Peng WANG, et al.
Hydrophilic Desalination
Hydrophilic disc uses solar power to separate salt from water
by Nick Lavars
Current approaches to water desalination are tremendously expensive and energy-intensive, so the search is very much on for new technologies that can get the job done more efficiently. Scientists in Melbourne have put forward one rather promising solution, developing a new kind of system that heats up and purifies water using only the power of the Sun.

The device was developed by scientists at Australia's Monash University, who say that water treatment accounts for around three percent of the world's energy supply. Like other researchers around the globe, they have turned to sunlight to try and lighten the load, this time directing it toward what is known as a solar steam generator.

In simple terms, these devices concentrate sunlight onto a body of water, heating it up and causing it to evaporate. The resulting steam can then be used to drive turbines that produce electricity in concentrated solar power plants, perhaps sterilize medical equipment cheaply for the developing world, or simply to separate salt from water.

But one problem with the lattermost application is that the salt tends to gather on the surface of the material, which makes it difficult to produce pure water. The Monash University researchers worked around this problem with an intricately designed solar steam generator that prevents the salt from spoiling the broth.

It consists of a disc crafted from super-hydrophilic filter paper, a material that attracts water, which is coated with a layer of carbon nanotubes that convert sunlight into heat. Water is fed into the center of the disc via a simple cotton thread, where the heat turns it into steam that builds up on the disc while pushing the salt to the edge.

In this way, the device removes almost 100 percent of salt from the water, a level that leader of the team Professor Xiwang Zhang assures us is "high enough for practical applications." The salts that accumulate at the edges, meanwhile, can also be harvested for use.

Zhang and his team tested out the device using salty water from a bay in South Australia, and found that it absorbed 94 percent of the light across the solar spectrum. It worked whether wet or dry, with light exposure heating up the device from 25 to 50° C (77 to 122° F) when dry and from 17.5 to 30° C (63.5 to 86° F) when wet, within just one minute.

"This device can produce six to eight liters (1.6 to 2.1 gal) of clean water per square meter (of surface area) per day," Zhang tells New Atlas. "We are working to further improve the water production rate."

Zhang and his colleagues hope that with further work, the device could be put to use providing clean water to remote communities that are currently without access. But its value mightn't end there. The technology could be used in other areas where more efficient water purification methods might come in handy, such as mining and wastewater treatment.

We hope this research can be the starting point for further research in energy-passive ways of providing clean and safe water to millions of people, illuminating environmental impact of waste and recovering resource from waste," says Zhang.
Supplementary Video 6

Solar panel generates fresh water and electricity

A new system for removing salt from seawater using the waste heat from solar panels has been created by Peng Wang and colleagues at King Abdullah University of Science and Technology in Saudi Arabia. The team installed a multistage membrane distillation (MSMD) device directly underneath the solar panels so that the system occupies the same footprint as the solar panels.

Energy and water are two crucial resources that are often connected. Creating freshwater from seawater consumes about 15% of electricity generated in Arab countries, for example, and finding carbon-free sources of energy for desalination is a huge challenge facing countries in the driest regions of the world.

Wang’s team have answered this challenge by creating a desalination system that uses waste heat produced by solar power plants. While solar cells can convert about 20% of sunlight into electricity, the remaining 80% simply heats up the solar panels. The team’s MSMD device comprises three stacked layers of water distillation channels that run parallel to solar panels. Each layer is separated by porous hydrophobic membranes and heat conduction layers.
Evaporation and condensation

Within each layer, seawater in the uppermost channel is evaporated by waste heat from the solar panel, and then condenses to freshwater inside a second channel on the other side of the membrane. This desalinated water then flows into a storage container, while the remaining seawater, along with the rest of the waste heat, pass down to the layer below, where the process repeats.

Salt-free drinkable water comes at a cost

Wang and colleagues show that the MSMD device can be installed directly underneath existing solar panels; requiring no specialized mounting equipment, and no extra requirements for land use. While previous attempts at this technique came at the cost of overall solar panel performance, the researchers observed virtually no decrease in power generation efficiency in their system. At the same time, the MSMD device was able to desalinate up to 1.64 l of fresh water per square metre per hour. According to team member Wenbin Wang, this is more than double the water output of traditional solar stills, which use a one-stage design.

The team points that new technology could encourage energy and water companies to work together in dry regions. Furthermore, they point out that creating fresh water offers a way of mitigating the inherent low efficiency of solar panels and could make their deployment more attractive.

