2d material-based membrane protected by a polymeric film and method of fabricating thereof

Abstract

Disclosed is a 2D material-based membrane protected by a polymeric film, wherein the 2D material-based membrane is graphene or graphene oxide (GO). Also disclosed is a method of fabricating a 2D material-based membrane protected by a polymeric film as disclosed herein, by coating the polymeric film on one side or both sides of the 2D material-based membrane.

Description

2D MATERIAL-BASED MEMBRANE PROTECTED BY A POLYMERIC FILM AND METHOD OF FABRICATING THEREOFFIELD OF THE INVENTION

[0001] The present invention generally relates to a 2D material-based membrane coated by a polymeric film, as well as a method of fabricating thereof.BACKGROUND

[0002] Membranes based on nanostructured 2D materials are composed of stacked layers of thin sheets with lateral dimensions on the order of micrometres and interlayer distances of a few nanometers. This creates a lamellar stacked structure with nanochannels, enabling their application in the separation processes [1] [2]. For this purpose, a diversity of 2D materials has been investigated, e.g., the graphene family, metal dichalcogenides, layered oxides, zeolites, metal-organic frameworks (MOFs), MXenes, covalent organic frameworks (COFs), etc. [3] [4] [5] [6],

[0003] Nowadays, membrane technologies are developed for their wide application in the industrial separation and purification of components from mixtures of liquids, vapours, and gases [7], Water purification and desalination via membrane distillation, processes in chemical synthesis, solvent extraction and hydrogen separation are some examples [8] [3]. Pervaporation (PV) and vapour permeation (VP) have emerged as promising options for the separation process of liquid and vapour mixtures. For instance, the extraction of ethanol and other organic solvents from aqueous solutions by PV and VP can be an efficient process with low energy consumption [9] [8] . Among the 2D materials, graphene oxide (GO) has shown great potential in membranes for water separation and purification due to the unimpeded water transport through the nanochannels while blocking the permeation of other molecules [2],

[0004] Although 2D materials-based membranes made at the laboratory scale exhibit unique characteristics with high potential for these applications, they do not meet all the requirements for large-scale processes, typical from the industry [7]. The highly hydrophilic character of free-standing GO membranes poses significant technical challenges for utilising them in real-world separation processes [9]. In a previous invention, the inventors developed self-standing membranes based on crosslinked graphene oxide (GO) with selectivity properties that allow their application in liquids, vapours, and gas separation [7],

[0005] Large area laminate self-standing membranes with thicknesses of up to several micrometres do not offer enough structural stability to the typical pressures, mechanical loads, handling and harsh environments of the industry

[0010] . Another operational factor that can affect the separation performance of 2D matcrials-bascd membranes is their structural response in the presence of solvents (liquids or vapours), which can cause swelling and delamination, hr industrial conditions, it is crucial for membranes to maintain their structural stability, mechanical strength and stiffness over a suitable lifetime

[0011] . Specifically, the stability and performance of GO membranes are significantly impacted by water and moisture.

[0006] Thus, there is a need for some protective support that allows the 2D materials-based membranes to be used in separation processes involving physical conditions, which would otherwise damage the free-standing membranes. The present invention uses of polymeric permeable films for the mechanical support of 2D materials-based membranes such as GO or graphene self-standing membranes. GO or graphene self-standing membranes were protected with permeable polymeric films, tested in separation processes of aqueous solutions, and evaluated regarding durability and resistance to gas pressures.SUMMARY

[0007] The present disclosure describes 2D matcrials-bascd membranes protected with polymeric permeable films to extend their operational life and applications, and the method of fabricating thereof.

[0008] In one aspect, the present disclosure refers to a 2D material-based membrane protected by a polymeric film, wherein the 2D material-based membrane is graphene or graphene oxide (GO).

[0009] In another aspect, the present disclosure refers to a method of fabricating a 2D material- based membrane protected by a polymeric film as disclosed herein, by coating the polymeric film on one side or both sides of the 2D material-based membrane; wherein the 2D material-based membrane is graphene or graphene oxide (GO).

[0010] Advantageously, the applied protection of the polymeric film improves the mechanical strength and stiffness of the 2D materials-based membranes so that they can resist higher operational pressures. The 2D material-based membrane protected by a polymeric film exhibits structural stability that allows applications at the typical pressures, mechanical loads, handling and harsh environments of the industry.

[0011] Advantageously, the selectivity properties of the protected 2D material-based membrane are enhanced by the protection with a film of an appropriate polymer according to the separ ation process to be applied.

[0012] Advantageously, the 2D material-based membrane protected by a polymeric film has demonstrated higher durability and shelf-life than the unprotected ones.

[0013] Advantageously, due to the improvement in mechanical properties, an enhancement in handling of the 2D material-based membrane protected by a polymeric film has been achieved.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0015] Figure l is a photograph of the self-standing GO membrane with one-side protection by a permeable polymeric film.

[0016] Figure 2 is a photograph showing simultaneous PV process for GO self-standing membranes, one-side protected GO membrane and pure PVA film.

[0017] Figure 3 is a bar graph showing separation factor (a), and PSI of one-side protected membranes, the free-standing membranes and pure PVA films for PV process of ethanol / water mixture with concentration 80 wl% at 23 °C.

[0018] Figure 4 are photographs of gas permeation module (left) and experimental setup for gas testing and gas permeation.

[0019] Figure 5 is a photograph of GO membrane wrapped around a porous SiC tube and protected by a PVA film.

