WO2019156635A1 - Graphene frameworks membranes for separation of immiscible liquids - Google Patents

Graphene frameworks membranes for separation of immiscible liquids Download PDF

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Publication number
WO2019156635A1
WO2019156635A1 PCT/SG2019/050074 SG2019050074W WO2019156635A1 WO 2019156635 A1 WO2019156635 A1 WO 2019156635A1 SG 2019050074 W SG2019050074 W SG 2019050074W WO 2019156635 A1 WO2019156635 A1 WO 2019156635A1
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graphene
metal organic
porous graphene
polymer
pda
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PCT/SG2019/050074
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French (fr)
Inventor
Hongwei Duan
Teik Thye Lim
Van Cuong MAI
Jiajing Zhou
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Nanyang Technological University
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Publication of WO2019156635A1 publication Critical patent/WO2019156635A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B01D17/0202—Separation of non-miscible liquids by ab- or adsorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B01D17/04—Breaking emulsions
    • B01D17/045—Breaking emulsions with coalescers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0211—Graphene or derivates thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/028—Molecular sieves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/028—Molecular sieves
    • B01D71/0281—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/70—Polymers having silicon in the main chain, with or without sulfur, nitrogen, oxygen or carbon only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
    • B01D71/82—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74 characterised by the presence of specified groups, e.g. introduced by chemical after-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • B01J20/205—Carbon nanostructures, e.g. nanotubes, nanohorns, nanocones, nanoballs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/223—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material containing metals, e.g. organo-metallic compounds, coordination complexes
    • B01J20/226—Coordination polymers, e.g. metal-organic frameworks [MOF], zeolitic imidazolate frameworks [ZIF]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3202—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
    • B01J20/3204—Inorganic carriers, supports or substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3214—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the method for obtaining this coating or impregnating
    • B01J20/3217—Resulting in a chemical bond between the coating or impregnating layer and the carrier, support or substrate, e.g. a covalent bond
    • B01J20/3219—Resulting in a chemical bond between the coating or impregnating layer and the carrier, support or substrate, e.g. a covalent bond involving a particular spacer or linking group, e.g. for attaching an active group
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
    • B01J20/3268—Macromolecular compounds
    • B01J20/327—Polymers obtained by reactions involving only carbon to carbon unsaturated bonds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
    • B01J20/3268—Macromolecular compounds
    • B01J20/3272—Polymers obtained by reactions otherwise than involving only carbon to carbon unsaturated bonds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3289—Coatings involving more than one layer of same or different nature
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/198—Graphene oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/219—Specific solvent system
    • B01D2323/226—Use of ionic liquids

Definitions

  • the present disclosure relates to a porous graphene composite comprising silanized graphene particles, and a graphene composite membrane comprising such a porous graphene composite.
  • the present disclosure also relates to a method of producing the porous graphene composite and the graphene composite membrane.
  • the coating layer typically alters the chemical property of a pristine surface, for example, leading to a change in surface wettability.
  • Coating on a plate-like substrate such as a superhydrophobic and superamphiphobic coating, may enhance self-cleaning ability, anti-corrosion, anti-icing, anti-fogging or anti-microbial property.
  • the coating on a substrate may form a composite also for use in separating substances.
  • membranes based on surface wetting behaviour have been developed to separate oil/water mixture
  • membranes for separation of immiscible organic liquids do not seem to have proliferated. This is because separation of immiscible organic solvents is much more complicated as the mixture contains liquids that possess surface tension very close to each other and relatively lower than that of water.
  • the wettability of a membrane may have to be systematically controlled to maintain the surface energy between two components of a liquid mixture.
  • surface wettability of a material can be controlled and tailored by changing either the surface chemistry or the surface morphology.
  • the surface chemistry of a material can be tuned by coating various low surface energy molecules on it without changing its surface topography. Meanwhile, the surface morphology can be tailored by introducing hierachical micro/nano scale porosity on the surface of the material.
  • membrane materials have also been fabricated for separation of immiscible organic liquids, which include nanofibrous membrane, rounghness- enhanced copper mesh, non-woven fabric membrane, etc. These membranes, however, are based on“re-entrant” surface topography which showed high separation efficiency but required multiple steps for fabrication and are less environmetal friendly.“Re-entrant” surface topography is formed from a structural component that is arranged in a repeated manner and each of the arranged structural components has the same morphology, such as T-shaped, mushroom- like, trapezoidal, matchstick-like, fibrous-shaped, or microspherical.
  • porous structure fabricated via ice-templating method is considered a green method where the liquid-repellency is tailored by varying the entrapped air inside the pores but this process tends to be energy intensive.
  • 3D porous graphene framework has already been used in its bulk cylindrical form for various environmental treatment applications such as, oil adsorption, water soluble contaminants removal, and use as an oil/water separation superhydrophobic membrane.
  • 3D porous graphene framework has already been used in its bulk cylindrical form for various environmental treatment applications such as, oil adsorption, water soluble contaminants removal, and use as an oil/water separation superhydrophobic membrane.
  • graphene oxide sheets tend to self-assemble into a large-scale 3D bulk structure in a homogeneous medium, the pores on their wall surface close, and this limits further surface modification of the porous graphene network for tuning of surface wettability for separation of immiscible liquids.
  • the material should at least be capable of separating immiscible liquids in a highly efficient, cost effective, energy effective manner with high throughput.
  • a porous graphene composite comprising silanized graphene particles, wherein the silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer, and wherein a layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks.
  • porous graphene particles coated with the polymer drying the porous graphene particles coated with the polymer; mixing the porous graphene particles with metal organic frameworks; and depositing a silanization agent on the porous graphene particles to form the porous graphene composite.
  • FIG. 1A is a schematic illustration of preparation of tailored superamphiphobic three dimensional (3D) silanized graphene -polydopamine-zeolitic imidazolate frameworks (GH-PDA-Z) from a graphene oxide/dopamine/ionic liquid dispersion, including the loading of metal organic frameworks nanocrystals on GH- PDA surface and modification of the resulting surface by silanization.
  • 3D three dimensional
  • FIG. 1B is a schematic illustration of the preparation of filtration membrane by drop casting silanized GH-PDA-Z on Ni foam for separation of immiscible liquids in an organic solvent mixture.
  • FIG. 2A shows a scanning electron micrograph (SEM) image of the 3D porous micron-sized GH-PDA powder. The scale bar denotes 100 mih.
  • FIG. 2B shows a SEM image of the 3D porous micron-sized GH-PDA powder of FIG. 2A at a higher magnification.
  • the scale bar denotes 10 mih.
  • FIG. 2C shows a SEM image of GH-PDA-Zi, which corresponds to an initial concentration of GH-PDA colloids at 28.6 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used.
  • the scale bar denotes 2 mih.
  • FIG. 2D shows a SEM image of GH-PDA-Z 2 , which corresponds to an initial concentration of GH-PDA colloids at 7.15 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used.
  • the scale bar denotes 2 mih.
  • FIG. 2E shows a SEM image of GH-PDA-Z3, which corresponds to an initial concentration of GH-PDA colloids at 2.86 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used.
  • the scale bar denotes 2 mih.
  • FIG. 2F shows a SEM image of GH-PDA-Z4, which corresponds to an initial concentration of GH-PDA colloids at 1.43 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used.
  • the scale bar denotes 2 mih.
  • FIG. 3A shows an optical photograph of a porous micron-sized GH-PDA colloidal powder and a cylindrical shaped bulk GH-PDA hydrogel.
  • FIG. 3B shows a SEM image of the solid state of GH-PDA colloid.
  • the scale bar denotes 2 mih.
  • FIG. 3C shows a SEM image of the solid state of GH-PDA hydrogel.
  • the scale bar denotes 2 mih.
  • FIG. 3D shows a SEM image of methanol dispersed GH-PDA hydrogel.
  • the scale bar denotes 2 mih.
  • FIG. 4A shows a SEM image of 3D porous GH-PDA after surface modification with fluorosilane. Specifically, FIG. 4A shows silanized GH-PDA. The scale bar denotes 2 mih.
  • FIG. 4B shows a SEM image of the silanized 3D porous GH-PDA of FIG. 4A at a higher magnification. The scale bar denotes 500 nm.
  • FIG. 4C shows a SEM image of silanized GH-PDA-Zi.
  • the scale bar denotes 2 mih.
  • FIG. 4D shows a SEM image of silanized GH-PDA-Z 2 .
  • the scale bar denotes
  • FIG. 4E shows a SEM image of silanized GH-PDA-Z3.
  • the scale bar denotes 2 mih.
  • FIG. 4F shows a SEM image of silanized GH-PDA-Z4.
  • the scale bar denotes 2 mih.
  • FIG. 5A shows a Fourier transform infrared (FTIR) spectra of GH-PDA, GH- PDA-Z2, silanized GH-PDA, and silanized GH-PDA-Z2 colloidal powders.
  • FIG. 5B shows the X-ray photoelectron spectra (XPS) of GH-PDA, GH-PDA-
  • silanized GH-PDA and silanized GH-PDA-Z2 colloidal powders.
  • FIG. 5C shows the X-ray diffraction (XRD) spectra of GH-PDA, GH-PDA-Z2, and silanized GH-PDA-Z2 colloidal powders.
  • the XRD spectrum of silanized GH- PDA is not shown as no peaks were observed.
  • FIG. 5D shows the Brunauer-Emmett-Teller (BET) analysis of GH-PDA, GH-
  • FIG. 6 shows a FTIR spectrum of GH-PDA colloids after washing several times with methanol.
  • FIG. 7 A shows the XPS analysis of Cls of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
  • FIG. 7B shows the XPS analysis of Ols of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
  • FIG. 7C shows the XPS analysis of Fls of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
  • FIG. 7D shows the XPS analysis of Si2p of GH-PDA, GH-PDA-Z2, silanized
  • FIG. 8A shows the energy-dispersive X-ray spectroscopy (EDS) analysis of silanized GH-PDA-Z 2 , indicating the presence of Zn atoms even after surface modification with fluorosilane. Platinum (Pt) appears in the spectrum because the material was sputtered with Pt nanoparticles for EDS analysis.
  • EDS energy-dispersive X-ray spectroscopy
  • FIG. 8B shows the EDS data of silanized GH-PDA-Z 2 , indicating the presence of Zn atoms even after surface modification of GH-PDA-Z 2 with fluorosilane. Pt appears in the data because the material was sputtered with Pt nanoparticles for EDS analysis.
  • FIG. 9 shows the XRD of ZIF-8 nanoparticles before and after heat treatment at 200°C for 10 mins.
  • the durability of ZIF-8 nanoparticles at high temperature is tested by heating the particles in a chamber at 200°C for 10 mins.
  • the crystal lattice of ZIF-8 stays unchanged after heat treatment. This result supports the durability of ZIF- 8 nanoparticles structure during surface modification at high temperature.
  • FIG. 10B shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Zi.
  • FIG. 10C shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z 2 .
  • FIG. 10D shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z3.
  • FIG. 10E shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z4.
  • FIG. 11 shows the advancing contact angle (images in top row) and receding contact angle (images in bottom row) of 3 pL formamide droplet on the surface of silanized GH-PDA, silanized GH-PDA-Zi, silanized GH-PDA-Z 2 , silanized GH- PDA-Z3, and silanized GH-PDA-Z4, all of which are coated on a glass slide (left to right).
  • FIG. 12A shows a plot of the static contact angle of glycerol (Gly), formamide (FM), ethylene glycol (EG), and n-hexane (Hex), on the surface of silanized GH- PDA-Z 2 coated glass over 100 days.
  • FIG. 12B shows a plot of the static and sliding contact angles of a water droplet on the surface of silanized GH-PDA-Z 2 coated glass over 100 days.
  • FIG. 12C shows the static contact angle of glycerol, formamide, ethylene glycol, and n-hexadencane (HDC) on the surface of silanized GH-PDA-Z 2 coated glass at different temperatures.
  • FIG. 12D shows the static and sliding contact angles (CA) of a water droplet on the surface of silanized GH-PDA-Z 2 coated glass at different temperatures.
  • FIG. 14A shows a SEM image of bare Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
  • FIG. 14B shows a SEM image of silanized Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
  • FIG. 14C shows a SEM image of silanized GH-PDA-Z 4 coated Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
  • FIG. 14D shows a plot of the static contact angle of different surface tension liquid droplets on surface of bare Ni foam, silanized Ni foam and silanized GH-PDA- Z 4 coated Ni foam.
  • FIG. 15A shows a plot of the efficiency of separating carbon tetrachloride from different polar solvents, wherein the separation efficiency with respect to each different polar solvent is represented by the respective bars.
  • GLY represents glycerol
  • FM represents formamide
  • EG represents ethylene glycol.
  • the efficiency is calculated by volume percentage of passing liquids.
  • FIG. 15B shows a plot of the efficiency of separating formamide from non polar solvents, wherein the separation efficiency with respect to each different non polar solvent is represented by the respective bars.
  • CF represents chloroform
  • CTC represents carbon tetrachloride
  • DEE represents diethyl ether
  • PTE represents petroleum ether
  • HEX represents n-hexane. The efficiency is calculated by volume percentage of passing liquids.
  • FIG. 15C shows the calculated flux through the membrane for formamide separated from different non-polar solvents.
  • FIG. 15D shows a plot of the re-generation and filtration flux of membrane using formamide and chloroform after 20 cycles.
  • FIG. 16A shows the optical images (Ai to A 3 ) for separation of formamide (FM)/chloroform (CF) mixture with bare Ni foam.
  • Formamide is colored by methylene blue (denoted by FM).
  • FIG. 16B shows the optical images (Bi to B 3 ) for separation of FM/CF mixture with silanized GH-PDA-Z 2 coated Ni foam.
  • Formamide is colored by methylene blue (denoted by FM).
  • FIG. 16C shows the optical images (Ci to C 3 ) for separation of FM/CF mixture with silanized GH-PDA-Z 4 coated Ni foam.
  • Formamide is colored by methylene blue (denoted by FM).
  • FIG. 17A shows an optical photograph of separation of chloroform/formamide mixture using silanized Ni foam as the separation membrane. First, formamide (FM) stays on top and chloroform (CF) stays at bottom.
  • FIG. 17B shows an optical photograph where the mixture of FM and CF is poured through the separation membrane.
  • FIG. 17C shows an optical photograph where the FM stays on top with the separation membrane while CF passes through the separation membrane.
  • FIG. 17D shows an optical photograph where more of the liquid mixture is poured through, and a part of FM penetrates through the membrane due to intrusion pressure.
  • FIG. 18A shows an optical photograph of separation of n-hexane/formamide mixture using silanized GH-PDA-Z 4 coated Ni foam as the separation membrane.
  • n-hexane HEX
  • FM formamide
  • FIG. 18B shows an optical photograph where the mixture of HEX and FM is poured through the separation membrane.
  • FIG. 18C shows an optical photograph where the FM stays on top with the separation membrane while HEX quickly passes through the separation membrane.
  • FIG. 18D shows an optical photograph with complete separation of HEX
  • FIG. 19A shows an optical photograph of separation of n-hexane/formamide mixture using silanized GH-PDA-Z 2 coated Ni foam as the separation membrane.
  • n-hexane (HEX) stays on top of formamide (FM).
  • FIG. 19B shows an optical photograph where the mixture of HEX and FM is poured through the separation membrane.
  • FIG. 19C shows an optical photograph where the FM stays on top with the separation membrane while HEX quickly passes through the separation membrane.
  • FIG. 19D shows an optical photograph with complete separation of HEX and FM.
  • FIG. 20A shows a SEM image of silanized GH-PDA-Z 2 coated Ni foam membrane.
  • the scale bar denotes 100 pm.
  • FIG. 20B shows a SEM image of the silanized GH-PDA-Z 2 coated Ni foam membrane of FIG. 20A at a higher magnification.
  • the scale bar denotes 50 pm.
  • FIG. 21 A illustrates the filtration efficiency of n-hexane from water, glycerol, formamide, and ethylene glycol using silanized GH-PDA-Z 2 coated Ni foam.
