阅读说明：本技术 可透性石墨烯和可透性石墨烯膜 (Permeable graphene and permeable graphene membrane ) 是由 D.H.徐 S.皮内达 A.默多克 Z.J.韩 K.奥斯特里科夫 M.谢 T.范德兰恩 于 2018-03-06 设计创作，主要内容包括：连续的可透性石墨烯薄膜,其具有两层或更多层石墨烯且其中纳米通道或纳米孔延伸穿过所述膜。每个纳米通道由在所述两层或更多层相邻片材中相邻石墨烯晶粒的边缘失配之间的流体连通的一系列间隙组成,所述纳米通道提供从可透性石墨烯薄膜的一个面到另一个面的流体通道。此外,包括被连续的可透性石墨烯薄膜覆盖的可透性支撑膜的膜及所述膜的制备方法。以及所述膜在例如水净化和脱盐中的用途。(A continuous, permeable graphene thin film having two or more layers of graphene and wherein nanochannels or nanopores extend through the film. Each nanochannel is comprised of a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing a fluid channel from one face of the permeable graphene membrane to the other face. In addition, a membrane comprising a permeable support membrane covered by a continuous permeable graphene thin film and a method for preparing the membrane. And the use of the membrane in, for example, water purification and desalination.)

1. A continuous permeable graphene film comprising two or more layers of graphene and nanochannels or nanopores providing fluid channels from one face to the other face of the permeable graphene film, the nanochannels or nanopores providing fluid channels from one face to the other face of the permeable graphene film.

2. The continuous permeable graphene film of claim 1, comprising two or more layers of graphene forming nanochannels, wherein each nanochannel consists of a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing fluid channels from one face of the permeable graphene film to the other.

3. The continuous, permeable graphene film according to claim 1 or claim 2, comprising 2-10 layers.

4. The continuous, permeable graphene film according to claim 2 or claim 3, wherein the gaps are located at grain boundary interfaces in the graphene film.

5. A permeable membrane comprising a permeable support membrane covered by a continuous permeable graphene thin film according to any one of the preceding claims.

6. The permeable membrane of claim 5, further comprising an adhesive.

7. The permeable membrane of any one of the preceding claims, wherein the continuous permeable graphene thin film has a thickness of 0.7 to 3.7 nm.

8. The permeable membrane of any one of the preceding claims, wherein the continuous permeable graphene thin film has a functional pore size in the range of 0.34-3.0 nm.

9. The permeable membrane of any one of the preceding claims, wherein the membrane is a bi-component membrane, wherein the permeable support membrane and the graphene thin film are adjacent to each other or attached to each other.

10. The permeable membrane of any one of the preceding claims, comprising a permeable support membrane sandwiched between two continuous permeable graphene films, each continuous permeable graphene film having a plurality of nanochannels or nanopores extending therethrough.

11. The permeable membrane of any one of the preceding claims, wherein the permeable support membrane is a porous polymeric membrane.

12. The permeable membrane of any one of the preceding claims, wherein the permeable support membrane is a commercially available porous polymer MD (membrane distillation) membrane.

13. A method of preparing a deposited permeable continuous nanochannel graphene thin film comprising the steps of: heating a metal substrate and an excess carbon source in a sealed ambient environment to a temperature at which a carbon-containing vapor is generated from the carbon source such that the vapor contacts the metal substrate; maintaining the temperature for a time sufficient to form a graphene lattice; cooling the sample at a reduced cooling rate under reduced pressure for a delay time; and then flash cooling the substrate under reduced pressure to form the deposited permeable nanochannel graphene.

14. The method of claim 13, wherein the ambient environment is air at atmospheric pressure or a vacuum.

15. The method of claim 13 or 14, wherein the metal substrate is a transition metal substrate.

16. The method of any one of claims 13 to 15, wherein the metal substrate is nickel or copper.

17. The method of claim 16, wherein the metal substrate is nickel and the ambient environment is air at atmospheric pressure.

18. The method of claim 16, wherein the metal substrate is copper and the ambient environment is a chamber that is evacuated prior to sealing and heating.

19. The method of any one of claims 13 to 18, wherein the carbon source is biomass or is derived from biomass.

20. The process of any one of claims 13 to 19, wherein the process does not use a feed gas.

21. The method of any one of claims 13 to 20, wherein the heating step employs a carbon rich environment.

22. The method of any one of claims 13 to 21, wherein the metal substrate and carbon source are heated to a temperature in the range of 650-900 ℃ sufficient to form a graphene lattice.

23. The method of any one of claims 13 to 22, wherein the slowed cooling rate occurs at a rate of 5 ℃ to 10 ℃/minute.

24. The method of any one of claims 13 to 23, wherein the flash cooling occurs at a rate of 25 ℃/minute to 100 ℃/minute.

25. A method of preparing a deposited permeable continuous nanochannel graphene thin film on a support membrane comprising preparing a deposited permeable continuous nanochannel graphene thin film on a substrate according to any one of claims 13 to 24; separating the film from the substrate to provide a free permeable continuous nanochannel graphene film; and applying the free permeable continuous nanochannel graphene thin film onto the support membrane.

26. The method of claim 25, wherein the deposited permeable continuous nanochannel graphene film is separated from the substrate by dissolving the underlying metal substrate in an acidic environment to produce a free permeable continuous nanochannel graphene film.

27. The method of claim 23 or 24, comprising the step of utilizing an adhesive attached to the free permeable continuous nanochannel graphene film.

28. The method of claim 27, wherein the adhesive attached to the free permeable continuous nanochannel graphene film is applied to the support membrane.

29. The method of claim 28, wherein the adhesive is removed after the graphene thin film is applied to the support film.

30. The method of claim 29, wherein the binder is removed by dissolution.

31. A method according to any one of claims 27 to 29, wherein the binder is PMMA and the process is carried out via an intermediate PMMA in combination with a permeable continuous nanochannel graphene film and the PMMA layer can be removed, for example by dissolution, or it can remain in the final product.

32. A method of purifying a contaminant-contaminated feed water, comprising providing the feed water to the permeable membrane of any one of claims 5 to 12 such that the feed water contacts the continuous permeable graphene membrane as a feed side; passing water through the permeable membrane to a filtrate side to provide a filtrate and thereby retain the contaminants on the feed water side.

33. The method of claim 32, wherein the feed water is industrial wastewater or water for desalination.

34. The method of claim 32 or 33, wherein the industrial wastewater is from mining, agriculture, or material processing.

35. The method of any one of claims 32 to 34, wherein the contaminant is a surfactant, oil or petroleum, or a residue of a surfactant, oil or petroleum product.

36. The method of any one of claims 32 to 35, wherein the permeable graphene side of the membrane remains charge neutral over a wide pH range, such as from pH2 to pH 13.

37. The method of any one of claims 32 to 36, wherein the permeable graphene side of the membrane is anti-fouling.

38. The method of any one of claims 33 to 37, wherein the contaminant is a hydrated ion or a solvated ion.

39. The method of claim 38, wherein the hydrated or solvated ions have a size greater than 0.9nm³Of (c) is used.

40. The method of claim 32, wherein the feed water is water for desalination containing inorganic species and organic species.

41. According to the rightThe method of claim 40, wherein the inorganic species comprises Na⁺And Cl^-。

42. The method of any one of claims 32 to 41, wherein the influent water is seawater.

43. The method of any one of claims 32 to 42, wherein the feed water is acidic or basic outside the physiological pH range.

Technical Field

The present invention relates to permeable graphene films, permeable graphene membranes, methods for manufacturing said films and membranes and uses thereof, in particular in connection with water filtration. In particular, the present invention relates to permeable nanoporous and nanochannel graphene. The permeable graphene thin film can be prepared by a single step process comprising a thermal process in ambient air followed by cooling under vacuum without the use of expensive feed gases, and it further can use renewable biomass as a carbon source. The permeable graphene membrane comprises a permeable support membrane covered by a continuous permeable graphene thin film of the present invention.

Background

Graphene exhibits unique electronic, optical, chemical and mechanical properties. Supported horizontal graphene as an active functional material has revolutionized many fields due to its extremely high electron mobility (electrons move about 100 times faster in graphene than in silicon), very low absorption in the visible spectrum, and relative flexibility and elasticity (compared to inorganics such as indium tin oxide). For example, graphene is potentially useful in flexible, transparent, and wearable electronics, in energy storage devices (e.g., fuel cells, supercapacitors, photovoltaic cells, lithium ion batteries, etc.), in diagnostic and therapeutic devices (e.g., biosensors, bioelectronic devices, drug delivery), in water purification (e.g., point-of-use filtration membranes), and in catalysis (e.g., to facilitate hydrogen evolution reactions). Controlling defect content, microstructure, and surface chemistry in graphene would be critical to maximizing the potential of graphene in these applications.

Graphene can be manufactured by a variety of methods. To date, the mass production of graphene, which would be necessary for a wide range of commercial uses, is the goal of a few general processes, most notably:

mechanically milled graphite and dispersed in solution, followed by self-assembly.

Thermal graphitization of SiC.

Chemical Vapor Deposition (CVD) onto a metal substrate.

Of these three methods, CVD onto metal substrates is most promising because it produces graphene thin films of sufficiently high quality to enable the potential of graphene to be more fully realized. CVD also allows roll-to-roll graphene synthesis.

The quality of the prepared graphene is critical to its ability to function as a high performance material. High quality graphene with perfect sp rules from ideal²Carbon films have a minimum of defects and are also very thin, that is, the bulk material produced contains as few layers of carbon atoms as possible.

The quality of graphene can be quantitatively expressed in terms of its electronic and optical properties. A small number of defects results in a very low sheet resistance, which can typically be about 200 Ω/sq. Defects in graphene can reduce in-plane carrier transport, which can compromise the promising properties required for efficient field emission, ultra-fast sensing, and nanoelectronic based devices.

Very thin films, such as those having only one, two, or three carbon atom layers, are highly transparent and have a transmission of up to 97%, which can be used in optical displays.

Other forms of thicker films and graphene (e.g., crystallites and coatings) may be used in other contexts, such as catalysis and filtration. The ability to control the thickness of the grown graphene is highly desirable.

However, CVD to metal substrates has some inherent limitations. The CVD apparatus itself is complex and expensive. CVD consumes a very large amount of energy and, like other thermal methods currently used, requires a low pressure vacuum environment. This means that there is a significant capital cost associated with CVD as well as ongoing operating costs. Furthermore, the cost of vacuum equipment increases exponentially with the size of the vacuum chamber, which limits the ability of manufacturers to scale up the process in a cost effective manner.

CVD also requires the use of expensive highly purified feed gases. The use of gases such as hydrogen for substrate passivation and methane and ethylene as carbon source gases also means that additional hazard protection needs to be implemented.

CVD also requires a relatively long period of time, on the order of hours, for the growth, annealing and cooling steps to occur. This inherent requirement means that CVD does not readily enable rapid mass production of affordable graphene.

Finding new methods for graphene is a very active area of effort, and many researchers are studying synthetic routes for high quality graphene that are safe, inexpensive, and easy to scale up.

The present applicant has described in their earlier patent application PCT/AU2016/050738 a graphene synthesis method which enables inexpensive mass production of high quality graphene.

Changing the morphology of graphene may create additional uses. One particularly desirable modification would be to produce porous graphene. It has been envisaged that graphene sheets with holes passing from one side of the graphene membrane to the other will have utility for air purification (particulate, volatile organic compound filtration), water purification (coal bed gas wastewater treatment, mine wastewater treatment, heavy metal removal); liquid-liquid separation such as osmosis, reverse osmosis, desalination, membrane distillation, solvent extraction and solvent separation; air purification and catalysis; an energy storage device; medical devices (bioelectronic devices, drug delivery), etc.

In order to be usable, porous graphene needs to be manufactured in an economical and reproducible manner. To date, it has proven difficult to obtain porous graphene of high quality having a useful pore structure and on a scale sufficient for commercial availability.

Graphene films or layers with channels from one side to the other may unexpectedly appear due to intrinsic defects such as (i) those generated during graphene transfer [ Suk, j.w. et al, ACS Nano 2011,5, 6916-. These multi-step processes involve the use of purified gases, extensive vacuum processing and long high temperature annealing. These defects are sporadic and isolated and may require additional polymer chemistry to seal the accompanying larger defect sites (i.e., cracks and fissures) [ Jain, t. et al, NatNano 2015,10, 1053-; o' Hern, S.C. et al, NanoLetters 2015,15, 3254-3260; o' Hern et al ACS Nano 2012,6, 10130-.

Numerous techniques have been used to attempt to create pores in graphene.

One method is ion bombardment. This method is limited to very small scale work and is an expensive process requiring ultra-high vacuum conditions [ WO 2014152407; US 20130270188; US 8894796; o' her n, S.C. et al, NanoLetters 2014,14, 1234-1241; surwade, S.P. et al, Nat Nano 2015,10, 459-; celebi, K. et al, Science 2014,344, 289-292; russo, c.j.; golovchenko, j.a., a.proceedings of national Academy of sciences2012,109,5953-5957 ].

Uv etching is also used, but the density of the formed pores is very low and there is a broad pore size distribution [ Koenig, s.p. et al, Nat Nano 2012,7, 728-732; liu, L. et al, Nano Letters 2008,8, 1965-; huh, S. et al, ACS Nano 2011,5, 9799-.

Block copolymer and nanosphere (template) lithography were also used. This method is very complex and multi-step and requires additional lithographic techniques to carefully remove the template residues without further damaging the graphene [ US 20140154464; safron, N.S. et al, Advanced Materials 2012,24, 1041-; liang, X, et al, Nano Letters 2010,10, 2454-2460; jackson, e.a.; hillmyer, m.a., ACS Nano 2010,4, 3548-.

High voltage electrical pulses are also used, although these are also limited to small scale production and require complex settings [ Rollings, r.c. et al, Nature Communications 2016,7, 11408; kuan, A.T. et al, Applied Physics letters 2015,106,203109 ].

Electron beam lithography is also used. In addition to being a small scale process, the high energy electron beam used also produces undesirable defects such as induced amorphization and deposition of carbon atoms on graphene [ US 20130309776; garaj, s. et al, nature2010,467, 190-193; merchant, C.A. et al, Nano Letters 2010,10, 2915-; garaj, S. et al, Proceedings of the National Academy of Sciences 2013,110, 12192-; schneider, g.f. et al, Nature Communications 2013,4, 2619; fischbein, M.D.,M.,AppliedPhysics Letters 2008,93,113107]。

the prior art for preparing nanoporous graphene is all carried out as an additional post-processing step after CVD synthesis of graphene thin films and therefore includes all the inherent disadvantages therein, such as the need to use purified gases, extensive vacuum treatment and long high temperature annealing. The techniques used to date also suffer from a number of disadvantages such as difficulty in scaling up to industrially usable sizes of film, high cost, high complexity and lack of consistency and control in subsequent films.

Graphene is potentially useful as an ultrathin film with atomically defined nanochannels having diameters close to those of the hydrated ions. The original monolayer of graphene is impermeable to standard gases (e.g., helium)¹. Introducing selective defects throughout the graphene lattice can potentially enable water molecules to penetrate. As noted above, recent advances in post-synthesis reactive processing of CVD graphene have produced atomically thin permeable membranes potentially suitable for water purification.^2,3,4However, these techniques involve a series of highly controlled, resource intensive and complex procedures that are difficult to uniformly implement at high density and large scale. Thus, the ability of CVD graphene thin films for water purification and desalination is still limited to small scale demonstration (micron scale).²Furthermore, although CVD synthesis provides good control over the growth of graphene thin films, this method is still an expensive process due to the need for compressed gas and extensive vacuum operations. Furthermore, the hydrophobicity of CVD graphene often creates an additional barrier for water purification membranes. Thus, these technical challenges hinder the commercial viability of CVD graphene thin films for water purification.⁵

Graphene has potential as a water purification material. Concerns over the environmental impact of clean water supplies and industrial wastewater make water treatment a worldwide problem requiring simple and effective solutions.