[0020] Figure 6 is a photograph of encapsulated self-standing GO membrane in permeable polymeric films.

[0021] Figure 7 is a bar graph showing separation factor (a), and PSI for the encapsulated membranes, free-standing membranes and pure PVA films for PV of ethanol / water mixture with concentration 50 wt% at 23 °C.

[0022] Figure 8 are photographs of GO membrane on the bottom of the glass container covered by the liquid PTMSP solution (a) and PTMSP glassy polymer (b).

[0023] Figure 9 arc photographs of graphene membrane covered with PTMSP.DETAILED DESCRIPTION

[0024] The present disclosure refers to protecting 2D materials-based membranes with polymeric permeable films to extend then- operational life and applications. Self-standing graphene oxide- based membranes were fabricated and protected by coating or by encapsulation with permeable polymeric films. The selection of a particular polymer is dependent on the specific application of the membrane. The properties of the chosen polymer contribute to enhancing the overall characteristics of the membrane. The procedure for protecting the 2D materials-based self-standing membranes can be performed using water-soluble polymers and non- water- soluble glassy polymers. The protection of 2D materials-based membranes with polymeric films is performed as one-side protection or as encapsulation (both-sides protection). Graphene oxide or graphene self-standing membranes were protected with permeable polymeric films, tested in separation processes of aqueous solutions and gases, and evaluated regarding the enhancement in durability and resistance to gas pressures.

[0025] In one aspect, the present disclosure refers to a 2D material-based membrane protected by a polymeric film, wherein the 2D material-based membrane is graphene or graphene oxide (GO).

[0026] In one example, the 2D material-based membrane is graphene. In another example, the 2D material-based membrane is graphene oxide (GO). In another example, the 2D materialbased membrane is selected from the group consisting of metal dichalcogenides, layered oxides, zeolites, metal-organic frameworks (MOFs), MXenes, and covalent organic frameworks (COFs)

[0027] In one example, the 2D material-based membrane is non- self- standing. The nonself-standing 2D material-based membrane covers a ceramic, metallic, polymeric, or composite supporting substrate, before being protected by a polymeric film. The purpose of covering a non-self- standing 2D material-based membrane on a ceramic, metallic, polymeric, or composite supporting substrate is to protect and enhance the physical strength of the non-self- standing 2D material-based membrane.

[0028] In another example, the 2D material-based membrane is self-standing.

[0029] In one example, the self-standing 2D material-based membrane is Graphene Oxide (GO). In another example, the self-standing 2D material-based membrane is graphene. In another example, a self-standing Graphene Oxide (GO) membrane comprises a plurality of layers of crosslinked GO sheets, which is fabricated using a crosslinking agent to crosslinkbetween oxygen-containing functional groups of neighbour GO sheets, wherein the crosslinking agent is a metallic oxide or a carbide. These crosslinking agents provide mechanical stability to the membranes and affect the mass transport mechanisms inside the membranes.

[0030] In one example, the crosslinking agent is a metallic oxide selected from the group consisting of Iron (III) oxide (FC2O3), aluminium oxide (AI2O3), calcium sulfate (CaSOO, niobium pentoxide (NbzOs), Bi-2212 (Bi2Sr2CaCu2Ox), an oxide of a transition metal, an oxide of an alkaline earth metal, an oxide of a post-transition metal, aluminosilicate, and a multication oxide selected from the group consisting of YBaCO and BSCCO. In another example, the crosslinking agent is a combination of the metallic oxide as disclosed herein. In another example, the crosslinking agent is AhO i / CaSO450 / 50 wt.%.

[0031] In another example, the crosslinking agent is a carbide selected from the group consisting of silicon carbide (SiC), TiC, ZrC, HfC, VC, NbC, TaC, Cr7C3. C13C2. MoC, and M02C.

[0032] The fabrication method of the self-standing GO membrane is based on the interaction of a crosslinking agent with GO, giving rise to crosslinking between the oxygencontaining functional groups of neighbor GO sheets. In one example, the oxy gen-containing functional group is an epoxide group. In another example, the oxygon-containing functional group is a hydroxyl group. In another example, the oxy gen-containing functional group is a carboxyl group. In another example, the oxygen-containing functional group is a carbonyl group.

[0033] The approach of incorporating metallic cations into graphene -related materials via the disclosed method of using metallic oxides and carbides as cation sources and crosslinking agents leads to strong interactions between the crosslinking agents and the oxygen-containing functional groups, therefore the formation of crosslinking structures by Metal-O-C and / or Metal-C bonds.

[0034] As most metallic oxides are insoluble in w ater, the interaction initially occurs mainly between the oxides and the GO functional groups, which then causes the formation of crosslinking sites with the metallic cations. This process takes place in different forms, depending on the specific metallic oxide and the particular procedure of membrane preparation.

[0035] In a first embodiment of the fabrication method of the self-standing 2D materialbased membrane as disclosed herein, the method comprises the following steps:a. preparing a suspension of GO in distilled water or a water / ethanol solution via sonication for 0.5 - 1 h; b. casting or spraying the suspension of GO uniformly on a solid porous surface of a metallic oxide, a mixture of metallic oxides, or a carbide to form a layer; c. drying the layer at room temperature; d. sequentially repeating steps b and c until the GO membrane comprising a plurality of layers of crosslinked GO sheets is formed; e. peeling off the GO membrane off from the solid porous surface, or detaching the GO membrane from the solid porous surface by immersing the GO membrane in distilled water containing a surfactant.

