Graphene Oxide Desalination
Nature Nanotechnology volume 12, pages 546–550 (2017)
Tunable sieving of ions using graphene
Jijo Abraham, Kalangi S. Vasu, Christopher D. Williams, Kalon
Gopinadhan, Yang Su, Christie T. Cherian, James Dix, Eric
Prestat, Sarah J. Haigh, Irina V. Grigorieva, Paola Carbone,
Andre K. Geim & Rahul R. Nair
Graphene oxide membranes show exceptional molecular permeation
properties, with promise for many applications1,2,3,4,5. However,
their use in ion sieving and desalination technologies is limited
by a permeation cutoff of ~9 Å (ref. 4), which is larger than the
diameters of hydrated ions of common salts4,6. The cutoff is
determined by the interlayer spacing (d) of ~13.5 Å, typical for
graphene oxide laminates that swell in water2,4. Achieving smaller
d for the laminates immersed in water has proved to be a
challenge. Here, we describe how to control d by physical
confinement and achieve accurate and tunable ion sieving.
Membranes with d from ~9.8 Å to 6.4 Å are demonstrated, providing
a sieve size smaller than the diameters of hydrated ions. In this
regime, ion permeation is found to be thermally activated with
energy barriers of ~10–100 kJ mol–1 depending on d. Importantly,
permeation rates decrease exponentially with decreasing sieve size
but water transport is weakly affected (by a factor of <2). The
latter is attributed to a low barrier for the entry of water
molecules and large slip lengths inside graphene capillaries.
Building on these findings, we demonstrate a simple scalable
method to obtain graphene-based membranes with limited swelling,
which exhibit 97% rejection for NaCl.
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 The invention relates to graphene oxide laminate membranes
that are physically constrained. This invention also relates to
methods of purifying water using said membranes and methods of
making said membranes.
 The removal of solutes from water finds application in many
 This may take the form of the purification of water for
drinking or for watering crops or it may take the form of the
purification of waste waters from industry to prevent
environmental damage. Examples of applications for water
purification include: the removal of salt from sea water for
drinking water or for use in industry; the purification of
brackish water; the removal of radioactive ions from water which
has been involved in nuclear enrichment, nuclear power generation
or nuclear clean-up (e.g. that involved in the decommissioning of
former nuclear power stations or following nuclear incidents); the
removal of environmentally hazardous substances (e.g. halogenated
organic compounds, heavy metals, chlorates and perchlorates) from
industrial waste waters before they enter the water system; and
the removal of biological pathogens (e.g. viruses, bacteria,
parasites, etc) from contaminated or suspect drinking water.
 In many industrial contexts (e.g. the nuclear industry) it
is often desirable to separate dangerous or otherwise undesired
solutes from valuable (e.g. rare metals) solutes in industrial
waste waters in order that the valuable solutes can be recovered
and reused or sold.
 Graphene is believed to be impermeable to all gases and
liquids. Membranes made from graphene oxide are impermeable to
most liquids, vapours and gases, including helium. However, an
academic study has shown that, surprisingly, graphene oxide
membranes having a thickness around 1 µ?? composed of oxygen rich
functionalities are permeable to water even though they are
impermeable to helium. These graphene oxide sheets allow unimpeded
permeation of water (10<10>times faster than He) (Nair ef
Science, 2012, 335, 442-444). Such GO laminates are particularly
attractive as potential filtration or separation media because
they are easy to fabricate, mechanically robust and offer no
principal obstacles towards industrial scale production.
 Sun et al (Selective Ion Penetration of Graphene Oxide
Membranes; ACS Nano 7, 428 (2013)) describes the selective ion
penetration of graphene oxide membranes in which the graphene
oxide is formed by oxidation of wormlike graphite. The membranes
are freestanding in the sense that they are not associated with a
support material. The resultant graphene oxide contains more
oxygen functional groups than graphene oxide prepared from natural
graphite and laminates formed from this material have a wrinkled
surface topography. Such membranes differ from those of the
present invention because they do not show fast ion permeation of
small ions and also demonstrate a selectivity which is
substantially related to chemical and electrostatic interactions
rather than size of ions.