An important technology for water purification is membrane filtration, and a particularly important subset of membrane filtration is membrane distillation, otherwise known as MD. Membrane distillation complements industrial reverse osmosis processes. Using different temperatures rather than transmembrane pressures, membrane distillation achieves high rejection (rejection) at a range of salt concentrations while maintaining flux. MD has several significant disadvantages, namely that heating and maintaining the feed water temperature is an energy intensive process, and MD membranes cannot handle a wide variety of contaminant mixtures.^7,9Recently, the problem of energy intensive processes has been addressed by using carbon nanotube/polymer composites as an effective way to locally generate heat at the membrane interface.¹⁰However, some key issues of MD and similar membrane filtration processes remain open. Firstly, when inWhen common chemical or oil-based contaminants are introduced during MD filtration, the membranes exhibit significant fouling behavior, which can rapidly degrade membrane performance and lead to irreversible degradation of the membrane.^11,12Such scaling problems during MD operation reduce water recovery, do not sustain contaminant filtration, increase the need for harsh chemical cleaning, and quickly shorten the service life of the membrane. Second, conventional MD membranes fail to insulate against heat transfer across the membrane, often resulting in low water vapor flux and performance degradation during long term operation, which remains another significant challenge.¹³

Third, no membrane is known to maintain filtration performance under harsh (high salt, acid and/or base concentrations) conditions.

Such limitations of conventional films underscore the need for new materials to achieve antifouling films that can address these challenges. Improved MD films have been produced by several techniques, such as phase inversion and electrospinning of polymers. However, most of these methods cannot obtain such an antifouling film: it exhibits high water vapor flux and long term stability during MD operation with a mixture of various membrane destructive contaminants.^14,15

Despite the presence of tiny intrinsic pores that restrict the passage of water vapor, CVD graphene thin films have numerous physicochemical properties that are valuable for MD applications. These include their good mechanical strength, thermal and chemical stability, hydrophobicity, atomically thin thickness, and high out-of-plane thermal resistance (low thermal conductivity in the Z direction).^16,17Recently, incorporation of graphene flakes into membranes has been shown to improve the performance of water purification processes.¹⁸However, until now, the broad prospects and potentials of 2D graphene membranes for water purification have not been realized.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Throughout the specification and claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, unless the context clearly dictates otherwise; that is, to be interpreted in the meaning of "including, but not limited to".

The invention

SUMMARY

In one broad aspect, the present invention provides a continuous permeable graphene film having nanochannels or nanopores providing fluid channels from one face of the permeable graphene film to another. The film may contain, for example, 1-40 layers of graphene.

In another broad aspect, the present invention provides a continuous permeable graphene film comprising two or more layers of graphene and nanochannels or nanopores providing fluid channels from one face to the other face of the permeable graphene film. The film may contain, for example, 2-40 layers of graphene.

More preferably, the present invention provides a continuous permeable graphene film as described above in a broad aspect, comprising two or more layers of graphene forming nanochannels, wherein each nanochannel consists of a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing a fluid channel from one face of the permeable graphene film to the other.

According to a first aspect, the present invention provides a continuous permeable graphene film comprising two or more layers of graphene, and wherein nanochannels extend through the film, each nanochannel consisting of a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing a fluid channel from one face to the other face of the permeable graphene film.

The gap is located at a boundary of a grain boundary in the graphene film.

The two or more layers may preferably comprise 2 to 40 layers of graphene, or more preferably 2 to 10 layers of graphene.

As used herein, "continuous permeable graphene film" refers to a graphene film comprising pores or nanochannels having openings extending from one side of the film to the other (that is, the pores or nanochannels provide a fluid channel through the z-axis of the graphene film). The graphene film allows the permeation of gases having any suitable molecular size or the flow of any fluid or substance through the film at the location where the pores or channels are present. In the case of porous graphene, the continuous openings may be in one or more layers of sheet material, for example in 1-5 layers of graphene sheet material. For nanochannel graphene, the openings are in the form of interconnected continuous channels spanning 2-10 or up to 2-40 layers of graphene sheets. The channel is created by a mismatched stack of graphene sheets.

Preferably, the gap is located near the grain boundary of the graphene thin film. It is also preferred that the nanochannel graphene thin film has a functional pore size of 0.37-3 nm.

According to a second aspect, the present invention provides a permeable membrane comprising a permeable support membrane covered by a continuous permeable graphene film having a plurality of nanochannels extending therethrough.

Preferably, the continuous permeable graphene film comprises two or more layers of graphene, and wherein nanochannels extend through the continuous permeable graphene film, each nanochannel comprising a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing a fluid channel from one face of the permeable graphene film to the other face.

That is, the present invention provides a permeable membrane comprising a permeable support membrane covered by a continuous permeable graphene thin film of the first aspect.

The two or more layers of graphene may preferably comprise 2 to 40 layers of graphene, or more preferably 2 to 10 layers of graphene.

In some embodiments, the continuous permeable graphene thin film has a thickness of 0.7 to 3.7nm, for example, the continuous permeable graphene thin film has a thickness of 1.7 nm.

In some embodiments, the continuous, permeable graphene thin film has a functional pore size in the range of 0.34-3.0nm, preferably 0.34 nm.

Preferably, the permeable membrane is a bi-component membrane, wherein the permeable support membrane and the graphene thin film are adjacent to each other or connected to each other.

In an alternative embodiment, the present invention provides a permeable membrane comprising a permeable support membrane sandwiched between two continuous permeable graphene films, each continuous permeable graphene film having a plurality of nanochannels or nanopores extending therethrough.

In yet another alternative embodiment, the membrane may also be a composite membrane, wherein a graphene thin film is incorporated into the permeable support membrane.

Preferably, the permeable support membrane is a porous polymer membrane, for example, the permeable support membrane is a porous polymer membrane selected from PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), polyethylene and polysulfone. However, any porous membrane or substrate that provides sufficient support to the graphene may be used.

The permeable support membrane may be a commercially available porous polymer MD (membrane distillation) membrane, for example, a commercially available porous polymer MD membrane distillation membrane having a pore size of 0.1 μm or more. The commercially available porous polymer MD membrane distillation membrane may also have a thickness of 100-200 μm.¹⁰

According to a third aspect, the present invention provides a method of preparing a deposited permeable continuous nanochannel graphene thin film, comprising the steps of: heating a metal substrate and an excess carbon source in a sealed ambient environment to a temperature at which a carbon-containing vapor is generated from the carbon source such that the vapor contacts the metal substrate; maintaining the temperature for a time sufficient to form a graphene lattice; cooling the sample at a reduced cooling rate under reduced pressure for a delay time; and then flash cooling the substrate under reduced pressure to form the deposited permeable nanochannel graphene.

The method may further comprise the step of isolating the permeable continuous nanochannel graphene thin film by standard procedures (such as those disclosed herein).

As used herein, "delay time" refers to the time that the deposited graphene thin film is allowed to cool inside a sealed environment when the sealed environment is cooled after the formation of the graphene lattice.

Preferably, the ambient environment is air or vacuum at atmospheric pressure. Importantly, unlike most processes in the art, the process of the present invention does not use one or more compressed gases. No feed gas is required. As used herein, "feed gas" includes any purified gas typically used for etching, capping, or as a carbon source material in CVD processes, and the term specifically includes, but is not limited to, hydrogen, argon, nitrogen, methane gas, ethane gas, ethylene gas, and acetylene gas.

The metal substrate may be a transition metal substrate, preferably the metal substrate is nickel or copper, most preferably nickel. The metal substrate may be in any suitable form, such as a flat foil or wire.

When the metal substrate is nickel, the ambient environment is preferably air at atmospheric pressure. Preferably, the metal substrate is nickel with a purity of 99% and higher, most preferably the metal substrate is polycrystalline nickel.

Alternatively, when the metal substrate is copper, the ambient environment is preferably a chamber that is evacuated prior to sealing and heating.

The carbon source may advantageously be biomass or be derived from biomass or purified biomass. The biomass or purified biomass may be, for example, long chain triglycerides (fatty acids), such as soybean oil, or it may be a cellulosic material. Renewable biomass may be used. The carbon source may be in any form, such as a liquid or solid form, with liquids generally being considered advantageous.

The process does not use a feed gas.

Preferably, the heating step is carried out in a carbon-rich environment or in a carbon-excess environment. Preferably, the metal substrate and the carbon source are both located in one heating zone during the heating step.

Preferably, the sealed environment is an inert container such as quartz, glass, or other dielectric heat resistant container. Most preferably, the sealed environment is contained within a quartz tube.

The metal substrate and carbon source are preferably heated to a temperature in the range of 650-900 c, such as 800 c or 900 c, sufficient to form a graphene lattice. The temperature is maintained for a suitable period of time, ideally 0-3 minutes, sufficient to form a graphene lattice.

Preferably, heating is maintained in the heating zone and flash cooling occurs in the cooling zone. The graphene lattice is preferably transferred from the heating zone to the cooling zone prior to flash cooling so that the delay time is zero or close to zero.

Preferably, the graphene lattice is flash cooled under reduced pressure by transferring the lattice from the heating zone to a cooling zone under vacuum.

Preferably, the rate of flash cooling is from 25 ℃/min to 100 ℃/min.

Preferably, the graphene lattice is transferred from the heating zone to the cooling zone such that the delay time is from 1 to 5 minutes.

Preferably, the slowed cooling rate occurs at a rate of 5 ℃ to 10 ℃/minute, more preferably the slowed cooling rate occurs at a rate of 10 ℃/minute in the heating zone.

The method may further include the step of separating the deposited graphene thin film from the substrate to provide a graphene thin film. For example, the method may further include the step of removing or separating the continuous permeable graphene film from the metal substrate to produce a free continuous permeable graphene film.

A method of preparing a deposited permeable continuous nanochannel graphene film on a support membrane comprises preparing a deposited permeable continuous nanochannel graphene film on a substrate according to the third aspect, separating the film from the substrate to provide a free permeable continuous nanochannel graphene film, and applying the free permeable continuous nanochannel graphene film to the support membrane.

The method may further include the step of separating the deposited graphene thin film from the substrate to provide a graphene thin film. The permeable or nano-permeable graphene thin film may be separated by any conventional means.

The permeable or nano-permeable graphene thin film may be separated by any conventional means. For example, it may be separated from the underlying metal substrate by dissolving the substrate in an acidic environment. In particular, the nickel substrate can be advantageously dissolved in H₂SO₄Or HCl or FeCl₃In, or the copper substrate may be dissolved in any of the aforementioned solvents or HNO₃In (1).

The method may include the step of utilizing an adhesive attached to the free permeable continuous nanochannel graphene film. The adhesive may be removed after the graphene thin film is applied to the support film, or it may remain in use. That is, the final product comprises the deposited permeable continuous nanochannel graphene thin film, adhesive layer, and support film. The adhesive layer is permeable.

For example, the continuous permeable graphene film may be removed, for example, by a PMMA-assisted process, to produce an intermediate PMMA-bonded graphene film that is removed from the underlying metallic growth substrate. The PMMA-bound graphene thin film is then applied to a support film. The PMMA layer can be removed, for example, by dissolution, or it can remain in the final product.

As used herein, the term "separating" or the like refers to removing or lifting formed graphene from an underlying substrate to separate a graphene thin film.

The present invention provides a method of purifying feed water contaminated with contaminants comprising providing the feed water to a permeable graphene membrane according to the invention such that the feed water contacts a continuous permeable graphene membrane as a feed side, passing water through the permeable membrane to a filtrate side to provide a filtrate, and thereby retaining contaminants on the feed water side.

The permeable graphene film is nanoporous graphene, or more preferably, nanochannel graphene, comprising two or more layers of graphene, and wherein nanochannels extend through the film, each nanochannel consisting of a series of gaps in fluid communication between edge mismatches of adjacent graphene grains in the two or more adjacent sheets, the nanochannels providing a fluid channel from one face of the permeable graphene film to the other. The nanoporous graphene thin film or nanochannel graphene thin film may be supported by a conventional film substrate.

According to a fifth aspect, the present invention provides a method of purifying feed water contaminated with contaminants, comprising providing the feed water to a permeable graphene membrane or a permeable membrane according to the invention such that the feed water contacts the continuous permeable graphene membrane as a feed side, passing water through the permeable membrane to a filtrate side to provide a filtrate, and thereby retaining contaminants on the feed side.

Preferably, the process is membrane distillation and feed water is provided to the permeable membrane at an elevated temperature relative to the filtrate.

In a more preferred embodiment, the process is membrane distillation and the feed water is provided to the permeable membrane at an elevated temperature relative to the filtrate, and a continuous permeable graphene membrane is used to thermally insulate the filtrate side from the feed side.

The feed water may contain a range of inorganic and organic species such as, for example, surfactants, oils or petroleum, or residues of surfactants, oils or petroleum products. Specific examples of inorganic species include Na⁺And Cl^-。

In one embodiment, the feed water is industrial wastewater or water for desalination. For example, the industrial wastewater may be from mining, agriculture, or material processing.

In a particularly preferred embodiment, the influent water is seawater and the contaminant is salt. The permeable membranes of the present invention are particularly suitable for desalination processes such as reverse osmosis, and more particularly membrane distillation.

The method is also applicable to very high pH (above pH 9 to about pH13) or very low pH (based on pH 5 to about pH 2) or where the feed water is acidic or basic outside of the physiological pH range (pH 5-9), but it will be understood that the filtration method is applicable to any pH.

In the methods of the invention, the permeable graphene side of the membrane remains charge neutral over a wide pH range (e.g., pH2 to pH13 or pH 3 to 10 or pH 4 to 9).

The contaminants to be filtered may be hydrated ions or solvated ions. More particularly, the contaminants to be filtered are those having a size greater than 0.9nm³Hydrated ions or solvated ions of radius (b).

According to a sixth aspect, the present invention provides a method of separating a feed solution containing hydrated ions or solvated ions comprising providing the feed solution to a permeable graphene membrane or permeable membrane according to the present invention, such that feed water contacts the continuous permeable graphene membrane as a feed side, water is passed through the permeable membrane to a filtrate side to provide a filtrate, and thereby hydrated ions or solvated ions are retained on the feed water side.

In another aspect, the present invention provides a continuous, permeable graphene film comprising 1-40 layers of graphene and having a plurality of pores or channels extending through the film.

Preferably the pores have an opening size of 5-100 nm. Preferably, the pore density is uniform throughout the film, and more preferably the pore density is 50 to 220 pores per μm.

More particularly, in this aspect, the present invention provides a continuous permeable nanoporous graphene film comprising 1-5 layers of graphene and having a plurality of pores extending through the film, the pores having an opening size of 5-100 nm.

The invention also provides a method for preparing the deposited permeable nano-porous graphene film, which comprises the following steps: heating a metal substrate and an excess carbon source in a sealed ambient environment to a temperature at which a carbon-containing vapor is generated from the carbon source, such that the vapor contacts the metal substrate, maintaining the temperature for a time sufficient to form a graphene lattice, and quenching the graphene lattice under reduced pressure to form a deposited permeable nanoporous graphene film.

Preferably, heating is maintained in the heating zone and flash cooling occurs in the cooling zone.

Preferably the ambient environment is air at atmospheric pressure or a vacuum. Most preferably, the ambient environment is air at atmospheric pressure.