[0036] In one example, in step a of the first embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, the GO is suspended in distilled water. In another example, in step a of the first embodiment of the method as disclosed herein, the GO is suspended in a water / ethanol solution. In one example, the concentration of GO in the suspension is 0.5 - 10 mg / mL. In another example, when GO is suspended in a water / ethanol solution, the ethanol is 2 - 70 wt.%. In step a of the first embodiment of the fabrication method as disclosed herein, the suspension of GO in distilled water or a water / ethanol solution is prepared through homogenization by mild sonication in a sonication bath at room temperature for 0.5-1 h.

[0037] After homogenization, the prepared suspension of GO is uniformly cast or sprayed on a solid porous surface of a metallic oxide or a mixture of metallic oxides, which can be composed of AI2O3, CaSO4, FerOs, FC3O4. FeO, NbrOs, and other oxides of transition metals and alkaline earth metals, post-transition metals, aluminosilicates, multi-cation oxides like the low-temperature superconductor series YBaCO, BSCCO and other multi-cation oxides, as well as carbides like SiC.

[0038] A homogeneous GO membrane is assembled by sequentially casting or spraying several layers and drying each one of them before depositing the next layer. In one example, the quantity of the suspension of GO used to form each layer is 0.1 - 6 mL / cm2.

[0039] In one example, the number of layers of crosslinked GO sheets is at least 3 if the suspension of GO is casted on the solid porous surface. In one example, the number of layers of crosslinked GO sheets is at least 10 if the suspension of GO is sprayed on the solid porous surface.

[0040] A minimal time of one hour is necessary to let dry the first layer under ambient conditions. The second, third, and fourth layers need a minimal drying time of 3, 6, and 12 h respectively. Any further layer needs about 12 h to dry at room temperature under ambient conditions.

[0041] In one example, the resulting dry membrane can be integrally peeled off from the solid surfaces. In another example, the resulting dry membrane can be detached with the help of immersion in distilled water containing a surfactant agent which is water-soluble, selected from the group consisting of SDS, hydroxides, and other surfactant substances.

[0042] In the first embodiment of the fabrication method of the self-standing 2D materialbased membrane as disclosed herein, after detaching, the GO membrane is washed for at least 1 h in distilled water.

[0043] In a second embodiment of the fabrication method of the self-standing 2D materialbased membrane as disclosed herein, the method comprises the following steps: a. preparing a suspension of GO in distilled water or a water / ethanol solution via sonication for 0.5 to 1 h; b. preparing a suspension of the crosslinking agent in distilled water or a water / ethanol solution via sonication for 1 to 4 h; c. preparing a suspension of the crosslinking agent and GO in distilled water or a water / ethanol solution by mixing the suspension of GO prepared in step a and the suspension of the crosslinking agent prepared in step b and sonicating for 0.5 to 1 h; d. casting or spraying the suspension of the crosslinking agent and GO uniformly on a solid surface to form a layer; e. drying the layer at room temperature; f. sequentially repeating steps d and e until the GO membrane comprising a plurality of layers of crosslinked GO sheets is formed; g. peeling off the GO membrane off from the solid surface, or detaching the GO membrane from the solid surface by immersing in distilled water containing a surfactant.

[0044] In one example, in steps a-c of the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, the crosslinking agent and GO are suspended in distilled water. In another example, in steps a-c of the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, the crosslinking agent and GO arc suspended in a water / ethanol solution.

[0045] In one example, in step a of the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, the concentration of GO in the suspension is 0.5 - 10 mg / mL. In another example, when the crosslinking agent and GO is suspended in a watcr / cthanol solution, the ethanol is 2 - 70 wt.%.

[0046] In the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, in step a, the suspension of GO in distilled water or a water / ethanol solution is prepared by mild sonication in a sonication bath at room temperature for 0.5 to 1 h.

[0047] In the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, in step b, a suspension of the crosslinking agent in distilled water or a water / ethanol solution is prepared by mild sonication in a sonication bath for 1 to 4 h.

[0048] In the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, in step c, the suspension of GO prepared in step a and the suspension of the crosslinking agent prepared in step b were mixed and subjected to mild sonication at room temperature for 0.5 to 1 h in a sonication bath.

[0049] In the second embodiment of the fabrication method of the self-standing 2D material- based membrane as disclosed herein, it is important that the suspension of GO in step a or the suspension of GO and crosslinking agent in step c can be continuously sonicated for up to about 1 h. Longer sonication time is needed for the suspension of the crosslinking agent in step b, before mixing with the suspension of GO in step c.

[0050] After sonication, the suspension of the crosslinking oxide and GO is uniformly casted or sprayed onto a solid surface. The solid surface can be any solid surface, for example, one made of a metallic, ceramic, or polymeric material, or combinations thereof.

[0051] A homogeneous GO membrane is assembled by sequentially casting or spraying several layers and drying each one of them before depositing the next layer. In one example, the quantity of the suspension of the crosslinking oxide and GO used to form each layer is 0.1 - 6 mL / cnr.

[0052] In one example, the number of layers of crosslinked GO sheets is at least 3 if the suspension of the crosslinking oxide and GO is casted on the solid surface. In one example, the number of layers of crosslinked GO sheets is at least 10 if the suspension of the crosslinking oxide and GO is sprayed on the solid surface.