 This study found that sodium salts permeated quickly
through GO membranes, whereas heavy metal salts permeated much
more slowly. Copper sulphate and organic contaminants, such as
rhodamine B are blocked entirely because of their strong
interactions with GO membranes. According to this study, ionic or
molecular permeation through GO is mainly controlled by the
interaction between ions or molecules with the functional groups
present in the GO sheets. The authors comment that the selectivity
of the GO membranes cannot be explained solely by ionic-radius
based theories. They measured the electrical conductivities of
different permeate solutions and used this value to compare the
permeation rates of different salts. The potential applied to
measure the conductivities can affect ion permeation through
 Other publications (Y. Han, Z. Xu, C. Gao. Adv. Fund.
Mater. 23, 3693 (2013); M. Hu, B. Mi. Environ. Sci. Technol. 47,
3715 (2013); H. Huang et al. Chem. Comm. 49, 5963 (2013)) have
reported filtration properties of GO laminates and, although
results varied widely due to different fabrication and measurement
procedures, they reported appealing characteristics including
large water fluxes and notable rejection rates for certain salts.
Unfortunately, large organic molecules were also found to pass
through such GO filters. The latter observation is disappointing
and would considerably limit interest in GO laminates as molecular
sieves. In this respect, we note that the emphasis of these
studies was on high water rates that could be comparable to or
exceed the rates used for industrial desalination. Accordingly, a
high water pressure was applied and the GO membranes were
intentionally prepared as thin as possible, 10-50 nm thick. It may
be that such thin stacks contained holes and cracks (some may
appear after applying pressure), through which even large organic
molecules could penetrate.
 Recently, Joshi et al have described the use of graphene
oxide laminate membranes as size exclusion membranes (R. K. Joshi
et al., 2014, Science, 343, 752-754; see also WO2015/075451).
These membranes selectively excluded solutes having a hydration
radius greater than about 4.5 A. allowing solutes with a smaller
radius to pass through. Molecular permeation through GO membranes
is believed to occur along graphene channels that develop between
GO sheets, and their sieving properties are defined by the
interlayer spacing, d, which depends on the humidity of the
surrounding. Immersing GO membranes in liquid water leads to
intercalation of 2-3 layers of water molecules between individual
GO sheets, which results in swelling and d ~ 13.5 A. The effective
pore-size of 9 A in these swollen membranes (excluding the space
occupied by carbon atoms) is larger than a typical size of
hydrated ions and restricts possible uses of GO for size-exclusion
based ion sieving. Unfortunately, many solutes which might be
desirable to be able to filter out, including for example NaCI,
have hydration radii which are below 4.5 A and are not effectively
excluded from passing through the membrane.
 WO2016/ 189320 (PCT/GB2016/051539) describes how
graphene oxide laminate membranes could be modified, either by
including graphene flakes or by including cross-linking agents, to
improve the level of exclusion of solutes that have hydration
radii which are below 4.5 A, e.g. NaCI.
BRIEF SUMMARY OF THE DISCLOSURE
 In a first aspect of the invention is provided a water
filtration membrane, said membrane comprising a graphene oxide
(GO) laminate comprising a plurality of graphene oxide flakes the
planes of which are orientated parallel to one another, said GO
laminate having a first pair of oppositely disposed faces which
are oriented parallel to the planes of the plurality of graphene
oxide flakes, said GO laminate also having a second pair of
oppositely disposed faces which are oriented perpendicular to the
planes of the plurality of graphene oxide flakes and a third pair
of oppositely disposed faces which are oriented perpendicular to
the planes of the plurality of graphene oxide flakes; wherein the
GO laminate membrane is enclosed by a first encapsulating material
that covers each of the first pair of faces of the GO laminate and
each of the second pair of oppositely disposed faces of the GO
laminate and wherein the third pair of oppositely disposed faces
are either not enclosed or are enclosed by a second encapsulating
material, said second encapsulating material being porous...
Science 343, 752–754 (2014).