In one embodiment, the ambient environment is air at atmospheric pressure. Although the invention has been described with respect to air, artificially produced gases or combinations of gases that simulate the action of air may be used if desired. Such artificial gas combinations can be used under pressure to simulate the effect achieved by air at ambient pressure.

In another embodiment, the ambient environment is a chamber that is evacuated prior to heating, preferably less than 1mm Hg.

The metal substrate may be a transition metal substrate, preferably the metal substrate is nickel or copper, most preferably nickel. The metal substrate may be in any suitable form, such as a flat foil or wire.

If the metal substrate is nickel, the ambient environment is air at atmospheric pressure. Preferably, the metal substrate is nickel with a purity of 99% and higher, most preferably the metal substrate is polycrystalline nickel.

Alternatively, the metal substrate is copper and the ambient environment is a chamber that is evacuated prior to sealing and heating.

The carbon source may advantageously be biomass or be derived from biomass or purified biomass. The biomass or purified biomass may be, for example, long chain triglycerides (fatty acids), such as soybean oil, or it may be a cellulosic material. Renewable biomass may be used. The carbon source may be in any form, such as a liquid or solid form, with liquids generally being considered advantageous.

The process does not use a feed gas. As used herein, "feed gas" includes any purified gas typically used for etching, capping, or as a carbon source material in a CVD process, and the term specifically includes, but is not limited to, hydrogen, argon, nitrogen, methane gas, ethane gas, ethylene gas, and acetylene gas.

Preferably, the heating step employs a carbon excess environment. Preferably, the metal substrate and the carbon source are both located in one heating zone during the heating step.

Preferably, the sealed environment is an inert container such as quartz, glass, or other dielectric heat resistant container. Most preferably, the sealed environment is contained within a quartz tube.

The metal substrate and carbon source are preferably heated to a temperature in the range of 650-900 c, such as 800 c or 900 c, sufficient to form a graphene lattice. The temperature is maintained for a suitable period of time, ideally 0-3 minutes, sufficient to form a graphene lattice.

Preferably, the rate of flash cooling is from 25 ℃/min to 100 ℃/min.

Preferably, the graphene lattice is flash cooled under reduced pressure by transferring the lattice from the heating zone to a cooling zone under vacuum.

The present invention provides a continuous permeable nanoporous graphene film comprising 1-5 layers of graphene, the film being prepared by a process comprising the steps of: heating a metal substrate and an excess carbon source in a sealed ambient environment to a temperature at which a carbon-containing vapor is generated from the carbon source, such that the vapor contacts the metal substrate, maintaining the temperature for a time sufficient to form a graphene lattice, and subsequently quenching the graphene lattice under reduced pressure to form a deposited permeable nanoporous graphene film.

In another aspect, the present invention provides a continuous permeable graphene film having nanochannels and nanopores that provide fluid channels from one face of the permeable graphene film to the other face. The film may contain, for example, 1-40 layers of graphene.

The present invention also provides a permeable membrane comprising a permeable support membrane covered by a continuous permeable graphene film having a plurality of nanochannels and nanopores extending therethrough.

Brief Description of Drawings

Fig. 1A shows a cross-sectional view of nanoporous permeable graphene of the invention.

Figure 1B shows a cross-sectional view of a structure of nanochannel permeable graphene suitable for making permeable membranes of the present invention.

Fig. 2 shows an apparatus for preparing nanoporous and nanochannel permeable graphene of the present invention.

Fig. 3A shows time and temperature profiles for preparing nanoporous permeable graphene of the invention.

Fig. 3B shows the time and temperature profiles for preparing the nanochannel permeable graphene of the present invention.

Fig. 4A and 4B show the growth of crystalline domains and the edge mismatch of graphene sheets, respectively.

Fig. 5 shows a TEM of the nanochannel graphene of the present invention, specifically identifying the edge mismatch of the graphene sheets, (a) on a 50nm scale and (b) on a 10nm scale.

Fig. 6 shows growth parameters for various graphenes, including nanochannel permeable graphene suitable for making permeable membranes of the present invention.

Fig. 7 shows different minimum precursor amounts for forming graphene for different tube furnace sizes.

Fig. 8 is a schematic of permeable graphene thin film synthesis and its use as an anti-fouling water desalination membrane via membrane distillation. This schematic (a) illustrates the synthesis of permeable graphene from renewable sources (such as soybean oil) via an ambient air CVD process using a polycrystalline Ni substrate. The synthesized permeable graphene film was wet transferred to a commercial PTFE-based MD membrane for water desalination testing. It is believed that the mechanism (b) of water purification and desalination can be achieved by unique graphene characteristics, such as overlapping of graphene domains with grain boundaries. Furthermore, the hydrophobic and out-of-plane thermal resistance properties of CVD graphene serve as advantageous features in forming an antifouling long-term flux stable MD membrane.

FIG. 9 characteristics of a permeable graphene membrane enabling permeation of water vapor and water desalination and purification. Several nanoscopic features in the permeable graphene membrane enable water permeation and desalination. The microscopic morphology of the graphene film was studied using SEM, revealing the graphene film on the PTFE film at (a) low magnification and (b) high magnification. Many ripples on the surface of the graphene thin film are observed, and the high transparency of the graphene thin film allows one to observe the underlying PTFE film. (c) TEM images at low magnification and corresponding (d) bright-field and (e) dark-field images show many small graphene domains, with many thick black lines corresponding to the overlap of grain boundaries, which form channels for water vapor passage.

FIG. 10 detailed TEM characterization of overlapping domains forming nanochannels in a permeable graphene thin film. (a) TEM images of overlapping domain boundaries (darker contrast regions) of extended nanochannels were formed in the permeable graphene thin film. The SAED mode (and associated line profile in the supplemental information) confirms that the marked regions are (b) single-layer graphene with a rotation axis of 29.5 °, (c) overlapping domains forming nanochannels-250 nm wide, (d) turbostratic double-layer graphene with rotation axes of-7.6 ° and 25.1 °. The darker contrast areas are evidenced by overlapping misoriented graphene domain boundaries or nanochannels due to the monolayer to bilayer transition and the shift in the respective axes of rotation on either side of the feature. The inset shows a representative plot of overlapping domain boundaries with equivalent domain rotation but narrow nanochannel widths.

Fig. 11 additional structural features of the permeable graphene thin film. Additional characterization of the graphene film revealed its rough surface texture and changes in thickness. These features are advantageous for creating a bottleneck area for water vapor permeation. The presence of multiple nano-crystalline domains indicates the presence of numerous channels for water vapor permeation. (a) AFM topography images of the edges of graphene films deposited on mica substrates; the dark area on the left hand side of the image is the mica substrate; the brighter areas are graphene films and the bright spots are likely residues from the wet transfer process. (b) Relative height histogram of AFM image (a). The high narrow peak near 0nm height represents the mica substrate, the broader distribution represents the graphene film, and the tails up to 18nm height most likely represent the wet transfer process residue. (c, d) Raman Spectroscopy analysis of the intensity ratios of ID/IG and I2D/IG.

Fig. 12 comparison of desalting performance of commercially available MD membranes and permeable graphene-based membranes in different polluted environments (high concentration brine, brine containing high concentration SDS, brine containing high concentration mineral oil). Water vapor flux and desalination performance of commercially available PTFE-based MD membranes and permeable graphene-based membranes. (a) Commercially available PTFE-based MD membranes and (b) permeable graphene-based membranes in DCMD process for 72 hours at 70gL^-1NaCl solution was used as feed. (c) Commercially available PTFE-based MD membranes and (d) permeable graphene-based membranesAt 70gL^-1NaCl solution and 1mM Sodium Dodecyl Sulfate (SDS) were used as feed. The flow rate for these DCMD tests was maintained at 6Lh in both the feed and permeate streams^-1. In a DCMD process (e) a commercial PTFE-based MD membrane and (f) a permeable graphene-based membrane, the feed solution contains 1gL^-1Mineral oil and 70gL^-1NaCl and 1mM NaHCO₃And lasts for 48 hours during the DCMD. The feed temperature and permeate temperature were 60 ℃ and 20 ℃, respectively. The flow rate for these DCMD tests was maintained at 30Lh in both the feed and permeate streams^-1. The results show that the permeable CVD graphene-based membrane exhibits strong antifouling properties while being able to achieve rapid water vapor permeation and good salt rejection.

Figure 13 comparison of desalination performance of commercial MD membrane and permeable graphene-based membrane with untreated seawater from sydney harbor. Membrane distillation performance of untreated seawater from the sydney harbor area was used. (a) Water vapor flux and desalting performance of commercially available PTFE-based MD membranes and (b) permeable graphene-based membranes in DCMD process for 72 hours. The feed temperature and permeate temperature were 60 ℃ and 20 ℃, respectively. The flow rates for all DCMD tests in the feed and permeate streams were maintained at 30Lh^-1. The results again demonstrate the strong antifouling properties of the permeable graphene films, as well as high and stable water vapor flux over long operating times. In addition, a stable 100% salt rejection was maintained.

Fig. 14 additional SEM images disclosing surface features and morphology of permeable graphene and commercially available MD membranes. Large area uniformly covered graphene on top of a commercially available MD membrane consisting of Polytetrafluoroethylene (PTFE) polymer, SEM images of the commercially available PTFE-based MD membrane/permeable graphene interface, and SEM of the original PTFE-based MD membrane are disclosed. (a) Large area low magnification images of permeable graphene films on PTFE membranes. Obviously, many corrugated structures exist. (b) The boundary between graphene and PTFE membrane. (c) A higher magnification SEM image of the PTFE membrane, the microporous network structure is clear.

Figure 15. additional TEM images revealing the overlap of grain boundaries in few-multilayer graphene thin films used for film testing. TEM images of large area graphene on Cu TEM grids are revealed, dark lines on the TEM images (red arrows) pointing to indicate mismatched overlapping regions of graphene grain boundaries.

FIG. 16 TEM image of predominantly single or double layer graphene with nanochannels. Single to double layer graphene with nanochannels was synthesized to clearly show the existence of overlap of graphene domain boundaries. The bands of the darker contrast area represent the nanochannel (red arrow).

FIG. 17. stitching of low magnification TEM images of predominantly single or double layer graphene on a lace carbon TEM grid (montage). The areas showing extensions of darker contrast and highlighted with red in (b) are folded or overlapping domain boundaries (nanochannels) of graphene sheets, which can be confirmed by SAED analysis. Multilayers can also be seen as areas with darker contrast and defined sharp edges.

Fig. 18 optical transmission spectrum of permeable graphene. And obtaining the optical transmittance of the permeable graphene film from the glass slide after the transfer. The sampling area is 2cm². The 85% transmission indicates a few to many graphene films.

Figure 19 a single raman spectrum acquired from a selected region of a permeable graphene sample. Raman spectroscopy indicates the presence of multi-layered graphene, with variations in the number of layers of graphene.

FIG. 20 test setup for water desalination and purification. The test was performed in a continuous cross-flow system, where a permeable graphene membrane was placed between the feed side and the permeate side.

FIG. 21. original PTFE membranes were subjected to repeated MD experiments with saline, SDS/saline mixtures, and mineral oil/saline mixtures. All fouling experiments were repeated twice to demonstrate the reproducibility of the properties of the original PTFE-based membranes. (a, b) shows brine (70 gL)^-1NaCl), (c, d) shows a sample prepared with an SDS/saline mixture (1mM SDS/70 gL)^-1NaCl). The results show that rapid deterioration of the film performance is observed. Similarly, (e, f) shows the use of a mineral oil/brine mixture (1 gL)^-1Mineral oil and 70gL^-1NaCl and 1mM NaHCO of₃) The experiment was repeated. The results show that a significant reduction in water vapor flux is observed, and with TOCThe level increased and the salt rejection decreased to 85-90% in 48 hours, indicating that the oil passed through the membrane.

Figure 22. MD experiments were repeated on permeable graphene membranes with saline, SDS/saline mixtures, and mineral oil/saline mixtures. All fouling experiments were repeated twice to demonstrate the repeatability of the permeable graphene-based membrane performance. (a, b) shows brine (70 gL)^-1NaCl), (c, d) shows a sample prepared with an SDS/saline mixture (1mM SDS/70 gL)^-1NaCl). The results show a stable water flux and achieved for 72 hours of MD operation>A salt rejection of 99.9%. Similarly, (e, f) shows the use of a mineral oil/brine mixture (1 gL)^-1Mineral oil and 70gL^-1NaCl and 1mM NaHCO of₃) The experiment was repeated. In this case, the TOC of the permeate water was also monitored to show the oil removal rate in the 48 hour MD run. The results show that a slight decrease in water vapor flux is observed, and salt rejection is observed within 48 hours>99.9 percent and stable deoiling rate.

Figure 23 membrane performance of permeable graphene at different cross-flows and with different feed temperatures. To investigate the factors affecting water vapor transport in permeable graphene-based membranes, different process parameters such as (a) cross-flow rate of feed water and (b) feed water temperature were varied to see the change in water vapor permeation. The results show that the water vapor flux increases with increasing cross-flow rate of the water stream. Similarly, as the temperature of the feed water increases, the water vapor flux also increases. In all cases, the permeate side of the permeable graphene-based membrane maintained a stable water vapor flux throughout the duration of the MD run. All tests used saline solution (70 gL)^-1NaCl of (ll) was used).

FIG. 24. testing of commercially available PVDF-based MD membranes with mineral oil/saline mixtures and SDS/saline mixtures. Another widely used MD membrane is a PVDF-based MD membrane (Durapore). Commercial PVDF-based membrane tests were performed under (a) mineral oil/brine mixtures and (b) SDS/brine mixtures to demonstrate that the fouling problem for low surface tension liquids is not limited to PTFE-based MD membranes, but is a general problem for MD membranes. The results show that significant flux reduction, as well as reduced salt rejection, was observed for both cases (a) the mineral oil/brine mixture and (b) the SDS/brine mixture, indicating membrane failure during the brief MD run time.

Figure 25 post-test photographs of the mineral oil/brine mixture and the particle size distribution and permeable graphene containing the mineral oil/brine mixture used for the experiments. (a) A photograph of the mineral oil/brine mixture used in the experiment is shown and one can see that a stable oil emulsion has been formed. (b) An oil size distribution curve is shown showing that the oil content is mostly 1 to 3 μm in size and a few have a size of 78nm to 180 nm. (c) Is a photograph of the permeable graphene after the test. After 48 hours of filtration testing, a significant amount of oil content was visible on the surface of the graphene film.

Figure 26.120 hours long term membrane performance of permeable graphene with seawater collected from sydney harbor. Long-term (120 hours, 5 days) membrane performance tests were performed with seawater collected from sydney harbor to demonstrate the practical application and long-term stability of permeable graphene-based membranes. The results show that stable water flux and stable salt rejection > 99.9% was achieved by permeable graphene within 120 hours of MD operation, revealing the excellent ability of permeable graphene as a long-term stable membrane material for fouling prevention.

FIG. 27 AFM topography measurements of permeable graphene films. The cross-sectional profile of the graphene thin film on the mica substrate is extracted from fig. 3 a. AFM topography measurements indicate that the surface of the permeable graphene film is rough, which is reflected by the graphene film height varying in the range of 0.7nm to 3.7 nm. The wet transfer residue is a few nanometers high. The rough surface of the permeable graphene film creates a favorable morphology for water vapor permeation.

