Graphene membrane filter for gas separation

Abstract

To provide an efficient gas selective filter using a graphene membrane.SOLUTION: The invention relates to carbon-supported crack- and tear-free graphene membranes of large area useful for selective gas separation, and a method of preparation and uses thereof. In particular, the invention relates to carbon-supported crack- and tear-free graphene membranes having good gas separation performance, in particular high H2 permeance and H2 / CH4 selectivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention generally relates to the field of gas selective separation filters, particularly those useful for separating gas mixtures, especially in relation to carbon capture resulting from the separation of H2 and N2 from, for example, gas waste or spills, CO2 and hydrocarbons. More specifically, the present invention relates to filters using atomic-thickness graphene porous membranes. [Background technology]

[0002] Within the framework for addressing global warming and its identified contributing factors, one developed option is the reduction of greenhouse gas emissions through carbon capture and subsequent underground sequestration of carbon dioxide from gas flows. Carbon capture and storage is a strategy for mitigating CO2 emissions from large point sources, such as coal-fired power plants. Furthermore, the effective separation of CO2 / CH4 is also necessary for biogas processing, which mainly contains approximately 60 vol.% CH4 and 40 vol.% CO2, and large-scale H2 processing requires cost-effective and efficient means to separate it from other less desirable chemical species, particularly CO2. Polymer membranes have been applied to industrial gas separation for decades, and their gas selectivity has been commercialized for separating various gases (Sanders et al., 2013, Polymer., 54, pp. 4729-4761). However, they face performance limitations due to the trade-off between inherent selectivity and performance (Park et al., 2017, Science 356), and primarily due to physical aging involving the plasticization of the polymer film in the gas channel over time, which affects the filtration-free volume (Sanders et al., 2013, above).

[0003] Atomic-thick graphene films with molecularly selective nanopores represent the thinnest molecular barriers conceivable and can therefore be considered the ultimate membrane for molecular separation. Several molecular simulations have shown that two-dimensional nanopores in graphene can provide unprecedented gas permeance on a scale larger than that obtained with conventional membranes (Blankenburg et al., 2010, Small 6, pp. 2266-2271; Du et al., 2011, J. Phys. Chem. C, 115, pp. 23261-23266; Liu et al., 2013, Solid State Commun., 175-176, pp. 101-105). Such high-flow membranes can substantially reduce the membrane area required to separate a given volume of gas mixture, offering a new solution to the long-standing problem of membrane scaling up in this field. Therefore, due to its chemical robustness and high mechanical strength, graphene lattices are extremely suitable for gas separation, even with a high porosity of as high as 5%. Recently, several etching methods have been developed to create sub-nanometer pores in graphene, yielding promising sieving capabilities for liquids and dissolved ions. However, demonstrations of gas sieving capabilities have been limited. Specific evidence has only been obtained by measuring the contraction rate of bilayer graphene microballoons in which pores were created in graphene micromechanically exfoliated by UV treatment (Koenig et al., 2012, Nat. Nanotechnol., 7, pp. 728-732). Generally, most liquid, ion, and gas transport studies are conducted in micron-sized graphene regions, which contributes to limiting micromechanical exfoliation, as well as the occurrence of cracks and fissures, during the transfer of chemically vapor-deposited (CVD) derived graphene.

[0004] In fact, single-layer graphene produced by CVD is considered particularly suitable for fabricating large-area films due to the scalability of the CVD process (Polsen et al., 2015, Sci. Rep. 5, p. 10257). However, after CVD, some need to transfer the graphene from a non-porous catalyst metal foil (e.g., Cu) to a porous substrate in order to fabricate the film. Conventional transfer methods always result in cracks and fissures in the graphene film, so to date, suspended, crack- and fissure-free single-layer graphene films have been limited to a few micrometers in area (Suk et al., 2011, ACS Nano, 5, pp. 6916-6924). Of the several transfer techniques developed to date, wet transfer techniques have been the most investigated due to their versatility, enabling graphene transfer to a wide range of supports (Zhang et al., 2017, Adv. Mater. 29, pp. 1-7). In short, the graphene film is coated with a mechanically reinforced polymer layer, such as a 100-200 nm thick poly(methyl methacrylate) (PMMA) film. Subsequently, a metal foil is etched in an etchant bath, leaving the polymer-coated graphene suspended in the liquid bath. Finally, the suspended film is scooped onto the surface of the desired substrate, and the polymer film is dissolved and removed, exposing the graphene surface. However, when a porous support is used, the noticeable cracks and fissures that occur in the graphene film are mainly due to the strong capillary forces on the suspended graphene film during the solvent drying stage (Lee et al., 2014, ACS Nano, 8, pp. 2336-2344).