[0053] Similar to the first embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, multiple layers of GO sheets can be added, and a minimal time is necessary for drying each layer at room temperature under ambient conditions. A minimal time of one hour is necessary to let dry the first layer under ambient conditions. The second, third, and fourth layers need a minimal drying time of 3, 6, and 12 h respectively. Any further layer needs about 12 h to dry at room temperature under ambient conditions.

[0054] In one example, the resulting dry membrane can be integrally peeled off from the solid surfaces. In another example, the membranes can be detached with the help of immersion in distilled water containing a surfactant agent which is water-soluble, selected from the group consisting of SDS, hydroxides, and other surfactant substances.

[0055] In the second embodiment of the fabrication method of the self-standing 2D material-based membrane as disclosed herein, after detaching, the GO membrane is washed for at least 1 h in distilled water.

[0056] The self-standing GO membrane fabricated using the method as disclosed herein exhibits a cracks-free and uniform surface and is mechanically stable and bendable. The membrane has unaffected integrity after immersion in water for months. As further improved properties, these self-standing GO membranes have potentially improved high adsorption capability, which allows applications for energy storage and solid-state hydrogen storage. The self-standing GO membrane fabricated using the method as disclosed herein also showed a high selectivity in vapours and liquids, mainly due to the ordered stacking microstructure of laminates in the self-standing membranes.

[0057] In another example, a self-standing Graphene Oxide (GO) or graphene membrane is fabricated using a method selected from the group consisting of spray coating, bar / doctor blade coating, slot-die coating, spin coating, dip coating, and pressure-assisted assembly.

[0058] The self- standing 2D material-based membrane as disclosed herein demonstrates superior strength resistance and mechanical stability. As such, these self-standing 2D materialbased membranes possess physical properties that allow them to be subjected to the process of covering by polymeric films as disclosed herein without affecting them physically.

[0059] In one example, the polymeric film is coated on one side of the 2D material-based membrane. In another example, the polymeric film is coated on both sides of the 2D material-based membrane. As used herein, the term "encapsulation" or grammatical variations of that term, refer to coating the 2D material-based membrane on both sides.

[0060] In one example, the coating of the polymeric film on one side or both sides of the 2D material-based membrane is by casting. In another example, the coating of the polymeric film on one side or both sides of the 2D material-based membrane is by spraying. In another example, the coating of the polymeric film on one side or both sides of the 2D material-based membrane is by dip coating.

[0061] The procedure for protecting the 2D materials-based self-standing membranes can be performed using water-soluble polymers like Poly(vinyl alcohol) (PVA), Styrene-butadiene rubber (SBR), Carboxy methyl cellulose (CMC), Polyacrylic Acid (PAA), Polysaccharides; non- water- soluble glassy polymers, which include but are not limited to polystyrene (PS), polyvinyl acetate (PVAc), polylactic acid (PLA), Poly(l -trimethylsilyl- 1 -propyne) (PTMSP), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polysulfone (PSU), polyether sulfone (PESU), polyimide (PI), and polycarbonate (PC); their composites or a combination thereof.

[0062] In one example, the polymeric film is made of a water-soluble polymer selected from the group consisting of poly(vinyl alcohol) (PVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and a polysaccharide.

[0063] In one particular example, the polymeric film is made of a water-soluble polymer PVA. The PVA film is manufactured by the following process:(a) homogenizing 0.005 to 0.1 mg / mL PVA in a vortex mixer with speed, temperature and time ranging between 200-600 rpm, 90-110 °C and 2-5 hours, respectively;(b) preparing crosslinked PVA films by adding the crosslinking agent Glutaraldehyde (GA) and 37% concentrated hydrochloric acid (HC1) and homogenizing the mixture in a vortex mixer for approximately 1 min. The quantities of HC1 and GA are 0.2-4 pL and 0.2-11 pL, respectively, for 1 mL of the PVA solution.(c) immediately casting the mixture from step (b) onto a solid surface to form a homogeneous permeable film; and(d) drying the homogeneous permeable film at room temperature for at least 24 h and subjecting it to thermal treatment at a temperature of 35-50 °C for 1-5 h.

[0064] In another example, the polymeric film is made of a non-water-soluble glassy polymer selected from the group consisting of polystyrene (PS), polyvinyl acetate (PVAc),polylactic acid (PLA), poly(l-trimethylsilyl-l-propyne) (PTMSP), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polysulfone (PSU), polyether sulfone (PESU), polyimide (PI), and polycarbonate (PC).

[0065] In another particular example, the polymeric film is made of a non-watcr- soluble glassy polymer PTMSP. APTMSP solution is prepared by dissolving 3 wt% of PTMSP in toluene or cyclohexane in a sonication bath with a frequency of 80 kHz for 30 min and a temperature of 25 °C.

[0066] In another example, the polymeric film is a polymer composite of PTMSP and graphene.

[0067] In another particular example, the polymeric film is made of a polymer composite of PTMSP and graphene, which comprises about 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3 wt% of graphene. In another example, the polymer composite of PTMSP and graphene is manufactured by the following process:(a) dispersing graphene in toluene with a concentration of 1.0-3.0 mg / mL in a sonication bath for about 3 h at about 25 °C.(b) mixing and homogenizing graphene / toluene solution and PTMSP solution (described above) under sonication for about 30 min at about 25 °C to obtain 0.5-4 wt% graphcnc / PTMSP permeable polymer composite films.

[0068] The main object of this invention is to protect self-standing 2D materials-based membranes with polymeric permeable films to extend their operational life and applications. Self- standing membranes were fabricated by the method described herein and protected by coating on one side or by encapsulation with permeable polymeric films using the procedures described herein.