As a next step, the team wants to study how the system could be used in an agricultural setting – with the water used for irrigation.!divAbstract

Spatially isolating salt crystallisation from water evaporation for continuous solar steam generation and salt harvesting
Yun Xia, et al.
As a low-cost green technology, solar steam generation using nanostructured photothermal materials has been drawing increasing attention in various applications, e.g. seawater desalination, and zero liquid discharge of industrial wastewater. However, the crystallisation of salts on the surface of photothermal materials during steam generation leads to a gradual decline in the water evaporation rate. Herein, this challenge was overcome by a novel design involving controlled water transport, edge-preferential crystallisation and gravity-assisted salt harvesting. The crystallisation sites of the salt were spatially isolated from the water evaporation surface, achieving continuous steam generation and salt harvesting in over 600 hours of non-stop operation. The study provides new insights into the design of solar steam generators and advances their applications in sustainable seawater desalination and wastewater management.
24 July 2019
Water solutions without a grain of salt

Monash University researchers have developed technology that can deliver clean water to thousands of communities worldwide.
This solar steam generation system produces clean water from salty (ocean) water with almost 100 per cent salt removal.
It provides a solution to water shortages in regional areas where grid electricity isn’t available.  

An estimated 844 million people don’t have access to clean water, while every minute a newborn dies from infection caused by lack of safe water and an unclean environment.

Seawater desalination and wastewater recycling are two ways to ease the problem of water shortage, but conventional approaches are energy-intensive and based on the combustion of fossil fuels. In fact, water treatment uses about 3 per cent of world’s energy supply.

Researchers at Monash University have developed energy-passive technology that’s able to deliver clean, potable water to thousands of communities, simply by using photothermal materials and the power of the sun.

Led by Professor Xiwang Zhang from Monash University’s Department of Chemical Engineering, researchers have developed a robust solar steam generation system that achieves efficient and continuous clean water production from salty water with almost 100 per cent salt removal. Through precisely controlling salt crystallisation only at the edge of the evaporation disc, this novel design also can harvest the salts.

The feasibility and durability of the design have been validated using seawater from Lacepede Bay in South Australia. This technology is a promising solution to water shortages in regional areas where grid electricity isn’t available.

The findings were published in the international journal Energy & Environmental Science.

“Water security is the biggest challenge the world faces in the 21st century, especially as population grows and the effects of climate change take shape. Developing and under-resourced communities feel the effects of these factors the most,” Professor Zhang said.

“Utilising solar energy for water treatment has been widely considered as one of the sustainable solutions towards addressing the scarcity of clean water in some communities, without sacrificing our environment or resources.

“Despite the significant progress achieved in material development, the evaporation process has been impeded by the concentration of salt on the surface, which affects the quality of water produced.”

Researchers created a disc using super-hydrophilic filter paper with a layer of carbon nanotubes for light absorption. A cotton thread, with a 1mm diameter, acted as the water transport channel, pumping saline water to the evaporation disc.

The saline water is carried up by the cotton thread from the bulk solution to the centre of the evaporation disc. The filter paper traps the pure water and pushes the remaining salt to the edges of the disc.

The light absorbance was measured to 94 per cent across the entire solar spectrum. The disc also exhibited a rapid temperature increase when exposed to light in both dry and wet states, rising from 25C to 50C and 17.5C to 30C respectively within one minute.

This technology has also great potential in other fields, such as industry wastewater zero liquid discharge, sludge dewatering, mining tailings management and resource recovery. Future studies will look to extend the technology to these applications with industry support.

“Our study results advance one step further towards the practical application of solar steam generation technology, demonstrating great potential in seawater desalination, resource recovery from wastewater, and zero liquid discharge,” Professor Zhang said.

“We hope this research can be the starting point for further research in energy-passive ways of providing clean and safe water to millions of people, illuminating environmental impact of waste and recovering resource from waste.”

Professor Zhang is the Director of the ARC Research Hub for Energy-efficient Separation (EESep), which aims to develop advanced separation materials, innovative products and smart processes to reduce the energy consumption of separation processes that underpin Australian industry.

He has just received a $50,000 grant from Perpetual for a separate project looking at securing better water for rural Australia and the South-east Asian region.
Nature Communications volume 10, Article number: 3012 (2019)

Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation
Wenbin Wang, et al.
The energy shortage and clean water scarcity are two key challenges for global sustainable development. Near half of the total global water withdrawals is consumed by power generation plants while water desalination consumes lots of electricity. Here, we demonstrate a photovoltaics-membrane distillation (PV-MD) device that can stably produce clean water (>1.64 kg·m−2·h−1) from seawater while simultaneously having uncompromised electricity generation performance (>11%) under one Sun irradiation. Its high clean water production rate is realized by constructing multi stage membrane distillation (MSMD) device at the backside of the solar cell to recycle the latent heat of water vapor condensation in each distillation stage. This composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system and thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a fresh water producer...