[0005] Celebi et al., 2014, Science, 344, pp. 289-292, describes how to obtain a 2,500 μm graphene layer by overcoating one graphene layer with another to conceal cracks in individual layers. 2Films (bilayer graphene films) have been reported. Using a focused ion beam (FIB), relatively large pores (>7.6 nm) were drilled in graphene, and the effusion of gas transport in this drilled bilayer graphene film was observed. From the effusion of transport, the gas selectivity predicted by Knudsen diffusion (H2 / CO2 selectivity up to 4), and an enormous H2 permeability (ca. 10 -2 molm -2 s -1 Pa -1 ) were derived. Recently, Boutilier et al., 2017, ACS Nano, 11, 5726 - 5736, reported the fabrication of centimeter-scale single-layer nanoporous graphene using a combination of ion bombardment and O2 plasma. However, due to the presence of cracks generated during transfer in graphene films, the separation selectivity close to that predicted by Knudsen diffusion (separation selectivities of 8 and 3.2 for He / SF6 and H2 / CH4, respectively) was limited. Nevertheless, using transport modeling, these demonstrated the existence of nanopores highly suitable for gas separation that sieved molecules in the film. Graphene oxide (GO) films have a low H2 permeability (10 -7 molm -2 s -1 Pa -1 ) and have been successfully used for H2 / CO2 separation (Li et al., 2013, Science, 342, 95 - 8). However, there is room for doubt regarding the reproducible synthesis and stability of GO membranes due to the difficulty in predicting the exact structure of GO flakes and the unstable bent bonds in the GO lattice. Overall, demonstrating the separation of gas mixtures from fully scaled-up single-layer graphene films requires a) transferring large-area graphene to a porous support without generating cracks and tears, and b) developing methods to produce a narrow pore size distribution (PSD) in graphene, and thus remains elusive (Wang et al., 2017, Nat. Nanotechnol., 12, 509 - 522).

[0006] Therefore, the development of a new method for fabricating suspended graphene films that possess size-selective pores, have a narrow pore size distribution, and are free from cracks and fissures is extremely desirable from the standpoint of large-scale deployment of nanoporous two-dimensional membranes, which have been hampered by the technical limitations described above. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Sanders et al., 2013, Polymer, 54, pp. 4729-4761. [Non-Patent Document 2] Blankenburg et al., 2010, Small 6, pp. 2266-2271 [Non-Patent Document 3] Du et al., 2011, J. Phys. Chem. C, 115, pp. 23261-23266 [Non-Patent Document 4] Liu et al., 2013, Solid State Commun., pp. 175-176, 101-105. [Non-Patent Document 5] Koenig et al., 2012, Nat. Nanotechnol., 7, pp. 728-732. [Non-Patent Document 6] Polsen et al., 2015, Sci. Rep. 5, p. 10257. [Non-Patent Document 7] Suk et al., 2011, ACS Nano, 5, pp. 6916-6924. [Non-Patent Document 8] Zhang et al., 2017, Adv. Mater. 29, pp. 1-7. [Non-Patent Document 9] Lee et al., 2014, ACS Nano, 8, pp. 2336-2344. [Non-Patent Document 10] Celebi et al., 2014, Science, 344, pp. 289-292. [Non-Patent Document 11] Boutilierら, 2017, ACS Nano, 11, pages 5726~5736 [Non-licensed Document 12] Li, 2013, Science, 342, pp. 95-98 [Non-licensed Document 13] Wang, 2017, Nat. Nanotechnol., 12, pp. 509-522. [Non-licensed Document 14] Rodriguez, 2007, Adv. Funct. Mater., 17, pp. 2710-2716. [Non-licensed Document 15] Yooら, 2015, Sci. Adv., 1(6), pages 1~7 [Non-licensed Document 16] Jackson, EA, Hillmyer, MA Nanoporous Membranes Derived from Block Copolymers: From Drug Delivery to Water Filtration. ACS Nano 2010, 4, pp. 3548~3553 [Non-licensed Document 17] Robeson, 2008, J. Memb. Sci., 320, 390-400 pages [Non-licensed Document 18] Meyerら, 2007, Nature, 446, pages 60~63 [Non-licensed Document 19] Agrawal, 2017, J. Phys. Chem. C., 121, pp. 14312~14321 [Non-licensed Document 20] Cancado, 2011, Nano Lett., 11, pp. 3190-3196 [Non-licensed Document 21] Drahushukら, 2012, Langmuir, 28, pages 16671~16678 [Non-licensed Document 22] Yuan, 2017, ACS Nano 11, pp. 7974-7987 [Non-licensed Document 23] Jiang et al., 2009, Nano Lett., 9, pp. 4019-402. [Non-Patent Document 24] Yuan et al., 2013, ACS Nano, 7, pp. 4233-4241. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] A general objective of the present invention is to provide an efficient gas selective filter using a graphene membrane for gas separation (e.g., H2 / CO2, H2 / CH4, CO2 / N2, and CO2 / CH4 separation).

[0009] One specific objective of the present invention is to provide an efficient gas selective filter for CO2 capture.

[0010] It is advantageous to obtain a gas selective filter with high gas permeance, combined with high separation selectivity, particularly for H2 / CO2, H2 / CH4, CO2 / N2, and / or CO2 / CH4.

[0011] It is advantageous to obtain a gas selective filter that has stable gas separation performance over multiple separation cycles, particularly over multiple heating and cooling cycles.

[0012] It is particularly advantageous to obtain a gas selective filter that has stable gas separation performance over multiple separation cycles, especially under high pressure (e.g., membrane differential pressure up to at least 7 bar).

[0013] Obtaining crack- and tear-free atomic-thickness, large-area graphene films for gas selective filters is advantageous.

[0014] Obtaining crack- and fissure-free atomic-thickness graphene films that demonstrate production costs feasible for large-scale use is advantageous.

[0015] While it is possible to transfer a fairly large area of ​​CVD single-layer graphene onto a porous support, obtaining an atomic-thickness graphene film support that does not impair the gas-filtration properties of graphene is advantageous.

[0016] It is advantageous to obtain a cost-effective method for preparing large-area, atomic-thickness graphene films free of cracks and fissures, which are useful for selective gas separation.

[0017] A fairly large area (for example, 1 mm) 2 It is advantageous to obtain a method for transferring the above-mentioned CVD single-layer graphene to a supporting structure without cracks or fissures.

[0018] It is advantageous to have an easily scalable method for optimizing the separation performance of graphene films according to target specifications (e.g., supply specifications, as well as purity and recovery requirements).