Fig. 28 an additional benefit of incorporating permeable graphene in the MD membrane. The MD experiment is shown with a high water entry temperature (90 c). The permeate vapor flux and feed temperature to the membrane surface and permeate vapor temperature were recorded over 4 hours of MD operation. All tests used saline solution (70 gL)^-1NaCl of (ll) was used). The actual feed water temperature difference and permeate vapor flux were then calculated during the MD run time. First, (a) water vapor fluxThe curve shows the wetting behavior of the pristine PTFE membrane, exhibiting a sharp increase in water vapor flux over 4 hours, which fails to maintain stable performance at high feed temperatures. However, when incorporated into permeable graphene thin films, high and stable water vapor flux was maintained during the duration of the MD run, demonstrating excellent membrane stability of the permeable graphene-based membrane at high temperature gradients, which could potentially broaden the stable operating temperature window of the MD process. (b) The actual temperature difference recorded for the original PTFE membrane and the permeable graphene-based membrane is shown. The results show that permeable graphene is able to maintain a higher temperature gradient during the duration of MD run compared to the original PTFE membrane, demonstrating the potential thermal benefit of using graphene thin films in MD processes.

FIG. 29 mechanical strength measurements of permeable graphene/PTFE membranes and pristine PTFE membranes. In order to investigate the change in mechanical strength of the membrane after mixing permeable graphene, (a) the original PTFE membrane and (b) after mixing permeable graphene were subjected to a mechanical strength test. The results show that when incorporating a permeable graphene thin film, the mechanical strength of the film is slightly improved. The improvement is small compared to bulk (120 μm thick) PTFE membranes due to the thin nature of the permeable graphene thin film (several nm thick).

FIG. 30 contact angle measurements of permeable graphene/PTFE membranes and commercially available PTFE membranes. The method comprises the following steps: graphene/PTFE films. CA 81.3+/-0.51 deg. The following: PTFE membrane only. CA 131.32+/-8.63 deg. The permeable graphene membrane was shown to be more hydrophilic than the PTFE membrane.

FIG. 31 Raman analysis of post-test samples was performed under SDS/saline mixtures. To qualitatively visualize the different adsorption behavior of SDS on the original PTFE membrane and the permeable graphene surface, raman analysis was performed on post-test (72 hours) samples tested under SDS/saline mixtures. (a, b) show a portion of the post-test samples of (a) the original PTFE membrane and (b) the permeable graphene/PTFE membrane. (c, d) show the individual Raman spectra of (c) the original PTFE membrane and (d) the permeable graphene/PTFE membrane after testing. Subsequently, in order to qualitatively verify the difference in adsorption behavior, Raman area mapping (Raman area mapping) of SDS peak intensity was performed on the (e) original PTFE membrane and (f) permeable graphene/PTFE membrane samples after the test. The results show that a significantly higher SDS peak intensity was observed for the original PTFE membrane compared to the case of the permeable graphene/PTFE membrane. These findings indicate that the adsorption of SDS on the original PTFE membrane is significantly higher and reveal different adsorption interactions between the SDS molecules and the PTFE membrane surface and the permeable graphene surface.

Fig. 32 zeta potential measurements of permeable graphene and pristine PTFE membranes. Zeta potential measurements show that the graphene thin films of the present invention show almost negligible charge (charge neutrality) under varying pH conditions, as shown by the almost flat line around 2-4mV under varying pH conditions. The original PTFE membrane exhibited a negative surface charge under varying pH conditions.

FIG. 33 shows a cross section of 1cm²Cost analysis (US $) of the integration of permeable graphene onto PTFE membranes.

FIG. 34. comparison of key physicochemical properties between light crude oil and mineral oil used as feed solutions.

FIG. 35. analysis of the composition of seawater from Sydney harbor.

Detailed description of the invention

The present invention relates to a low cost, highly efficient nanoporous and nanochannel graphene, and to membranes prepared from these graphene, particularly membranes suitable for water filtration and purification, including water desalination. The graphene thin film is synthesized in a single step rapid thermal process in an ambient air environment and can use a renewable form of biomass, soybean oil, as a precursor. The process does not require any compressed gas. More importantly, the graphene developed in this method does not involve any post-synthesis treatment in order to create nanopores in the graphene film for water transport.

In contrast, the graphene layers of the membranes of the present invention exhibit a unique combination of microstructural features that enable water vapor permeation and promote their advantageous performance in desalination processes that require hydrophobic membranes, such as Membrane Distillation (MD).

Reverse Osmosis (RO) and MD are techniques whereby water can be purified-in a practical sense, these are desalination methods. Both involve contacting the membrane with brine or other types of salt solutions and collecting desalinated water (ideally potable water) from the filtrate side of the membrane.

RO is a pressure-driven process in which the applied pressure is used to counteract the natural flow gradient between the high osmotic pressure on the brine feed side and the low osmotic pressure on the pure filtrate side. They are particularly susceptible to fouling and clogging due to the high pressures applied to the RO membranes. Achieving and maintaining the necessary high operating pressures is also complicated and requires a large amount of energy. Desalination of water using RO membranes can also result in the production of retentate solutions with very high concentrations of NaCl, for example. These super concentrated salt solutions are very harmful to the environment and present significant difficulties in disposal.

Instead, MD is a thermally driven process and produces a solution that must be disposed of, which itself can be harmful to the environment. In this case, heat rather than pressure is used to offset the osmotic pressure difference. MD can be run at relatively low temperatures, such as the type of temperature that salt solutions can achieve by simple solar heating. It is also feasible to operate the MD system in such a way that it does not produce large amounts of very high salinity species.

In MD, water vapor passes through the membrane. Thus, in addition to requiring the membrane to be hydrophobic, the process is also relatively insensitive to the chemistry of the membrane, but the pore size is important because undesirable species must not be allowed to pass through the membrane.

MD is a rapidly emerging technology that is particularly promising for the treatment (desalination and purification) of seawater, industrial wastewater and brines obtained from Reverse Osmosis (RO) and various desalination processes.⁷In the MD process, water purification is driven by a vapor pressure gradient across a porous and hydrophobic membrane. This situation is caused by the parallel flow of the hot feed solution and permeate streams, with water vapor being formed at the interface of the hot feed side of the membrane and being transported to the opposite, cold permeate side.⁸

Key advantageous features of the MD process include: water production almost independent of feed solution salinity, potential to reject most non-volatile components (e.g. dissolved salts, organics, colloids) (this technique has the potential to produce clean water in a single filtration process) and use low grade waste heat to drive the processThe ability of the program. These advantages enable MD to be a promising green technology for zero liquid discharge desalination and purification processes in various water treatment applications.⁹

The permeable membrane of the present invention is formed from a permeable graphene layer disposed on a conventional MD membrane. The permeable graphene layer has nanochannels formed by controlled edge mismatch. The edge mismatch between the layers allows water to enter the planar space between graphene sheets, spaced approximately 0.34nm apart-surprisingly found to be well suited for the passage of small species (such as water) while filtering out the spacing of larger species (such as hydrated ions or larger molecules). The graphene layer remains on the MD membrane via non-bonding interactions, and no other mechanism is required to remain adhered. The MD membrane has larger pores than graphene and therefore does not participate in the filtering out of larger species, its role is to provide mechanical support for the atomically thin graphene layer.

Thus, the morphology of the graphene layer is critical to the success of the present invention. The present invention utilizes as a starting point the basic method of graphene synthesis disclosed in applicant's earlier application PCT/AU2016/050738, the contents of which are incorporated herein by reference.

It has been found that by carefully controlling the density of free carbon in the deposition chamber and by cooling the deposited material under vacuum with a controlled predetermined temperature profile, the morphology of the resulting graphene can be controlled.

The methods for forming both the simple nanoporous graphene of the invention and the nanochannel graphene of the invention have the same general steps until the end of the annealing process, with the distinction occurring in the cooling step.

It has been found that by carefully controlling the density of free carbon in the deposition chamber and by cooling the deposited material under vacuum with a controlled predetermined temperature profile, the morphology of the resulting graphene can be controlled to produce graphene in a porous or nanoporous form, both of which have excellent potential for use as a filter or permeable membrane.

In one type of morphology, the graphene thin films of the present invention are 1-5 layers thick and have pores that span directly across the 1-5 layers of graphene that are about 5-100nm wide, i.e., the pores are 5-100nm wide and 1-5 graphene layers deep, respectively. This is referred to herein as "nanoporous graphene". This structure is illustrated in fig. 1 a.

In another type of morphology, the graphene film is 2 or more layers (e.g., 2-10 layers) of graphene, and the permeability is provided by nanochannels. This is referred to herein as "nanochannel graphene. The nanopore is more complex in structure than a simple pore, but results from modification of the simple pore during deposition. A cross-section of the nanochannel region is illustrated in fig. 1 b.

Without wishing to be bound by theory, it is believed that during the annealing stage, graphene begins to form at multiple nucleation sites on the metal substrate and begins to form individual discrete nanocrystalline domains. The orientation of the domains may or may not be aligned. This is seen in fig. 4 a. As each of these nanocrystals grows during the annealing stage, its edges move outward as indicated by the arrows. Eventually, the nano-crystalline domains begin to invade each other. If the domains happen to be aligned, the individual nanocrystalline domains will coalesce in a manner known as "perfect stitching". In the case where perfect splicing occurs, the two discrete nano-crystalline domains will form a single nano-crystalline domain. Each nano-crystalline domain grows to a size of about 100nm to 500 nm.

Nanochannels are created as nanocrystalline regions of graphene are formed in each successive graphene. Each subsequent graphene layer has its own nanocrystalline region, and subsequent overlaying at some location of the mismatched layer of the continuous film results in the establishment of a tortuous nanochannel path that spans 2-10 layers of graphene.

However, if the domains are not aligned, or in other words 'mismatched', and the crystal continues to grow, one of the nanocrystalline domains will overlay itself over the other domain. FIG. 4b illustrates the growth of mismatched graphene domains. The graphene sheets are about 0.37nm apart.

In the present invention, once the graphene annealing is stopped and the vacuum is applied, the entrapped gas in the system under the graphene is pumped out through the graphene film. Subsequent "rapid cooling" of the porous graphene results in recovery of simple porous graphene.

In another aspect of the present invention, the mechanism of nanoporous graphene, until pore formation, must be the same, but the delay phase occurring at high temperature does not "quickly freeze" the porous graphene structure, but instead allows some sustained growth reaction. Limited regrowth of the crystalline domains results in 5nm to 100nm pores filled with graphene sheets and mismatched edges formed near the grain boundary regions. In this way, according to fig. 1b, regions with closely adjacent mismatched edges are formed through all layers of the film.

Water molecules, for example, can pass in the channels between graphene layers and also at mismatched edges. Water molecules can also pass through adjacent layers if there is a mismatch in the layers. The closer the mismatch regions are, the shorter the tortuous path the molecules must take through the graphene layer. In the present invention, the nanochannel graphene has a mismatch in all layers in close proximity due to the pre-formed pores.

The channel size of the nanochannel graphene is thus between 0.37nm (the typical stacking distance of graphene sheets) and up to about 3nm, and initial data indicate that the nanoporous graphene acts as a 0.37-3nm film.

Furthermore, by controlling this slow cooling phase, the graphene sheet thickness can also be controlled. For example, the slower the cooling, the thicker the sheet, and the less graphene overlap (overlapping and overlapping).

Graphene morphologies particularly useful for preparing permeable filtration membranes are graphene films having 2 or more layers (e.g., 2-10 layers) of graphene, wherein permeability is provided by the nanochannels. This is referred to herein as "nanochannel graphene. A cross-section of the nanochannel region is illustrated in fig. 1 b.

As described above, the initial steps of forming nanoporous and nanochannel graphene materials are the same. The steps are now described with reference to nanochannel graphene materials. The process of the invention is carried out in an oven in a sealed container (1). A general configuration is illustrated in fig. 2.

Typically, the vessel (1) is an inert tube, such as a tube made of quartz, alumina, zirconia or the like. It is desirable to select the container dimensions so as to be relatively compatible with the substrate being coated, that is, to minimize the amount of dead space in the container.

The oven may be any type of oven suitable for heating the container to a temperature of about 800 ℃. One type of oven found to be suitable is a thermal CVD furnace (OTF-1200X-UL, MTI Corp), which is suitable for heating tubular containers. One example of a suitable tubular vessel is a quartz tube having a length of 100cm and a diameter of 5 cm.

The method of the invention involves placing the growth substrate (2) and the carbon source (3) in close proximity to each other in a container. They may be placed directly into the tube or, more typically, in an inert crucible (4), such as an alumina crucible, prior to placement into the tube. The container is then sealed and placed in an oven or placed in an oven and sealed. When the metal is nickel, no gas evacuation or flushing is required and the atmosphere in the sealed container at the start of the process is air. A common mechanical seal will suffice. The container need not be sealed to withstand significant pressure differences.

The metal substrate (metal foil or metal wire) and the carbon source are placed adjacent to each other. The exact distance is not critical as long as both the substrate and the carbon source are within the heating zone. Due to the rapid thermal expansion of the vapor from the carbon source, the vapor concentration will be fairly uniform throughout the heating zone. If desired, a degree of vacuum may be applied to assist the precursor flow within the heating zone.

The carbon source and the substrate are positioned within the vessel such that both are in the heating zone (5) while the vessel is in the oven.

The substrate is a metal substrate, most desirably a transition metal substrate, such as a nickel substrate. The inventors have determined that little advantage is obtained by using nickel with a purity higher than 99.5%. Nickel of 99.9% or higher purity is suitable for use in the present invention, but it does not produce significant advantages over 99.5% or 99% pure nickel, which can be obtained at a fraction of the cost of higher purity materials.

The substrate (2) may be relatively thin. One type of suitable substrate is a polycrystalline Ni foil (25 μm, 99.5%) or also a polycrystalline Ni foil (25 μm, 99%).

Without wishing to be bound by theory, it is believed that Ni acts as a catalyst to decompose hydrocarbon species into smaller building blocks essential for graphene synthesis.

Other transition metals may be used, with minor changes. For example, although nickel is a useful substrate under ambient atmospheric conditions, copper can be used as a substrate for growing graphene by evacuating any ambient air in the tube at the start of the process. The rest of the process is otherwise the same. However, regardless of the substrate, the process of the present invention avoids the use of expensive compressed gases as required in prior art processes.

The presence of air does not appear to adversely affect the use of the nickel substrate, but, in the absence of any gas (i.e., no air), the copper substrate provides for the growth of more graphene domains. In such cases, the amount of carbon needs to be adjusted to compensate for the absence of oxygen that would otherwise react with the available carbon. Substrates that are more susceptible to competing oxidation reactions will advantageously react under conditions that require an additional evacuation step.

After cooling, the substrate (2) is removed and the graphene grown thereon is analyzed (6), including by TEM microscopy.

The carbon source may be any source of material that provides volatile carbon at temperatures between 200 and 650 ℃ at ambient pressure. For example, animal or vegetable fats have been found to be useful in their raw form.

One particularly useful carbon source is raw soybean oil, which is of formula C₁₈H₃₆O₆The triglyceride of (a). Richer biomass and industrial byproducts, such as cellulosic materials, can be used. The present inventors have determined that it is not necessary to use highly purified materials as a carbon source.

It has been found that in order to obtain the nanochannel form of graphene described herein, it is necessary to create a predetermined "slightly carbon-rich or carbon-rich" environment in the deposition chamber. The molar amount of carbon per unit volume in the deposition chamber was found to be an important parameter. To form a nanochannel graphene thin film, it was found necessary to create a deposition environment that was slightly more carbon rich than the environment required to form the simple graphene thin film in PCT/AU2016/050738 previously filed by the applicant. However, it is to be avoided that the chamber is supersaturated with carbon, since that would result in very thick graphene.

The following calculations refer to soybean oil and 0.00196m³To explain how to calculate the amount of carbon in the chamber and the range of carbon rich environments suitable for preparing the porous and nanoporous graphene thin films of the invention.

