agent silver concentration is higher than this, the viscosity of the liquid is increased for this purpose. Also, silver particles produced are likely to aggregate. On the other hand, the production efficiency is low silver concentration is less than this. Note that the amount of ferrous sulfate may be any amount greater slightly than equimolar to the silver nitrate as long sufficiently reduced silver nitrate.

[0012] The amount of sodium citrate is suitably 2 to 7 times the number of moles of silver, about three times is preferable. The amount of sodium citrate is less than this, the adsorption amount for the fine silver particles is reduced, I can not be sufficiently suppressed aggregation. On the other hand, I will be difficult to handle the amount of sodium citrate is more than the above range, the viscosity of the liquid is increased.

[0013] It is possible to pre-mixed sodium citrate and ferrous sulfate, at room temperature, was charged with silver nitrate solution to the mixed solution, the reduction of silver nitrate. When submitting a silver nitrate solution in a mixed solution of sodium citrate and ferrous sulfate, the manufacturing method of the present invention, in a short time of 10 seconds the introduction of the silver nitrate solution.
By charging in a short time the silver nitrate solution, silver nanoparticles having a uniform particle size as a result.

[0014] Long time, for example, when added over a few minutes to ten minutes, the silver nitrate solution, the growth of particles silver particles formed in the mixing early at the core, caused by the reduction of silver nitrate, which is supplied thereafter was initially generated Since the spent, coarse particles become mixed, it becomes irregular silver particles having a particle size as a result.

[0015] After switching on the silver nitrate solution in a mixed solution of sodium citrate and ferrous sulfate, several tens of seconds, and stirred at a rotation speed of 300rpm around, and to complete the uniform reaction throughout. There is no need to stir vigorously at 1000rpm or more. Silver is reduced by this reaction, the particle size can be obtained colloidal silver solution containing (silver nanoparticles) ultra-fine silver particles in the nanometer size.

[0016] Recovered after the solid-liquid separation by centrifugal separation of the silver colloid solution was washed with sodium citrate solid separated. To obtain a colloidal silver solution in which silver nanoparticles are dispersed by dispersing in water the solid was collected.

[0017] According to the production method of the present invention, it is possible that the particle size of the average particle size of 20nm or less to obtain a uniform spherical silver nanoparticles. Also, when mixing the silver nitrate solution, there is no need to stir vigorously, thus, the production method of the present invention may be excessive device is small, to produce a Ginnano particles efficiently.

[0018] I shows examples and comparative examples of the present invention are described below. 500mL aqueous solution containing a concentration of 0.5mol / L and 0.25mol / L, was added in 3 seconds nitrate 100mL solution concentration of 0.83mol / L each of sodium citrate and Example 1] Ferrous sulfate . Temperature is 20 ℃, after mixing, I was stirred for 30 seconds at 300rpm. It was centrifuged at 3000rpm colloidal silver solution to be produced in the reaction, it was re-dispersed in water and by recovering the solids to obtain a silver colloidal solution of 10 wt% silver solids. It was spherical silver nanoparticles of uniform size 6 ~ 7nm was observed with TEM (transmission electron microscope) of silver particles in the colloidal solution.

[0019] 500mL aqueous solution containing a concentration of 0.9mol / L and 0.5mol / L, was added in 5 seconds nitrate 100mL solution concentration of 1.7mol / L each of sodium citrate and Example 2 ferrous sulfate . Temperature is 20 ℃, after mixing, I was stirred for 30 seconds at 300rpm. It was centrifuged at 3000rpm colloidal silver solution to be produced in the reaction, it was re-dispersed in water and by recovering the solids to obtain a silver colloidal solution of 10 wt% silver solids. It was spherical nanoparticles with uniform size 6 ~ 7nm was observed with TEM (transmission electron microscope) of silver particles in the colloidal solution.

[0020] Were reacted in the same manner as in Example 1 were added in 3 min addition rate conditions COMPARATIVE EXAMPLE silver nitrate solution. The solid was recovered by centrifugation in the same manner as in Example 1 colloidal solution obtained in this way, to obtain a silver colloidal solution of 10 wt% silver solids dispersed in water it. As a result of TEM observation of the silver particles in the colloidal solution, with the silver particles to the minimum diameter of several nm are mixed from the maximum diameter of 70nm, the particles are partially aggregated was observed.