[0019] The object of the present invention is to provide a gas selective filter containing a graphene membrane, and a method for preparing a gas selective filter containing a graphene membrane that is cost-effective, has good gas selectivity, and has high performance. [Means for solving the problem]

[0020] The object of the present invention is achieved by providing a gas selective separation filter according to claim 1 and a method for preparing a gas selective separation filter according to claim 5.

[0021] A method for preparing a gas selective separation filter, a) A step of providing a graphene film on a sacrificial support layer, b) A step of coating the graphene film with an organic precursor on a porous carbon substrate, c) A step of thermally decomposing an organic precursor in an inert atmosphere so that the organic precursor is converted into the porous carbon substrate on a graphene film, wherein the porous carbon substrate has a porosity in the range of 5% to 90%. d) A step of placing a composite of a porous carbon substrate and a graphene film onto a macroporous support structure, e) Before or after step d), a step of removing at least a portion of the sacrificial support layer and flowing the gas through the entire composite of the porous carbon substrate and the graphene film. Methods including the above are disclosed herein.

[0022] Also disclosed herein is a gas selective filter comprising a nanoporous graphene film having a thickness of approximately 0.34 to 2 nm and a porosity greater than 0.001%, a porous carbon substrate on which the graphene film is mounted, having a porosity in the range of 5% to 90% and an H2 permeance exceeding that of the graphene film, and a porous support structure in which the graphene film and the porous carbon substrate are mechanically supported.

[0023] Also disclosed herein is the use of gas selective filters comprising a graphene membrane on a porous carbon substrate for separating gases, particularly H2, N2, and / or CH4 from CO2 and from high molecular weight hydrocarbons (e.g., C2H2, C2H4, C2H6, C3H6, C3H8).

[0024] According to another aspect of the present invention, a method for improving the gas filtration performance of a nanoporous graphene membrane, (i) A step of providing a graphene film on a porous support, (ii) A step of treating the graphene film with ozone at a temperature of 25°C to 300°C, typically 25°C to 100°C, with an ozone concentration of 1% to 25% and a treatment time of 1 millisecond to 1 day, typically about 1 second to about 60 minutes. Methods including the above are further disclosed herein.

[0025] This delicious, (iii) The process may further include storing the graphene film in an atmospheric or inert environment at a temperature of 25°C to 200°C.

[0026] In a favorable embodiment, the H2 permeance of the graphene film is approximately 10-8 molm -2 s -1 Pa -1 From about 10 -4 molm -2 s -1 Pa -1 (For example 10 -7 from 10 -6 molm -2 s -1 Pa -1 )

[0027] In advantageous embodiments, the porosity of the graphene film is formed by pores in the nanoporous graphene film having an average size of about 0.2 nm to about 0.5 nm, preferably about 0.25 nm to 0.3 nm. The porosity of the nanoporous graphene film is preferably greater than 0.01%, more preferably greater than 0.1%, and can be up to 5%.

[0028] In advantageous embodiments, the porous carbon substrate has a porosity of more than 10%, more specifically in the range of 20% to 70%, formed by pores having an average size (i.e., width or diameter of the localized pore circle) in the range of about 10 nm to about 1000 nm, preferably in the range of 10 nm to about 100 nm.

[0029] The porous carbon substrate according to the embodiment of the present invention has an H2 permeance that is at least 10 times higher, and generally more than 100 times higher, than that of a graphene film.

[0030] The porous support structure may have pores with an average size ranging from 0.01 μm to 100 μm, for example, from 0.1 μm to 20 μm, or more specifically, from 1 μm to 10 μm.

[0031] The porous support structure has a porosity in the range of 2% to 60%, preferably more than 5%, for example, 5% to 25%, which contributes to making the increase in resistance to the gas flow through the filter negligible or slight, thereby ensuring sufficient structural strength and good permeance (compared to graphene films).

[0032] The porous support structure may have a thickness ranging from 10 μm to 10,000 μm, typically from 20 μm to 100 μm (e.g., 50 μm).

[0033] Advantageously, the porous carbon substrate ideally supports the graphene layer, thereby enabling the removal of the sacrificial support layer and, in particular, limiting the thermal and mechanical stresses in the graphene layer during the transfer process, allowing the graphene layer to be placed on a mechanical support structure without inducing cracks or fissures in the graphene layer. The porosity of the carbon substrate is easily configured due to its ideal properties, avoiding excessive resistance to gas flow compared to a graphene film, and further avoiding excessively large pores that would weaken the support of the graphene layer. The compatibility of graphene with the carbon substrate is also highly advantageous for bonding the graphene layer to the porous carbon layer and suppressing relative thermal expansion.

[0034] In an advantageous embodiment, the step of removing at least a portion of the sacrificial support layer includes etching the portion of the sacrificial support layer in an etching chamber containing an etchant for etching the sacrificial support layer.

[0035] In an advantageous embodiment, the etching step is performed before placing the porous carbon support and graphene film onto the macroporous support structure to obtain a self-supporting composite of the porous carbon substrate and graphene film suspended in an etching solution.

[0036] However, in the variation, within the scope of the present invention, the porous carbon support and graphene film formed on the sacrificial support layer can be placed on the macroporous support structure before all or part of the sacrificial support layer is removed. As a result, the sacrificial support layer may be at least partially removed, although various layers may be placed on the macroporous support structure. The macroporous support structure may consist of a porous carbon substrate positioned relative to the macroporous support structure, or a sacrificial layer positioned relative to the macroporous support structure. In the latter variation, the removal of the sacrificial layer may be partial due to the pores of the macroporous support structure, and may be limited to the surface area of ​​the exposed sacrificial layer.