Science 14 Feb 2014:
Vol. 343, Issue 6172, pp. 752-754
Precise and ultrafast molecular sieving
through graphene oxide membranes.
Joshi, R. K. et al.
Graphene-based materials can have well-defined nanometer pores and
can exhibit low frictional water flow inside them, making their
properties of interest for filtration and separation. We
investigate permeation through micrometer-thick laminates prepared
by means of vacuum filtration of graphene oxide suspensions. The
laminates are vacuum-tight in the dry state but, if immersed in
water, act as molecular sieves, blocking all solutes with hydrated
radii larger than 4.5 angstroms. Smaller ions permeate through the
membranes at rates thousands of times faster than what is expected
for simple diffusion. We believe that this behavior is caused by a
network of nanocapillaries that open up in the hydrated state and
accept only species that fit in. The anomalously fast permeation
is attributed to a capillary-like high pressure acting on ions
inside graphene capillaries.
Membranes based on graphene can simultaneously block the passage
of very small molecules while allowing the rapid permeation of
water. Joshi et al. (p. 752; see the Perspective by Mi)
investigated the permeation of ions and neutral molecules through
a graphene oxide (GO) membrane in an aqueous solution. Small ions,
with hydrated radii smaller than 0.45 nanometers, permeated
through the GO membrane several orders of magnitude faster than
predicted, based on diffusion theory. Molecular dynamics
simulations revealed that the GO membrane can attract a high
concentration of small ions into the membrane, which may explain
the fast ion transport.
Environ. Sci. Technol., 2016, 50 (7), pp 3875–3881
Selective removal of technetium from water
using graphene oxide membranes
Williams, C. D. & Carbone, P.
The effective removal of radioactive technetium (99Tc) from
contaminated water is of enormous importance from an environmental
and public health perspective, yet many current methodologies are
highly ineffective. In this work, however, we demonstrate that
graphene oxide membranes may remove 99Tc, present in the form of
pertechnetate (TcO4–), from water with a high degree of
selectivity, suggesting they provide a cost-effective and
efficient means of achieving 99Tc decontamination. The results
were obtained by quantifying and comparing the free energy changes
associated with the entry of the ions into the membrane
capillaries (?Fperm), using molecular dynamics simulations.
Initially, three capillary widths were investigated (0.35, 0.68,
and 1.02 nm). In each case, the entry of TcO4– from aqueous
solution into the capillary is associated with a decrease in free
energy, unlike the other anions (SO42–, I–, and Cl–) investigated.
For example, in the model with a capillary width of 0.68 nm,
?Fperm(TcO4–) = -6.3 kJ mol–1, compared to ?Fperm(SO42–) = +22.4
kJ mol–1. We suggest an optimum capillary width (0.48 nm) and show
that a capillary with this width results in a difference between
?Fperm(TcO4–) and ?Fperm(SO42–) of 89 kJ mol–1. The observed
preference for TcO4– is due to its weakly hydrating nature,
reflected in its low experimental hydration free energy.
Chem. Soc. Rev. 39, 228–240 (2010).
The chemistry of graphene oxide.
Dreyer, D. R., Park, S., Bielawski, C. W. & Ruoff, R. S.
The chemistry of graphene oxide is discussed in this critical
review. Particular emphasis is directed toward the synthesis of
graphene oxide, as well as its structure. Graphene oxide as a
substrate for a variety of chemical transformations, including its
reduction to graphene-like materials, is also discussed. This
review will be of value to synthetic chemists interested in this
emerging field of materials science, as well as those
investigating applications of graphene who would find a more
thorough treatment of the chemistry of graphene oxide useful in
understanding the scope and limitations of current approaches
which utilize this material (91 references).
Adv. Mater. 27, 249–254 (2015).
Facile fabrication of freestanding
ultrathin reduced graphene oxide membranes for water
Freestanding ultrathin rGO membranes, with thicknesses down to
17 nm, are fabricated via a facile approach using hydroiodic acid
vapor and water-assisted delamination. These unique membranes
provide the potential for addressing the key challenge that limits
the performance of current forward osmosis membranes.