First, the oxygen consumption in the reactor during growth using soybean oil must be calculated. The oil degrades to carbon, but is largely converted to carbon dioxide, which cannot react under the conditions of the present invention to produce graphene.

Carbon excess to form simple graphene films

For 0.00196m³The laboratory experimentally determined that the optimal amount of soybean oil (liquid at ambient temperature) as a carbon source needed to form a simple few-layer graphene film was 0.14 mL. 0.14mL can be considered to define a "carbon neutral" environment for the chamber, i.e., neither so carbon-lean as to cause oxidation of the metal, nor sufficiently carbon-rich as to allow formation of porous or nanoporous graphene.

Average Density Using Soybean oil (0.917g mL)^-1) And average chemical composition (linoleic acid-52%, oleic acid-25%, palmitic acid-12%, linolenic acid-6%, stearic acid-5%), calculated to be 0.0081mol of C and 0.0151mol of H initially present in the growth chamber. The amount of oxygen provided by the soybean oil is about-0.0001 mol and is therefore negligible.

The ambient air process employed in the case of nickel means that oxygen in the deposition chamber needs to be considered as this will participate in the thermal degradation of the soybean oil. This breakdown of soybean oil will be a complex process, producing a large number of molecular fragments that consume O through different reaction pathways₂。

Possible combustion reactions include:

C+O₂→CO₂1C to 1O₂--(1)

4CH₃+7O₂→4CO₂+6H₂O1C vs. 1.75O₂--(2)

2C₂H₂+5O₂→4CO₂+2H₂O1C to 2.5O₂--(3)

4C₂H₅+13O₂→8CO₂+10H₂O1C to 3.25O₂--(4)

2C₂H₆+7O₂→4CO₂+6H₂O1C to 3.5O₂--(5)

2H₂+O₂→2H₂O consumption of O only₂--(6)

Using the growth chamber dimensions and STP conditions, it was calculated that 0.0168mol of O was present₂(g) In that respect In addition, it is also noted that at the temperatures involved in the ambient air process, CO is present₂No further decomposition occurs.

If O is consumed by reaction of C only₂(reaction (1) above), then O₂There will be a slight excess, the remainder being 0.0087 mol. However, all other reaction pathways have higher O₂The consumption rate. For example, if only C is passed₂H₅Consuming O by reaction of₂(reaction (3) above), then all of O₂All will be consumed and C will be in excess, with the remainder being 0.0035 mol. All these reaction pathways will likely proceed and thus O₂The combined consumption of (C) will produce an excess of C in the chamber. The amount of carbon source used in the experiment, 0.14mL soybean oil, was sufficient to consume just O in the growth chamber₂An excess of C is generated, whereby the graphene of the present invention can be formed. The excess for forming the optimal graphene can be quantified as per 0.00196m³0.0035mol C, or 0.00179mol C excess per liter, i.e. 0.00179mol C per liter, can be used for graphene deposition.

Carbon excess to form permeable graphene thin films

To form both nanoporous and nanochannel permeable graphene, it was found that an excess of soybean oil was required, every 0 a.00196m³About 0.15 or 0.19 ml. More than 0.14mL of this additional 0.01-0.05mL of soybean oil is directly attributable to the carbon available for deposition, since the oxygen in the chamber is mostly consumed by a base amount of 0.14mL of soybean oil.

Soybean oil is mainly C₁₈Oil having a weighted average MWT of about 278. 0.14mL of soybean oil corresponds to about 0.008 moles of carbon, so an additional 0.01mL would add an additional about 0.0006 moles of carbon to the deposition chamber, and an additional 0.02mL would add an additional 0.0012 moles of carbon to the deposition chamber.

Thus, using 0.15mL will result in every 0.00196m³0.0041(0.0035+0.0006) moles of carbon, or 0.00209 moles excess C per liter.

Using 0.19mL will result in every 0.00196m³0.0059(0.0035+0.0024) moles of carbon, or 0.003 mole excess C per liter.

Thus, the carbon environment that should be used contains about 0.002mol C excess carbon per liter of chamber volume-about 0.0018 to 0.003mol C excess per liter of chamber volume. Tables 1 and 2 provide guidance for calculating the amount of precursor based on the length of the tube used.

One skilled in the art will appreciate that different carbon sources (e.g., different oil compositions) will result in different precursor amounts needed for graphene growth. Similarly, different chamber sizes will require different precursor amounts for graphene growth, but the principles explained herein will enable the calculation of the correct precursor amount.

Method of forming nanoporous graphene

The carbon source is sealed in a chamber at ambient temperature along with the substrate and heating source. This is shown in fig. 3B at point a.

The furnace temperature was then raised to about 800 c over a period of 20-30 minutes (B). Typical ramp rates shown at (ab) are 25-35 deg.C/min. During the temperature ramp phase (-300-350 ℃), the precursor vaporizes and the long carbon chains in the soybean oil begin to decompose via thermal dissociation into gaseous carbon building blocks. Those skilled in the art will appreciate that the exact dissociation temperature will vary based on the chemical and physical properties of the carbon source precursor material. At the same time, the gaseous carbon building block is within the entire tube and towards the Ni foil growth substrateAnd (4) diffusion. As the temperature in the furnace is gradually increased to 800 ℃, the carbon precursor is further decomposed into simpler carbon units, thereby generating graphene on the surface of the metal substrate. Furthermore, as the temperature increases, the carbon solubility in Ni increases and the carbon building blocks begin to dissolve into the Ni bulk. Starting at 500 ℃, a graphitization process takes place, wherein the carbon atoms start as sp²The configurations arrange themselves. And forming the graphene crystal lattice from 500 ℃ to 800 ℃.

Graphene formation was observed to occur from 650 ℃, although the best quality graphene (in terms of low defects) was obtained from about 800 ℃.

Once the desired temperature is reached, the furnace is kept at that temperature, for example 800 ℃ (for 10-15 min for 99.5% purity Ni foil) to enable growth. The graphene grains grow during this annealing process. The annealing time (bc) can be shortened by using a lower purity film. For example, if 99% pure Ni foil is used, the annealing time can be reduced to about 3 minutes.

To form the nanoporous graphene of the invention, the process is performed as described above using a slightly carbon rich environment until the annealing step C is complete. The annealing step is performed at atmospheric pressure (i.e. no pressure control is performed except for sealing the tube). Once the annealing is complete, the sample is immediately removed from the heating zone (typically an oven) and moved to a cooling zone where a vacuum is applied, and the sample is flash cooled at a rate of about 20-30 ℃ per minute with the vacuum applied, more typically about 25 ℃ per minute (or as quickly as possible without damaging the equipment). During this step, unconsumed gases are removed from the tube and graphene growth is stopped before cooling begins. Due to rapid cooling, the sheet thickness is 1-5 layers of graphene. The pore size is 5-100 nm.

Method of forming nanochannel graphene

To form the nanochannel graphene, the process is performed as described above using a carbon-rich environment until the annealing step is complete.

As before, the furnace temperature was then raised to about 800 ℃ (B) over a period of 20-30 minutes. Typical ramp rates shown at (ab) are 25-35 deg.C/min.

Once the desired temperature is reached, the furnace is kept at that temperature, for example 800 ℃ (for 10-15 min for 99.5% purity Ni foil) to enable growth. The annealing process is carried out for an annealing time (bc).

The annealing step in the above process was performed at atmospheric pressure (i.e., no pressure control was performed except for sealing the tube). This process is described with reference to fig. 3B. Once the anneal is complete at (C), a delay step (cd) is employed, but before the flash cooling is initiated at (D).

During this delay step, which is typically about 1 to 5 minutes, the heat source is turned off and a vacuum is applied at (C), but the substrate and chamber remain in place. The cooling rate during this time is about 10 deg.C/min, more advantageously about 0-10 deg.C/min.

The length of time in the delay (cd) stage determines the exact nature of the nanochannel structure. Once the delay phase is complete (at D), the chamber is removed from the oven and allowed to flash cool (de) to room temperature at a rate of about 20-30 ℃/minute, more typically about 25 ℃/minute with the vacuum applied (or as quickly as possible without damaging the equipment).

Slower cooling rates also result in thicker graphene, typically 2-10 layers, with channel sizes of 0.37-3 nm.

Growth conditions are summarized in fig. 6 for a series of graphene, including impermeable graphene, nanoporous graphene and nanochannel graphene that can be used in the films of the invention.

Methods of forming graphene containing both nanochannels and nanopores

The mechanism of formation of the permeable graphene is described in detail above. It has been noted that if the process of forming nanochannel graphene is stopped at an early stage of growth, it is possible to obtain a graphene thin film having both nanopores and nanochannels. As described for nanochannel graphene, the longer the growth process is allowed to continue, the greater the extent of nanochannel formation and the lower the likelihood of obtaining pores in the graphene.

Mechanism of forming permeable graphene

Without wishing to be bound by theory, it is believed that during the annealing stage, graphene begins to form at multiple nucleation sites on the metal substrate and begins to form individual discrete nanocrystalline domains. The orientation of the domains may or may not be aligned. This is seen in fig. 4 a. As each of these nanocrystals grows during the annealing stage, its edges move outward as indicated by the arrows. Eventually, the nano-crystalline domains begin to invade each other. If the domains happen to be aligned, the individual nanocrystalline domains will coalesce in a manner known as "perfect stitching". In the case where perfect splicing occurs, the two discrete nano-crystalline domains will form a single nano-crystalline domain. Each nano-crystalline domain grows to a size of about 100nm to 500 nm.

Nanochannels are created as nanocrystalline regions of graphene are formed in each successive graphene. Each subsequent graphene layer has its own nanocrystalline region, and subsequent coverage at some locations of the mismatched layer of the continuous film results in the establishment of a tortuous nanochannel path that spans 2-10 layers of graphene.

However, if the domains are not aligned, or in other words "mismatched," and the crystal continues to grow, one of the nanocrystalline domains will overlay itself over the other domain. FIG. 4b illustrates the growth of mismatched graphene domains. The graphene sheets are about 0.37nm apart.

In the present invention, once the graphene annealing is stopped and the vacuum is applied, the entrapped gas in the system under the graphene is pumped out through the graphene film. Subsequent "rapid cooling" of the porous graphene results in recovery of simple porous graphene.

As discussed above, water molecules, for example, can pass in the channels between graphene layers, and can also pass at mismatched edges. Water molecules can also pass through adjacent layers if there is a mismatch in the layers. The closer the mismatch regions are, the shorter the tortuous path the molecules must take through the graphene layer. In the present invention, the nanochannel graphene has a mismatch in all layers in close proximity due to the pre-formed pores.

The channel size of the nanochannel graphene is thus between 0.37nm (the typical stacking distance of graphene sheets) and up to about 3nm, and retention data shown in more detail below indicate that the nanoporous graphene acts as a 0.37-3nm film.

Furthermore, by controlling this slow cooling phase, the graphene sheet thickness can also be controlled. For example, the slower the cooling, the thicker the sheet, and the less graphene overlap.

The presence of air does not appear to adversely affect the use of the nickel substrate, but, in the absence of any gas (i.e., no air), the copper substrate provides for the growth of more graphene domains. In such cases, the amount of carbon needs to be adjusted to compensate for the absence of oxygen that would otherwise react with the available carbon. Substrates that are more susceptible to competing oxidation reactions will advantageously react under conditions that require an additional evacuation step.

After cooling, the substrate (2) is removed and the graphene grown thereon is analyzed (6), including by TEM microscopy.

Permeable graphene-based films and mechanisms for water vapor permeation across overlapping grain boundaries

The permeable graphene membrane is grown by an ambient air CVD process as described in more detail above and elsewhere,⁶and then wet transferred to a commercially available Polytetrafluoroethylene (PTFE) MD membrane. This process is described in fig. 8 (part a). Unlike conventional CVD methods, ambient air graphene synthesis techniques do not require any expensive and explosive purification of the compressed gas.^19,20The source of graphene growth is replaced with a low cost, safe and renewable biological source (such as soybean oil). The ambient air CVD process enables the growth of continuous graphene thin films on polycrystalline Ni substrates with high density nanocrystalline grain boundaries that desirably act as water vapor permeable channels. The graphene was then wet transferred to a conventional supporting commercially available PTFE MD membrane. PMMA-assisted transfer can be used and removed prior to testing the graphene-based membrane in water purification (see table S1 cost analysis).⁶Fig. 8 (b) shows a newly proposed water permeation mechanism in CVD graphene thin films. Previous studies have shown that waterThe infiltration is performed through pores in the CVD graphene, which are generated after growth in an energy intensive, non-scalable process.^2,21,22,23In contrast, the present invention demonstrates that a few to multi-layer nanocrystalline CVD graphene thin film (with overlapping grain boundaries that act as efficient water vapor permeation channels) enables robust antifouling desalination films. The membrane can filter out salts and destroy water-borne contaminants such as surfactants and oils.

Structural properties and characteristics of permeable graphene thin films

The morphological and structural properties of the graphene thin films were analyzed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) (fig. 9 and 14). It is evident from SEM images taken at low and high magnification that the transferred graphene thin film was uniformly coated with PTFE film (fig. 9 a-b). The graphene thin film appeared to conform to the film surface as shown by the visible wrinkles in the graphene thin film above the partially visible underlying film. In addition, the distribution of domain size, domain orientation and thickness within the graphene film is characterized. A continuous few-layer graphene film with randomly oriented, overlapping stacked graphene layers was identified in low-magnification TEM, which generally shows a hexagonal morphology indicating single crystallinity (fig. 9 c). Bright-field (fig. 9d) and dark-field (fig. 9e) TEM imaging show that the underlying few layers of graphene are polycrystalline with misoriented domains (in the range-200 nm to 600 nm), indicated by the change in contrast at the domain boundaries and the presence of moire fringes (periodic fringes) in the graphene domains. Importantly, slight overlap of domain boundaries in multiple regions of the sample was observed-these serve as potential channels for the passage of water molecules (fig. 15 a-b).²⁴These channels have an overlap of about 10nm and extend along the length of the grain boundaries by about 400nm-1 μm according to TEM image contrast. The channel height is the interlayer spacing of graphene, specifically, for turbostratic CVD graphene layers grown on nickel in this experiment, this value is 0.34 nm.²⁵High resolution TEM and Selective Area Electron Diffraction (SAED) analysis of these nanochannels is limited due to the multilayer thickness and small channel width compared to the pore size of the selected regions.

To provide conclusive evidence of the presence of nanochannels in permeable graphene, samples of predominantly monolayer or bilayer graphene with wider nanochannels were synthesized. Darker contrast nanochannels with varying channel lengths >1 μm and varying channel widths >100nm can be seen (fig. 10a and 16, fig. 17). Wider nanochannel SAED is possible and demonstrates the presence of overlapping domain boundaries rather than folds or wrinkles of the graphene film. In particular, FIG. 10 shows that-250 nm wide nanochannels are formed over a length of 2.5 μm due to misoriented overlap of the monolayer region (left side of FIG. 10 a) and turbostratic bilayer region (right side of FIG. 10 a). The darker contrast regions demonstrate overlapping, misoriented graphene domain boundaries (or nanochannels) due to the monolayer to bilayer transition and the shift in the respective axes of rotation on either side of the feature (29.5 ° on the monolayer side (fig. 10b) and-7.6 ° and 25.1 ° on the turbostratic bilayer side (fig. 10d)) (see inset to fig. 10a, which is a schematic showing the relative rotation of the domains). Notably, although the presence of nanochannels can be demonstrated using predominantly single or double layer graphene thin films grown by ambient air CVD processes, these samples are fragile and inferior films compared to few to many layers of graphene. The unique morphology of ideal permeable few-layer graphene films, i.e., high density of submicron polycrystalline grains with large number of grain boundaries, and overlapping of mismatched graphene boundaries that produce nanochannels, will produce multiple channels to transport water vapor efficiently.