[0037] While removal of the sacrificial layer by etching is preferred, other removal methods may be practiced within the scope of the present invention, such as electrochemical foaming techniques that exfoliate the graphene from the Pt support, allowing the Pt support to be reused.

[0038] The step of placing the composite of the porous carbon substrate and the graphene film onto the macroporous support is preferably carried out by a wet transfer process in a liquid bath.

[0039] The organic precursor is preferably coated in solution onto a graphene film layer formed on a sacrificial support layer, and the solution is then dried until a film of the organic precursor forms on the surface of the graphene film.

[0040] The porous support structure has the function of mechanically supporting the porous carbon substrate and the graphene film, and should exhibit negligible or only slight resistance to the gas flow through the filter associated with the graphene film. Furthermore, the solid surface area of ​​the support structure should cover as little of the graphene film as possible in order to expose as much of the graphene surface area as possible to the gas flow. Preferably, the porous support structure has a porosity of more than 5%. The pores of the porous support preferably have an average diameter of more than 0.01 μm, preferably less than 100 μm, for example, in the range of 0.1 μm to 20 μm, more specifically in the range of 1 μm to 10 μm, in order to ensure good support of the porous carbon substrate (particularly to avoid cracking of the carbon substrate).

[0041] In advantageous embodiments, the graphene film is a chemically vapor-deposited (CVD) graphene layer, in particular a substantially monolayer of CVD-derived graphene having a thickness of about 0.34 to 2 nm.

[0042] In advantageous embodiments, the sacrificial support layer comprises or consists of an etchable metal foil, preferably a Cu film or foil, in the range of about 0.1 to 1000 μm, typically with a thickness of 1 to 100 μm, for example, in the range of 10 to 50 μm. The thickness of the sacrificial layer is configured to provide good mechanical support during the formation of the graphene film and the subsequent coating of the precursor material of the porous carbon support, and further allows for efficient removal of the sacrificial layer.

[0043] In advantageous embodiments, the porous carbon structure organic precursor is an amphiphilic block copolymer.

[0044] Other features and advantages of the present invention are evident from the claims, detailed description and drawings. [Brief explanation of the drawing]

[0045] [Figure 1] This is a schematic diagram illustrating the preparation of a gas selective filter having a graphene film using a carbon substrate-assisted transfer method according to an embodiment of the present invention. [Figure 2]This figure shows the characterization of the structure of the graphene film supported on the porous carbon substrate according to the embodiment of the present invention obtained in Example 1. Its components are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging described in Example 2. a-b) SEM image of the porous tungsten substrate, showing a 5 μm pore arrangement spread over an area of ​​1 mm² on a tungsten foil (50 μm thick). c) SEM image of the carbon substrate on the graphene film according to the embodiment of the present invention on the porous tungsten-supported substrate. d) SEM image of the porous carbon substrate on the upper surface of the graphene. e) TEM image of the porous carbon substrate and single-layer graphene film of the present invention on a TEM grid. f) Diffraction pattern of graphene passing through the porous carbon substrate and single-layer graphene film according to the embodiment of the present invention. g) Cross-sectional SEM image of the porous carbon substrate and single-layer graphene film according to the embodiment of the present invention. h) Typical Raman spectrum from single-layer LPCVD graphene. [Figure 3] This figure shows a schematic diagram of the gas permeance test setup described in Example 3. [Figure 4a] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs from internal defects in graphene. a) H2 permeance as a function of temperature, obtained by a single gas permeance test. [Figure 4b] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in the graphene. b-d) Selectivity of different gases after a single gas permeance test, b) H2 / CH4. [Figure 4c] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in the graphene. b-d) Selectivity of different gases after a single gas permeance test, c) H2 / CO2. [Figure 4d]This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in the graphene. b-d) Selectivity of different gases after a single gas permeance test, d) He / H2. [Figure 4e] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs from internal defects in graphene. e) Extracted activation energy for gases with different dynamic diameters. [Figure 4f] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs from internal defects in the graphene. f) H2 permeance as a function of temperature, obtained by a mixture gas permeance test. [Figure 4g] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in graphene. g) Different gas separation factors after a mixed gas permeance test, g) H2 / CH4. [Figure 4h] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in graphene. g-i) Separation factors of different gases after a mixed gas permeance test, h) H2 / CO2. [Figure 4i] This graph reports the results of the gas separation performance of eight CVD graphene films (M1-M8) according to the embodiment of the present invention described in Example 3. Gas transport occurs due to internal defects in graphene. g-i) Separation factors of different gases after a mixed gas permeance test, i) He / H2. [Figure 5a] This graph reports the stability test of internal defects in the graphene film of the present invention, as described in Example 3. a) H2 and CH4 permeances under three consecutive temperature cycles. [Figure 5b] This graph reports the stability test of internal defects in the graphene film of the present invention, as described in Example 3. b) Gas permeance of different gases as a function of test pressure (1-7 bar) at 100°C. [Figure 5c] This graph reports the stability test of internal defects in the graphene film of the present invention, as described in Example 3. c) Separation factor between H2 and CH4 as a function of test pressure (1-7 bar) at 100°C. [Figure 6a] This graph reports the characterization of an ozone-treated graphene film according to an embodiment of the present invention described in Example 4. a) Raman spectra of O3-treated graphene films under different conditions. [Figure 6b] This graph reports the characterization of an ozone-treated graphene film according to an embodiment of the present invention described in Example 4. b) Histogram of ID / IG values ​​of O3-treated graphene films using different treatments. [Figure 6c] This graph reports the characterization of an ozone-treated graphene film according to an embodiment of the present invention described in Example 4. c) CO bond content of O3-treated graphene films treated at different reaction temperatures and reaction times. [Figure 6d] This graph reports the characterization of an ozone-treated graphene film according to an embodiment of the present invention described in Example 4. d) C=O bond content of O3-treated graphene films treated at different reaction temperatures and reaction times. [Figure 7a]This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the film. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. a-b) M2, a) H2 and CH4 permeance after O3 treatment at 25°C for 2 minutes. [Figure 7b] This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the films. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. a-b) M2 treated with O3 at 25°C for 2 minutes, b) H2 / CH4 and H2 / CO2 selectivity. [Figure 7c] This graph reports the gas separation performance results of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the film. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. c-d) Permeance of M8, H2 and CH4 after O3 treatment at 100°C for 2 minutes. [Figure 7d]This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the films. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. c-d) M8 treated with O3 at 100°C for 2 minutes, d) H2 / CH4 and H2 / CO2 selectivity. [Figure 7e] This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the film. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. e-f) Permeance of M6, e) H2 and CH4 after O3 treatment at 80°C for 1 minute. [Figure 7f] This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. In short, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for a period of 1 to 10 minutes, which led to an improvement in the gas separation performance of the films. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. e~f) M6 treated with O3 at 80°C for 1 minute, f) H2 / CH4 and H2 / CO2 selectivity. [Figure 7g]This graph reports the results of the gas separation performance of several ozone-treated graphene films according to the present invention, as described in Example 4. Briefly, graphene films in which internal defects due to CVD growth act as transport pathways were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, which led to an improvement in the gas separation performance of the films. The improvement in performance is determined by the internal defects (average pore size, pore density), as well as the temperature and treatment time of the ozone treatment. g) Gas separation performance trajectories after different ozone treatments (data for M8 was obtained at 200°C, other data were measured at 150°C, light-colored markers represent the gas performance of the initial graphene film, while dark-colored markers represent the gas performance of the graphene film functionalized from the corresponding film). [Modes for carrying out the invention]