  • FIG. 21B illustrates the regeneration of the membrane with a testing sample of n-hexane/formamide mixture.
  • FIG. 22 shows the ultraviolet-visible light (UV-Vis) spectra of methylene blue dyed formamide at different organic dye contents and filtrates after separation of mixture between formamide and low surface tension solvents using silanized GH- PDA-Z 4 coated Ni foam membrane.
  • the different solvents used for this include chloroform, carbon tetrachloride, diethyl ether, petroleum ether, and n-hexane.
  • the present disclosure provides for a porous graphene composite comprising silanized graphene particles, and a method of producing such a porous graphene composite.
  • the present disclosure also provides for a graphene composite membrane comprising the porous graphene composite, and a method of making such a graphene composite membrane.
  • composite refers to a material formed from two or more different components, and having a functional and/or a structural property that is different from that of the individual components.
  • the porous graphene composite is advantageous because it can be used in the separation of immiscible liquids, even those that have comparable surface tensions.
  • the immiscible liquids may be a mixture containing two or more immiscible liquids.
  • the term“immiscible” as used herein refers to two or more liquids that do not chemically react with one another and maintain their distinct phases even when they are mixed with one another.
  • An example to illustrate this may be a water/oil mixture. Even when water and oil are mixed, there is no chemical reaction between water and oil. Both water and oil maintain their distinct water phase and oil phase, respectively.
  • the present porous graphene composite is usable for separating immiscible liquids, it may be described as an open pore superamphiphobic three-dimensional micron-sized graphene frameworks.
  • superamphiphobic refers to a material with low affinity (or high repellency) for water as well as for liquids of high surface tension. That is to say, a superamphiphobic surface can repel both water and oils with a contact angle higher than 150°.
  • the surface tension of the oil may be at least 30 mN/m (e.g. n-hexadecane). Meanwhile, an amphiphobic surface only exhibits a contact angle that is lower than 150° but higher than 90° for both water and oils.
  • the porous graphene composite may be coated onto a porous substrate to form a graphene composite membrane.
  • a substrate may even be a metal foam, such as but not limited to, a nickel foam.
  • the coated nickel foam as a non-limiting example, can be used to demonstrate the effective separations of immiscible organic liquids, and the present method of forming such a porous graphene composite and the graphene composite membrane are shown, by way of an example, in FIG. 1A and 1B, respectively.
  • the micron-sized graphene frameworks with open pore was constructed using an ionic liquid (IL) and a polymer precursor, such as dopamine.
  • ionic liquid refers to a salt in which the ions are poorly coordinated, thereby resulting in a liquid having a boiling point below l00°C, or even at room temperature (i.e. room temperature ionic liquid).
  • room temperature ionic liquid In an ionic liquid, at least one ion has a delocalized charge and one component is organic, which prevents the formation of a stable crystal lattice.
  • polymer precursor refers to a compound convertible to form a polymer.
  • the surface wettability and surface energy of the graphene frameworks were tuned based on the surface tension of the immiscible liquids that are to be separated, by controlling the wall thickness of the graphene frameworks, which in turn defines the pore diameters of the porous graphene composite and the resultant membrane, by loading of metal organic frameworks (MOFs) and subsequent surface modification with a silanization agent, e.g. a fluorosilane of 1H,1H,2H,2H- perfluorodecyltriethoxysilane, to further lower the surface energy of the resultant porous graphene composite.
  • MOFs metal organic frameworks
  • a silanization agent e.g. a fluorosilane of 1H,1H,2H,2H- perfluorodecyltriethoxysilane
  • metal organic frameworks refers to compounds consisting of metal ions or clusters coordinated to organic ligands to form one-, two-, or three dimensional structures.
  • pore diameter refers to the maximal length of a line segment passing through the centre and connecting two points on the periphery of a pore.
  • the present porous graphene composite can also be coated onto a non-porous substrate to demonstrate that it can form a protective coating with self-cleaning, anti corrosion, anti-icing, anti-fogging and/or anti-microbial property, as it prevents materials from seeping through.
  • a protective coating with self-cleaning, anti corrosion, anti-icing, anti-fogging and/or anti-microbial property, as it prevents materials from seeping through.
  • Such an advantage may be demonstrated by depositing the present porous graphene composite onto a glass substrate.
  • the superamphiphobic graphene coated glass also demonstrates how surface wettability depends on the change in surface topography.
  • the present porous graphene composite and the present method described herein offer a solution of using porous graphene for both surface coating and separation of immiscible organic liquids, which are scalable and provide for fabrication of devices for efficient coating and separation of immiscible liquids, which are in turn promising for applications in the industrial and environmental sectors.
  • a porous graphene composite comprising silanized graphene particles, wherein the silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer, and wherein a layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks.
  • the term“particles” as used herein refers to granules, fibers, flakes, spheres, powders, platelets and other forms and shapes, which may be regular or irregular.
  • the term“particles” also includes references to a cluster or agglomerate formed from several particles, and such clusters or agglomerates may be referred to as a“framework”.
  • the polymer may comprise a catechol group.
  • the polymer is derived from the polymer precursor which also comprises the catechol group.
  • the polymer precursor may comprise a catechol group according to various embodiments.
  • both the polymer and the polymer precursor may comprise a catechol group. There may be more than one catechol group on the polymer and the polymer precursor.
  • Examples of the polymer precursor may include dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, epigallocatechin, etc., and accordingly, examples of the polymer may include polydopamine or a polymer generated from tannic acid, 1,2- dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, epigallocatechin, etc.
  • the polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
  • Other polymer precursor, which can reduce graphene oxide to graphene and form a polymer coating on the graphene may be used.
  • the metal organic frameworks may comprise zeolitic imidazolate (or imidazole) frameworks (ZIF) (e.g. ZIF-8), zirconium- 1,4 benzodicarboxylic acid (UIO-66), iron-2,6 naphthalenedicarboxylic acid (MIL-88), nickel-zinc based metal organic frameworks (e.g. ZIF-9, ZIF-67, Ni-ZIF-8), or zinc e benzodicarboxylic acid (MOF-5).
  • ZIF zeolitic imidazolate
  • IAO-66 zirconium- 1,4 benzodicarboxylic acid
  • MIL-88 iron-2,6 naphthalenedicarboxylic acid
  • MIL-88 nickel-zinc based metal organic frameworks
  • MOF-5 zinc e benzodicarboxylic acid
  • the amount of metal organic frameworks coated on the porous graphene particles and/or the polymer may be based on the graphene content present in the porous graphene particles.
  • the metal organic frameworks may be present in an amount based on the graphene content of the porous graphene particles according to various embodiments.
  • the graphene content may be less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks.
  • the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks. In some embodiments, the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks. Further advantageously, using the graphene content with respect to the amount of metal organic frameworks allows for concentration-induced nucleation and growth of the metal organic frameworks on the graphene particles and/or the polymer, which circumvents pH-induced methods for controlling coating density and wall thickness of the metal organic frameworks.
  • the one or more layers of crystals may have a thickness of 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 10 nm or less, etc.
  • This thickness refers to the wall thickness of the porous graphene particle.
  • the porous graphene particles may be coated with a polysiloxane, such that the surface of the porous graphene particles may be disposed with a thin layer of polysiloxane.
  • the thin layer of polysiloxane helps to modify the surface chemistry of the porous graphene particles without altering the porosity (i.e. pore sizes) of the porous graphene particles.
  • the polysiloxane may help to increase oleophobicity of the resultant porous graphene composite to enhance separation of the immiscible liquids and prevent certain liquids from seeping through in order to provide the self-cleaning, anti-corrosion, anti-icing, anti-fogging and/or anti-microbial property.
  • the polysiloxane may be formed by depositing a layer of silanization agent, such as a fluorosilane, on the porous graphene particles comprising the polymer and the metal organic frameworks.
  • the polysiloxane may bind to the catechol groups of the polymer by covalent interactions.
  • the polysiloxane may also bind to the metal organic frameworks by covalent interactions, as the polysiloxane comprises one or more Si-OH groups that can form covalent bonding with the metal organic frameworks and their crystals.
  • the layer of polysiloxane may be covalently attached to the metal organic frameworks or the catechol group and the metal organic frameworks.
  • the present disclosure also describes a method of producing the porous graphene composite.
  • the method may comprise contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group, drying the porous graphene particles coated with a polymer, mixing the porous graphene particles with metal organic frameworks, and depositing a silanization agent on the porous graphene particles to form the porous graphene composite.
  • contacting the graphene oxide may comprise adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid. Addition of the polymer precursor helps to reduce the graphene oxide to graphene, and the polymer precursor converts to a polymer coating the graphene.
  • Other polymer precursor that reduces graphene oxide to graphene and forms a polymer coating the graphene may be used.
  • Such a polymer precursor may be termed a reducing agent in the present disclosure as it reduces the graphene oxide to graphene.
  • the aqueous solution may comprise or consist of water.
  • the aqueous solution may be a mixture of water and alcohol, such as a water-ethanol solution.
  • An aqueous solution may be used as both graphene oxide and the polymer precursor (e.g. dopamine) can be dissolved therein to obtain a homogeneous solution before adding the ionic liquid, so as to have the ionic liquid uniformly mixed into the homogeneous solution.
  • the polymer precursor e.g. dopamine
  • the polymer precursor having the catechol group may comprise dopamine, tannic acid, l,2-dihydroxylbenzene, 1,2,3- trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
  • the catechol group present in the polymer precursor is also present on the polymer coating the graphene.
  • the polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, 1,2,3- trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin, in various embodiments.
  • an ionic liquid may be added.
  • the aqueous solution containing the graphene oxide particles after being added with the polymer precursor and ionic liquid, may be heated to a temperature ranging from 75°C to 95°C for about 12 hours, and such an aqueous solution may be, freeze-dried as an example, to obtain a collodial powder of the porous graphene particles coated with the polymer.
  • the ionic liquid may be coated onto the graphene particles and/or the polymer.
  • the ionic liquid stabilizes the porous graphene particles and prevents the porous graphene particles from disintegrating when the porous graphene particles are redispersed into a liquid.
  • the ionic liquid may comprise l-butyl-3- methylimidazolium tetrafluoroborate.
  • Other ionic liquids that may be used include 1- butyl-3-methylimidazolium hexafluorophosphate, l-butyl-3-methylimidazolium methanesulfonate, l-butyl-3-methylimidazolium tetrachloroaluminate, l-butyl-3- methylimidazolium thiocyanate, l-butyl-3-methylimidazolium acetate, l-butyl-3- methylimidazolium chloride, l-butyl-3-methylimidazolium hydrogen sulfate, etc.
  • Drying of the porous graphene particles coated with the polymer may be performed in various embodiments.
  • the porous graphene particles are dried before mixing with the metal organic frameworks because the drying induces p-p bonding of GH-PDA, thereby helping the porous graphene particles maintain their structure when redispersed in an alcohol, such as methanol, for mixing with the metal organic frameworks.
  • the colloidal powder of porous graphene particles may be redispersed in an alcohol containing metal organic frameworks precursors that form the metal organic frameworks.
  • mixing of the porous graphene particles with the metal organic frameworks may be carried out in the presence of an alcohol.
  • the alcohol may comprise methanol, ethanol, or isopropanol. Alcohol is used as it is a solvent that helps in developing crystals of the metal organic frameworks on the porous graphene particles.
  • the metal organic organic frameworks precursors depend on the metal organic frameworks to be coated on the porous graphene particles and/or the polymer.
  • the metal organic frameworks may comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc e benzodicarboxylic acid.
  • the metal organic frameworks precursors may comprise a mixture of zinc nitrate and 2-methyl imidazole.
  • mixing of the porous graphene particles may comprise mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles.
  • the graphene content may be less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks.
  • the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks.
  • the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks.
  • Advantages of coating metal organic frameworks based on the graphene content have already been explained above. For instance, using the graphene content with respect to the amount of metal organic frameworks advantageously allows for concentration-induced nucleation and growth of the metal organic frameworks on the graphene particles and/or the polymer, which circumvents pH-induced methods for controlling coating density and wall thickness of the metal organic frameworks.
  • the mixing of the porous graphene particles and the metal organic frameworks, and/or the metal organic frameworks precursors may include overnight stirring. After stirring, a colloidal powder of the porous graphene particles, now coated with the polymer and the metal organic frameworks, may be obtained by any suitable forms of drying, e.g. freeze-drying.
  • the present method may include depositing a silanization agent onto the porous graphene particles, the polymer, and/or the metal organic frameworks.
  • the depositing of a silanization agent may comprise mixing the porous graphene particles with the silanization agent.
  • the silanization agent may form a layer of polysiloxane on the porous graphene particles, the polymer, and/or the metal organic frameworks. Advantages of having a layer of polysiloxane coated thereon, and hence the use of a silanization agent, have already been described above.
  • the silanization agent may comprise a fluorosilane comprising lH,lH,2H,2H-perfluorodecyltriethoxysilane.
  • fluorosilane that may be used includes lH,lH,2H,2H-perfluorooctyltriethoxy silane, 1H,1H,2H,2H- perfluorohexyltriethoxysilane, etc.
  • the wetting behavior may be tuned using different fluorosilane due to the different chain length of the fluorosilane.
  • the present disclosure also provides for a graphene composite membrane used in the separation of immiscible liquids, wherein the graphene composite membrane may comprise the porous graphene composite that has already been described above.
  • Embodiments described in the context of the present porous graphene composite and the method of producing the present porous graphene composite are analogously valid for the present graphene composite membrane described herein, and vice versa.
  • the graphene composite membrane may be obtained by depositing the present porous graphene composite onto a substrate. Any suitable means of deposition may be used.
  • the porous graphene composite may be coated on a substrate.
  • the substrate may comprise a glass, a metal foam, a cellulose paper, or polyurethane.
  • the graphene composite membrane may be used in separating immiscible liquids.
  • the immiscible liquids may have different surface tension.
  • the graphene composite membrane can separate two immiscible liquids having comparable surface tensions, wherein the difference in surface tension may be as low as 2.3 mN/m.
  • the present disclosure further provides for a method of producing a graphene composite membrane.
  • a method may include the steps of producing the porous graphene composite.
  • such a method may comprise contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group, drying the porous graphene particles coated with the polymer, mixing the porous graphene particles with metal organic frameworks, depositing a silanization agent on the porous graphene particles to form the porous graphene composite, and coating a substrate with the porous graphene composite to form the graphene composite membrane.
  • contacting the graphene oxide may comprise adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid.
  • the polymer precursor may comprise dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
  • the polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
  • the ionic liquid may comprise 1 -butyl-3 -methylimidazolium tetrafluoroborate.
  • Other ionic liquids that may be used have already been described above.
  • Advantages of the polymer precursor, the polymer coated on the porous graphene particles, and the ionic liquid, have already been mentioned above when describing embodiments of the present porous graphene composite, the present graphene composite membrane, and the present method of producing the porous graphene composite.
  • mixing of the porous graphene particles may comprise mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles.
  • the graphene content is less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks.
  • the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks.
  • the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks.
  • the metal organic frameworks may comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc- 1,4 benzodicarboxylic acid.
  • the mixing of the porous graphene particles with the metal organic frameworks may be carried out in the presence of an alcohol in various embodiments.
  • the alcohol may comprise methanol, ethanol, or isopropanol.
  • depositing of a silanization agent may comprise mixing the porous graphene particles with the silanization agent.
  • the silanization agent may comprise a fluorosilane comprising 1H,1H,2H,2H- perfluorodecyltriethoxysilane. Other fluorosilane that may be used has already been discussed above.
  • the silanization agent may form a layer of polysiloxane on the porous graphene particles, the polymer, and the metal organic frameworks. Advantages of forming a layer of polysiloxane, and hence the use of the silanization agent, have already been described above.
  • the porous graphene composite as described above may be deposited onto a substrate, wherein the substrate may comprise a glass, a metal foam, a cellulose paper, or polyurethane.
  • the graphene composite membrane may be used as a protective coating with self-cleaning, anti corrosion, anti-icing, anti-fogging and/or anti-microbial property, as it prevents materials from seeping through.