[0069] The selection of a particular polymer is dependent on the specific application of the membrane. The properties of the chosen polymer should contribute to enhancing the overall characteristics of the membrane. For instance, for applications in water purification a hydrophilic polymer contributes to the preferential selectivity of water over other substances; meanwhile a hydrophobic polymer is appropriate for applications that involve extracting organic solvents from aqueous solutions. Polymers with high mechanical resistance and selectivity to specific gases or vapors are desirable for separation processes involving high pressures of gases and vapors.

[0070] The resulting 2D material-based membrane protected by a polymeric film has a thickness of about 30-100 pm, selected from the group consisting of about 30 pm, about 35 pm, about 40 pm, about 45 pm, about 55 pm, about 60 pm, about 65 pm, about 70 pm, about 75 pm, about 80 pm, about 85 pm, about 90 pm, about 95 pm, about 100 pm, or more.

[0071] The resulting 2D material -based membrane protected by a polymeric film can withstand up to 5 bars of pressure, thus have higher durability and shelf-life than the unprotected 2D material-based membrane, can resist higher operational pressures and enables enhanced handling. In another example, the resulting 2D material-based membrane protected by a polymeric film can withstand at least up to 5 bars of pressure, for example, up to 6 bars, up to 7 bars, up to 8 bars, up to 9 bars, up to 10 bars, or higher pressure.

[0072] The selectivity properties of the resulting 2D material-based membrane protected by a polymeric film is enhanced according to the separation process to be applied, hr one example, an enhancement in the selectivity to water over ethanol is demonstrated due to the encapsulation of the GO membrane with a hydrophilic material such as PVA.

[0073] In this invention, the protection of self-standing 2D materials-based membranes with polymeric films is performed in two different ways:

[0074] In one example, the protection of self-standing 2D materials-based membranes with polymeric films is by one-side protection: A polymer in solution is cast or coated on one side of a self-standing 2D materials-based membrane or a non-self-standing 2D materials-based membrane (where the membrane covers a ceramic, metallic, polymeric, or composite supporting substrate), resulting in the membrane being supported by a permeable polymeric film after curing or drying.

[0075] In another example, the protection of self-standing 2D materials-based membranes with polymeric films is by Encapsulation (both-sides protection): After one-side protection procedure by a first polymeric film, a second polymeric film is cast on the other side of the 2D materials-based membrane. In one example, the second polymeric film is the same as the first polymeric film. In another example, the second polymeric film is the different from the first polymeric film.

[0076] It is recommended that for both one-side protection and encapsulation, polymer permeable films cover a larger area than the membrane.

[0077] In another aspect, the present disclosure refers to a method of fabricating a 2D material- based membrane protected by a polymeric film as disclosed herein, by coating thepolymeric film on one side or both sides of the 2D material-based membrane; wherein the 2D material-based membrane is graphene orgraphene oxide (GO).

[0078] In one example, the 2D material-based membrane is graphene. In another example, the 2D material-based membrane is graphene oxide (GO). In another example, the 2D materialbased membrane is selected from the group consisting of metal dichalcogenides, layered oxides, zeolites, metal-organic frameworks (MOFs), MXcncs, and covalent organic frameworks (COFs).

[0079] After coating, the method further comprises drying the coated 2D material -based membrane. In one example, the drying is at room temperature. In another example, the drying is at room temperature for at least 24 h. In another example, the drying is via thermal treatment at a temperature between 35 and 50 °C for 1 to 5 h. In another example, the drying is at room temperature followed by the thermal treatment as disclosed herein.

[0080] The present invention may have the following commercial applications: a) Membranes for separation processes of pervaporation and vapour permeation for liquid and vapour mixtures of water with ethanol, methanol and other organic solvents. b) Membranes for separation processes of gas mixtures, including H2, CO2, N2, CFU and other gases. c) Materials for gas transport and storage, including H2, CO2, N2, CH4 and other gases.

[0081] As used in this application, the singular form “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a metal” includes a plurality of metals, including mixtures and combinations thereof.

[0082] As used herein, the term “comprising” means “including.” Variations of the word "comprising", such as “comprise” and “comprises,” have correspondingly varied meanings. Thus, for example, a composition “comprising” X may consist exclusively of X or may include one or more additional unrecited components.

[0083] As used herein, the term “about” in the context of concentration of a substance, size of a substance, length of time, or other stated values means + / - 5% of the stated value, or + / - 4% of the stated value, or + / - 3% of the stated value, or + / - 2% of the stated value, or + / - 1 % of the stated value, or + / - 0.5% of the stated value.

[0084] Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosedranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0085] The invention illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising", "including", "containing", etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied herein disclosed may be resorted to by those skilled in the ait, and that such modifications and variations are considered to be within the scope of this invention.

[0086] The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0087] Unless otherwise, indicated, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[0088] Other embodiments are within the following claims and non-limiting examples.EXAMPLES

[0089] Non-limiting examples of the disclosure will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the disclosure.

[0090] Example 1 - Methods of preparing polymeric films

[0091] 1.1. Example of water-soluble polymer solution preparation

[0092] A solution of 99% hydrolyzed PVA of 11,000 molecular mass in H2O was prepared using a proportion varying from 0.005 to 0.1 mg / mL. The solution was homogenized in a vortex mixer with speed, temperature and time ranging between 200 to 600 rpm, 90 to 110 °C and 2 to 5 hours, respectively.