[0046] The term "graphene film" refers to a graphene layer, particularly a graphene monolayer obtained, for example, by CVD. For example, a single-layer graphene film has a thickness in the range of approximately 0.34 to 1 nm. However, the graphene film according to embodiments of the present invention may also include a bilayer graphene or a portion having a bilayer graphene, and it is understood that achieving a highly uniform monolayer across the entire surface area of ​​the film may not be efficient in industrial-scale film manufacturing.

[0047] The term "sacrificial support layer" refers to a support suitable for a graphene film (e.g., Cu, Ni, Pt, or any other metallic substrate on which a single layer of graphene can be synthesized), particularly a non-porous support, which may be sacrificed before or after the graphene film is applied to the structural (mechanical) support.

[0048] The expression "organic precursor for porous substrates" refers to any organic agent that can form a film on the graphene surface and, after thermal decomposition, can be converted into a porous carbon substrate having pores ranging from approximately 10 nm to approximately 1000 nm. In a particular embodiment, examples of porous organic precursors include block copolymers, particularly amphiphilic block copolymers, and more specifically, block copolymers that, when coated as thin films, undergo phase separation into hydrophilic regions (e.g., polyvinylpyridine) and hydrophobic regions (e.g., polystyrene) upon drying, such as those described in Rodriguez et al., 2007, Adv. Funct. Mater., 17, pp. 2710-2716, or Yoo et al., 2015, Sci. Adv., 1(6), pp. 1-7, or Jackson, EA, Hillmyer, MA Nanoporous Membranes Derived from Block Copolymers: From Drug Delivery to Water Filtration. ACS Nano 2010, 4, pp. 3548-3553. In a particular embodiment, a block copolymer soluble in N,N-dimethylformamide is preferably used as the porous carbon structure organic precursor according to the present invention.

[0049] The term "membrane performance" refers to the combination of membrane gas permeance and its gas selectivity. Typically, in the field of gas separation, 10 -8 molm -2 s -1 Pa -1 The above H2 permeance and H2 / CH4 selectivity of 6 or higher are considered to indicate good film performance.

[0050] Referring to the drawings, particularly Figure 1, an illustration of a method for preparing a gas selective filter comprising a crack- and fissure-free single-layer graphene film according to an embodiment of the present invention. The illustrated method for preparing a gas selective filter generally includes the steps of: providing a graphene film on a sacrificial support layer; coating the graphene film with an organic precursor of a porous carbon substrate; thermally decomposing the organic precursor in an inert atmosphere such that the organic precursor is converted on the graphene film into the porous carbon substrate, wherein the porous carbon substrate has a porosity in the range of 5% to 90% and an H2 permeance at least 10 times higher than the H2 permeance of graphene; placing a composite of the porous carbon substrate and the graphene film on a macroporous structural support; and removing at least a portion of the sacrificial support layer to allow the gas to flow through the entire composite of the porous carbon substrate and the graphene film. The porous substrate may be flat, highly flexible, or, for example, tubular.