[0021] Process diagram showing the manufacturing method of the present invention



PLASMA SYNTHESIS OF METAL OXIDE NANOPARTICLE
JP2005132716

Also published as:  EP1514846 (A1) // KR20050027058 (A) // CN1607181 (A) //   CA2481150 (A1)

Abstract --- PROBLEM TO BE SOLVED: To provide a method for manufacturing particles containing metal oxides, nanoparticles in particular, which are specifically nano-size particles containing titanium dioxide. SOLUTION: The process for synthesizing nano-size metal oxide particles in a plasma reactor comprises a process (a) where one or a plurality of reactant flows containing an oxidizing agent and a halogenated metal, a halogenated silicon, and a coarse tail controlling agent selected from a group comprising halogenated compounds of phosphorus, germanium, boron, tin, niobium, chromium, silver, gold, palladium, aluminum, and their mixtures are supplied simultaneously and a process (b) where the reactant flows and the oxidizing agent are brought into contact with plasma having a sufficient temperature to form metal oxide-containing nanoparticles having an average particle diameter of <100 nm and containing a small amount of particles having a diameter of >200 nm.



Silver Comprising Nanoparticles and Related Nanotechnology
US2005008861


Abstract --- Nanoparticles comprising silver and their nanotechnology-enabled applications are disclosed; doped metal oxides, silver comprising complex nanoparticle compositions, silver nanoparticles, methods of manufacture, and methods of preparation of products from silver comprising nanoparticles are presented; And anti-microbial formulations are discussed. Color photochromaticity and related applications are disclosed.



Synthesis Metal Nanoparticle
US6929675


Abstract --- A method for providing an anhydrous route for the synthesis of amine capped coinage-metal (copper, silver, and gold) nanoparticles (NPs) using the coinage-metal mesityl (mesityl=C<SUB>6</SUB>H<SUB>2</SUB>(CH<SUB>3</SUB>)<SUB>3</SUB>-2,4,6) derivatives. In this method, a solution of (Cu(C<SUB>6</SUB>H<SUB>2</SUB>(CH<SUB>3</SUB>)<SUB>3</SUB>)<SUB>5</SUB>, (Ag(C<SUB>6</SUB>H<SUB>2</SUB>(CH<SUB>3</SUB>)<SUB>3</SUB>)<SUB>4</SUB>, or (Au(C<SUB>6</SUB>H<SUB>2</SUB>(CH<SUB>3</SUB>)<SUB>3</SUB>)<SUB>5 </SUB>is dissolved in a coordinating solvent, such as a primary, secondary, or tertiary amine; primary, secondary, or tertiary phosphine, or alkyl thiol, to produce a mesityl precursor solution. This solution is subsequently injected into an organic solvent that is heated to a temperature greater than approximately 100 DEG C. After washing with an organic solvent, such as an alcohol (including methanol, ethanol, propanol, and higher molecular-weight alcohols), oxide free coinage NP are prepared that could be extracted with a solvent, such as an aromatic solvent (including, for example, toluene, benzene, and pyridine) or an alkane (including, for example, pentane, hexane, and heptane). Characterization by UV-Vis spectroscopy and transmission electron microscopy showed that the NPs were approximately 9.2+-2.3 nm in size for Cu DEG , (no surface oxide present), approximately 8.5+-1.1 nm Ag DEG spheres, and approximately 8-80 nm for Au DEG .



Nanoprisms and Method of Making Them
US7135054

Abstract --- The invention is a novel photo-induced method for converting large quantities of silver nanospheres into nanoprisms, the nanoprisms formed by this method and applications in which the nanoprisms are useful. Significantly, this light driven process results in a colloid with a unique set of optical properties that directly relate to the nanoprism shape of the particles. Theoretical calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and the first identification of two distinct quadrupole plasmon resonances for a nanoparticle. Finally, unlike the spherical particles from which they derive and which Rayleigh light scatter in the blue, these nanoprisms exhibit scattering in the red, permitting multicolor diagnostic labels based not only on nanoparticle composition and size but also on shape.



METHOD FOR MANUFACTURING SILVER NANOPARTICLE
JP2003253311

Abstract --- PROBLEM TO BE SOLVED: To provide a new technology which can manufacture silver nanoparticles even from an insoluble silver salt. SOLUTION: This manufacturing method comprises, when manufacturing the silver nanoparticles by reducing a silver salt in a solvent, employing an insoluble salt of a silver halide (particularly silver chloride or silver bromide) for the silver salt, dissolving it in a solvent, and reducing it in the presence of a protective agent consisting of a compound soluble in a solvent and having a ligating property to silver. A preferable protective agent is a thiol like thiocholine bromide. Then, a monodisperse liquid of the silver nanoparticles is obtained, which are dispersed in the solvent while being coated and protected by the protective, agent.


METHOD FOR PRODUCING METAL NANOPARTICLES
WO2008003522

Abstract --- This invention provides a method for producing a composition comprising colloidal nanoparticles of metals including silver, gold, zinc, mercury, copper, palladium, platinum, or bismuth, by contacting a metal or metal compound with bacteria. An embodiment of the method comprises a step of incubating probiotic bacteria with an aqueous solution comprising at least 4 mM of a silver or gold salt. A resulting nanosilver-containing composition is useful as a highly efficient antimicrobial agent, for instance when impregnated onto a carrier, or an algicide agent or a herbicide agent.




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