[0093] Crosslinked PVA films were prepared by adding the crosslinking agent Glutaraldehyde (GA) and 37% concentrated hydrochloric acid (HC1) immediately before use. The quantity of HC1 and GA can vary between 0.2 to 4 qL and 0.2 to 11 pL, respectively, for 1 ml of the PVA solution. The solution with the crosslinking agents was homogenized in a vortex mixer for approximately 1 min. A film with a thickness between 1 and 50 pm can be prepared by drop-casting the prepared solution with crosslinking onto a solid surface. The film is left to dry at room temperature for at least 24 h and then submitted to further thermal treatment in an oven at a temperature between 35 and 50 °C for 1 to 5 h.

[0094] In one particular example, a solution with a concentration of 0.02 mg / mL was prepared and homogenised in a vortex mixer at a speed of 400 rpm and a temperature of 100 °C for 3 h. Immediately before casting the polymeric solution, 10 pL of GA and 10 pL of HC1 were added to 5 ml of 0.02 mg / ml PVA solution and homogenised in a vortex mixer for 1 min. The solution should be used immediately after preparation to form a homogeneous permeable film.

[0095] 1.2. Example of non-water-soluble glassy polymers solution preparation

[0096] A poly(l -trimethylsilyl- 1 -propyne) solution was prepared by dissolving 3 wt% of PTMSP in toluene in a sonication bath with a frequency of 80 kHz for 30 min and a temperature of 25 °C.

[0097] 1.3. Example of polymer composite solution preparation

[0098] Composites of PTMSP and graphene were prepared. Graphene was by dispersed in toluene with a concentration of 1.0 mg / mL in a sonication bath for 3 h at 25 °C. Graphene / toluene solution and PTMSP solution (described above) were mixed and homogenised under sonication for 30 min at 25 °C to obtain 0.5 to 4 wt% graphene / PTMSP permeable polymer composite films.

[0099] Example 2 - Results for producing protected membranes by permeable polymers films and their applications

[0100] 2.1. One-side protected membranes by water-soluble permeable polymers films

[0101] 2.1 (a) Flat protected membranes

[0102] In the present invention, a self-standing GO membrane [7] (with a thickness of around 5 pm and an area of about 20 cm2) was horizontally levelled on a plastic container. A PVA solution was cast onto the membrane. The sample was dried for 24 h at room temperature, followed by drying in oven at 40 °C for 2 h. Figure 1 shows a self-standing GO membrane with one-side protection by PVA permeable film, with a total thickness of around 35 pm.

[0103] Application in pervaporation process for water-ethanol separation

[0104] The membranes were tested in a PV process applied to a binary mixture of water and ethanol with a concentration of 80 wt% at 23 °C for 24 h. For comparison, simultaneous tests were performed using one-side protected GO membranes, unprotected self-standing GO membranes and pure PVA films. Figure 2 shows the membranes under testing, and Figure 3 presents the performance obtained for all the membranes.

[0105] Pressure testing

[0106] The mechanical resistance of one-side protected GO membranes was evaluated under gas pressure. The membranes were set in a stainless-steel permeation module in the experimental apparatus shown in Figure 4 and submitted to H2, CO2, N2, and CH4 gases with pressures of up to 3 bars for 1 h. The membranes stood the pressure without detectable structural damage. Due to the sensors' up-limit range, the apparatus set up for gas permeation tests is limited to operating up to 3 bars of pressure.

[0107] 2.1 (b) Tubular protected membranes

[0108] GO self-standing membranes covering porous SiC tubes [7] with an external diameter of 1.0 cm and a length of 15 cm were protected by one-side water-soluble permeable polymeric films. The permeable polymer protection was prepared by casting and dip casting in PVA solution.

[0109] PVA films with a thickness of around 30 pm on the GO membrane were obtained. For comparison, another SiC tube wrapped with a self-standing GO membrane was kept without PVA coating.

[0110] The membrane-over-tube systems were tested in a PV process applied to a binary mixture of water and ethanol with a concentration of 96 wt% (over the azeotropic point) at 70 °C for 18 h. As a result, a selectivity water / ethanol of around 96 was obtained for both, protected and unprotected membrane systems. However, the PVA film's protection effect onGO membranes becomes evident after testing. The shelf-life enhancement is demonstrated by comparing both membrane-over-tube systems after one year of storing at room temperature and humidity between 80% and 90% (laboratory environment). Figure 5 shows the unprotected membrane delaminated and unwrapped from the SiC tube (upper tube in Figure 5). Conversely, the protected membrane remained intact (bottom tube in Figure 5, respectively) and presented the same PV performance.

[0111] 2.2. Encapsulated flat membranes by water-soluble permeable polymers films

[0112] In the present invention, a self-standing GO membrane [7] (with a thickness of around 5 pm and an area of about 30 cm2) was horizontally levelled on a plastic container. A PVA solution was cast onto the membrane and dried (24 h at room temperature, followed by drying in an oven at 40 °C for 2 h). The one-side protected membrane was flipped to expose the self-standing GO membrane (non-protected side), and the protection procedure was repeated. Figure 6 shows an encapsulated self-standing GO membrane in permeable polymeric films with a total thickness of around 75 pm.

[0113] Application in pervaporation process for water-ethanol separation

[0114] The encapsulated GO membrane was tested in a PV process applied to a binary mixture of water and ethanol with a concentration of 50 wt% at 23 °C for 6 h. For comparison, the same process was applied to a non-protected self-standing GO membrane and a pure PVA film simultaneously. Figure 7 presents the PV's performance results for encapsulated membranes, self-standing membranes and PVA films.[001 15] Pressure testing

[0116] The encapsulated GO membrane was tested for mechanical resistance to gas pressure using the same procedure described above for the one-side protected membrane. The membranes resist 3 bars of pressure without detectable structural damage.