  • the graphene composite membrane may be used in separation of immiscible liquids.
  • the word“substantially” does not exclude“completely” e.g. a composition which is“substantially free” from Y may be completely free from Y. Where necessary, the word“substantially” may be omitted from the definition of the invention.
  • the articles“a”,“an” and“the” as used with regard to a feature or element include a reference to one or more of the features or elements.
  • the term“about” or“approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.
  • the present disclosure relates to a composite, a composite membrane comprising the composite, and methods of making both the composite and composite membrane.
  • the membrane can also be used as a coating for anti-corrosion prevention and/or a coating that provides for an anti-microbial surface due to its superamphiphobic and superhydrophobic property.
  • Example 1 Materials
  • HDC n-hexadecane
  • CF chloroform
  • DCM dichloromethane
  • MeOH methanol
  • EtOH ethanol
  • Graphene oxide was prepared from natural graphite powder via modified Hummer’s method. Briefly, the solid mixture of P2O5 and K2S2O8 was dissolved completely in concentrated H2SO4 at 80°C. 12 g of natural graphite was then added accordingly. The mixture was kept stirring for 8 hours followed by cooling down to room temperature and diluted by 2 L of deionized (DI) water. The supernatant was then decanted and washed several times until pH level of the liquid reached to 7. Final product was dried in air at l00°C for 12 hours.
  • DI deionized
  • Example 3 Preparation of Graphene-Polydopamine (GH-PDA) Colloid
  • Example 4 Preparation of Graphene-Polydopamine-Zeolitic Imidazolate Framework (GH-PDA-Z)
  • GH-PDA colloidal powder was dispersed in a mixture of MID (60 mM) and Zn(N0 3 ) 2 (30 mM), which were dissolved in methanol with different concentrations of graphene.
  • the mixture of GH-PDA colloid and ZIF-8 precursors was mixed overnight under stirring.
  • the composite product was finally centrifuged at 6000 rpm in 10 mins and washed several times with methanol.
  • Example 5 Surface Modification of GH-PDA, GH-PDA-Z and The Coating Procedure
  • GH-PDA colloidal powder was mixed with 50 pL of PFDTS in a small vial.
  • the vial which was covered by an aluminum paper, was then placed in an oven at 200°C for 10 mins.
  • silanized GH-PDA was dispersed again in ethanol and then drop cast on substrates, e.g. glass (1.5 cm xl.5 cm) or Ni foam (1.5 cm x 1.5 cm).
  • substrates e.g. glass (1.5 cm xl.5 cm) or Ni foam (1.5 cm x 1.5 cm). Coated substrates were dried at 50°C for several days followed by additional drying at l00°C for 1 hour. The same procedure was applied for GH-PDA- Z samples.
  • various simple mixtures of formamide and another low surface tension solvent, such as chloroform, carbon tetrachloride, diethyl ether, petroleum ether, and n-hexane were poured through a funnel-liked silanized GH-PDA-Z 4 coated Ni-foam, respectively (FIG. 15B and 15C). Control experiments such as filtration using bare Ni foam and silanized GH-PDA-Z 2 coated Ni foam also are conducted using a mixture of formamide and chloroform.
  • V in litres
  • Vj and V 2 are the volume of collected oil and the volume absorbed by the membrane, respectively.
  • the filtration flux is calculated by following expression:
  • Example 8 Summary of Present Method and Discussion
  • the method disclosed herein provides for the preparation of an open pore, superamphiphobic 3D micron-sized graphene frameworks with fine surface tunability.
  • the material was coated on both flat and porous substrates, such as a glass and a nickel (Ni) foam (FIG. 1B), respectively.
  • the superamphiphobic graphene coated glass was used to demonstrate how surface wettability depends on the change in surface topography.
  • the coated Ni foam demonstrates the effective separation of immiscible organic liquids mixtures.
  • FIG. 1A micron-sized graphene frameworks with open pores were fabricated using ionic liquid (IL).
  • the surface wettability and surface energy of the graphene frameworks were tuned according to the surface tension of the immiscible liquids by precisely controlling its wall thickness and/or the pore diameter via metal organic frameworks (MOFs) loading, followed by surface modification with low surface energy PFDTS.
  • MOFs metal organic frameworks
  • the present method offers an advantageous solution of using porous graphene for both the surface coating and the separation of immiscible organic liquid mixtures.
  • the present method is also scalable and provides for fabrication of devices for efficient coating and separation of immiscible liquids, and hence, is promising for the industrial and environmental sectors.
  • Example 9 Results and Discussion - Fabrication of Graphene/MQFs Building Block and Tailored Surface Repellency Coatings
  • FIG. 1A The strategy of fabricating superamphiphobic 3D porous graphene framework membrane is illustrated in FIG. 1A.
  • an ionic liquid was added to an aqueous dispersion of GO and DA to create an open pore 3D micron-sized PDA- coated graphene frameworks (GH-PDA).
  • GH-PDA open pore 3D micron-sized PDA- coated graphene frameworks
  • the surface topography of the graphene frameworks was tuned by controlling the coated wall thickness, and hence the pore diameter, via deposition of various amount of porous crystalline metal organic frameworks (MOFs) to form GH-PDA-Z.
  • MOFs porous crystalline metal organic frameworks
  • both GH-PDA and GH-PDA-Z frameworks were modified by coating a thin layer of low surface energy fluorosilane.
  • the porous silanized graphene/MOFs composite materials were then drop cast on glass and Ni foam to fabricate the tailored superamphiphobic coating for surface wettability investigation and studies for the membrane separation of immiscible liquids, respectively.
  • the colloidal particles When the ionic liquid was added to the colloidal dispersion of GO and DA, the colloidal particles agglomerate to form macro-clusters, and an aqueous percolating network containing colloidal suspension of GO and DA surrounded by the ionic liquid molecules is formed. This is due to neutralization of the surface charges of colloidal particles by the ions carrying opposite charge from the ionic liquid, leading to de- stabilization of colloidal suspension of graphene oxide in a water/ionic liquid mixture. Then, the colloidal mixture was heated overnight at 90 C when GO is reduced by DA, to form 3D GH-PDA hydrogel particles inside the colloidal agglomerates.
  • GH-PDA colloidal hydrogel was then filtered and freeze-dried to obtain an open pore micro sized light-weight powder which retains its porous structure while being dispersing in methanol under mild sonication (FIG. 2A and 2B).
  • SEM images of both the freeze- dried GH-PDA samples show 3D porous structures (FIG. 3B and 3C)
  • the bulk GH- PDA hydrogel completely loses its 3D porous structure when redispersing in methanol with sonication (FIG. 3D).
  • the 3D porous network of bulk GH-PDA sample was broken down inside its bulk structure due to the ultrasonic energy, whereas, the 3D open porous structure of GH-PDA formed inside the micron-sized small colloidal clusters remains stable via p-p interactions and cation-p bonding between the ionic liquid and graphitic carbon skeleton.
  • the surface topography of the 3D porous micron-sized GH-PDA frameworks was precisely tuned by depositing varying amount of porous crystalline MOFs on the surface of GH-PDA colloids.
  • MOFs zeolite (i.e.
  • ZIF-8 zeolitic) imidazole (or imidazolate) frameworks
  • PDA polydopamine
  • ZIF-8 nanoparticles were successfully deposited on the surface of GH-PDA by simple mixing of porous GH-PDA powder and a methanol solution of MOFs precursors (FIG. 2C to 2F).
  • the coating density and coated wall thickness of ZIF-8 on 3D porous GH-PDA colloids are highly dependent on the weight percent of graphene used.
  • This concentration-induced nucleation and growth of ZIF-8 nanocrystals is very useful for controlling the coating density and coated wall thickness of ZIF-8 on the surface of 3D porous GH-PDA frameworks besides pH-induced size distribution of ZIF-8. Therefore, the surface topography of 3D porous GH-PDA frameworks is tunable by controlling the pore diameter with varying coated wall thickness via deposition of various amounts of porous crystalline ZIF-8 particles on it.
  • the surface chemistry needs to be tailored to control the wettability of 3D porous GH-PDA frameworks.
  • Surface chemistry can be tailored by applying a thin low surface energy molecular coating layer on the surface of the material.
  • a thin coating layer of fluorosilane was applied onto the surface of the 3D porous GH-PDA-Z frameworks, which binds to the catechol groups of PDA via covalent interactions and strongly interacts with ZIF-8 particles.
  • FIG. 4A to 4F are SEM images for demonstrating ZIF-8 loaded 3D graphene frameworks after silanization, named as silanized GH-PDA-Z frameworks. It is to be noted FIG. 4A and FIG. 4B show silanized GH-PDA without loading of ZIF-8 nanoparticles.
  • the thin molecular coating layer of fluorosilane does not change the macroscale porosity of graphene skeletons.
  • the surface chemistry of GH-PDA- Z frameworks can be tailored without changing the surface topography.
  • an exemplary sample GH-PDA-Z 2 was chosen among other ZIF-8 loaded GH-PDA samples.
  • the observed additional peaks in the spectral region of 500 cm 1 to 1350 cm 1 and the humps in between 1350 cm 1 to 1500 cm 1 assigned to the respective plane bending and stretching of imidazole ring confirmed the successful ZIF-8 deposition on graphene framework.
  • the small peak at 1584 cm 1 corresponding to the stretching vibration of C-N from imidazole and peaks for aromatic and aliphatic C-H stretch at 2929 cm 1 and 3135 cm 1 further confirmed the ZIF-8 coating on GH-PDA.
  • a new peak at 1214 cm 1 corresponds to the covalent C-F bonds as well as the peaks at 778 cm 1 and 1075 cm 1 correspond to the bending and stretching vibration of Si-O-Si, respectively, which confirmed the successful modification of GH-PDA and GH-PDA-Z 2 frameworks by fluorosilane.
  • compositional changes of porous graphene before and after loading with ZIF-8 particles and further modification by fluorosilane are characterized by X-ray photoelectron spectroscopy (XPS) as shown in FIG. 5B and FIG. 7A to 7E. While the peaks of Cls, Nls and Ols are observed for GH-PDA colloids, a new peak of Zn2p is observed for the GH-PDA-Z 2 sample, indicating the presence of ZIF-8 coating on its surface.
  • the XPS spectra of silanized GH-PDA and GH-PDA-Z 2 show additional peaks of Fls and Si2p indicating the successful surface modification of graphene frameworks by fluorosilane.
  • the BET surface area of GH-PDA-Z 2 increases to 646.36 m 2 g _1 due to the combined contribution coming from micropores of ZIF-8 particles and mesopores of graphene.
  • the surface area of both silanized GH-PDA colloid and GH-PDA-Z 2 decreases sharply to 15.60 m 2 g _1 and 24.63 m 2 g _1 , respectively.
  • silanized GH-PDA colloid displayed the best ability to repel these solvents, exhibiting contact angle of more than 146 ° as compared to GH-PDA-Z colloidal frameworks.
  • the repellency dropped sharply in the case of silanized GH-PDA-Z4 as shown by the decrease in contact angles which are less than 150 ° with all polar solvents.
  • Silanized GH-PDA-Z4 therefore, shows the lowest contact angles for all solvents compared to other samples.
  • silanized GH-PDA-Z4 does not show super-repellency for high surface tension solvents, displaying 0 ° contact angle of all non-polar solvents, i.e. lower ability to repel low surface tension liquids.
  • silanized GH-PDA to silanized GH-PDA-Z3 showed super- repellence for FM with small difference between advancing and receding contact angle whereas silanized GH-PDA-Z4 displayed a large difference (FIG. 11). This result reveals lesser amount of air entrapment inside the pores of silanized GH-PDA- Z 4 compared to former surfaces due to thicker wall coating.
  • the durability of coating surfaces over time and temperature was also studied via contact angle measurements on silanized GH-PDA-Z2, which was taken as an exemplary sample.
  • the static contact angle values of both high as well as low surface tension solvents remained unchanged at more than 150 ° and at nearly 0 ° , respectively, over 100 days (FIG. 12A).
  • Example 10 Results and Discussion - Dependence of Super-Repellency on Surface Structure
  • porous structure is formed mostly by assembly of 2D materials and/or ice-templation of cross-linked 2D materials. Therefore, it is more complicated to investigate effect of structure parameters to surface wettability.
  • pore height (H) of porous coating structure has been considered as the main factor causing transition from superamphiphobicity to quasi- superamphiphobicity corresponding to Cassie-Baxter to Wenzel transition.
  • Cassie-Baxter model represents a metastable state.
  • FIG. 13A and 13B illustrate how the change of wall thickness affects the volume of air trapped leading to the change in surface repellence of liquids droplet.
  • GH-PDA-Z 4 is much smaller than 150°, implying the transition from Cassie-Baxter state to Wenzel state. These values indicate that presence of smaller air fraction in silanized GH-PDA-Z 2 and silanized GH-PDA-Z 4 creates less oleophobicity compared to silanized GH-PDA. This is obvious when either nanoscale porosity or microscale is dominant compared to each other in the hierarchical structure.
  • Laplace pressure is considered as the driving force, because it causes the contact line to move downward making the curve at solid/liquid/air interface (FIG. 13A and 13B).
  • Laplace pressure, AP Lap is proportional to curvature of liquid (K) which is, however, inversely proportional to the radius of a curved surface.
  • Example 11 Results and Discussion - Surface Coating and Separation of Immiscible Liquids Mixture
  • the filtration membrane was made by drop casting silanized GH-PDA-Z 4 on Ni foam to separate simple mixture of immiscible solvents.
  • the layers of silanized GH-PDA-Z 4 not only decreases the surface energy of Ni foam but also helps to increase its surface roughness.
  • the increase in surface roughness strengthens the repellence of liquid if the contact angle is higher than the intrinsic value or allow the liquid to penetrate if the contact angle is lower than the intrinsic value.
  • the intrinsic value refers to the minimum contact angle on a flat surface of which lower than that value, liquids can penetrate through the surface if surface roughness is increased. In case of contact angle higher than intrinsic value, the liquids can be retained on the surface if surface roughness is increased.
  • silanized GH-PDA-Z4 coated Ni foam only shows lyophobicity up to n-hexadecane (27.5 mN/m) with contact angle of 80.5+1.5°, while it shows superlyophilicity to other liquids having surface tension below 27.5 mN/m which spread on the membrane and permeate through it quickly. Based on this property, silanized GH-PDA-Z4 is a good candidate to separate immiscible liquid mixture to maintain high efficiency.
  • FIG. 15B and 15C show the separation efficiency of formamide from different low surface tension solvents and corresponding flux are near or above 3000 Lm 2 h _1 , respectively.
  • a mixture of formamide and chloroform was used. After each filtration, the membrane was washed with ethanol and dried in air at 80°C. It is clear to see that the membrane is good to filter formamide out of chloroform at high efficiency (more than 83%) and the flux is maintained higher than 3000 Lm 2 h _1 after 20 cycles of filtration (FIG. 15D). This result is promising for a long-term application of membrane.
  • Formamide was colored with methylene blue (MB) and can be seen floating on top of the mixture as the density of chloroform (CF) is higher than formamide.
  • Bare Ni foam, silanized GH-PDA-Z2 and silanized GH-PDA-Z4 coated Ni foam membranes were used for the separation. Bare Ni foam membrane cannot selectively separate the mixture components, and allows both the liquids to pass through it (FIG. I6A1 to I6A3). Meanwhile, silanized GH-PDA-Z2 coated Ni foam membrane repelled both the liquids and hence cannot filter the mixture (FIG. I6B1 to I6B3).
  • silanized GH-PDA-Z 4 maintains the surface energy of the membrane in between the close surface tensions immiscible liquids, allowing successful separation.
  • both the silanized GH- PDA-Z 4 and the silanized GH-PDA-Z2 coated Ni foam membranes show successful separation of formamide out of n-hexane (FIG. 18A to 18D and FIG.
  • filtrate solutions of formamide and low surface tension solvents were characterized using UV-Vis spectroscopy.
  • a calibration curve of MB was made by using different concentration of MB dissolved in formamide which showed the main adsorption peak at 654 nm.