In this work, we report a strategy for simultaneous production of fresh water and electricity by an integrated solar PV panel-membrane distillation (PV-MD) device in which a PV panel is employed as both photovoltaic component for electricity generation and photothermal component for clean water production. In a typical solar cell, 80–90% of the absorbed solar energy is undesirably converted to heat, and thereafter passively and wastefully dumped into the ambient air32. In this work, a MSMD device is integrated on the backside of a commercial solar cell to directly utilize its waste heat as a heat source to drive water distillation. Under one Sun illumination, the water production rate of the PV-MD is 1.79 kg m−2 h−1 for a 3-stage device, which is three times higher than that of the conventional solar stills. At the same time, the PV panel generates electricity with energy efficiency higher than 11%, which is the same as that recorded on the same PV panel without the back MD device and which is at least 9 times higher than those achieved in the previously published works. The undoubted benefit of the integration of PV and water distillation is the highly efficient co-generation of clean water and electricity in one device at the same time on the same land, which directly reduces land area requirement and the cost of the mounting system as compared to two physically separate systems (PV and solar distillation). Moreover, working directly with commercial solar cells makes the PV-MD device close to practical applications. This strategy provides a potential possibility to transform an electricity generation plant from otherwise a water consumer to a fresh water producer.

Structure of the MSMD device...

Each stage of the MSMD device was composed of four separate layers: a top thermal conduction layer, a hydrophilic porous layer of water evaporation layer, a hydrophobic porous layer of MD membrane for vapor permeation, and a water vapor condensation layer. Aluminum nitride (AlN) plate was used as the thermal conduction layer because of its extremely high thermal conductivity (>160 W m−1 K−1) and its anti-corrosion property in salty water34. The hydrophobic porous layer was made of an electrospun porous polystyrene (PS) membrane. The water evaporation layer and condensation layer were of the same material, a commercial hydrophilic quartz glass fibrous (QGF) membrane with non-woven fabric structure.

In each stage of the MSMD device (Supplementary Fig. 2), the heat is conducted through the thermal conduction layer to the underlying hydrophilic porous layer. The source water inside the hydrophilic porous layer is thus heated up to produce water vapor. The water vapor passes through the hydrophobic porous membrane layer and ultimately condenses on the condensation layer to produce liquid clean water. The driving force for the water evaporation and vapor condensation is the vapor pressure difference caused by the temperature gradient between the evaporation and condensation layers. In each stage, the latent heat of water vapor, which is released during the condensation process, is utilized as the heat source to drive water evaporation in the next stage. The multistage design ensures the heat can be repeatedly reused to drive multiple water evaporation–condensation cycles. In a traditional solar still, the heat generated from the sunlight via photothermal effect only drives one water evaporation–condensation cycle, which sets up an upper theoretical ceiling of the clean water production rate, ~1.60 kg m2 h−1, under one-Sun condition in such a system. The multistage design makes possible to break the theoretical limit as demonstrated very recently by two groups27,28.

In this work, two source water flow modes, namely, dead-end mode and cross-flow mode, are designed for the MSMD device (Fig. 1). In the dead-end mode, the source water is passively wicked into the evaporation layer by hydrophilic quartz glass fibrous membrane strips via capillary effect. In this case, the concentration of salts and other non-volatile matters in the evaporation layer keeps increasing till reaching saturation in the end. A washing operation is indispensable to remove the salts accumulated inside the device for this mode, as reported in the previous works28. However, the passive water flow reduces the complexity of the device and gives a high water production rate in the early stage for this operation mode. In the cross-flow mode, the source water flows into the device driven by gravity or by a mechanical pump, and, it flows out of the device before reaching saturation. In this case, the outgoing water flow will take away a small amount of sensible heat, leading to a slight drop in clean water productivity in the early stage. However, it solves the salt accumulation problem and avoids the need for frequent cleaning and salt removal operation, which makes the device suitable for long-term operation.

In some experiments, a commercial spectrally selective absorber (SSA) (ETA@Al, Alanod Solar) was used to replace the PV panel for clean water production performance evaluation. This material can decrease the radiation heat loss during operation because it possesses a much smaller emissivity than PV panels, and that is why it was adopted in both of the previous works on solar membrane distillation28. We use the SSA-MD device to confirm that the multistage MD device we fabricated in this work is comparable with the state-of-the-art solar membrane distillation devices...