The structural properties of the graphene thin films were further examined by raman spectral mapping and Atomic Force Microscopy (AFM) (fig. 11). The multilayer graphene film was observed to grow continuously over the entire surface, with regions of varying thickness. AFM topography imaging of graphene films showed thickness ranging from 0.7nm to 3.7nm (-2 to 10 graphene layers) and an average film thickness of 1.7nm (fig. 11 a-b). The wet transfer process may generate contaminants (e.g., PMMA residues and Fe particles) on the graphene surface. In addition, the transmittance of the graphene thin film was measured to check the average film thickness. A transmission of 85% was observed at 550nm (fig. 18). Raman characterization indicated that the graphene was a few-layer polycrystalline film. Performing Raman spectrum mapping of ID/IG and I2D/IG intensity ratioEjection (which shows the defect distribution and relative thickness distribution of the graphene thin film) to determine defects in the thin film and thickness uniformity (fig. 11c-d and fig. 19). There are three distinct peaks, i.e., characteristic disordered peaks, in the Raman spectrum of graphene, which are from-1350 cm^-1Sp of (a)²Defects in carbon (D band); graphite peak from-1580 cm^-1Sp of (a)²Carbon in-plane vibration E2G mode (G-band); and a second order 2D band from-2670 cm^-1Three-dimensional inter-planar stacking of hexagonal carbon networks.²⁶The intensity ratio ID/IG was 0.1-0.3, while the intensity ratio I2D/IG was 0.6-1 (FIGS. 11 c-d). This disordered content can be attributed to defects, which result from grain boundary interactions by analysis of the G peak. The I2D/IG intensity ratio indicates that the film is composed of few layers of graphene, with film thicknesses varying from 2 to 10 atomic layers. These characterizations agree well with the structure of the graphene thin film as determined by TEM and other characterizations.

Graphene-based membranes for water desalination containing scale-forming contaminants and seawater desalination from sydney harbor

Performance of permeable graphene-based membranes (graphene/PTFE-based MD membranes) was performed by direct contact MD (dcmd) using a series of solution mixtures containing high salt solutions in the presence of surfactants, mineral oil and real seawater collected from sydney harbor. Water vapor flux and salt rejection were measured to characterize the purification of water by graphene membranes. The performance of the permeable graphene-based membrane was based on a commercial PTFE MD membrane (Ningbo Changqi, thickness 120 μm, pore size 0.4 μm). This test was conducted in a continuous co-current cross-flow system as illustrated in fig. 20.

NaCl feed solution (70 gL) was used^-1NaCl, typical brine concentration), both permeable graphene-based membranes and commercial PTFE membranes showed similar salt rejection rates, reaching 99.9% after 72 hours of operation. A relatively higher water vapor flux was observed for the permeable graphene-based membrane compared to the original PTFE-based MD membrane (fig. 12 a-b). Furthermore, to explore the controlling factor for water vapor permeation in permeable graphene-based membranes, the membranes were tested at different water flow cross-flow rates and at different temperature gradients generated by increasing the inlet water temperature (fig. 21).The results show that a systematic increase in water vapor flux is observed with increasing cross-flow rate of the water stream (fig. 21 a). Similarly, as the temperature gradient increased, a systematic increase in water vapor flux was observed (fig. 21b), revealing that both the cross-flow rate of water and the temperature gradient are important factors in controlling the permeation of water vapor through the permeable graphene. Furthermore, in both cases, the permeable graphene-based membrane shows a stable water vapor flux throughout the duration of the MD run at different cross-flows and at different temperature gradients.

During MD separation, low surface tension liquids (i.e., salt solutions containing surfactants such as Sodium Dodecyl Sulfate (SDS)) cause detrimental pore fouling and/or wetting in MD membranes, which results in significant deterioration of membrane performance (see fig. 22).^27,28Therefore, to explore the capacity of permeable graphene-based membranes under such solution mixtures containing harmful soils, both pristine PTFE membranes and permeable graphene-based membranes were tested under salt solutions containing surfactants (such as SDS). For the treated brine/SDS feed solution (70 gL)^-1NaCl with 1mM SDS) significant fouling was clear at a glance and the water flux was from 40Lm over 44 hours^-2h^-1Down to 8Lm^-2h^-1(FIG. 5 c). In addition, a significant reduction in salt rejection from 100% to 95% was observed. In contrast, the permeable graphene-based membranes exhibited stable and high water vapor flux (50 Lm) over 72 hours of MD operation under similar operating conditions^-2h^-1) And stable salt rejection (100%) (fig. 12 d).

Permeable graphene-based membranes were also tested, containing high concentrations of oil compounds, another common contaminant that causes significant wetting and fouling problems in widely used MD membranes, such as commercially available PTFE and PVDF-based MD membranes (fig. 12e-f and see fig. 22). When brine/mineral oil (emulsion mixture for experiment and oil size distribution thereof see FIGS. 23a-b, and FIG. 34) feed solution (1 gL) was treated^-1Mineral oil and 70gL^-1Of NaCl and 1mM NaHCO₃) When, significant fouling was apparent for the original PTFE-based MD membrane (fig. 12). This is achieved by a water flux of 48 hours50Lm^-2h^-1Rapidly degraded to 19Lm^-2h^-1And a significant reduction in the desalination capacity of the membrane from 100% to 89%. In contrast, the permeable graphene-based membrane was superior to the commercial PTFE-based MD membrane, exhibiting significantly improved salt rejection (100% to 99.9%) and water vapor flux retention (52 Lm) for MD operation for 48 hours under similar conditions^-2h^-1To 39Lm^-2h^-1) (FIG. 12). Although a significant amount of oil was visible on the graphene surface after MD runs, the results show that unlike the case of commercially available PTFE-based MD membranes, there was negligible wetting or fouling of the membrane surface in permeable graphene-based membranes. All experiments were repeated to demonstrate the reproducible performance of the inventive membranes. During repeated experiments, the Total Organic Carbon (TOC) level in the permeate stream was monitored over 48 hours (to check for oil removal) (see fig. 22 e-f). The results show that stable organic carbon leaching was achieved within 48 hours of MD operation, revealing a stable oil removal rate via permeable graphene-based membranes. Furthermore, all repeated experiments revealed that the permeable graphene-based membranes of the present invention exhibit reproducible, stable, antifouling properties, as well as excellent salt rejection and deoiling rates in salt water and salt waters containing membrane fouling contaminants (such as surfactants and oils). Overall, the MD of the present invention using permeable graphene demonstrates the potential to enable direct membrane-based purification of liquids containing mixtures of damaging water-borne contaminants that conventional membranes are unable to transport without expensive multi-stage pretreatment.

Desalination of seawater from sydney harbor using permeable graphene-based membranes

To demonstrate the practical applicability of permeable graphene-based membranes in real desalination cases, untreated real seawater feed (total dissolved solids of 34.2 gL) was used^-1) A water desalination test was performed (fig. 13). Real seawater was collected from sydney harbor, NSW, australia (see table S3 for analysis of seawater). Seawater collection stations are of paramount importance to the domestic environment and ongoing industrial activities. The results show that commercial PTFE-based MD membranes foul when untreated seawater is treated, with a continuous decrease in water vapor flux (40 Lm) over 72 hours^-2h^-1To 20Lm^-2h^-1) And the salt rejection decreased slightly (100% to 99%) (fig. 13). In contrast, the permeable graphene-based membrane showed excellent performance in salt rejection (100%) while maintaining a high water vapor flux (50 Lm) over 72 hours^-2h^-1To 46Lm^-2h^-1) And long term stability, in real seawater desalination, at 4cm²The permeable graphene-based membrane is treated with 0.4-0.5L of seawater per day. Furthermore, to demonstrate the long-term stability of permeable graphene-based membranes under real seawater feed, membrane performance was tested for extended MD run duration (120 hours) (see fig. 26). The results show that stable water vapor flux was observed within 120 hours of MD operation, along with excellent salt rejection of 99.99%, demonstrating excellent long-term stability of the permeable graphene-based membrane. Furthermore, even under long run of MD with real seawater (which has multiple components), the concentration polarization effect is negligible for permeable graphene-based membranes. Overall, the present results indicate that the ambient air-derived CVD graphene thin films of the present invention are promising active materials for MD and demonstrate a promising application where hydrophobic CVD graphene thin films can be applied for water purification. Furthermore, the work of the present invention demonstrates the synergistic effect of applying novel 2D nanomaterials in solving key problems in membrane water purification.

The membranes of the present invention exhibit relatively high water vapor flux through the graphene membrane compared to commercially available PTFE-based MD membranes. This indicates that there are numerous potential areas in the graphene film that allow water vapor transport in a fast flow. Unlike previous studies where post-processing techniques would create nanopores in the graphene surface, the inventors did not observe nanopores in the traditional sense in the few-layer graphene microstructures of the present invention. Rather, a multi-layered graphene film with numerous graphene grain boundaries caused by small domain sizes and numerous overlapping regions of adjacent graphene grains with mismatched graphene grain boundaries is observed.

These nanochannels, created by mismatched and overlapping graphene domains, appear to contribute to the rapid transport of water vapor.³⁰Using MDS patternThe possibility of water molecule transport through such overlapping graphene domains is real and this further validates the observed efficient water transport through the graphene-based membrane. Recently, another advantageous advantage of using graphene in water transport has been demonstrated in that minimal resistance is created when water or water vapor is transported between graphene sheets.³¹In addition, various characterizations (i.e., AFM, SEM, and TEM) show that the number of layers of the porous graphene thin film of the present invention on the microscopic region may have variations due to misorientation, overlapping, and submicron-sized grains. Recent studies have shown that such structural properties promote deformation (i.e., wrinkling) of the graphene thin film.^30,32Such nanoscopic wrinkling will increase the surface roughness of the porous graphene thin films of the present invention and create an ideal surface structure (i.e., nanoscopic bottleneck sites) to facilitate water vapor ingress and rapid permeation.

Thermal insulation effect by permeable graphene and mechanical strength of permeable graphene-based film

Another important aspect to be considered in membrane distillation is heat transfer. A major drawback of conventional MD membranes is their inability to provide thermal insulation across the membrane between the hot feed and cold permeate sides.¹³The continuous loss of heat through the membrane results in low water vapor flux and a reduction in water vapor flux over long run times, which is one of the unresolved problems in MD membranes.^16,17,33Graphene is a two-dimensional nanomaterial with high thermal conductivity anisotropy due to sp in the graphene lattice²High thermal conductivity is observed for bonding in the X-Y direction and poor thermal conductivity due to weak van der waals interactions is observed in the Z direction, which is an advantageous feature for MD applications.^16,17,34,35To explore the thermal benefits of incorporating a permeable graphene thin film in a membrane distillation membrane, experiments were conducted to measure water flux and temperature on the feed side of the membrane and the permeated vapor temperature to calculate the actual temperature difference at high temperature gradients (Δ T ═ 70 ℃) to clearly see the thermal insulation effect in small membrane areas and compare it to the original PTFE MD membrane (fig. 28). As expected, high feed water temperatures result in lower liquid inlet pressures, which lead to membrane degradation of commercially available PTFE MD membranes, asTo provide a rapid increase in water vapor flux over a brief duration of the MD process. While the permeable graphene-based membrane showed stable water vapor flux even at high inlet water temperatures (fig. 28 a).

More importantly, the permeable graphene-based membrane was able to maintain a stable and higher actual temperature gradient compared to the original PTFE membrane (fig. 28b), providing experimental evidence for the thermal insulating effect of the permeable graphene thin film, and also demonstrating the potential to increase the stable operating temperature window of the MD method using permeable graphene.

Another important property of the film is its mechanical strength. The permeable membrane of the present invention showed a slight improvement in mechanical strength after mixing permeable graphene compared to the original PTFE membrane (fig. 29).

Antifouling properties of graphene films

Surface energy plays a key role in the anti-fouling and anti-wetting properties of MD films, which are ideally highly hydrophobic (i.e., high water contact angles). Although the graphene-based films of the present invention were moderately hydrophobic (contact angle of 81.3 °), they exhibited significantly superior antifouling and anti-wetting ability compared to the highly hydrophobic surface (contact angle of 131.3 °) of the commercially available PTFE-based MD film (fig. 30). Thus, there is an additional factor that will prevent contaminant molecules from blocking or attaching to the water vapor channels. To better understand the antifouling properties of the permeable graphene thin films of the present invention, adsorption energy simulations were performed to study the interaction between contaminating particles (such as SDS) and nanochannels at grain boundaries. The calculation showed that the adsorption energy Ead of one SDS molecule on the grain boundary was-2.36 eV, and H₂The adsorption energy of O is-0.12 eV, indicating that the interaction between graphene and contaminant molecules is weak physical adsorption. Similar adsorption energies are expected for molecules with chemical structures similar to SDS (e.g., mineral oil). In addition, due to the kinetic energy provided by the flow of the continuous feed water, weak physical adsorption of contaminants on the graphene surface is overcome.

To experimentally verify the weak physical adsorption behavior between SDS and the graphene surface of the present invention, the experiment was repeated with the original PTFE membrane and the permeable graphene-based membrane using an SDS/brine mixture for 72 hours, followed by drying the sample without any cleaning process and analysis using raman spectroscopy. SDS is known to have a distinct and unique raman peak, and the SDS raman intensity was area mapped to find the relative difference in SDS adsorption on the original PTFE membrane and permeable graphene surface (fig. 31). The result shows that obviously lower SDS Raman intensity is observed on the permeable graphene surface, and experiments show that compared with the original PTFE membrane, the interaction between the graphene surface and SDS is weaker, and the adsorption energy simulation is enhanced.

While the presence of polycrystalline, mismatched graphene domains and grain boundaries is disadvantageous in some graphene applications (i.e., high speed electronics, etc.), the results of the present invention indicate that such morphologies are advantageous for water purification applications and provide the key advantage of facilitating rapid permeation of water vapor and its effective filtration of contaminants.

Thus, the permeable membrane of the present invention is treating high salinity water (i.e., 70 gL) without any post-synthesis pore design^-1NaCl) showed high water flux (for 4 cm)²Is-50 Lm^-2h^-1At most 0.5L per day), excellent salt rejection (99.9%), and excellent antifouling properties by filtering out common water-borne contaminants.

Performance under extreme pH and brine conditions

Water treatment is an important part of many different industries, including mining, agriculture, and materials processing. Water from these sources is treated in a number of different steps, but at some point they always involve a reverse osmosis step. This step is critical to removing dissolved salts from the solution. Typical RO membrane specifications require a flow rate of 44.6Lm at an applied pressure of 1551kPa and a feed NaCl concentration of 0.034M^-2.h^-1The removal rate was 99.5%. Prior to the RO step, the water must be treated to ensure that the membranes do not foul with the presence of organics or other contaminants. Even once the potential foulants have been removed, problems still exist when extreme pH solutions or salinity are present.

Instead of RO, membrane distillation does not require a pressure gradient, but relies on a temperature gradient to produce a water flux. Can use waste heat sources to generateThis temperature gradient. Even if the filtrate salt concentration changes, the MD process maintains flux, but the flux is not as high as RO and the process is still considered to be in the primary stage. In addition, MD suffers from fouling and pH issues. Membranes are difficult to handle at extreme pH and the process is significantly less effective under these conditions relative to neutral conditions. Composite polyamine membranes have been used at pH1 and 13. The optimum flux achieved with a 0.034M NaCl feed in RO mode at 1000kPa was 16Lm^-2.h^-1The NaCl eliminating rate is as high as 85%.