  • the absence of any peak at 654 nm in the UV-Vis spectra of the filtrates indicates that the filtrate was free of formamide and the slight weight loss of formamide may be due to sticking of formamide on the membrane surface.
  • Example 12 Summary of Discussion and Results
  • silanized graphene/MOFs composite frameworks coated glass coating surfaces from silanized GH-PDA to GH-PDA-Z 2 display superamphiphobicity, which provide for promising applications in protective coating.
  • silanized GH-PDA-Z 4 coated Ni foam performed well in separating immiscible organic mixture liquids with close surface tension.
  • the tailorable wettability and filtration ability of the as-prepared graphene framework provide for numerous applications in environmental treatment, marine, medicine or petrochemical industries.
  • Membrane filtration is demonstrated by drop casting the silanized graphene/MOFs composite frameworks on Ni foam substrate instead of a glass piece.
  • the graphene/MOFs composite not only changes surface wettability of pristine Ni foam but also enhances its surface roughness leading to a coated membrane as described above, which is advantageous over bare Ni foam and silanized Ni foam in terms of liquid repellency.
  • the as-prepared membrane can efficiently separate formamide from a mixture having low surface tension solvents at a flux near to or higher than 3000 Lm 2 h _1 under gravity with separation efficiency higher than 83% and with good repeatability over 20 cycles.

Abstract

The present disclosure provides for a porous graphene composite comprising silanized graphene particles. The silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer. A layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks. The method of producing such a porous graphene composite is also provided. The method comprises contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group, drying the porous graphene particles coated with the polymer, mixing the porous graphene particles with metal organic frameworks, and depositing a silanization agent on the porous graphene particles to form the porous graphene composite. A graphene composite membrane used in the separation of immiscible liquids, and a method of producing such a graphene composite membrane, are also provided in the present disclosure. No suitable figure to be published with the abstract

Description

GRAPHENE FRAMEWORKS MEMBRANES FOR SEPARATION OF
IMMISCIBLE LIQUIDS
Cross-Reference To Related Application
[0001] This application claims the benefit of priority of Singapore Patent Application No. 10201801088Q, filed 8 February 2018, the content of it being hereby incorporated by reference in its entirety for all purposes.
Technical Field
[0002] The present disclosure relates to a porous graphene composite comprising silanized graphene particles, and a graphene composite membrane comprising such a porous graphene composite. The present disclosure also relates to a method of producing the porous graphene composite and the graphene composite membrane.
Background
[0003] Fabrication of coating structures has gained significant attention during the last decade because of their potential applications in various industries. The coating layer typically alters the chemical property of a pristine surface, for example, leading to a change in surface wettability. Coating on a plate-like substrate, such as a superhydrophobic and superamphiphobic coating, may enhance self-cleaning ability, anti-corrosion, anti-icing, anti-fogging or anti-microbial property. The coating on a substrate may form a composite also for use in separating substances.
[0004] One type of separation that has gained attention is liquid separation, especially the separation of immiscible liquids. Mixtures of immiscible liquids are widely used in various processes such as in the food, agricultural, textile printing, petroleum or medicine industries. Components of the mixtures may need to be separated and recovered after their use to recycle them and/or avoid environmental pollution. Conventional means for separating immiscible liquids, such as distillation, are time consuming and costly due to high energy consumption, low flux and low efficiency. Other separation means have been developed to mitigate such issues. One example is the separation membrane, which serves as a potential choice for high throughput and energy efficient separation of immiscible liquids. To effectively separate immiscible liquids, e.g. oil and water, plenty of materials with various surface wettability have been investigated, which include carbon based adsorbents, modified metal mesh, sand or boron nitride, etc. Despite such materials, the mechanism of membrane separation may depend on the surface wettability of the material with respect to the immiscible liquids. For example, to separate oil and water, if the surface of a membrane is made superhydrophilic and underwater oleophobic. It tends to repel oil but allow water to pass through the membrane. In contrast, superhydrophobic and underwater oleophilic membranes tend to repel water but allow oil to penetrate.
[0005] Although membranes based on surface wetting behaviour have been developed to separate oil/water mixture, membranes for separation of immiscible organic liquids do not seem to have proliferated. This is because separation of immiscible organic solvents is much more complicated as the mixture contains liquids that possess surface tension very close to each other and relatively lower than that of water. As an example, the mixture of formamide iy = 58.2 mN/m) and chloroform iy = 27.5 mN/m) is more difficult to separate than a mixture of water (y = 72.7 mN/m) and chloroform. To separate liquids with close surface tensions, the wettability of a membrane may have to be systematically controlled to maintain the surface energy between two components of a liquid mixture. In general, surface wettability of a material can be controlled and tailored by changing either the surface chemistry or the surface morphology.
[0006] The surface chemistry of a material can be tuned by coating various low surface energy molecules on it without changing its surface topography. Meanwhile, the surface morphology can be tailored by introducing hierachical micro/nano scale porosity on the surface of the material.
[0007] Other membrane materials have also been fabricated for separation of immiscible organic liquids, which include nanofibrous membrane, rounghness- enhanced copper mesh, non-woven fabric membrane, etc. These membranes, however, are based on“re-entrant” surface topography which showed high separation efficiency but required multiple steps for fabrication and are less environmetal friendly.“Re-entrant” surface topography is formed from a structural component that is arranged in a repeated manner and each of the arranged structural components has the same morphology, such as T-shaped, mushroom- like, trapezoidal, matchstick-like, fibrous-shaped, or microspherical.
[0008] In another instance, porous structure fabricated via ice-templating method is considered a green method where the liquid-repellency is tailored by varying the entrapped air inside the pores but this process tends to be energy intensive.
[0009] Besides the above, three dimensional (3D) porous graphene framework has already been used in its bulk cylindrical form for various environmental treatment applications such as, oil adsorption, water soluble contaminants removal, and use as an oil/water separation superhydrophobic membrane. Moreover, as graphene oxide sheets tend to self-assemble into a large-scale 3D bulk structure in a homogeneous medium, the pores on their wall surface close, and this limits further surface modification of the porous graphene network for tuning of surface wettability for separation of immiscible liquids.
[0010] To address the above issues, there is a need to provide for a material that ameliorates one or more of the abovementioned limitations. The material should at least be capable of separating immiscible liquids in a highly efficient, cost effective, energy effective manner with high throughput.
[0011] There is also a need to provide for a method of producing such a material.
Summary
[0012] In a first aspect, there is provided for a porous graphene composite comprising silanized graphene particles, wherein the silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer, and wherein a layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks.
[0013] In another aspect, there is provided for a method of producing a porous graphene composite, the method comprising:
contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group;
drying the porous graphene particles coated with the polymer; mixing the porous graphene particles with metal organic frameworks; and depositing a silanization agent on the porous graphene particles to form the porous graphene composite.
[0014] In another aspect, there is provided for a graphene composite membrane used in the separation of immiscible liquids, wherein the graphene composite membrane comprises the porous graphene composite described according to the first aspect.
[0015] In another aspect, there is provided for a method of producing a graphene composite membrane, the method comprising:
contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group;
drying the porous graphene particles coated with the polymer;
mixing the porous graphene particles with metal organic frameworks;
depositing a silanization agent on the porous graphene particles to form the porous graphene composite; and
coating a substrate with the porous graphene composite to form the graphene composite membrane.
Brief Description of the Drawings
[0016] The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:
[0017] FIG. 1A is a schematic illustration of preparation of tailored superamphiphobic three dimensional (3D) silanized graphene -polydopamine-zeolitic imidazolate frameworks (GH-PDA-Z) from a graphene oxide/dopamine/ionic liquid dispersion, including the loading of metal organic frameworks nanocrystals on GH- PDA surface and modification of the resulting surface by silanization.
[0018] FIG. 1B is a schematic illustration of the preparation of filtration membrane by drop casting silanized GH-PDA-Z on Ni foam for separation of immiscible liquids in an organic solvent mixture. [0019] FIG. 2A shows a scanning electron micrograph (SEM) image of the 3D porous micron-sized GH-PDA powder. The scale bar denotes 100 mih.
[0020] FIG. 2B shows a SEM image of the 3D porous micron-sized GH-PDA powder of FIG. 2A at a higher magnification. The scale bar denotes 10 mih.
[0021] FIG. 2C shows a SEM image of GH-PDA-Zi, which corresponds to an initial concentration of GH-PDA colloids at 28.6 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used. The scale bar denotes 2 mih.
[0022] FIG. 2D shows a SEM image of GH-PDA-Z2, which corresponds to an initial concentration of GH-PDA colloids at 7.15 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used. The scale bar denotes 2 mih.
[0023] FIG. 2E shows a SEM image of GH-PDA-Z3, which corresponds to an initial concentration of GH-PDA colloids at 2.86 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used. The scale bar denotes 2 mih.
[0024] FIG. 2F shows a SEM image of GH-PDA-Z4, which corresponds to an initial concentration of GH-PDA colloids at 1.43 wt%, wherein the wt% refers to the amount of graphene present based on the amount of zeolitic imidazolate frameworks used. The scale bar denotes 2 mih.
[0025] FIG. 3A shows an optical photograph of a porous micron-sized GH-PDA colloidal powder and a cylindrical shaped bulk GH-PDA hydrogel.
[0026] FIG. 3B shows a SEM image of the solid state of GH-PDA colloid. The scale bar denotes 2 mih.
[0027] FIG. 3C shows a SEM image of the solid state of GH-PDA hydrogel. The scale bar denotes 2 mih.
[0028] FIG. 3D shows a SEM image of methanol dispersed GH-PDA hydrogel. The scale bar denotes 2 mih.
[0029] FIG. 4A shows a SEM image of 3D porous GH-PDA after surface modification with fluorosilane. Specifically, FIG. 4A shows silanized GH-PDA. The scale bar denotes 2 mih. [0030] FIG. 4B shows a SEM image of the silanized 3D porous GH-PDA of FIG. 4A at a higher magnification. The scale bar denotes 500 nm.
[0031] FIG. 4C shows a SEM image of silanized GH-PDA-Zi. The scale bar denotes 2 mih.
[0032] FIG. 4D shows a SEM image of silanized GH-PDA-Z2. The scale bar denotes
2 mih.
[0033] FIG. 4E shows a SEM image of silanized GH-PDA-Z3. The scale bar denotes 2 mih.
[0034] FIG. 4F shows a SEM image of silanized GH-PDA-Z4. The scale bar denotes 2 mih.
[0035] FIG. 5A shows a Fourier transform infrared (FTIR) spectra of GH-PDA, GH- PDA-Z2, silanized GH-PDA, and silanized GH-PDA-Z2 colloidal powders. The FTIR peaks of C=0 and C=C are highlighted with blue and green color strip, respectively, while the characteristic peak positions are indicated with an arrow.
[0036] FIG. 5B shows the X-ray photoelectron spectra (XPS) of GH-PDA, GH-PDA-
Z2, silanized GH-PDA, and silanized GH-PDA-Z2 colloidal powders.
[0037] FIG. 5C shows the X-ray diffraction (XRD) spectra of GH-PDA, GH-PDA-Z2, and silanized GH-PDA-Z2 colloidal powders. The XRD spectrum of silanized GH- PDA is not shown as no peaks were observed.
[0038] FIG. 5D shows the Brunauer-Emmett-Teller (BET) analysis of GH-PDA, GH-
PDA-Z2, silanized GH-PDA, and silanized GH-PDA-Z2 colloidal powders.
[0039] FIG. 6 shows a FTIR spectrum of GH-PDA colloids after washing several times with methanol.
[0040] FIG. 7 A shows the XPS analysis of Cls of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
[0041] FIG. 7B shows the XPS analysis of Ols of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
[0042] FIG. 7C shows the XPS analysis of Fls of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
[0043] FIG. 7D shows the XPS analysis of Si2p of GH-PDA, GH-PDA-Z2, silanized
GH-PDA colloid and silanized GH-PDA-Z2. [0044] FIG. 7E shows the XPS analysis of Zn2p of GH-PDA, GH-PDA-Z2, silanized GH-PDA colloid and silanized GH-PDA-Z2.
[0045] FIG. 8A shows the energy-dispersive X-ray spectroscopy (EDS) analysis of silanized GH-PDA-Z2, indicating the presence of Zn atoms even after surface modification with fluorosilane. Platinum (Pt) appears in the spectrum because the material was sputtered with Pt nanoparticles for EDS analysis.
[0046] FIG. 8B shows the EDS data of silanized GH-PDA-Z2, indicating the presence of Zn atoms even after surface modification of GH-PDA-Z2 with fluorosilane. Pt appears in the data because the material was sputtered with Pt nanoparticles for EDS analysis.
[0047] FIG. 9 shows the XRD of ZIF-8 nanoparticles before and after heat treatment at 200°C for 10 mins. The durability of ZIF-8 nanoparticles at high temperature is tested by heating the particles in a chamber at 200°C for 10 mins. The crystal lattice of ZIF-8 stays unchanged after heat treatment. This result supports the durability of ZIF- 8 nanoparticles structure during surface modification at high temperature.
[0048] FIG. 10A shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA.
[0049] FIG. 10B shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Zi.
[0050] FIG. 10C shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z2.
[0051] FIG. 10D shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z3.
[0052] FIG. 10E shows the static contact angle measurement of different liquid droplets with different surface tensions on the surface of silanized GH-PDA-Z4.
[0053] FIG. 11 shows the advancing contact angle (images in top row) and receding contact angle (images in bottom row) of 3 pL formamide droplet on the surface of silanized GH-PDA, silanized GH-PDA-Zi, silanized GH-PDA-Z2, silanized GH- PDA-Z3, and silanized GH-PDA-Z4, all of which are coated on a glass slide (left to right). [0054] FIG. 12A shows a plot of the static contact angle of glycerol (Gly), formamide (FM), ethylene glycol (EG), and n-hexane (Hex), on the surface of silanized GH- PDA-Z2 coated glass over 100 days.
[0055] FIG. 12B shows a plot of the static and sliding contact angles of a water droplet on the surface of silanized GH-PDA-Z2 coated glass over 100 days.
[0056] FIG. 12C shows the static contact angle of glycerol, formamide, ethylene glycol, and n-hexadencane (HDC) on the surface of silanized GH-PDA-Z2 coated glass at different temperatures.
[0057] FIG. 12D shows the static and sliding contact angles (CA) of a water droplet on the surface of silanized GH-PDA-Z2 coated glass at different temperatures.
[0058] FIG. 13 A shows the SEM image (top) and the schematic illustration (bottom) for the curved three-phase contact lines with side view and top view, with a droplet deposited on a thin (D 1 = 1 /K I ) microscale pore coating surface.
[0059] FIG. 13B shows the SEM image (top) and the schematic illustration (bottom) for the curved three-phase contact lines with side view and top view, with a droplet deposited on a thick (D2= 1 /K2) microscale pore coating surface.
[0060] FIG. 14A shows a SEM image of bare Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
[0061] FIG. 14B shows a SEM image of silanized Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
[0062] FIG. 14C shows a SEM image of silanized GH-PDA-Z4 coated Ni foam. A droplet of 3 pL formamide on top of the membrane is shown in the inset. The scale bar denotes 50 pm.
[0063] FIG. 14D shows a plot of the static contact angle of different surface tension liquid droplets on surface of bare Ni foam, silanized Ni foam and silanized GH-PDA- Z4 coated Ni foam.
[0064] FIG. 15A shows a plot of the efficiency of separating carbon tetrachloride from different polar solvents, wherein the separation efficiency with respect to each different polar solvent is represented by the respective bars. GLY represents glycerol, FM represents formamide, EG represents ethylene glycol. The efficiency is calculated by volume percentage of passing liquids. [0065] FIG. 15B shows a plot of the efficiency of separating formamide from non polar solvents, wherein the separation efficiency with respect to each different non polar solvent is represented by the respective bars. CF represents chloroform, CTC represents carbon tetrachloride, DEE represents diethyl ether, PTE represents petroleum ether, HEX represents n-hexane. The efficiency is calculated by volume percentage of passing liquids.