Synthesis of the polystyrene membrane

The hydrophobic polystyrene membrane was fabricated by electrospinning method. Polystyrene was firstly dissolved in DMF by mild stirring for 6 h to obtain 25 wt% homogeneous solution. The solution was placed in three 5-mL syringes equipped with metal needle of 0.52 mm inner diameter and then ejected with a feeding rate of 5.0 mL h−1. The voltage was set at 30 KV and the distance between the collector and the needle was 10 cm...

Device assembly

The QGF, PS membrane and AlN were assembled as shown in Supplementary Fig. 1a. To avoid blocking the wick of the dead-end device by PU foam, the wick was firstly wrapped by plastic film. The PU foam precursor was obtained by mixing the part A and part B of the PU system as 1:1 weight ratio and then was painted on the side of the device. The device was kept at 50 °C for 12 h to complete the foaming. The assembly of cross-flow MSMD was similar to that of the dead-end MSMD, except that the wick was replaced with the silicon tube with the diameter of 1 mm.
Simultaneous production of clean water and electricity

The device was put on the top of a square heat sink with a length of 5 cm which was immersed in bulk water. Water was transported from bulk water to the device by capillary effect and transpiration effect via a small QGF membrane belt which was connected to the distillation layer. In a practical scenario, the flow rate of the source water in the cross-flow PV-MD can be controlled by a flow control valve or flow meter. In our experiments, an ISMATEC tubing pump was used to control the flow rate of the source water more precisely. Solar irradiation was provided by a solar simulator (Newport 94043A) with a standard AM 1.5 G spectrum optical filter. A 100 mL cup was used to collect clean water and the amount of water collected was monitored and recorded real-time. To reduce the evaporation of the collected clean water in the cup, a funnel was put on the top of the cup. The square photothermal material or square solar cell with the length of 3.9 mm was put on the top of the device. Photovoltaic responses (J–V curves) of the solar cell were measured by a Keithley 2400 series source meter. For the cycling test, after each cycle, 3 pieces of Kimwipes tissue (11 × 21 cm) were connected to the inlets of the dead-end devices and stayed there for 3 h to extract the concentrated water remaining in the QGF membranes. For each new cycle, salt water was wicked into the QGF membrane and extracted by the tissue again. This procedure was repeated at least for 3 times to ensure that the QGFs were cleaned....

[ PDF ]

Inventor: WANG PENG [SA] SHI YIFENG [SA]     
A solar-powered system including a chamber (202) that is bordered by an evaporation layer (206) and a condensation layer (208); and a photothermal layer (210) located over the evaporation layer (206) so that sun rays incident on the photothermal layer (210) are transformed into heat and the heat is supplied to the evaporation layer (206) for evaporating water. The sun rays incident on the photothermal layer (210) do not pass through the condensation layer (208) prior to arriving at the photothermal layer.

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A solar-powered system (200) includes a support portion (201A); and an evaporation portion (201B) having a pumping layer (212) and a photothermal layer (214). The support portion (201A) pumps a fluid (222) to the evaporation portion (201B), the pumping layer (212) evaporates the fluid (222) based on solar power; and the photothermal layer (214) is insulated from the pumping layer (212).

[ PDF ]

Embodiments of the present disclosure provide structures or membranes including photothermal nanomaterials, devices including the structure, methods of use, methods of desalination, and the like.

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Disclosed herein are surface-modified membranes and other surface-modified substrates exhibiting switchable oleophobicity and oleophilicity in aqueous media. These membranes and substrates may be used for variety of applications, including controllable oil/water separation processes, oil spill cleanup, and oil/water purification. Also provided are the making and processing of such surface-modified membranes and other surface-modified substrates.

[ PDF ]

Described herein are patterned superhydrophobic surfaces, substrates, devices, and systems including the patterned superhydrophobic surfaces, and methods of making and uses thereof.

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Methods are provided for growing a thin film of a nanoscale material. Thin films of nanoscale materials are also provided. The films can be grown with microscale patterning. The method can include vacuum filtration of a solution containing the nanostructured material through a porous substrate. The porous substrate can have a pore size that is comparable to the size of the nanoscale material. By patterning the pores on the surface of the substrate, a film can be grown having the pattern on a surface of the thin film, including on the top surface opposite the substrate. The nanoscale material can be graphene, graphene oxide, reduced graphene oxide, molybdenum disulfide, hexagonal boron nitride, tungsten diselenide, molybdenum trioxide, or clays such as montmorillonite or lapnotie. The porous substrate can be a porous organic or inorganic membrane, a silicon stencil membrane, or similar membrane having pore sizes on the order of microns.


Methods and composition for preparation of mesoporous carbon material are provided. For example, in certain aspects methods for carbonization and activation at selected temperature ranges are described. Furthermore, the invention provides products prepared therefrom.

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