To improve the performance of membranes operating in multiple modes, 2D materials have been tested. Graphene-based membranes have been shown to filter out various salts in solution during osmosis. Graphene oxide and graphene powder have been successfully incorporated into membranes, the best performance reported is the forward osmosis mode, with an osmotic pressure of 7500kPa, a NaCl rejection of 97%, and a water flux of 0.5L.m^-2.h^-1Wherein the feed NaCl concentration was 0.1M. Chemical vapor deposition grown graphene with post-growth pore generation has also been explored for use as membrane materials. The filtration of hydrated ions with sub-nanometer radius is not accessible, and the radius is more than 0.9nm³The best performing membranes achieved a minimum of 90% removal. The 2D material grown by CVD, modified or unmodified, was not shown to be an effective film for operation in MD mode. To the best of the applicant's knowledge, no graphene-based film has been shown to work under severe conditions. Furthermore, no membrane currently exists that can withstand harsh conditions and maintain performance, water flux and desalination levels for industrially applicable amounts of time.

Permeable nanochannel graphene prepared according to the methods of the present invention is wet transferred (e.g., via a PMMA-assisted wet transfer process) onto widely used MD membranes, such as polyvinylidene fluoride (PVDF) and Polytetrafluoroethylene (PTFE) MD membranes.

The use of binder materials (such as PMMA) enables the permeable graphene to be used with other chemically intolerant membrane substrates (such as PVDF membranes), where the removal of the binder from the permeable graphene limits the range of support membranes that it can use.

It has been surprisingly found that permeability on a PTFE support membraneNanochannel graphene is an effective purification membrane for extreme pH water that will filter not only solvated salt ions, but also H₃O⁺And OH^-Solvating the ions, which allows us to obtain water as permeate at neutral pH, regardless of the extreme pH range of the feed water.

Furthermore, the use of a similar film of PMMA binder/graphene on a less chemically resistant PVDF support film results in the support film being protected by chemically robust permeable graphene.

The surface characteristics of the permeable nanochannel graphene thin films of the present invention were analyzed by Scanning Electron Microscopy (SEM). The transferred permeable graphene film was seen to be uniformly coated on the supporting PTFE membrane by both low-magnification SEM and high-magnification SEM. High magnification SEM images revealed small nanoscale graphene domains with graphene grain boundaries.

The graphene film has the advantages of low thickness variation, low defect, good structural quality and multi-layer graphene film containing polycrystalline graphene domains.

TEM and scanning TEM (stem) analysis of permeable graphene thin film samples after filtration testing provides further evidence for their excellent ability to act as effective purification membranes. The used graphene films contained very small amounts of salt residues, indicating antifouling properties. These may be nanoparticles or uneven surface deposits for the minimal salt residues present. In rare cases, salt residues accumulate along the length of the overlapping domains, suggesting that the mechanism of water transport is through the permeable nanochannels of graphene membranes.

Comparison of the Membrane Performance of PTFE MD membranes and permeable graphene/PTFE membranes for the purification of extreme pH Water

To demonstrate the ability of permeable graphene to purify aqueous mixtures of extreme pH water containing solvated salt ions, a series of solution mixtures were prepared comprising a salt solution containing 0.1M sulfuric acid (35 gL)^-1) And a salt solution containing 0.1M sodium hydroxide (35 gL)^-1). By adjusting the amount of sulfuric acid and sodium hydroxide solution, the pH of the feed water was adjusted to pH2 for acidic feed water and pH13 for alkaline feed water. Then go toPermeable graphene/PTFEMD membrane testing was performed by direct contact MD. Water vapor flux, salt rejection and pH were monitored continuously over 72 hours of the test period. Similarly, for comparison, performance testing of the original PTFE MD membrane was performed.

With an acidic feed solution (35 gL)^-1NaCl/0.1M H₂SO₄pH 2) shows that the chemically resistant virgin PTFE membrane retains its structural integrity and mechanical stability after 72 hours of testing. However, a gradual decrease in pH was observed over 72 hours, pH reached 6.0 at the end of 72 hours, and salt rejection decreased. More importantly, membrane fouling was evident as the water vapor flux was controlled by 23Lm over 72 hours^-2h^-1Continuously reduced to 17Lm^-2h^-1. SEM analysis of the PTFE membrane after 72 hours testing showed partial pore blocking of the membrane. In addition, after testing, photographs of the membrane also showed signs of potential damage or changes in surface properties relative to the original PTFE membrane. The membrane contacted with the acidic feed solution showed a dark black color at the end of the 72 hour test. However, when incorporating permeable graphene on PTFE membranes, stable neutral pH permeate was maintained for 72 hours of operation and stable salt rejection of 99.9% and 25Lm were observed^-2h^-1Stable water flux. This indicates that the membrane of the present invention has antifouling property, excellent desalting ability and excellent H₃O⁺Filtering capability. When using alkaline feed solution (35 gL)^-1NaCl/0.1M NaOH, pH13) the original PTFE membrane showed an increase in pH, reaching 7.5 at the end of 72 hours, and a decrease in salt rejection from 99.9 to 97%. In the case of the alkaline solution, the membrane performance sharply decreases from around 48 hours, unlike the case of the acidic solution, which shows gradual decrease in membrane performance. More importantly, membrane fouling was more pronounced in the case of alkaline solutions, as is evident from the flux curves where water vapor flux from 23Lm was observed over 72 hours^-2h^-1Continuously drops to 12Lm^-2h^-1. Post-test SEM analysis of the PTFE membrane showed significant pore blocking of the membrane after 72 hours. The films also show promise in terms of reduced physical stability and film discoloration, as in the acid water entry experimentsCan damage the original PTFE film. However, when a permeable graphene membrane was mixed on a PTFE membrane, stable neutral pH, excellent and stable salt rejection (99.9%) and stable water flux (25 Lm) were observed for 72 hours of operation^-2h^-1). Unlike unmodified PTFE membranes, the nanochannel graphene membranes of the present invention exhibit excellent antifouling properties, desalination capability, and OH^-Filtering capability. After 144 hours of testing (72 hours of acidic filtration followed by 12 hours of cleaning followed by 72 hours of alkaline solution), the nanochannel graphene membrane showed good structural integrity, with a large amount of salt accumulated on the surface of the graphene. Overall, in the case of water mixtures with extreme pH (pH 2 and pH13), even the purification capacity of chemically-tolerant PTFE decreases significantly within 72 hours, whereas the permeable graphene membranes of the present invention provide excellent, antifouling, stable, long-term membrane performance within 144 hours of MD operation, making permeable graphene membranes promising candidates that may enable single-step, multi-stage free purification of low and high pH caustic chemical or mining wastewater.

Comparison of PVDF MD film and permeable graphene-based film with PMMA Binder for Membrane Performance for extreme pH Water purification

To demonstrate the broader applicability of permeable graphene on different support films, PMMA adhesives are used as they are typically used as adhesives for graphene wet transfer. In this case, the binder does not have to be removed, which enables the use of other widely used but less chemically resistant PVDF MD films as support layers for PMMA binder/nanochannel graphene. The use of binders in permeable graphene enables its wider integration into other types of polymer-based films.

A mixture of water of the same extreme pH (35 gL) was used^-1NaCl/0.1M H₂SO₄pH2 and 35gL^-1NaCl/0.1m naoh, pH13) MD tests were performed on the comparative PVDF film and the composite PVDF/PMMA/nanochannel graphene film of the invention over 72 hours. Water vapor flux, salt rejection and pH were monitored continuously over 72 hours of the test period. However, in severe casesIn the case of a failure of the membrane, the experiment was stopped 72 hours ago.

With an acidic feed solution (35 gL)^-1NaCl/0.1M H₂SO₄pH 2) showed significant performance degradation of the original PVDF MD membrane over a short run-time (10 hours). After 10 hours, the structural integrity of the membrane was lost, with the hard membrane becoming soft and unable to retain its shape. More importantly, its role as a filtering layer for solvated ions and pH removal fails in a short period of time. A rapid decrease in pH was observed, with a pH of 3.5 reached at the end of 10 hours and the salt rejection decreased to 61%. In this case, the water vapor flux is from 23Lm in 10 hours^-2h^-1Quickly increased to 140Lm^-2h^-1Evidence of potential damage or surface property changes of PVDF membranes upon contact with acidic feed solutions is revealed. However, when a permeable graphene film containing a PMMA binder was mixed on a PVDF film, a stable neutral pH was obtained, and an excellent stable salt rejection of 99.9% and 20Lm were observed for 72 hours of operation^-2h^-1Stable average water flux (20.5 Lm)^-2h^-1To 19.8Lm^-2h^-1). This again reveals the antifouling properties, excellent desalting ability and excellent H of the permeable graphene thin film with binder₃O⁺Filtering capability. Compared to the case of permeable graphene without PMMA binder, a water vapor flux of from 25Lm was observed^-2h^-1Slightly down to 20Lm^-2h^-1. Similarly, a basic feed solution (35 gL)^-1NaCl/0.1M NaOH, pH13) were tested on the membranes. The original PVDF MD membrane showed significant performance degradation over a short run period (20 hours). Again a rapid increase in pH was observed, reaching a pH of 9.6 at the end of 20 hours, and a rapid decrease in salt rejection from 99.9% to 53%. As with the acidic feed solution, the water vapor flux was from 23Lm in 20 hours^-2h^-1Rapidly increased to 72Lm^-2h^-1. PVDF films also show signs of surface property changes as they lose their structural integrity and severe discoloration is observed. However, when a permeable stone containing a PMMA binder is mixed on a PTFE filmWhen a graphene film was used, a stable neutral pH was obtained, and an excellent and stable salt rejection of 99.9% and 21Lm were observed for 72-hour operation^-2h^-1Stable average water flux (20.5 Lm)^-2h^-1To 21Lm^-2h^-1) Again, the antifouling properties, excellent desalting ability and excellent OH of the permeable graphene thin film with the binder are revealed^-Filterability, which is different from the case of the original PVDF membrane.

To investigate the structural integrity of the underlying membrane, the graphene thin film was peeled off the PVDF support film. The base PVDF membrane maintained its structural integrity after 72 hours of filtration of the acidic and basic feed water and was mechanically stable. More importantly, no discoloration of the base membrane was observed, with the permeable graphene of the present invention acting as an excellent protective layer for the less chemically resistant PVDF membrane. Overall, in the case of water mixtures with extreme pH (pH 2 and pH13), the binder-containing permeable graphene thin film acts as an excellent, antifouling, pH-neutralizing, long-term stable membrane in addition to protecting the chemically low-stability base membrane.

Maintaining properties of a support membrane by a chemically stable permeable graphene thin film

To further investigate the role of permeable graphene as a protective layer for supporting the membrane, a series of contact angle measurements were performed to determine changes in membrane surface properties. The MD process requires a highly hydrophobic membrane surface for efficient passage of water vapor, which is why PTFE and PVDF membranes are widely used in MD processes. The original PTFE membrane exhibited a highly hydrophobic surface, as evident by the formation of spherical droplets on the membrane surface with a high contact angle of 131 °. However, after 72 hours of MD operation, the contact angle decreased to 96 ° after testing with the acidic feed solution and to 107 ° after testing with the basic feed solution, as evidenced by the dome-shaped water drop. However, when incorporating the permeable nanochannel graphene, the contact angle of the graphene remained unchanged after the test, as did the surface properties of the underlying PTFE film, which showed clear spherical water droplets with contact angles of 121 °. To expose the underlying PTFE substrate, the graphene must be carefully scraped from the substrate. Due to the strong adhesion, graphene cannot be completely removed, which may explain the nuances of its original surface properties. These experiments clearly demonstrate the chemical stability of the permeable graphene and its role in maintaining the surface properties of the underlying membrane.

Similar effects have been observed in the case of PVDF membranes. The original PVDF film exhibited a highly hydrophobic surface with a high contact angle of 141 °. However, after 10 hours and 20 hours of testing with acidic and basic feed solutions, the contact angle of the PVDF membrane decreases sharply, down to 103 ° after testing with acidic feed water, and down to 64 ° after testing with basic feed solution. This is evidenced by the presence of dome-shaped water droplets on the membrane surface rather than the original more spherical droplets. However, when incorporating permeable graphene with a binder, post-test contact angle measurements showed 139 ° after testing with an acidic feed solution and 127 ° after testing with an alkaline feed solution and also retained the appearance of spherical water droplets on the membrane surface. These results enhance the role of the binder-containing permeable graphene in maintaining the surface properties of the less chemically resistant PVDF membrane. As in the case of the PTFE membrane above, the surface properties of the permeable graphene containing the binder are also maintained before and after the test using the acidic and basic water mixture. The chemical stability of graphene was demonstrated by performing raman area mapping ID/IG ratio on permeable nanochannel graphene samples on PTFE. Similar ID/IG ratios of 0.1 to 0.3 were observed both before and after the test, revealing that the structural properties of the permeable graphene thin films of the present invention are stable after testing with acidic or basic feed solutions. Overall, these measurements show the important role of chemically stable permeable graphene as an excellent membrane itself, as well as its role in maintaining the membrane surface properties of a less chemically stable membrane.

Without wishing to be bound by theory, it is believed that effective filtering of solvated ions in the influent water stream occurs at the grain boundary overlap of the graphene layers, which allows water to pass through, but does not allow solvated ions or larger species to pass through. The polycrystalline nature of our inventive nanochannel graphene thin films means that there are a large number of such grain boundaries, which results in a usable flux of water molecules.

Post-test SEM analysis of graphene samples showed that the graphene surface facing acidic and alkaline solutions was covered with salt particles. However, the membrane surface facing the membrane side showed a very clean graphene surface without any sign of salt on the surface, which was enhanced by EDX mapping of sodium ions on the graphene surface. This suggests that solvating ion leaching must occur at the surface of the nanochannel graphene film. To further investigate the following assumptions: the nanochannels are generated by overlapping of grain boundaries, the nanochannel graphene films form effective water channels and a desalting layer, and TEM analysis and EDX mapping are performed in the region with the overlapped grain boundaries.

TEM analysis of the post-test samples showed many regions with grain boundary overlap on the large area graphene thin film. In the regions where there is grain boundary overlap, severe accumulation of salt is observed along the grain boundaries, and the overlap regions are revealed by EDX mapping of sodium ions at the grain boundary overlap, which provides strong experimental evidence for the assumption that these boundary overlaps or mismatches serve as solvated ion filtering sites and water passing regions. Traces of other metal salts on the surface of the permeable nanochannel graphene were also observed after long runs of the MD process in acidic and basic environments, which is believed to be due to the slow dissolution of the metal alloy heating elements used to heat the feed solution.

Stable, antifouling pH removal by permeable graphene

The inventors have also discovered a number of other important advantageous features of using multi-layer graphene with nanochannels as an effective antifouling film that is stable under harsh acidic and basic conditions and can filter out solvated salt ions as well as H₃O⁺And OH^-Ions. Although there are some filtration membranes that can withstand such harsh pH conditions, those membranes can suffer damage after prolonged exposure, can exhibit poor salt rejection, and cannot obtain neutral pH water in the permeate stream.

Applicants' experiments show that even chemically resistant PTFE MD membranes are unable to neutralize the pH of feed solutions of extremely acidic or basic solutions, where long runs lead to degradation of the final membrane performance. To further investigate the ability of the graphene films of the present invention to neutralize pH in permeate streams, X-ray diffraction spectroscopy (XRD) measurements were performed experimentally and the interactions between solvate species in acidic and basic feed solutions and the nanochannel graphene films of the present invention were investigated using molecular dynamics simulations. XRD measurements of permeable nanochannel graphene on PTFE membranes were performed to determine the D-spacing of the graphene films before and after filtration. The change in D-spacing of the permeable nanochannel graphene thin films of the present invention was negligible, which explains the excellent membrane stability of the water permeation channels.