[0066] FIG. 15C shows the calculated flux through the membrane for formamide separated from different non-polar solvents.
[0067] FIG. 15D shows a plot of the re-generation and filtration flux of membrane using formamide and chloroform after 20 cycles.
[0068] FIG. 16A shows the optical images (Ai to A3) for separation of formamide (FM)/chloroform (CF) mixture with bare Ni foam. Formamide is colored by methylene blue (denoted by FM).
[0069] FIG. 16B shows the optical images (Bi to B3) for separation of FM/CF mixture with silanized GH-PDA-Z2 coated Ni foam. Formamide is colored by methylene blue (denoted by FM).
[0070] FIG. 16C shows the optical images (Ci to C3) for separation of FM/CF mixture with silanized GH-PDA-Z4 coated Ni foam. Formamide is colored by methylene blue (denoted by FM).
[0071] FIG. 17A shows an optical photograph of separation of chloroform/formamide mixture using silanized Ni foam as the separation membrane. First, formamide (FM) stays on top and chloroform (CF) stays at bottom.
[0072] FIG. 17B shows an optical photograph where the mixture of FM and CF is poured through the separation membrane.
[0073] FIG. 17C shows an optical photograph where the FM stays on top with the separation membrane while CF passes through the separation membrane.
[0074] FIG. 17D shows an optical photograph where more of the liquid mixture is poured through, and a part of FM penetrates through the membrane due to intrusion pressure.
[0075] FIG. 18A shows an optical photograph of separation of n-hexane/formamide mixture using silanized GH-PDA-Z4 coated Ni foam as the separation membrane. First, n-hexane (HEX) stays on top of formamide (FM). [0076] FIG. 18B shows an optical photograph where the mixture of HEX and FM is poured through the separation membrane.
[0077] FIG. 18C shows an optical photograph where the FM stays on top with the separation membrane while HEX quickly passes through the separation membrane.
[0078] FIG. 18D shows an optical photograph with complete separation of HEX and
FM.
[0079] FIG. 19A shows an optical photograph of separation of n-hexane/formamide mixture using silanized GH-PDA-Z2 coated Ni foam as the separation membrane. First, n-hexane (HEX) stays on top of formamide (FM).
[0080] FIG. 19B shows an optical photograph where the mixture of HEX and FM is poured through the separation membrane.
[0081] FIG. 19C shows an optical photograph where the FM stays on top with the separation membrane while HEX quickly passes through the separation membrane.
[0082] FIG. 19D shows an optical photograph with complete separation of HEX and FM.
[0083] FIG. 20A shows a SEM image of silanized GH-PDA-Z2 coated Ni foam membrane. The scale bar denotes 100 pm.
[0084] FIG. 20B shows a SEM image of the silanized GH-PDA-Z2 coated Ni foam membrane of FIG. 20A at a higher magnification. The scale bar denotes 50 pm.
[0085] FIG. 21 A illustrates the filtration efficiency of n-hexane from water, glycerol, formamide, and ethylene glycol using silanized GH-PDA-Z2 coated Ni foam.
[0086] FIG. 21B illustrates the regeneration of the membrane with a testing sample of n-hexane/formamide mixture.
[0087] FIG. 22 shows the ultraviolet-visible light (UV-Vis) spectra of methylene blue dyed formamide at different organic dye contents and filtrates after separation of mixture between formamide and low surface tension solvents using silanized GH- PDA-Z4 coated Ni foam membrane. The different solvents used for this include chloroform, carbon tetrachloride, diethyl ether, petroleum ether, and n-hexane. Detailed Description
[0088] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practised. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
[0089] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.
[0090] The present disclosure provides for a porous graphene composite comprising silanized graphene particles, and a method of producing such a porous graphene composite. The present disclosure also provides for a graphene composite membrane comprising the porous graphene composite, and a method of making such a graphene composite membrane. The term“composite” as used herein refers to a material formed from two or more different components, and having a functional and/or a structural property that is different from that of the individual components.
[0091] The porous graphene composite is advantageous because it can be used in the separation of immiscible liquids, even those that have comparable surface tensions. The immiscible liquids may be a mixture containing two or more immiscible liquids. The porous graphene composite can be used to separate two immiscible liquids, wherein the difference in their surface tension can be as low as 2.3 mN/m, for example, diiodomethane (y = 50 mN/m) and ethylene glycol iy = 47.7 mN/m). In the context of the present disclosure, the term“immiscible” as used herein refers to two or more liquids that do not chemically react with one another and maintain their distinct phases even when they are mixed with one another. An example to illustrate this may be a water/oil mixture. Even when water and oil are mixed, there is no chemical reaction between water and oil. Both water and oil maintain their distinct water phase and oil phase, respectively. [0092] As the present porous graphene composite is usable for separating immiscible liquids, it may be described as an open pore superamphiphobic three-dimensional micron-sized graphene frameworks. The term“superamphiphobic” as used herein refers to a material with low affinity (or high repellency) for water as well as for liquids of high surface tension. That is to say, a superamphiphobic surface can repel both water and oils with a contact angle higher than 150°. The surface tension of the oil may be at least 30 mN/m (e.g. n-hexadecane). Meanwhile, an amphiphobic surface only exhibits a contact angle that is lower than 150° but higher than 90° for both water and oils.
[0093] Advantageously, the porous graphene composite may be coated onto a porous substrate to form a graphene composite membrane. Such a substrate may even be a metal foam, such as but not limited to, a nickel foam. The coated nickel foam, as a non-limiting example, can be used to demonstrate the effective separations of immiscible organic liquids, and the present method of forming such a porous graphene composite and the graphene composite membrane are shown, by way of an example, in FIG. 1A and 1B, respectively.
[0094] As illustrated in FIG. 1A, the micron-sized graphene frameworks with open pore was constructed using an ionic liquid (IL) and a polymer precursor, such as dopamine. The phrase“ionic liquid” as used herein refers to a salt in which the ions are poorly coordinated, thereby resulting in a liquid having a boiling point below l00°C, or even at room temperature (i.e. room temperature ionic liquid). In an ionic liquid, at least one ion has a delocalized charge and one component is organic, which prevents the formation of a stable crystal lattice. The phrase“polymer precursor” as used herein refers to a compound convertible to form a polymer.
[0095] Subsequently, the surface wettability and surface energy of the graphene frameworks were tuned based on the surface tension of the immiscible liquids that are to be separated, by controlling the wall thickness of the graphene frameworks, which in turn defines the pore diameters of the porous graphene composite and the resultant membrane, by loading of metal organic frameworks (MOFs) and subsequent surface modification with a silanization agent, e.g. a fluorosilane of 1H,1H,2H,2H- perfluorodecyltriethoxysilane, to further lower the surface energy of the resultant porous graphene composite. Hence, the present porous graphene composite may be described as having fine surface tunability. The expression “metal organic frameworks” refers to compounds consisting of metal ions or clusters coordinated to organic ligands to form one-, two-, or three dimensional structures. The term“pore diameter” as used herein refers to the maximal length of a line segment passing through the centre and connecting two points on the periphery of a pore.
[0096] The present porous graphene composite can also be coated onto a non-porous substrate to demonstrate that it can form a protective coating with self-cleaning, anti corrosion, anti-icing, anti-fogging and/or anti-microbial property, as it prevents materials from seeping through. Such an advantage may be demonstrated by depositing the present porous graphene composite onto a glass substrate. The superamphiphobic graphene coated glass also demonstrates how surface wettability depends on the change in surface topography.
[0097] Holistically, the present porous graphene composite and the present method described herein offer a solution of using porous graphene for both surface coating and separation of immiscible organic liquids, which are scalable and provide for fabrication of devices for efficient coating and separation of immiscible liquids, which are in turn promising for applications in the industrial and environmental sectors.
[0098] With the above in mind, details of the present porous graphene composite and its method of production, and their various embodiments are described as follow.
[0099] In the present disclosure, there is provided for a porous graphene composite comprising silanized graphene particles, wherein the silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer, and wherein a layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks. The term“particles” as used herein refers to granules, fibers, flakes, spheres, powders, platelets and other forms and shapes, which may be regular or irregular. The term“particles” also includes references to a cluster or agglomerate formed from several particles, and such clusters or agglomerates may be referred to as a“framework”.
[00100] To obtain the porous graphene particles, graphene oxide particles may be mixed with a polymer precursor. The polymer precursor reduces graphene oxide to graphene. Hence, the polymer precursor may be termed as a reducing agent in the present disclosure. When the polymer precursor reduces the graphene oxide to graphene, it forms a polymer coated on the graphene particles, wherein the polymer is derived from the polymer precursor. Hence, it can be said that the silanized graphene particles are derived from graphene oxide particles.
[00101] In various embodiments, the polymer may comprise a catechol group. The polymer is derived from the polymer precursor which also comprises the catechol group. Hence, the polymer precursor may comprise a catechol group according to various embodiments. In various embodiments, both the polymer and the polymer precursor may comprise a catechol group. There may be more than one catechol group on the polymer and the polymer precursor. Examples of the polymer precursor may include dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, epigallocatechin, etc., and accordingly, examples of the polymer may include polydopamine or a polymer generated from tannic acid, 1,2- dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, epigallocatechin, etc. According to certain embodiments, the polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin. Other polymer precursor, which can reduce graphene oxide to graphene and form a polymer coating on the graphene may be used.
[00102] The graphene particles may be coated with metal organic frameworks. The metal organic frameworks may be deposited on the polymer that comprises the catechol group, or the graphene particles and the polymer that comprises the catechol group, according to various embodiments. In various embodiments, the metal organic frameworks may be present as one or more layers of crystals. The one or more layers of crystals may be deposited on the graphene particles and/or the polymer (comprising the catechol group). The coated metal organic frameworks crystals thus define the walls of the porous graphene particles, which in turn define the size of the pores in the porous graphene particles. Advantageously, the metal organic frameworks crystals help to control the wall thickness and pore size of the porous graphene particles, which define the surface roughness. Through surface modification, surface energy of the resultant porous graphene composite is also controlled. The surface energy affects the wettability of the porous graphene composite, which aids in the separation of immiscible liquids.
[00103] In various embodiments, the metal organic frameworks may comprise zeolitic imidazolate (or imidazole) frameworks (ZIF) (e.g. ZIF-8), zirconium- 1,4 benzodicarboxylic acid (UIO-66), iron-2,6 naphthalenedicarboxylic acid (MIL-88), nickel-zinc based metal organic frameworks (e.g. ZIF-9, ZIF-67, Ni-ZIF-8), or zinc e benzodicarboxylic acid (MOF-5).
[00104] In various embodiments, the amount of metal organic frameworks coated on the porous graphene particles and/or the polymer may be based on the graphene content present in the porous graphene particles. In other words, the metal organic frameworks may be present in an amount based on the graphene content of the porous graphene particles according to various embodiments. In various embodiments, the graphene content may be less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks. In some embodiments, the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks. In some embodiments, the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks. Further advantageously, using the graphene content with respect to the amount of metal organic frameworks allows for concentration-induced nucleation and growth of the metal organic frameworks on the graphene particles and/or the polymer, which circumvents pH-induced methods for controlling coating density and wall thickness of the metal organic frameworks.
[00105] Depending on the amount of the metal organic frameworks coated, the one or more layers of crystals may have a thickness of 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 10 nm or less, etc. This thickness refers to the wall thickness of the porous graphene particle.
[00106] After the polymer comprising the catechol group and the metal organic frameworks are formed on the graphene particles, the porous graphene particles may be coated with a polysiloxane, such that the surface of the porous graphene particles may be disposed with a thin layer of polysiloxane. The thin layer of polysiloxane helps to modify the surface chemistry of the porous graphene particles without altering the porosity (i.e. pore sizes) of the porous graphene particles. Particularly, the polysiloxane may help to increase oleophobicity of the resultant porous graphene composite to enhance separation of the immiscible liquids and prevent certain liquids from seeping through in order to provide the self-cleaning, anti-corrosion, anti-icing, anti-fogging and/or anti-microbial property. The polysiloxane may be formed by depositing a layer of silanization agent, such as a fluorosilane, on the porous graphene particles comprising the polymer and the metal organic frameworks. The polysiloxane may bind to the catechol groups of the polymer by covalent interactions. The polysiloxane may also bind to the metal organic frameworks by covalent interactions, as the polysiloxane comprises one or more Si-OH groups that can form covalent bonding with the metal organic frameworks and their crystals. In various embodiments, the layer of polysiloxane may be covalently attached to the metal organic frameworks or the catechol group and the metal organic frameworks.
[00107] The present disclosure also describes a method of producing the porous graphene composite. The method may comprise contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group, drying the porous graphene particles coated with a polymer, mixing the porous graphene particles with metal organic frameworks, and depositing a silanization agent on the porous graphene particles to form the porous graphene composite.
[00108] Embodiments described in the context of the present porous graphene composite are analogously valid for the present method described herein, and vice versa.
[00109] In various embodiments of the present method, contacting the graphene oxide may comprise adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid. Addition of the polymer precursor helps to reduce the graphene oxide to graphene, and the polymer precursor converts to a polymer coating the graphene. Other polymer precursor that reduces graphene oxide to graphene and forms a polymer coating the graphene may be used. Such a polymer precursor may be termed a reducing agent in the present disclosure as it reduces the graphene oxide to graphene. The aqueous solution may comprise or consist of water. The aqueous solution may be a mixture of water and alcohol, such as a water-ethanol solution. An aqueous solution may be used as both graphene oxide and the polymer precursor (e.g. dopamine) can be dissolved therein to obtain a homogeneous solution before adding the ionic liquid, so as to have the ionic liquid uniformly mixed into the homogeneous solution.
[00110] In various embodiments, the polymer precursor having the catechol group may comprise dopamine, tannic acid, l,2-dihydroxylbenzene, 1,2,3- trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin. The catechol group present in the polymer precursor is also present on the polymer coating the graphene. Accordingly, the polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, 1,2,3- trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin, in various embodiments.
[00111] After mixing with the polymer precursor, an ionic liquid may be added. The aqueous solution containing the graphene oxide particles, after being added with the polymer precursor and ionic liquid, may be heated to a temperature ranging from 75°C to 95°C for about 12 hours, and such an aqueous solution may be, freeze-dried as an example, to obtain a collodial powder of the porous graphene particles coated with the polymer. At this juncture, the ionic liquid may be coated onto the graphene particles and/or the polymer. Advantageously, the ionic liquid stabilizes the porous graphene particles and prevents the porous graphene particles from disintegrating when the porous graphene particles are redispersed into a liquid. This is because the ionic liquid forms p-p interactions and cation-p bonding with graphitic carbon skeleton of the graphene particles. In this way, even if the porous graphene particles are redispersed in a liquid via ultrasonic energy, the particles do not break down easily.
[00112] In various embodiments, the ionic liquid may comprise l-butyl-3- methylimidazolium tetrafluoroborate. Other ionic liquids that may be used include 1- butyl-3-methylimidazolium hexafluorophosphate, l-butyl-3-methylimidazolium methanesulfonate, l-butyl-3-methylimidazolium tetrachloroaluminate, l-butyl-3- methylimidazolium thiocyanate, l-butyl-3-methylimidazolium acetate, l-butyl-3- methylimidazolium chloride, l-butyl-3-methylimidazolium hydrogen sulfate, etc. [00113] Drying of the porous graphene particles coated with the polymer may be performed in various embodiments. The porous graphene particles are dried before mixing with the metal organic frameworks because the drying induces p-p bonding of GH-PDA, thereby helping the porous graphene particles maintain their structure when redispersed in an alcohol, such as methanol, for mixing with the metal organic frameworks.
[00114] The colloidal powder of porous graphene particles may be redispersed in an alcohol containing metal organic frameworks precursors that form the metal organic frameworks. In other words, mixing of the porous graphene particles with the metal organic frameworks may be carried out in the presence of an alcohol. The alcohol may comprise methanol, ethanol, or isopropanol. Alcohol is used as it is a solvent that helps in developing crystals of the metal organic frameworks on the porous graphene particles.