[0051] More specifically, the steps of the embodiment illustrated in Figure 1 are: a) A step of forming a support graphene film 1 by providing a CVD graphene film 3 (particularly a graphene monolayer) on a sacrificial support layer 2, b) A step of coating the graphene film 3 with a solution containing an organic precursor of a porous carbon substrate, and leaving the solution to dry until a film 4 of the organic precursor is formed on the surface of the graphene film, c) A step of thermally decomposing the organic precursor film 4 under an inert atmosphere so that the organic precursor film 4 is converted into a porous carbon substrate 5 on the surface of the graphene film 3, wherein the porous carbon layer has a porosity of about 5% to about 90%, typically 10% to 80%, preferably more than 20%, and typically less than 70%. d) A step of placing a composite of a porous carbon substrate and a graphene film on the sacrificial support layer 2 obtained in step c) in an etching chamber 7 containing an etchant 8, etching the sacrificial support layer 2, and obtaining a graphene film supported on a porous carbon substrate suspended in an etching solution. e) A step to obtain a gas-selective filter sheet 11 (of step f) which includes a layer combining the porous carbon substrate 5, the graphene film 3, and the macroporous support structure 10, obtained by transferring the graphene film 9, which is supported on a carbon substrate obtained in step d), onto a macroporous support 10. Includes.

[0052] According to one particular embodiment, the CVD graphene layer is synthesized by low-pressure chemical vapor deposition (LPCVD).

[0053] According to the embodiment, the graphene film has a thickness of approximately 0.34 nm to 2.0 nm.

[0054] According to the embodiment, the average pore size of the nanoporous graphene film is in the range of 0.2 nm to 0.5 nm, particularly in the range of about 0.25 nm to about 0.3 nm.

[0055] According to one particular embodiment, the sacrificial support layer 2 is a Cu foil with a thickness of about 10 to 100 μm, particularly about 10 to 50 μm, for example, about 25 μm.

[0056] According to one particular embodiment, the organic precursor of the porous carbon substrate is an amphiphilic block copolymer, particularly a block copolymer of polyvinylpyridine and polystyrene monomer, for example, the block copolymer polystyrene-co-poly(4-vinylpyridine) (PS-P4VP).

[0057] According to one particular embodiment, the coating solution used in step b) is a solution of turanose and the block copolymer polystyrene-co-poly(4-vinylpyridine) (PS-P4VP) dissolved in N,N-dimethylformamide, resulting in concentrations of turanose and the block copolymer of 1-10% and 1-10% (w / w), respectively.

[0058] According to another specific embodiment, the coating solution used in step b) is treated at a high temperature, for example, about 50 to about 200°C (e.g., 180°C), before coating in order to anneal the film and promote phase separation of hydrophilic and hydrophobic regions.

[0059] According to one particular embodiment, the coating in step b) is performed by spin coating.

[0060] According to another specific embodiment, the pyrolysis is carried out in step c) at approximately 400-1000°C, particularly at approximately 500°C, for approximately 1 hour.

[0061] According to another specific embodiment, the pyrolysis is carried out in step c) under an H2 / Ar flow.

[0062] According to another specific embodiment, the porosity of the porous carbon substrate 5 is such that the substrate has pores with an average diameter of 10 to 50 nm and a porosity of about 20 to 70%, resulting in the exposure of a considerable area of ​​graphene (i.e., not covered by the porous carbon substrate 5).

[0063] According to another specific embodiment, the etching solution is a solubilizer for the sacrificial support layer 2 (for example, a solution of 0.2 M Na2S2O8 in water for the Cu support layer).

[0064] According to another specific embodiment, the composite 9 of the porous carbon substrate and graphene film obtained in step d) is rinsed (e.g., in deionized water) to remove any residue.

[0065] According to another specific embodiment, the porous support structure 7 has pores with an average diameter greater than 0.01 μm and less than 100 μm, typically less than 20 μm.

[0066] According to another specific embodiment, the macroporous support structure 7 has a thickness of 10 μm to about 10,000 μm, typically 20 μm to about 100 μm.

[0067] According to further specific embodiments, the macroporous support structure 7 is selected from sintered ceramics (e.g., alumina, silica, etc.) and metals (stainless steel, Inconel, Hastelloy, etc.).

[0068] According to a further specific embodiment, the macroporous support structure 7 is a tungsten (W) foil having a thickness of about 20 to about 100 μm (e.g., 50 μm), a porosity of 2% to about 50%, typically 5% to 15%, and an average pore size of 0.1 μm to 100 μm, typically 1 μm to 10 μm, for example, about 5 μm.

[0069] According to a further specific embodiment, the gas selective filter sheet 11 obtained in step f) is approximately 10 -8 molm -2 s -1 Pa -1 From about 10 -4 molm -2 s -1 Pa -1 (For example 10 -7 from 10 -6 molm -2 s -1 Pa -1 It has an H2 permeance of ).

[0070] According to another further specific embodiment, the gas selective filter sheet 11 obtained in step f) has an H2 / CH4 selectivity of about 3 to about 1000 (e.g., about 20).

[0071] According to another further specific embodiment, the gas filtration performance of a graphene membrane is improved by subjecting the supported graphene membrane to ozone treatment in an inert atmosphere for about 1 ms to about 1 month, typically about 30 s to about 60 minutes.

[0072] According to another further specific embodiment, the method according to the present invention further includes a graphene film functionalization step g) by subjecting the gas selective filter sheet 11 to an ozone treatment in an inert atmosphere for about 1 ms to about 1 month, typically about 30 s to about 60 minutes.

[0073] According to another further specific embodiment, the method according to the present invention further comprises carrying out a functionalization step g) at a temperature of about 25°C to 200°C, more preferably 25°C to about 120°C.

[0074] According to another further specific embodiment, gas filtration performance can be optimized by improving gas filtration performance using ozone treatment conditions to handle different supply standards as well as purity and recovery rate requirements. For example, the separation process may require a selective membrane or an even more permeable membrane depending on the supply concentration, permeate purity (e.g., 90%, 95%, 99%, where higher purity requires a highly selective membrane), overall recovery rate (e.g., 80%, 90%, 95%), or cost (further cost reduction can be achieved by using a more permeable membrane).