Molecular Dynamics Simulation (MDS) confirms the mechanism of water transport through overlapping grains of graphene, the antifouling properties of permeable nanochannel graphene-based membranes in acidic and alkaline environments and the filtering out of hydrated ionic species as proposed by the present invention.

Examples

Comparative example 1 non-porous graphene thin film

This example is described in the applicant's co-pending PCT/AU2016/050738 and lists a "basic" process for preparing simple high quality graphene thin films.

The growth of graphene was carried out in a thermal CVD furnace (OTF-1200X-UL, MTI Corp). A quartz tube is used. Polycrystalline Ni foil (25 μm, 99.5% or 99%, AlfaAesar) was used as the growth substrate.

Two alumina crucibles were loaded into a quartz tube. One crucible contained a carbon source, which was 0.15-0.25mL soybean oil. The other crucible contained a square (10 cm)²) The Ni foil growth substrate of (1). The two crucibles were placed in close proximity in a quartz tube. The tube is positioned so that both crucibles are within the heating zone of the furnace. The open end of the quartz tube is then sealed.

The furnace temperature was raised to 800 ℃ (30 ℃/min) followed by holding the 99.5% pure Ni foil at this temperature for 15 minutes and holding the 99% pure Ni foil at 800 ℃ for 3 minutes to form a graphene lattice. Immediately after lattice formation, the growth substrate is moved from the heating zone to a cooling zone to enable cooling at a controlled rate (50-100 ℃/min) to allow the graphene lattice to segregate from the metal substrate to form deposited graphene.

Maintaining the pressure in the tube at ambient pressure. No additional gas was introduced into the quartz tube throughout the growth process.

Once cooled to ambient temperature, the substrate was removed from the tube and the as-grown graphene thin film was analyzed using conventional techniques as described below. The visible spectral transmittance was 94.3%. In addition, raman spectroscopy indicates that graphene is formed which has a relatively low proportion of defects and is very thin (three or less thin films). These characteristics indicate that the graphene obtained from the process is of high quality.

Graphene transfer assisted with poly (methyl methacrylate) (PMMA) was used. 46mg/mL of PMMA (M)_w996,000) was spin coated onto as-grown graphene on Ni foil (1 min at 3000 rpm). The sample was then dried in the open air for 12 hours. Subsequently, the underlying Ni foil was dissolved in 1M FeCl within 30 minutes₃In (1). The PMMA/graphene film then floats to the surface. It was washed several times with deionized water. The PMMA/graphene was then removed from the deionized water bath and transferred to a glass substrate. The PMMA was then dissolved with acetone and the sample was washed repeatedly with deionized water. The separated graphene on glass was then used for subsequent microscopy and electrical characterization. This transfer method is applicable to all permeable graphene thin films made according to the present invention.

Comparative example 2-thickness controlled non-porous graphene

Graphene growth was performed as described in example 1, with modification of the amount of graphene and the cooling rate. A quartz tube is used. Polycrystalline Ni foil (25 μm, 99.5% or 99%) was used as the growth substrate.

Two alumina crucibles were loaded into a quartz tube. One crucible contains a carbon source and the other crucible contains a Ni foil growth substrate. The two crucibles were placed in close proximity in a quartz tube. The tube is positioned so that both crucibles are within the heating zone of the furnace. The open end of the quartz tube is then sealed.

The furnace temperature was raised to 800 ℃ (30 ℃/min) followed by holding at this temperature for 15 minutes on 99.5% pure Ni foil and holding at 800 ℃ for 3 minutes on 99% pure Ni foil to allow graphene lattice formation.

Immediately after the growth step, the growth substrate is moved from the heating zone to the cooling zone and cooled at a controlled rate.

Maintaining the pressure in the tube at ambient pressure. No additional gas was introduced into the quartz tube throughout the growth process. Once cooled to ambient temperature, the substrate was removed from the tube and analyzed.

Inventive example 3-nanoporous graphene

Single step ambient air growth of graphene thin films with nano-sized pores in the graphene thin film

The growth of the porous graphene film was performed in a thermal CVD furnace (OTF-1200X-UL, MTI Corp) with a quartz tube. Polycrystalline Ni foil (25 μm, 99.5% or 99%, Alfa Aesar) was used as the growth substrate. Two alumina crucibles were loaded into a quartz tube, one crucible containing the precursor (0.15-0.16 mL soybean oil) and the other containing the Ni foil growth substrate. The two crucibles were placed in the heating zone of the furnace and the opening of the quartz tube was sealed. Next, the furnace temperature was raised to 800 deg.C (30 deg.C/min), followed by annealing at 800 deg.C for 3 minutes. During the annealing stage, the pressure in the tube is maintained at atmospheric pressure. Immediately after the annealing step, the growth substrate was removed from the heating zone to enable rapid cooling (25 ℃/min), immediately after the sample was removed from the heating zone all air inside the quartz tube was removed from the chamber, and the sample was cooled in the cooling zone under vacuum. No compressed gas was introduced into the quartz tube throughout the growth process.

Synthesis of permeable graphene: compressed gas-free, ambient air CVD of polycrystalline nanochannel graphene

The growth of the nano-permeable graphene thin film was performed in a thermal CVD furnace (OTF-1200X-UL, MTICorp) with a quartz tube. Polycrystalline Ni foil (25 μm, 99%, Alfa Aesar) was used as the growth substrate. The experimental schematic is shown in figure 2. Two alumina crucibles were loaded into a quartz tube, one crucible containing the precursor (0.17mL of soybean oil) and the other containing the Ni foil growth substrate. The two crucibles were placed in the heating zone of the furnace and the opening of the quartz tube was sealed. The growth of graphene proceeds with a temperature profile of gradual heating and rapid quenching. First, the furnace temperature was raised to 800 ℃ (30 ℃/min), followed by annealing at 800 ℃ for 3 minutes. During the annealing stage, the pressure in the tube is maintained at atmospheric pressure. Atmospheric pressure is maintained in the quartz tube throughout the heating stage (200 to 800 ℃) by venting this accumulated gas through the exhaust of the tube. The gas generated by vaporizing the precursor can be circulated, creating a controlled gas environment in the tube. After the heating phase, the pressure in the quartz tube was stabilized at atmospheric pressure. No additional gas was introduced into the quartz tube throughout the growth process. Such growth processes result in the formation of polycrystalline, few to many layers of graphene sheets with a large number of grain boundaries.

After the annealing step, all air in the quartz tube was removed from the chamber and the sample was cooled under vacuum for a delay time. After this delay time, the sample was rapidly cooled from the heating zone to segregate a uniform and continuous graphene film. Due to evaporation and thermal expansion of the precursor material, a small pressure build-up is observed within the tube. However, the cooling rate was controlled at a slower cooling rate (23-20 deg.C/min). A slower cooling rate is produced by introducing a delay in the removal of the sample from the heating zone. The delay in the movement of the sample into the cooling zone creates a nanocrystalline domain, multi-layered graphene (2 to 10 layers), with mismatched graphene overlap between graphene sheets. Such mismatched overlapping creates nano-permeability in graphene. No compressed gas was introduced into the quartz tube throughout the growth process.

TEM micrographs show multi-layered graphene (nanocrystalline graphene) with many grain boundaries (the grain boundaries are represented by thin black lines in the TEM image), where many mismatched overlapping regions in the graphene thin film (deeper lines in the TEM image) represent the presence of permeable channels between graphene layers.

To perform further TEM analysis to confirm the presence of nanochannels via ambient air CVD process, via the formation of overlap of graphene domain boundaries, thinner graphene thin films (mainly monolayer to bilayer) were synthesized by using a lower precursor amount of 0.155ml while keeping the other protocol the same.

Transfer of graphene

Graphene transfer assisted with poly (methyl methacrylate) (PMMA) was used. Briefly, 46mg/mL PMMA (Mw 996,000Sigma Aldrich) was spin coated onto the as-grown graphene on Ni foil (1 min at 3000 rpm). The sample was then dried in the open air for 12 hours or on a block heater (blockheater) at 80 ℃ for 10 minutes. Subsequently, the underlying Ni foil was dissolved in 1M FeCl within 30-120 minutes as required₃In (1). The PMMA/graphene film then floats to the surface. It was washed several times with Deionized (DI) water. The PMMA/graphene was then removed from the DI water bath and transferred to a membrane substrate. The PMMA was then dissolved with acetone and the sample rinsed with DI water.

To prepare a PMMA binder/permeable graphene/PVDF film, PMMA/permeable graphene samples were removed from the DI water bath and transferred to a PVDF film substrate and washed several times with DI water and dried before use. Similarly, to prepare permeable graphene on PTFE membrane, after PMMA/permeable graphene is removed, it is transferred to PTFE membrane, followed by dissolution of PMMA with acetone. The samples were dried in the open air prior to use. The samples were rinsed with DI water. A commercially available PTFE membrane (Ningbochangqi PTFE membrane) was used to prepare the permeable graphene/PTFE membrane. To synthesize PMMA binder/permeable graphene/PVDF film, PVDF film was manufactured using an electrospinning method.

Microscopy and microscopic analysis

Using a laser excited at 514nm with Ar and having a thickness of about 1 μm²The Renishaw inVia spectrometer of (1) for detecting the spot size performs raman spectroscopy. The Burget Sensors TAP150Al-G cantilever (fR 123kHz, Q1745 and k 2.1 Nm) was used^-1Free air amplitude 100nm and feedback set point 70%) Atomic Force Microscopy (AFM) images were obtained with an ashium Research MFP-3D AFM run in intermittent contact ("tapping") mode. Scaning Probe Image Processor (SPI) manufactured by Image Metrology A/S was usedP^TM) The software performs image analysis. Energy-filtered Transmission Electron Microscopy (TEM) was performed using a JEOL2200FS TEM microscope operated at 200 kV. Optical images were obtained with an Olympus BX51 light microscope. Transmittance measurements were obtained using a Varian Cary 5000UV-Vis spectrophotometer. Using 2cm²And recording the spectrum in the wavelength range of 300-400nm to 800 nm.

Membrane distillation arrangement

Direct Contact Membrane Distillation (DCMD) was performed using closed loop laboratory scale membrane testing equipment (fig. 20). The membrane cell is made of acrylic plastic to minimize heat loss to the surrounding environment. The flow channels are cut into the two acrylic blocks that make up the feed and permeate half-cells. Each channel is 0.3cm deep, 2cm wide and 2cm long; and the total active membrane area was 4cm². The temperature of the feed and distillate solutions was controlled by two heaters/coolers (Polyscience, IL, USA) and was continuously recorded by temperature sensors inserted at the inlet and outlet of the membrane cell. Both the feed stream and the distillate stream are circulated simultaneously by two gear pumps. Simultaneous application of 30Lh to both feed and distillate^-1Same cross-flow rate (corresponding to 9cm s)^-1Cross flow velocity) in order to minimize the pressure differential across the MD membrane. The weight change of the distillate tank was recorded by an electronic balance with a data logger (Mettler Toledo, OH, USA). All of the tubes used in the DCMD test cell were covered with an insulating foam to minimize heat loss.

Experimental protocol for brine membrane distillation

The MD fouling experiments were performed using the following four types of brine and mixtures of brine and contaminants, respectively: 70gL^-1NaCl solution, 70g L^-1NaCl solution with 1mM Sodium Dodecyl Sulfate (SDS), 70g L^-1NaCl solution with 1g L^-1Mineral oil and 1mM NaHCO₃(oil emulsions were prepared by vigorously mixing using a modular homogenizer at a speed of 20,000rpm for 30 minutes) and real seawater. The comparison between mineral oil and light crude oil is set forth in the supplementary information of table S2.

Four and one liter feed volumes and distillate volumes were used, respectively. In all experiments, the inlet feed solutionThe temperature is 60 ℃; while the temperature of the distillate inlet stream was 20 ℃. A new film sample was used for each experiment. The water vapor flux was continuously recorded by a digital balance. The conductivity of the distillate was measured every 5 minutes by means of a conductivity meter (HQ14d, Hach, CO). All feed solutions were treated by DCMD for 72 hours, except for the case of mineral oil testing (which was done for 48 hours) and the case of long-term stability demonstrated with real seawater feed (which was done for 120 hours). Total Organic Carbon (TOC) was analyzed using a TOC/TN analyzer (TOC-VCSH, Shimadzu, Kyoto). The membrane surface charge was measured by a SurPASS electrokinetic analyzer (Anton Paar CmbH, Graz, Austria). The zeta potential of the membrane surface was calculated from the measured flow potential using the Fairbrother-Maastin method. All flow potential measurements were performed in a background electrolyte solution (i.e., 10mM KCl). The background solution was also used to completely rinse the cell prior to pH titration using hydrochloric acid (0.5M) or potassium hydroxide (0.5M). The surface energy of the film was calculated by measuring the contact angle using three different liquids (two polar and one non-polar) with well-known surface tensions, using the lipdemetz van der waals (non-polar) method and the lewis acid-base (polar) method.³⁶The commercial PVDF MD membrane (Durapore, pore size 0.45 μm, thickness 280 μm) experiment was carried out with the same experimental protocol as for the PTFE membrane.

Experimental protocol for membrane distillation of acidic and basic water

Experiments were performed with 2 types of water with high pH (pH 13) and low pH (pH 2) with addition of a brine mixture. By directing 35g L^-1An acidic solution (pH 2) was prepared by adding 1M sulfuric acid to the NaCl solution to reach pH 2. Similarly, by 35g L^-1An alkaline solution (pH 13) was prepared by adding a 1M NaOH solution to the NaCl solution.

Four and one liter feed volumes and distillate volumes were used, respectively. In all experiments, the inlet feed solution temperature was 40 ℃; while the temperature of the distillate inlet stream was 20 ℃. The water vapor flux was continuously recorded by a digital balance. The conductivity of the distillate was measured every 5 minutes by means of a conductivity meter (HQ14d, Hach, CO). All feed solutions were treated by DCMD for 72 hours, except for the original PVDF membrane (where conductivity and flux were significantly improved). Fresh samples were used for all experiments except for the permeable graphene/PTFE membrane test, where the first 72 hours of testing under an acidic water mixture occurred. After testing, the samples were rinsed several times with DI water before testing for 72 hours under a basic water mixture.

Conclusion

Thus, it can be seen that the present invention provides high quality nanoporous or nanochannel graphene having a plurality of pores and channels, which is capable of acting as a membrane or filter, and has advantages such as being able to use renewable low quality biomass, air at atmospheric pressure, and lower temperatures without the need for post-treatment processes to form pores.

The present invention allows for the synthesis of high quality graphene films in ambient air environments via thermal chemical vapor deposition. The absence of a vacuum chamber means that the process of the invention can be highly scaled up. Ambient air synthesis according to the present invention facilitates streamlined integration into large-scale graphene production facilities, such as roll-to-roll or batch processing required for industrial production.

The present invention allows for thermal-based synthesis to be carried out without any purified compressed feed gas (e.g., methane, hydrogen, argon, nitrogen, etc.) that is expensive and/or highly explosive. The synthesis technology of the present invention does not require any purified feed gas, but rather can utilize much cheaper carbon source materials (such as renewable biomass) as precursors for the synthesis of graphene thin films. In particular, this enables the process of the invention to be technically sustainable and also to be significantly cheaper and safer than currently available processes.

The method of the present invention is thus a safe, environmentally friendly and resource efficient graphene synthesis technique.

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