[00115] The metal organic organic frameworks precursors depend on the metal organic frameworks to be coated on the porous graphene particles and/or the polymer. In various embodiments, the metal organic frameworks may comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc e benzodicarboxylic acid. In such embodiments or embodiments based on zeolitic imidazolate frameworks, the metal organic frameworks precursors may comprise a mixture of zinc nitrate and 2-methyl imidazole. The advantages of coating metal organic frameworks, onto the porous graphene particles, have already been explained above when describing the embodiments of the present porous graphene composite.
[00116] In various embodiments, mixing of the porous graphene particles may comprise mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles. In various embodiments, the graphene content may be less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks. In some embodiments, the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks. In some embodiments, the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks. Advantages of coating metal organic frameworks based on the graphene content have already been explained above. For instance, using the graphene content with respect to the amount of metal organic frameworks advantageously allows for concentration-induced nucleation and growth of the metal organic frameworks on the graphene particles and/or the polymer, which circumvents pH-induced methods for controlling coating density and wall thickness of the metal organic frameworks.
[00117] The mixing of the porous graphene particles and the metal organic frameworks, and/or the metal organic frameworks precursors may include overnight stirring. After stirring, a colloidal powder of the porous graphene particles, now coated with the polymer and the metal organic frameworks, may be obtained by any suitable forms of drying, e.g. freeze-drying.
[00118] After forming metal organic frameworks on the porous graphene particles and/or the polymer, the present method may include depositing a silanization agent onto the porous graphene particles, the polymer, and/or the metal organic frameworks. The depositing of a silanization agent may comprise mixing the porous graphene particles with the silanization agent. The silanization agent may form a layer of polysiloxane on the porous graphene particles, the polymer, and/or the metal organic frameworks. Advantages of having a layer of polysiloxane coated thereon, and hence the use of a silanization agent, have already been described above.
[00119] In various embodiments, the silanization agent may comprise a fluorosilane comprising lH,lH,2H,2H-perfluorodecyltriethoxysilane. Other fluorosilane that may be used includes lH,lH,2H,2H-perfluorooctyltriethoxy silane, 1H,1H,2H,2H- perfluorohexyltriethoxysilane, etc. The wetting behavior may be tuned using different fluorosilane due to the different chain length of the fluorosilane.
[00120] The present disclosure also provides for a graphene composite membrane used in the separation of immiscible liquids, wherein the graphene composite membrane may comprise the porous graphene composite that has already been described above.
[00121] Embodiments described in the context of the present porous graphene composite and the method of producing the present porous graphene composite are analogously valid for the present graphene composite membrane described herein, and vice versa.
[00122] The graphene composite membrane may be obtained by depositing the present porous graphene composite onto a substrate. Any suitable means of deposition may be used. In various embodiments, the porous graphene composite may be coated on a substrate. The substrate may comprise a glass, a metal foam, a cellulose paper, or polyurethane.
[00123] The graphene composite membrane may be used in separating immiscible liquids. In various embodiments, the immiscible liquids may have different surface tension. Advantageously, the graphene composite membrane can separate two immiscible liquids having comparable surface tensions, wherein the difference in surface tension may be as low as 2.3 mN/m.
[00124] The present disclosure further provides for a method of producing a graphene composite membrane. Such a method may include the steps of producing the porous graphene composite. Accordingly, such a method may comprise contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group, drying the porous graphene particles coated with the polymer, mixing the porous graphene particles with metal organic frameworks, depositing a silanization agent on the porous graphene particles to form the porous graphene composite, and coating a substrate with the porous graphene composite to form the graphene composite membrane.
[00125] Embodiments described in the context of the present porous graphene composite, the present methods of producing the porous graphene composite and graphene composite membrane, are analogously valid for the present graphene composite membrane described herein, and vice versa.
[00126] As already described above, in the present method, contacting the graphene oxide may comprise adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid. The polymer precursor may comprise dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin. The polymer comprising the catechol group may comprise polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin. The ionic liquid may comprise 1 -butyl-3 -methylimidazolium tetrafluoroborate. Other ionic liquids that may be used have already been described above. Advantages of the polymer precursor, the polymer coated on the porous graphene particles, and the ionic liquid, have already been mentioned above when describing embodiments of the present porous graphene composite, the present graphene composite membrane, and the present method of producing the porous graphene composite.
[00127] In the present method, mixing of the porous graphene particles may comprise mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles. In various embodiments, the graphene content is less than 28.6 wt% of the metal organic frameworks. If the graphene content is higher than 28.6 wt%, which means less metal organic frameworks are present, the porous graphene particles may not be sufficiently coated with the metal organic frameworks. In some embodiments, the graphene content may be less than 7.15 wt%, less than 2.86 wt%, or less than 1.43 wt%, of the metal organic frameworks. In some embodiments, the graphene content may be 7.15 wt%, 2.86 wt%, or 1.43 wt%, of the metal organic frameworks. In various embodiments, the metal organic frameworks may comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc- 1,4 benzodicarboxylic acid.
[00128] Advantages of coating metal organic frameworks based on the graphene content have already been explained above. For instance, using the graphene content with respect to the amount of metal organic frameworks advantageously allows for concentration-induced nucleation and growth of the metal organic frameworks on the graphene particles and/or the polymer, which circumvents pH-induced methods for controlling coating density and wall thickness of the metal organic frameworks.
[00129] The mixing of the porous graphene particles with the metal organic frameworks may be carried out in the presence of an alcohol in various embodiments. The alcohol may comprise methanol, ethanol, or isopropanol.
[00130] In various embodiments, depositing of a silanization agent may comprise mixing the porous graphene particles with the silanization agent. The silanization agent may comprise a fluorosilane comprising 1H,1H,2H,2H- perfluorodecyltriethoxysilane. Other fluorosilane that may be used has already been discussed above. The silanization agent may form a layer of polysiloxane on the porous graphene particles, the polymer, and the metal organic frameworks. Advantages of forming a layer of polysiloxane, and hence the use of the silanization agent, have already been described above.
[00131] To form the graphene composite membrane, the porous graphene composite as described above may be deposited onto a substrate, wherein the substrate may comprise a glass, a metal foam, a cellulose paper, or polyurethane. The graphene composite membrane may be used as a protective coating with self-cleaning, anti corrosion, anti-icing, anti-fogging and/or anti-microbial property, as it prevents materials from seeping through. The graphene composite membrane may be used in separation of immiscible liquids.
[00132] In the context of the present disclosure, the word“substantially” does not exclude“completely” e.g. a composition which is“substantially free” from Y may be completely free from Y. Where necessary, the word“substantially” may be omitted from the definition of the invention.
[00133] In the context of various embodiments, the articles“a”,“an” and“the” as used with regard to a feature or element include a reference to one or more of the features or elements.
[00134] In the context of various embodiments, the term“about” or“approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.
[00135] As used herein, the term“and/or” includes any and all combinations of one or more of the associated listed items.
[00136] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.
[00137] While the methods described above are illustrated and described as a series of steps or events, it will be appreciated that any ordering of such steps or events are not to be interpreted in a limiting sense. For example, some steps may occur in different orders and/or concurrently with other steps or events apart from those illustrated and/or described herein. In addition, not all illustrated steps may be required to implement one or more aspects or embodiments described herein. Also, one or more of the steps depicted herein may be carried out in one or more separate acts and/or phases.
Examples
[00138] The present disclosure relates to a composite, a composite membrane comprising the composite, and methods of making both the composite and composite membrane.
[00139] The membrane may be used to separate immiscible liquids, particularly but not limited to immiscible liquids with close surface tension values y, e.g. chloroform (y = 27.5 mN/m) and formamide (y = 58.2 mN/m), diiodomethane (y = 50 mN/m) and ethylene glycol (y = 47.7 mN/m). The membrane can also be used as a coating for anti-corrosion prevention and/or a coating that provides for an anti-microbial surface due to its superamphiphobic and superhydrophobic property.
[00140] Details of the present composite, composite membrane and methods of making them are discussed, by way of non-limiting examples, as set forth below.
[00141] Example 1 : Materials
[00142] Dopamine hydrochloride (98%), lH,lH,2H,2H-perfluorodecyltriethoxysilane (PFDTS) (96%), natural graphite powder, diphosphorous pentoxide (P2O5), potassium persulfate (K2S2O8), potassium permanganate (KMn04), l-butyl-3- methylimidazolium tetrafluoroborate (an ionic liquid, IL), zinc (II) nitrate hexahydrate (Zn(N03)2), 2-methyl imidazole (MID), hydrogen peroxide (H2O2), hydrochloric acid (HC1), sulfuric acid (H2SO4), glycerol (Gly), formamide (FM), ethylene glycol (EG) were purchased from Sigma-Aldrich. n-hexadecane (HDC), chloroform (CF), dichloromethane (DCM), diethyl ether, petroleum ether, n-hexane, methanol (MeOH), ethanol (EtOH), all were purchased from Fisher chemical.
[00143] Example 2: Preparation of Graphene Oxide
[00144] Graphene oxide (GO) was prepared from natural graphite powder via modified Hummer’s method. Briefly, the solid mixture of P2O5 and K2S2O8 was dissolved completely in concentrated H2SO4 at 80°C. 12 g of natural graphite was then added accordingly. The mixture was kept stirring for 8 hours followed by cooling down to room temperature and diluted by 2 L of deionized (DI) water. The supernatant was then decanted and washed several times until pH level of the liquid reached to 7. Final product was dried in air at l00°C for 12 hours.
[00145] 2 g of pre-treated graphene was dispersed again in concentrated H2S04 with an ice batch. 6 g of KMn04 was then added slowly to avoid the increase of temperature rapidly and the mixture was stirred for 2 hours at temperature below 20°C. The temperature was then increased to 40°C and maintained at that temperature for 10 hours. After completion, 90 mL of DI water was added and the dark brown mixture was stirred at the same temperature for another 30 mins. To terminate the reaction, 250 mL of DI water was added into mixture. The sample was naturally cooled to room temperature. The cooled suspension was further treated by 5 mL of H2O2 (35%).
[00146] A bright yellow color immediately appeared, confirming successful formation of GO. The product was then washed three times with HC1 5% and DI water. The final product of GO solution has a dark red-brown color with concentration at 10 mg/mL.
[00147] Example 3: Preparation of Graphene-Polydopamine (GH-PDA) Colloid
[00148] 20 mg of GO (10 mg/mL) was diluted to a solution with 2 mg/mL by DI water. The GO suspension was then sonicated for 2 hours using a sonicate probe. 10 mg of dopamine was then added to the GO solution followed by addition of 50 pL IL. The mixture was then sonicated to ensure that IL dissolved completely in water and heated in an oven at 90°C for 12 hours. After the reaction, black solid was collected by filtration under low pressure. The final GH-PDA colloidal powder was obtained after 2 days of freeze-drying. Another GH-PDA was prepared using the same method without adding any ionic liquids and filtration.
[00149] Example 4: Preparation of Graphene-Polydopamine-Zeolitic Imidazolate Framework (GH-PDA-Z)
[00150] 2 mg of GH-PDA colloidal powder was dispersed in a mixture of MID (60 mM) and Zn(N03)2 (30 mM), which were dissolved in methanol with different concentrations of graphene. The mixture of GH-PDA colloid and ZIF-8 precursors was mixed overnight under stirring. The composite product was finally centrifuged at 6000 rpm in 10 mins and washed several times with methanol. [00151] Example 5: Surface Modification of GH-PDA, GH-PDA-Z and The Coating Procedure
[00152] Surface modification was conducted. Briefly, 2 mg of GH-PDA colloidal powder was mixed with 50 pL of PFDTS in a small vial. The vial, which was covered by an aluminum paper, was then placed in an oven at 200°C for 10 mins. After naturally cooling to room temperature, silanized GH-PDA was dispersed again in ethanol and then drop cast on substrates, e.g. glass (1.5 cm xl.5 cm) or Ni foam (1.5 cm x 1.5 cm). Coated substrates were dried at 50°C for several days followed by additional drying at l00°C for 1 hour. The same procedure was applied for GH-PDA- Z samples.
[00153] Example 6: Filtration of Immiscible Liquid Mixtures
[00154] A simple mixture of carbon tetrachloride and another high surface tension solvent such as water, glycerol, formamide and ethylene glycol, which were colored by organic dyes, was poured through a funnel-liked silanized GH-PDA-Z4 coated Ni- foam which was pre-wetted by carbon tetrachloride (FIG. 15A). In addition, various simple mixtures of formamide and another low surface tension solvent, such as chloroform, carbon tetrachloride, diethyl ether, petroleum ether, and n-hexane, were poured through a funnel-liked silanized GH-PDA-Z4 coated Ni-foam, respectively (FIG. 15B and 15C). Control experiments such as filtration using bare Ni foam and silanized GH-PDA-Z2 coated Ni foam also are conducted using a mixture of formamide and chloroform.
[00155] The separation efficiency is calculated by following expression:
Figure imgf000027_0001
[00156] where V (in litres) is the original volume of oil. Vj and V2 are the volume of collected oil and the volume absorbed by the membrane, respectively. The filtration flux is calculated by following expression:
Figure imgf000027_0002
[00157] where V (in litres) is the volume of liquid passed through the membrane, A (m2) is effective area of the membrane and t (hr) is total time that liquids pass through the membrane. [00158] Example 7: Characterization
[00159] Scanning electron microscopy (SEM) was tested using FESEM (JSM-6700F, Japan). Fourier transform infrared spectrometry (FTIR) was tested using PerkinElmer Spectrum One FTIR. X-ray photoelectron spectroscopy (XPS) studies were conducted using a Kratos Axis Supra spectrophotometer with a dual anode monochromatic Ka excitation source. All binding energies for elements of interest were corrected against an adventitious carbon Cls core level at 284.8 eV. All XPS peaks were fitted using Shirley background together with Gaussian-Lorentzian function using CASA XPS software. Powder X-ray diffraction (XRD) patterns was obtained on Bruker AXSD2 Advanced X-ray diffractometer with monochromatized Cu Ka radiation (l = 1.54056 A, 40 kV and 20 mA). UV-vis spectra were recorded using a Shimadzu UV 1800 spectrophotometer.
[00160] Example 8: Summary of Present Method and Discussion
[00161] In the present disclosure, the method disclosed herein provides for the preparation of an open pore, superamphiphobic 3D micron-sized graphene frameworks with fine surface tunability. The material was coated on both flat and porous substrates, such as a glass and a nickel (Ni) foam (FIG. 1B), respectively. The superamphiphobic graphene coated glass was used to demonstrate how surface wettability depends on the change in surface topography. Meanwhile, the coated Ni foam demonstrates the effective separation of immiscible organic liquids mixtures. As illustrated in FIG. 1A, micron-sized graphene frameworks with open pores were fabricated using ionic liquid (IL). Subsequently, the surface wettability and surface energy of the graphene frameworks were tuned according to the surface tension of the immiscible liquids by precisely controlling its wall thickness and/or the pore diameter via metal organic frameworks (MOFs) loading, followed by surface modification with low surface energy PFDTS. The present method offers an advantageous solution of using porous graphene for both the surface coating and the separation of immiscible organic liquid mixtures. The present method is also scalable and provides for fabrication of devices for efficient coating and separation of immiscible liquids, and hence, is promising for the industrial and environmental sectors.
[00162] Example 9: Results and Discussion - Fabrication of Graphene/MQFs Building Block and Tailored Surface Repellency Coatings [00163] The strategy of fabricating superamphiphobic 3D porous graphene framework membrane is illustrated in FIG. 1A. First, an ionic liquid was added to an aqueous dispersion of GO and DA to create an open pore 3D micron-sized PDA- coated graphene frameworks (GH-PDA). Secondly, the surface topography of the graphene frameworks was tuned by controlling the coated wall thickness, and hence the pore diameter, via deposition of various amount of porous crystalline metal organic frameworks (MOFs) to form GH-PDA-Z. After that, the surface chemistry of both GH-PDA and GH-PDA-Z frameworks were modified by coating a thin layer of low surface energy fluorosilane. The porous silanized graphene/MOFs composite materials were then drop cast on glass and Ni foam to fabricate the tailored superamphiphobic coating for surface wettability investigation and studies for the membrane separation of immiscible liquids, respectively.