[0117] 2.3 Membranes protected by non-water-soluble glassy polymeric films

[0118] 2.3 (a) One-side-protected GO membrane

[0119] A self-standing GO membrane [7] (with a thickness of around 3 pm and an area of about 16 cm2) was horizontally levelled on a plastic container. A PTMSP solution was cast onto the membrane. The sample was dried for 48 h at room temperature. Figure 8 shows a GO membrane on the bottom of the glass container covered by the liquid solution (a) and covered by PTMSP glassy polymer (b). The total thickness of the protected membranes is approximately 40 pm.

[0120] 2.3 (b) One-side-protected GO membrane by glassy polymer composite films

[0121] A self-standing GO membrane [7] (with a thickness of around 3 pm and an area of about 10 cm2) was horizontally levelled on a plastic container. A solution containing a homogeneous mixture of PTMSP and 3 wt% of graphene was cast onto the membrane. The sample was dried for 48 h at room temperature.

[0122] Pressure testing and gas selectivity

[0123] The one-side protected GO membranes by PTMSP were tested for mechanical resistance to gas pressure using the same procedure described above up to 3 bars without detectable structural damage. Furthermore, the one- side protected membranes exhibited a permeability to CO2 of around 1,512 Barrer and a CO2 / N2 selectivity of 3.43.

[0124] 2.3 (c) graphene membrane covered with a PTMSP film

[0125] A graphene membrane was also covered with a PTMSP film using cyclohexane as a solvent. Fig. 9 is a photograph of the graphene membrane covered with PTSMP film. The PTMSP solution was previously prepared by mixing 100 mg of PTMSP with 5 mL of cyclohexane and sonicating for 1 hour. The graphene membrane was disposed on a petri dish. Then 5 mL of PTMSP solution was poured on top of the graphene membrane and dried for 24 hours at room temperature. After drying, the PTMSP film-protected graphene membrane was easily peeled off the petri dish with the help of methanol (Isopropyl Alcohol (IP A) can also be used to peel off the graphene membrane from the petri dish). This membrane was tested for permeation of gases, and it was shown to withstand pressures of at least up to 5 bar. Furthermore, the membrane shows selectivity of CO2 over N2 and H2.

[0126] The graphene membrane covered with a PTMSP film was tested for permeation of gases using the setup of Figure 4, which is a gas permeation module and experimental setup for gas testing and gas permeation in membranes.

[0127] Example 3 - Conclusions

[0128] The presented examples show an enhancement in the selectivity to water over ethanol due to the encapsulation of the GO membrane with a hydrophilic material. Even if the flux of the encapsulated membranes is, as expected, lower than the flux of the unprotected membranes, this effect is compensated by its durability. The protected membranes withstand operational and storage environmental conditions longer than unprotected membranes. Permeable films of hydrophilic polymers and hydrophobic glassy polymers effectively mechanically protect self-standing 2D material- based membranes. The potential forapplications in separating mixtures of liquids, vapours, and gases with varying requirements is wide open. It has been demonstrated that GO or graphene self-standing membranes were protected with permeable polymeric films, tested in separation processes of aqueous solutions and gases, and evaluated regarding the enhancement in durability and resistance to gas pressures.

[0129] In the literature, there arc reports of using polymeric film to cover composite membranes (not GO or graphene membrane), due to a technical hurdle that direct GO or graphene coating can destroy the GO or graphene membrane by the action of the solvent on the GO or graphene nanosheets. The physical properties of the 2D material-based membrane, such as the crosslinked GO membranes in the present invention allow them to be subjected to the process of coating by the polymers without affecting them physically. This has not been done before. The polymer protection in this invention is applied to a nearly 100 wt% GO membrane or a nearly 100 wt% graphene membrane and not to a polymer membrane that generally can include up to around 3 wt% GO or graphene or other materials as filler. Pure polymers and composites of polymers with fillers in small quantities are the subject of a vast number of publications from skilled persons dedicated to polymers, and that is a fundamentally different area of research from the present invention. In summary, 2D materials-based membranes in this invention arc completely and fundamentally different from other membranes made of other types of materials (polymers, metals, ceramics, or their composites) used in the literature. Such 2D material-based membrane as disclosed herein has superior strength resistance and mechanical stability, which allow them to be subjected to the process of covering by polymeric films as disclosed herein without affecting them physically.