[0075] Typically, the functionalization step g) is carried out at a temperature of approximately 0–60°C (e.g., 25°C) to improve the H2 / CH4 selectivity of the graphene film.

[0076] Typically, the functionalization step g) is carried out at a temperature of about 60 to 150°C, preferably 80 to 100°C, to improve the H2 permeance of the graphene film.

[0077] According to one particular embodiment, the gas selective filter according to the present invention can be used to treat synthesis gas (syngas) to advantageously separate H2 from CH4 and from high molecular weight hydrocarbons, or to remove impurities or to adjust the H2 / CO ratio for specific downstream applications.

[0078] The gas selective filter according to the present invention is used in combination with a dehydrogenation reactor as a membrane reactor (for example, to produce olefins from alkanes) to remove H2 and improve processing efficiency, and to increase the overall conversion rate. Furthermore, the graphene membrane according to the present invention may be suitable for carbon capture (separation of H2 / CO2, H2 / CH4, CO2 / N2, and CO2 / CH4).

[0079] The remarkable stability of the observation temperature of the gas selective filter according to the present invention makes it possible to use this filter as a useful alternative to polymer membranes with short lifecycles, particularly at high pressures (5-20 bar) and high temperatures (100-250°C).

[0080] The present invention, as described in the following examples, is presented for illustrative purposes only and is not limited thereto. [Examples]

[0081] Example 1: Method for transferring a single layer of graphene to a porous substrate with support assistance. The present invention provides a method for preparing a crack- and fissure-free atomic-thickness graphene film, which includes the step of transferring a single layer of graphene to a porous substrate with the assistance of a support, as illustrated in Figure 1 and described in detail below.

[0082] Step a: Provide CVD graphene synthesized on a sacrificial support layer. A supported graphene film 1 was prepared as a CVD graphene monolayer 3 supported on a sacrificial support layer 2 synthesized by low-pressure chemical vapor deposition (LPCVD) on copper foil (25 μm, 99.999% purity, Alfa-Aesar). Prior to CVD, the copper foil was annealed at 1000°C for 30 minutes in a CO2 atmosphere to remove most of the organic contaminants. Next, 8 sccm of H2 was induced to purge the CO2 and anneal the copper surface. Subsequently, 24 sccm of CH4 was added to start graphene crystallization. After graphene growth (30 minutes), the CH4 flow was switched off.

[0083] Step b: A process of coating a graphene film on a sacrificial support layer with a porous carbon structure organic precursor. As an organic precursor for the porous carbon structure according to the present invention, 0.2 g turanose (Sigma-Aldrich) and an amphiphilic block copolymer (0.1 g block copolymer, polystyrene-co-poly(4-vinylpyridine) (PS-P4VP) (Sigma-Aldrich)) were dissolved in N,N-dimethylformamide. The turanose helps to adjust the pore size of the subsequent carbon film. The resulting solution was treated at 180°C to improve hydrogen bonding between turanose and the P4VP region of the block copolymer, and then spin-coated onto the top surface of a graphene surface and dried at room temperature. The block copolymer film was then subjected to phase separation into hydrophobic and hydrophilic regions during drying, as previously described (Rodriguez et al., 2007, Adv. Funct. Mater., 17, pp. 2710-2716).

[0084] Step c: A process of converting the polymer into a porous carbon layer by thermal decomposition. The dried copolymer film formed in step (b) on the surface of the graphene film is then thermally decomposed at 500°C for 1 hour in an inert atmosphere (with H2 / Ar flow) to induce the formation of a porous carbon substrate 5 on the upper surface of the graphene layer 3, exposing a considerable area (approx. 50%) of graphene.

[0085] Step d: Step to remove the sacrificial support by etching. The composite structure 6, formed by a graphene layer 3 sandwiched between a newly generated porous carbon substrate 5 and a Cu sacrificial support layer 2 obtained in step (c), is then placed in an etching chamber 7 containing an etching solution 8 (0.2 M Na2S2O8 in water) (d1) to etch the Cu sacrificial support layer 2 and obtain a self-supporting graphene film 9 suspended in the etching solution 8 and supported by the carbon substrate (d2). This is then rinsed in deionized water to remove any residue from the etching of Cu (d3).

[0086] Step e: A step of transferring the composite of a porous carbon substrate and a graphene layer onto a macroporous support. Next, the graphene film 9 supported on the carbon substrate is transferred to a macroporous support 10 (for example, a 50 μm thick W foil with 5 μm pores, the pores being pre-integrated into the W foil by laser drilling, Figure 1, step e) by wet transfer in the etching chamber 7 by gently placing a W foil beneath the floating graphene film. As a result, the composite 9 of the porous carbon substrate and graphene layer is deposited on the macroporous support 10 when the fluid level in the etching chamber 7 is low.

[0087] Step f: Step to obtain a gas selective separation filter sheet. A gas-selective filter sheet 11, comprising a graphene film 3 on a porous carbon substrate 5 and a macroporous support structure 10 (e.g., W foil), is thus obtained and then removed from the etching chamber 7 for use in various applications. The filter sheet can be assembled into additional structural sheets and structural elements for integration into a filter unit for introduction into a gas flow device for gas separation. The filter unit can be assembled, for example, several centimeters depending on the application and the gas flow rate being processed. 2 For example, 1m 2 It may include multiple large filter sheets arranged in a honeycomb structure that covers the surface area up to [a certain point].