[00164] When the ionic liquid was added to the colloidal dispersion of GO and DA, the colloidal particles agglomerate to form macro-clusters, and an aqueous percolating network containing colloidal suspension of GO and DA surrounded by the ionic liquid molecules is formed. This is due to neutralization of the surface charges of colloidal particles by the ions carrying opposite charge from the ionic liquid, leading to de- stabilization of colloidal suspension of graphene oxide in a water/ionic liquid mixture. Then, the colloidal mixture was heated overnight at 90 C when GO is reduced by DA, to form 3D GH-PDA hydrogel particles inside the colloidal agglomerates. GH-PDA colloidal hydrogel was then filtered and freeze-dried to obtain an open pore micro sized light-weight powder which retains its porous structure while being dispersing in methanol under mild sonication (FIG. 2A and 2B). This shows the advantage of using ionic liquid to have a more stable porous structure over the cylindrical shaped bulk GH-PDA hydrogel as shown in FIG. 3A. Although SEM images of both the freeze- dried GH-PDA samples show 3D porous structures (FIG. 3B and 3C), the bulk GH- PDA hydrogel completely loses its 3D porous structure when redispersing in methanol with sonication (FIG. 3D). The 3D porous network of bulk GH-PDA sample was broken down inside its bulk structure due to the ultrasonic energy, whereas, the 3D open porous structure of GH-PDA formed inside the micron-sized small colloidal clusters remains stable via p-p interactions and cation-p bonding between the ionic liquid and graphitic carbon skeleton. [00165] The surface topography of the 3D porous micron-sized GH-PDA frameworks was precisely tuned by depositing varying amount of porous crystalline MOFs on the surface of GH-PDA colloids. Among various types of MOFs, zeolite (i.e. zeolitic) imidazole (or imidazolate) frameworks (ZIF-8) were selected because they are cheaper, easier to prepare and have established nanoscale sizes at different surfaces. In addition, ZIF-8 nanoparticles can easily be nucleated in situ on the surface of a thin layer of polydopamine (PDA) due to the metal chelating ability of PDA. In the present study, it was observed that ZIF-8 nanoparticles were successfully deposited on the surface of GH-PDA by simple mixing of porous GH-PDA powder and a methanol solution of MOFs precursors (FIG. 2C to 2F). The coating density and coated wall thickness of ZIF-8 on 3D porous GH-PDA colloids are highly dependent on the weight percent of graphene used. When higher amount of graphene (28.6 wt%) was taken with respect to ZIF-8, the porous surface of GH-PDA colloids (GH-PDA-Zi) were not fully coated by ZIF-8 as shown in FIG. 2C. When the amount was decreased to 7.15 wt%, the surface of porous GH-PDA colloids (GH-PDA-Z2) were uniformly coated with a thin conformal layer of ZIF-8 particles (FIG. 2D). The coated wall thickness on the porous GH-PDA colloids further increase with a decrease of the graphene concentration from 2.86 wt% (GH-PDA-Z3) to 1.43 wt% (GH-PDA-Z4), leading to successive reduction in pore diameter (FIG. 2E and 2F). Moreover, the macropores of the GH-PDA colloidal framework were almost fully covered at 1.43 wt% graphene content (FIG. 2F). Hence, by decreasing the mass ratio of GH-PDA with respect to ZIF-8, the amount of ZIF-8 particles required to coat porous GH-PDA frameworks increases. Therefore, when the GH-PDA amount lowered from 28.6 to 7.15 wt%, the number of nucleation active sites of ZIF-8 on graphene surface increases, leading to uniform thin surface coverage. However, with further increase in the amount of ZIF-8, the nuclei of ZIF-8 particles start to grow more and form multiple layers of ZIF-8 nanocrystals onto the wall of the GH-PDA framework. This concentration-induced nucleation and growth of ZIF-8 nanocrystals is very useful for controlling the coating density and coated wall thickness of ZIF-8 on the surface of 3D porous GH-PDA frameworks besides pH-induced size distribution of ZIF-8. Therefore, the surface topography of 3D porous GH-PDA frameworks is tunable by controlling the pore diameter with varying coated wall thickness via deposition of various amounts of porous crystalline ZIF-8 particles on it.
[00166] To prepare oleophobic membrane for separation of immiscible liquids, besides tuning the surface topography, the surface chemistry needs to be tailored to control the wettability of 3D porous GH-PDA frameworks. Surface chemistry can be tailored by applying a thin low surface energy molecular coating layer on the surface of the material. In the present example, a thin coating layer of fluorosilane was applied onto the surface of the 3D porous GH-PDA-Z frameworks, which binds to the catechol groups of PDA via covalent interactions and strongly interacts with ZIF-8 particles. FIG. 4A to 4F are SEM images for demonstrating ZIF-8 loaded 3D graphene frameworks after silanization, named as silanized GH-PDA-Z frameworks. It is to be noted FIG. 4A and FIG. 4B show silanized GH-PDA without loading of ZIF-8 nanoparticles.
[00167] The coated wall thickness on porous GH-PDA frameworks which changes from several ten nanometers (FIG. 2B and 4B) to nearly 100 nm (FIG. 2E and 4E) to around 400 nm (FIG. 2F and 4F) due to deposition of various amount of ZIF-8, as mentioned above, remains almost the same after silanization. However, the large variation in wall thickness from few nm up to 100 nm for GH-PDA-Zi is due to the non-uniform distribution of ZIF-8 nanoparticles on the surface (FIG. 2C and 4C). If the microscopic structure of all the ZIF-8 coated 3D porous graphene colloidal frameworks before (FIG. 2C to 2F) and after (FIG. 4C to 4F) silanization were compared, the thin molecular coating layer of fluorosilane does not change the macroscale porosity of graphene skeletons. Hence, the surface chemistry of GH-PDA- Z frameworks can be tailored without changing the surface topography.
[00168] The successful depositions of ZIF-8 and thin layer coating of fluorosilane on GH-PDA frameworks were confirmed by FTIR analysis (FIG. 5A). FTIR spectrum of GH-PDA displays the characteristic peaks at 1572 cm 1 and 1720 cm 1 corresponding to the respective stretching vibration of C=C and C=0 coming from the catechol group of PDA. Moreover, a small peak at 1060 cm 1 corresponding to the stretching vibration of B-F (-BF4) indicates that small amount of ionic liquid is still grafted on the graphene sheets even after washing in methanol. However, -BF4 peak disappears when GH-PDA was washed several times for further modification steps (FIG. 6). [00169] To show the coating of ZIF-8 particles on the GH-PDA frameworks, an exemplary sample GH-PDA-Z2 was chosen among other ZIF-8 loaded GH-PDA samples. The observed additional peaks in the spectral region of 500 cm 1 to 1350 cm 1 and the humps in between 1350 cm 1 to 1500 cm 1 assigned to the respective plane bending and stretching of imidazole ring confirmed the successful ZIF-8 deposition on graphene framework. Moreover, the small peak at 1584 cm 1 corresponding to the stretching vibration of C-N from imidazole and peaks for aromatic and aliphatic C-H stretch at 2929 cm 1 and 3135 cm 1 further confirmed the ZIF-8 coating on GH-PDA. Furthermore, a new peak at 1214 cm 1 corresponds to the covalent C-F bonds as well as the peaks at 778 cm 1 and 1075 cm 1 correspond to the bending and stretching vibration of Si-O-Si, respectively, which confirmed the successful modification of GH-PDA and GH-PDA-Z2 frameworks by fluorosilane.
[00170] The compositional changes of porous graphene before and after loading with ZIF-8 particles and further modification by fluorosilane are characterized by X-ray photoelectron spectroscopy (XPS) as shown in FIG. 5B and FIG. 7A to 7E. While the peaks of Cls, Nls and Ols are observed for GH-PDA colloids, a new peak of Zn2p is observed for the GH-PDA-Z2 sample, indicating the presence of ZIF-8 coating on its surface. The XPS spectra of silanized GH-PDA and GH-PDA-Z2 show additional peaks of Fls and Si2p indicating the successful surface modification of graphene frameworks by fluorosilane. However, the Zn2p peak from silanized GH-PDA-Z2 is not observed as the surface of ZIF-8 coating is now fully covered by the top thin layer of fluorosilane and therefore, not detected in XPS which is a surface- sensitive spectroscopic technique (FIG. 7E). However, the characteristic spectra for ZIF-8 nanoparticles are well observed in XRD diffraction patterns (XRD) in FIG. 5C and energy-dispersive X-ray spectroscopy (EDS) analysis (FIG. 8A and 8B). It means ZIF-8 crystals are still stable on the GH-PDA surface after coating of fluorosilane at high temperature (FIG. 9). The nitrogen-sorption isotherm study (FIG. 5D) for Brunauer-Emmett-Teller (BET) analysis was also performed to observe for any change in nanoscale porosity of GH-PDA colloidal frameworks before and after loading of ZIF-8 and also after coating of fluorosilane layer on their surfaces. The BET surface area of 180.40 irrg 1 for GH-PDA colloidal powder was obtained. Although this is slightly lower than the surface area of cylindrical bulk GH-PDA hydrogel (310 m2g_1), but it is comparable to those of meso/macropores prepared by sintering, or other hydrothermal methods. After ZIF-8 loading, the BET surface area of GH-PDA-Z2 increases to 646.36 m2g_1 due to the combined contribution coming from micropores of ZIF-8 particles and mesopores of graphene. However, after surface modification by fluorosilane, the surface area of both silanized GH-PDA colloid and GH-PDA-Z2 decreases sharply to 15.60 m2g_1 and 24.63 m2g_1, respectively. This reduction in surface area is coming from the thin layer coating of fluorosilane, in which polysiloxane networks are formed due to fast deposition filling the nanoscale pores of GH-PDA colloid and ZIF-8 in GH-PDA-Z2, keeping only the microscale pores to contribute in BET experiment. This result further supports the disappearance of Zn2p peak in XPS spectra of GH-PDA colloid and GH-PDA-Z2 samples.
[00171] The static contact angle of solvents with different surface tensions were measured on silanized GH-PDA and silanized GH-PDA-Z coated glass slides as shown in FIG. 10A to 10E. All the surfaces from silanized GH-PDA to GH-PDA-Z3 show super-repellence for high surface tension solvents from water (7 = 72.7 mN/m) to ethylene glycol (7 = 47.7 mN/m), exhibiting high static contact angle of more than 150°. Particularly, coating surfaces from silanized GH-PDA to GH-PDA-Z2 displayed superamphiphobicity with CAHDC (7 = 213 m /m) of more than 150°. These coating surfaces demonstrated their potential for protective coating purposes. Meanwhile, for low surface tension non-polar solvents from n-hexadecane (7 = 27.3 mN/m) to methanol (7 = 22.7 mN/m), glass surface coated with silanized GH-PDA colloid displayed the best ability to repel these solvents, exhibiting contact angle of more than 146° as compared to GH-PDA-Z colloidal frameworks. However, the repellency dropped sharply in the case of silanized GH-PDA-Z4 as shown by the decrease in contact angles which are less than 150° with all polar solvents. Silanized GH-PDA-Z4, therefore, shows the lowest contact angles for all solvents compared to other samples. Moreover, silanized GH-PDA-Z4 does not show super-repellency for high surface tension solvents, displaying 0° contact angle of all non-polar solvents, i.e. lower ability to repel low surface tension liquids.
[00172] For n-hexane having the lowest surface tension (7 = 18.4 mN/m) among all the solvents tested here, all surfaces showed no repellency exhibiting 0° contact angle. Therefore, the variation in static contact angle values confirms the change in surface wettability of silanized GH-PDA-Z by varying coated wall thickness with different ZIF-8 loading and fluorosilane coating. By increasing the ZIF-8 loading, the surface morphology of porous graphene is tuned towards nanoscale porosity which has lower ability to repel low surface tension liquids. These results are further confirmed by dynamic contact angle measurement, i.e. measuring the advancing and receding contact angles. A high surface tension liquid, formamide (FM), was used for this measurement. Surfaces of silanized GH-PDA to silanized GH-PDA-Z3 showed super- repellence for FM with small difference between advancing and receding contact angle whereas silanized GH-PDA-Z4 displayed a large difference (FIG. 11). This result reveals lesser amount of air entrapment inside the pores of silanized GH-PDA- Z4 compared to former surfaces due to thicker wall coating. The durability of coating surfaces over time and temperature was also studied via contact angle measurements on silanized GH-PDA-Z2, which was taken as an exemplary sample. The static contact angle values of both high as well as low surface tension solvents remained unchanged at more than 150° and at nearly 0°, respectively, over 100 days (FIG. 12A). Also, the static (about 170°) as well as sliding contact angle (less than 5°) values for water droplet remained unchanged over same storage condition (FIG. 12B). Similar observations were found when contact angles of the coated glass slide are measured by incubating them for 1 hour at various temperatures such as -196 C (liquid nitrogen), 100 C and 200 C before measurement (FIG. 12C and 12D), thus confirming high durability of superamphiphobic coating on glass slide over longer storage time and temperature.
[00173] Example 10: Results and Discussion - Dependence of Super-Repellency on Surface Structure
[00174] In this example, the dependence of super-repellence of liquids on surface morphology is explained using two theoretical models: Wenzel model and Cassie- Baxter model. The transition state between these models were also considered. These models are used to explain the repellency of a surface when a liquid droplet is deposited on it. Wenzel model (equation 1) mentions the roughness of a surface which can help enhance the wetting behavior.
[00175] cos Q* = r cos Q (1) [00176] where Q is the Young contact angle corresponding to the wettability of a flat surface, and r is surface roughness. It is noted that the value of r is always larger than 1. This means that the introduction of roughness on a flat surface always enhances its surface wettability depending on surface chemistry of material. Q is the Wenzel contact angle.
[00177] For Cassie-Baxter model (equation 2), in addition to surface roughness, this model includes the effect of air volume trapped underneath when a liquid droplet is deposited on a rough surface. In this case, the repellency of a rough surface is much higher than that of a flat surface for the same material because of the presence of trapped air.
[00178] cos 0* = (1 - <j)aiT ) cos Q - <j)aiT (2)
[00179] where faίt is the fraction of air underneath the pores, Q* is the Cassie-Baxter contact angle.
[00180] Unlike“re-entrant” or“T” shaped structures which are uniformly constructed in regular morphologies, the porous structure is formed mostly by assembly of 2D materials and/or ice-templation of cross-linked 2D materials. Therefore, it is more complicated to investigate effect of structure parameters to surface wettability. Recently, pore height (H) of porous coating structure has been considered as the main factor causing transition from superamphiphobicity to quasi- superamphiphobicity corresponding to Cassie-Baxter to Wenzel transition. Cassie-Baxter model represents a metastable state. Thus, it can be changed under certain conditions such as amount of air trapped underneath liquid droplet, surface tension of deposited liquid or break-in pressure (or intrusion pressure), therefore, it is termed as Cassie-Baxter to Wenzel transition. Here, the trapped air fraction ( fa ) was considered to investigate this transition by varying thickness of graphene wall, e.g. changing pore diameter of graphene unit (D) while keeping the same coating height (H). FIG. 13A and 13B illustrate how the change of wall thickness affects the volume of air trapped leading to the change in surface repellence of liquids droplet.