[0130] Industrial Applicability

[0131] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.References[1] S. Hong, C. Constans, M. V. Surmani Martins, Y. C. Seow, J. A. Guevara Carrio, and5. Garaj, “Scalable Graphene-Based Membranes for Ionic Sieving with Ultrahigh Charge Selectivity,” Nano Lett., vol. 17, no. 2, pp. 728-732, Feb. 2017, doi: 10.1021 / acs.nanolett.6b03837.[2] R. R. Nair, H. A. Wu, P. N. Jayaram, I. V. Grigorieva, and A. K. Geim, "Unimpeded Permeation of Water Through Helium-Leak-Tight Graphene-Based Membranes," Science, vol. 335, no. 6067, pp. 442-444, Jan. 2012, doi: 10.1 126 / science.12l 1694.[3] G. Liu, W. Jin, and N. Xu, "Two-Dimensional-Material Membranes: A New Family of High-Performance Separation Membranes," Angew. Chem. Jnt. Ed., NC>\. 55, no. 43, pp. 13384- 13397, Oct. 2016, doi: 10.1002 / anie.201600438.[4] Y. Tang et al., "Covalent organic frameworks combined with graphene oxide to fabricate membranes for H2 / CO2 separation," Sep. Purif. Technol., vol. 223, pp. 10-16, Sep. 2019, doi: 10.1016 / j.seppur.2019.04.069.[5] L. Ding et al., "MXene molecular sieving membranes for highly efficient gas separation," Nat. Commun., vol. 9, no. 1, p. 155, Jan. 2018, doi: 10.1038 / s41467-017-02529-6.[6] B. Z. Tang et al., "Ultrathin membranes of single-layered MoS2 nanosheets for high- permeance hydrogen separation," Nanoscale, vol. 7, no. 42, pp. 17649-17652, Oct. 2015, doi: 10.1039 / c5nr06321c.[7] Juan Alfredo Guevara Carrio, VSSL Prasad Talluri, Swamy T. Toolahalli, Sergio Graniero Echeverrigaray, and Antonio Helio Castro Neto, " 'Crosslinked graphene-based membranes: fabrication methods, characteristics, and applications in separation processes', ILO / NUS Ref: 2023-122-01, Singapore Provisional Patent Application, 20 / 07 / 2023"[8] J. A. G. Carrio, V. P. Talluri, T. S. Toolahalli, S. G. Echeverrigaray, and A. H. C. Neto, "Gas stripping-assisted vapour permeation using graphene oxide membrane -coated silicon carbide tube for effectively recovering ethanol from its diluted aqueous solution," In Review, preprint, Apr. 2023. doi: 10.21203 / rs.3.rs-2815739 / vl.[9] Y. Shin et al., "Highly Selective Supported Graphene Oxide Membranes for Water- Ethanol Separation," Sci. Rep., vol. 9, no. 1 , Art. no. 1 , Feb. 2019, doi: 10.1038 / s41598-019- 38485-y.

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Claims

Claims1. A 2D material-based membrane protected by a polymeric film, wherein the 2D materialbased membrane is graphene or graphene oxide (GO).

2. The 2D material- based membrane of claim 1, wherein the 2D material-based membrane is self-standing or non-self-standing.

3. The 2D material-based membrane of claim 2, where the non- self- standing 2D materialbased membrane covers a ceramic, metallic, polymeric, or composite supporting substrate.

4. The 2D material-based membrane of claim 2, wherein the self-standing 2D material-based membrane is a self-standing GO membrane comprising a plurality of layers of crosslinked GO sheets, wherein the self-standing GO membrane is fabricated using a crosslinking agent to crosslink between oxygen-containing functional groups of neighbour GO sheets, wherein the crosslinking agent is a metallic oxide or a carbide.

5. The 2D material-based membrane of claim 4, wherein the metallic oxide is selected from the group consisting of Iron (ITT) oxide (Fe2O3), aluminium oxide (AI2O3), calcium sulfate (CaSO4), niobium pentoxide (NbiOs), Bi-2212 (Bi2Sr2CaCu2Ox), an oxide of a transition metal, an oxide of an alkaline earth metal, an oxide of a post-transition metal, aluminosilicate, and a multi-cation oxide selected from the group consisting of YBaCO and BSCCO.

6. The 2D material-based membrane of claim 5, wherein the metallic oxide is AhOi / CaSCF 50 / 50 wt.%.

7. The 2D material-based membrane of claim 4, wherein the carbide is silicon carbide (SiC).

8. The 2D material-based membrane of claim 4, wherein the oxygen-containing functional groups are selected from the group consisting of epoxide, hydroxyl, carboxyl and carbonyl group.

9. The 2D material- based membrane of claim 1, wherein the polymeric film is coated on one side or both sides of the 2D material-based membrane.

10. The 2D material-based membrane of claim 10, wherein the polymeric film is made of a polymer selected from a group consisting of:(a) a water soluble polymer selected from the group consisting of poly(vinyl alcohol) (PVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and a polysaccharide;(b) a non-water-soluble glassy polymer selected from the group consisting of polystyrene (PS), polyvinyl acetate (PVAc), polylactic acid (PLA), poly(l -trimethylsilyl- 1 -propyne) (PTMSP), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polysulfone (PSU), polycthcr sulfone (PESU), polyimidc (PI), and polycarbonate (PC); and(c) a polymer composite of PTMSP and graphene.

11. The 2D material-based membrane of any one of claims 1-10, wherein the 2D materialbased membrane protected by a polymeric film can withstand up to 5 bars of pressure or more.

12. The 2D material-based membrane of any one of claims 1-11, wherein the polymeric film is coated on one side of the 2D material-based membrane by casting, spraying, or dip coating.

13. The 2D material-based membrane of any one of claims 12, wherein the same polymeric film or a different polymeric film is coated on the other side of the 2D material-based membrane by casting, spraying, or dip coating.

14. The 2D material-based membrane of any one of claims 1-13, wherein the polymeric film covers a larger area than the 2D material-based membrane.

15. A method of fabricating a 2D material-based membrane protected by a polymeric film of any one of claims 1-14, by coating the polymeric film on one side or both sides of the 2D material-based membrane; wherein the 2D material-based membrane is graphene or graphene oxide (GO).

16. The method of claim 15, further comprising drying the coated 2D material-based membrane.

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