[00181] In the case of a porous structure, if the influence of coating wall thickness (T) is ignored, fa can be approximately calculated by equation 3 as follows:
Figure imgf000036_0001
[00183] As ZIF-8 particles grow on graphene wall surface, it reduces pore diameter of the microporous graphene surface as well as increases coating wall thickness with increasing of its loading. Therefore, sum of T and D, ( T+D ), i.e. the average size of macropores of GH-PDA stays unchanged, and can be calculated to be equal to 2 pm, as can be seen from SEM images in FIG. 4C to 4F. Three samples, silanized GH- PDA, silanized GH-PDA-Z2 and silanized GH-PDA-Z4 with wall thickness (T) approximately equal to 55, 100 and 400 nm, respectively, were chosen for the calculation of air fraction of porous structure. The diameter (D) of those, therefore should be 1.945 pm, 1.90 pm and 1.6 pm, respectively. It is clearly seen that T< D/2 in all cases, thus, all samples can be considered as microscale porous structure rather than nanoscale porous in which T exactly equal to D/2. By substituting the values of T and D in equation 3, the air fraction fa can be calculated. Therefore, </)air for silanized GH-PDA, silanized GH-PDA-Z2 and silanized GH-PDA-Z4 are 0.97, 0.95 and 0.80, respectively. Substituting those air fraction values and Young contact angles into equation 2, the theoretical contact angle value of the liquid droplet can be derived. Therefore Q* F : for silanized GH-PDA, silanized GH-PDA-Z2 and silanized
GH-PDA-Z4 are calculated to be 163.8°, 159° and 137°, respectively. Q* EG for silanized
GH-PDA-Z4 is much smaller than 150°, implying the transition from Cassie-Baxter state to Wenzel state. These values indicate that presence of smaller air fraction in silanized GH-PDA-Z2 and silanized GH-PDA-Z4 creates less oleophobicity compared to silanized GH-PDA. This is obvious when either nanoscale porosity or microscale is dominant compared to each other in the hierarchical structure.
[00184] In order to explain the results, Laplace pressure, is considered as the driving force, because it causes the contact line to move downward making the curve at solid/liquid/air interface (FIG. 13A and 13B). Laplace pressure, APLap, is proportional to curvature of liquid (K) which is, however, inversely proportional to the radius of a curved surface.
[00185] DR1ar - 2kg (4) [00186] where K is the curvature at the sagging contact line and is inversely proportional to the radius a of a curved surface ( J = l/a). When pore diameter on the surface decreases, i.e. wall thickness increases, it causes an increase in Laplace pressure. This makes the three-phase contact line slide down from the top side of porous structure and move downward to the bottom, causing the penetration of liquid droplet. Therefore, a larger value of Laplace pressure causes easy penetration of liquid through a porous surface.
[00187] Example 11: Results and Discussion - Surface Coating and Separation of Immiscible Liquids Mixture
[00188] The filtration membrane was made by drop casting silanized GH-PDA-Z4 on Ni foam to separate simple mixture of immiscible solvents. The layers of silanized GH-PDA-Z4 not only decreases the surface energy of Ni foam but also helps to increase its surface roughness. The increase in surface roughness strengthens the repellence of liquid if the contact angle is higher than the intrinsic value or allow the liquid to penetrate if the contact angle is lower than the intrinsic value. The intrinsic value refers to the minimum contact angle on a flat surface of which lower than that value, liquids can penetrate through the surface if surface roughness is increased. In case of contact angle higher than intrinsic value, the liquids can be retained on the surface if surface roughness is increased. Therefore, when the static contact angle of high surface tension liquids on silanized GH-PDA-Z4 coated Ni foam, silanized Ni foam and bare Ni foam were compared, significantly higher static contact angle values for silanized GH-PDA-Z4 (FIG. 14C) than bare Ni foam (FIG. 14A) and silanized Ni foam (FIG. 14B) were obtained due to the increased surface roughness in silanized GH-PDA-Z4. FIG. 14D, in addition, confirms the result for other high surface tension liquids. However, with further decrease in the surface tension, silanized GH-PDA-Z4 coated Ni foam only shows lyophobicity up to n-hexadecane (27.5 mN/m) with contact angle of 80.5+1.5°, while it shows superlyophilicity to other liquids having surface tension below 27.5 mN/m which spread on the membrane and permeate through it quickly. Based on this property, silanized GH-PDA-Z4 is a good candidate to separate immiscible liquid mixture to maintain high efficiency.
[00189] Apart from the ability to separate the immiscible liquids, the separation efficiency as well as the repeatability of a membrane are highly desirable criteria for practical applications. Therefore, the separation efficiency of the silanized GH-PDA- Z4 coated Ni foam membrane from the mixture of all the high surface tension solvents was studied. The separation efficiency of carbon tetrachloride from different polar solvents was found to be higher than 97.5 % by volume (FIG. 15A).
[00190] In addition, FIG. 15B and 15C show the separation efficiency of formamide from different low surface tension solvents and corresponding flux are near or above 3000 Lm 2h_1, respectively. Moreover, to check the regeneration/repeatability of the membrane, a mixture of formamide and chloroform was used. After each filtration, the membrane was washed with ethanol and dried in air at 80°C. It is clear to see that the membrane is good to filter formamide out of chloroform at high efficiency (more than 83%) and the flux is maintained higher than 3000 Lm 2h_1 after 20 cycles of filtration (FIG. 15D). This result is promising for a long-term application of membrane. It is further demonstrated that the surface chemistry and surface topography of the membrane are very crucial for the separation of two immiscible liquids specially having close surface tensions. The mixture of chloroform (g = 27.5 mN/m) and formamide iy = 58.2 mN/m) was chosen as an example for this experiment (FIG. I6A1 to I6C3).
[00191] Formamide (FM) was colored with methylene blue (MB) and can be seen floating on top of the mixture as the density of chloroform (CF) is higher than formamide. Bare Ni foam, silanized GH-PDA-Z2 and silanized GH-PDA-Z4 coated Ni foam membranes were used for the separation. Bare Ni foam membrane cannot selectively separate the mixture components, and allows both the liquids to pass through it (FIG. I6A1 to I6A3). Meanwhile, silanized GH-PDA-Z2 coated Ni foam membrane repelled both the liquids and hence cannot filter the mixture (FIG. I6B1 to I6B3). When silanized GH-PDA-Z4 coated Ni foam membrane was used, low surface tension chloroform can easily pass through it while comparatively high surface tension formamide remains on top of the membrane (FIG. I6C1 to I6C3). The static angle values from FIG. 10A to 10E also support this observation. Furthermore, filtration of chloroform and formamide mixture using silanized Ni foam is also conducted as another control (FIG. 17A to 17D). Due to the high repellency to formamide, silanized Ni foam potentially separates formamide from chloroform (from FIG. 17A to 17C). However, when more liquid contacted the membrane surface, a part of formamide also penetrated through the membrane (FIG. 17D). This is caused by the fact that smooth surface has lower intrusion pressure than rough surface, meaning less polar liquid can be filtered using smooth membrane. Meanwhile, silanized GH-PDA-Z4 maintains the surface energy of the membrane in between the close surface tensions immiscible liquids, allowing successful separation. When a mixture of immiscible liquids with large difference in surface tensions are taken, e.g. formamide (g = 58.2 mN/m) and n-hexane iy = 18.5 mN/m), both the silanized GH- PDA-Z4 and the silanized GH-PDA-Z2 coated Ni foam membranes show successful separation of formamide out of n-hexane (FIG. 18A to 18D and FIG. 19A to 19D, respectively). The filtration of mixture of n-hexane with other high surface tension liquids was also performed by using silanized GH-PDA-Z2 coated Ni foam membrane (SEM images of membrane shown in FIG. 20A and 20B, and results shown in FIG. 21A and 21B). The high separation efficiency (more than 98.5%) and excellent regeneration ability were obtained using this membrane. Therefore, to separate immiscible liquids having large surface tension difference, e.g. separating n-hexane from the mixture of water, glycerol, formamide, ethylene glycol, etc., silanized GH- PDA-Z2 coated membrane appears to be an alternative. To further test the purity of the filtrate, filtrate solutions of formamide and low surface tension solvents were characterized using UV-Vis spectroscopy. A calibration curve of MB was made by using different concentration of MB dissolved in formamide which showed the main adsorption peak at 654 nm. The absence of any peak at 654 nm in the UV-Vis spectra of the filtrates (FIG. 22) indicates that the filtrate was free of formamide and the slight weight loss of formamide may be due to sticking of formamide on the membrane surface.
[00192] Example 12: Summary of Discussion and Results
[00193] In summary, a micron-sized 3D porous graphene frameworks that could easily be further modified by tuning the microscale pore diameter via MOF loading and tailoring the surface chemistry using thin layer coating of fluorosilane, was successfully prepared. Such modification can manipulate the surface topography of the graphene frameworks by varying the coated wall thickness and hence controlling the amount of entrapped air inside the pores of the material leading to different liquid repellency. Based on this tailored property, a series of coating surfaces and membranes obtained by drop casting this graphene material on glass and Ni foam, respectively, are used to modify surface of hydrophilic glass and to separate a high surface tension liquid from a low surface tension liquid. Among all the silanized graphene/MOFs composite frameworks coated glass, coating surfaces from silanized GH-PDA to GH-PDA-Z2 display superamphiphobicity, which provide for promising applications in protective coating. Meanwhile, silanized GH-PDA-Z4 coated Ni foam performed well in separating immiscible organic mixture liquids with close surface tension. Moreover, the tailorable wettability and filtration ability of the as-prepared graphene framework provide for numerous applications in environmental treatment, marine, medicine or petrochemical industries.
[00194] Example 13: Commercial and Potential Applications
[00195] The examples presented above demonstrate for a superamphiphobic coating based on silanized porous 3D graphene/MOFs composite frameworks building block. The surface wettability of the superamphiphobic composite frameworks is systematically tuned by deposition of different amount of MOFs crystals on surface of 3D graphene so that the surface energy is located between surface tension values of two immiscible organic liquids. The results show that the composite at 1.43 w% of graphene (silanized GH-PDA-Z4) demonstrates oleophobicity towards ethylene glycol (y = 47.7 mN/m) with CA=l37.5° and superoleophilicity towards dichloromethane iy = 26.5 mN/m) and lower surface tension liquids with CA of about 0°, revealing a high potential in terms of immiscible organic liquids separation.
[00196] Membrane filtration is demonstrated by drop casting the silanized graphene/MOFs composite frameworks on Ni foam substrate instead of a glass piece. The graphene/MOFs composite not only changes surface wettability of pristine Ni foam but also enhances its surface roughness leading to a coated membrane as described above, which is advantageous over bare Ni foam and silanized Ni foam in terms of liquid repellency. The as-prepared membrane can efficiently separate formamide from a mixture having low surface tension solvents at a flux near to or higher than 3000 Lm 2h_1 under gravity with separation efficiency higher than 83% and with good repeatability over 20 cycles. The superamphiphobic coating and coated Ni foam membrane described in the present disclosure are promising for the petroleum industry, marine time, medicinal, agricultrural and environmental sectors. [00197] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. A porous graphene composite comprising silanized graphene particles, wherein the silanized graphene particles are comprised of porous graphene particles coated with a polymer comprising a catechol group and having metal organic frameworks disposed on the polymer, and wherein a layer of polysiloxane is disposed on the metal organic frameworks or the polymer and the metal organic frameworks.
2. The porous graphene composite of claim 1, wherein the layer of polysiloxane is covalently attached to the metal organic frameworks or the catechol group and the metal organic frameworks.
3. The porous graphene composite of claim 1 or 2, wherein the polymer comprising the catechol group comprises polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
4. The porous graphene composite of any one of claims 1 to 3, wherein the metal organic frameworks are present as one or more layers of crystals.
5. The porous graphene composite of claim 4, wherein the one or more layers of crystals have a thickness of 450 nm or less.
6. The porous graphene composite of any one of claims 1 to 5, wherein the metal organic frameworks comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc- 1,4 benzodicarboxylic acid.
7. The porous graphene composite of any one of claims 1 to 6, wherein the metal organic frameworks are present in an amount based on the graphene content of the porous graphene particles.
8. The porous graphene composite of claim 7, wherein the graphene content is less than 28.6 wt% of the metal organic frameworks.
9. A method of producing a porous graphene composite, the method comprising: contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group;
drying the porous graphene particles coated with the polymer;
mixing the porous graphene particles with metal organic frameworks; and depositing a silanization agent on the porous graphene particles to form the porous graphene composite.
10. The method of claim 9, wherein contacting the graphene oxide comprises adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid.
11. The method of claim 9 or 10, wherein the polymer precursor comprises dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
12. The method of any one of claims 9 to 11, wherein the polymer comprising the catechol group comprises polydopamine or a polymer generated from tannic acid, 1,2- dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
13. The method of any one of claims 9 to 12, wherein the ionic liquid comprises 1 -butyl- 3 -methylimidazolium tetrafluoroborate .
14. The method of any one of claims 9 to 13, wherein mixing the porous graphene particles comprises mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles.
15. The method of claim 14, wherein the graphene content is less than 28.6 wt% of the metal organic frameworks.
16. The method of any one of claims 9 to 15, wherein mixing the porous graphene particles with the metal organic frameworks is carried out in the presence of an alcohol.
17. The method of claim 16, wherein the alcohol comprises methanol, ethanol, or isopropanol.
18. The method of any one of claims 9 to 17, wherein the metal organic frameworks comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc- 1,4 benzodicarboxylic acid.
19. The method of any one of claims 9 to 18, wherein depositing a silanization agent comprises mixing the porous graphene particles with the silanization agent.
20. The method of any one of claims 9 to 19, wherein the silanization agent comprises a fluorosilane comprising lH,lH,2H,2H-perfluorodecyltriethoxysilane.
21. A graphene composite membrane used in the separation of immiscible liquids, wherein the graphene composite membrane comprises the porous graphene composite of any one of claims 1 to 8.
22. The graphene composite membrane of claim 21, wherein the porous graphene composite is coated on a substrate.
23. The graphene composite membrane of claim 22, wherein the substrate comprises a glass, a metal foam, a cellulose paper, or polyurethane.
24. The graphene composite membrane of any one of claims 21 to 23, wherein the immiscible liquids have different surface tension.
25. A method of producing a graphene composite membrane, the method comprising:
contacting graphene oxide with a polymer precursor and an ionic liquid to form porous graphene particles coated with a polymer, wherein the polymer precursor and the polymer comprise a catechol group;
drying the porous graphene particles coated with the polymer;
mixing the porous graphene particles with metal organic frameworks;
depositing a silanization agent on the porous graphene particles to form the porous graphene composite; and
coating a substrate with the porous graphene composite to form the graphene composite membrane.
26. The method of claim 25, wherein contacting the graphene oxide comprises adding the polymer precursor to an aqueous solution comprising the graphene oxide before adding the ionic liquid.
27. The method of claim 25 or 26, wherein the polymer precursor comprises dopamine, tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
28. The method of any one of claims 25 to 27, wherein the polymer comprising the catechol group comprises polydopamine or a polymer generated from tannic acid, l,2-dihydroxylbenzene, l,2,3-trihydroxylbenzene, gallic acid, epicatechin gallate, or epigallocatechin.
29. The method of any one of claims 25 to 28, wherein the ionic liquid comprises 1 -butyl- 3 -methylimidazolium tetrafluoroborate .
30. The method of any one of claims 25 to 29, wherein mixing the porous graphene particles comprises mixing an amount of metal organic frameworks based on the graphene content of the porous graphene particles.
31. The method of claim 30, wherein the graphene content is less than 28.6 wt% of the metal organic frameworks.
32. The method of any one of claims 25 to 31, wherein mixing the porous graphene particles with the metal organic frameworks is carried out in the presence of an alcohol.
33. The method of claim 32, wherein the alcohol comprises methanol, ethanol, or isopropanol.
34. The method of any one of claims 25 to 33, wherein the metal organic frameworks comprise zeolitic imidazolate frameworks, zirconium- 1,4 benzodicarboxylic acid, iron-2,6 naphthalenedicarboxylic acid, nickel-zinc based metal organic frameworks, or zinc- 1,4 benzodicarboxylic acid.
35. The method of any one of claims 25 to 34, wherein depositing a silanization agent comprises mixing the porous graphene particles with the silanization agent.
36. The method of any one of claims 25 to 35, wherein the silanization agent comprises a fluorosilane comprising lH,lH,2H,2H-perfluorodecyltriethoxysilane.
37. The method of any one of claims 25 to 36, wherein the substrate comprises a glass, a metal foam, a cellulose paper, or polyurethane.
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