[0088] Example 2: Characterization of porous carbon layer and graphene film The structure and components of the porous carbon layer and graphene film of the present invention obtained in Example 1 were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging, as shown in Figure 2.

[0089] Scanning electron microscopy (SEM) was performed using an FEI Teneo SEM. Conductive coatings were not applied to the substrates before SEM. Transmission electron microscopy (TEM) imaging and electron diffraction of carbon substrates and composite graphene / carbon substrates were performed using an FEI Tecnai G2 Spirit Twin with a 120 keV incident electron beam.

[0090] High-resolution TEM (HRTEM) was performed using independent graphene films (without carbon film) transferred to a quantifoil TEM grid using conventional wet transfer techniques (Robeson et al., 2008, J. Memb. Sci., pp. 320, 390-400). Aberration-corrected (Cs) HRTEM was performed using a double-corrected Titan Themis 60-300 (FEI) equipped with a Wein-type monochromator. To reduce electron irradiation damage, an 80 keV incident electron beam was used for all experiments. The incident electron beam was monochromatic ("rainbow" mode illumination) to reduce the energy spread across the target region. HRTEM images were post-processed using a combination of bandpass and Gaussian filters.

[0091] Raman characterization is performed using a wet transfer method. 4 The analysis was performed on independent graphene (without carbon film) transferred onto an SiO2 / Si wafer. Single-point data acquisition and mapping were performed using a Renishaw micro-Raman spectrometer (532 nm, 2.33 eV, 100 × objective). Raman data analysis was performed using MATLAB®. Background was subtracted from the Raman data using the least-squares curve fitting tool (lsqnonlin) to calculate the peak heights of D and G.

[0092] Detailed examination of the supporting graphene film obtained in Example 1 using optical and electron microscopy revealed that, when comparing the surface of the composite of the transferred porous carbon substrate and graphene film with the surface of the macroporous substrate before transfer (Figures 2a-b), no visible cracks or fissures were found on the surface of the composite (Figure 2c). SEM images of the composite structure 6 formed by the graphene layer 3 sandwiched between the porous carbon substrate 5 and the Cu sacrificial support layer 2 obtained in step (c) (Figure 2d), and TEM images of the graphene film 9 supported on the carbon substrate obtained after etching the Cu foil in step d1 and after transfer on the TEM grid (before transfer on the macroporous support) (Figure 2e), revealed that pores with a diameter of 20-30 nm were presented in the carbon substrate after PSD (pore size distribution) analysis. In step d1, the selected-field electron diffraction (SAED) (Figure 2f) of the graphene film 9 supported on a carbon substrate, obtained after etching the Cu foil and collected on a TEM grid, showed typical diffraction peaks for suspended single-layer graphene with periodicities of 0.213 and 0.123 nm (Meyer et al., 2007, Nature, 446, pp. 60-63). The carbon substrate exhibited a broad ring shape, characteristic of amorphous carbon substrates, which contributed to the SAED (Figure 2f). No regions representing only the carbon substrate were found, indicating strong bonding between graphene and the carbon substrate during the thermal decomposition process. This is a very important and unexpected feature, enabling crack-free graphene transfer as the unbonded graphene layer would disintegrate and separate during the transfer process.

[0093] Interestingly, even the folding visible to the naked eye, as shown in Figure 2b, did not destroy the film, making this method extremely promising for the potential scaling up of single-layer graphene films.

[0094] SEM images of the carbon film indicated that the thickness of the carbon substrate was approximately 100 nm (Figure 2g).

[0095] Example 3: Porosity and gas separation performance of graphene film supported on a carbon substrate Using scanning tunneling microscopy (STM), we demonstrated that CVD-derived graphene possesses ultra-low density internal defects, including nanopores consisting of 10 to 13 missing carbon atoms, which are suitable for gas separation (Agrawal et al., 2017, J. Phys. Chem. C., 121, pp. 14312-14321). In this study, the defect density in CVD graphene was found to be 0.07 ± 0.02 of the carbon amorphous trajectory (Cancado et al., 2011, Nano Lett., 11, pp. 3190-3196) (I D / I G Using Figure 2h), 5.4 × 10⁻¹⁵ corresponds to a porosity of 0.025%. 10 individual defects / cm 2 This was the assessment. This represents the upper limit of gas-permeable nanopores, based on the pore size distribution in graphene, which consists of small pores that do not allow gas to pass through, such as those created by the absence of fewer than six carbon atoms, and larger pores suitable for gas separation.

[0096] The gas permeability of the graphene film achieved in Example 1 was tested by gas permeability tests as described below, illustrated in Figure 3, and compared with that from independent carbon substrates and macroporous W supports. In all cases, the permeance through the graphene film was significantly lower than that of the carbon and W supports, indicating that the graphene film was free from cracks or fissures. Prior to the test, the film was heated to 150°C to remove any impurities on the graphene surface. In a homemade permeation cell, the film was sealed directly to the top surface of the W support using a metal surface seal to ensure leak-free gas transport. Typically, the supply side (pure gas supply or mixed gas supply) was pressurized to 1.6–7.0 bar, while the permeation side, connected to a pre-calibrated mass spectrometer (MS), was maintained at 1 bar while sweeping with argon. The supply gas flow rate was regulated by a mass flow controller (MFC), and the supply pressure was controlled by adjusting a back pressure regulator introduced downstream. In another MFC, the Ar flow rate as the sweep gas was controlled, which delivered the permeate gas to a calibrated mass spectrometer (MS) for real-time analysis of the permeate concentration. In the mixture permeation test, equimolar gas mixtures were used on the supply side. To ensure uniformity in temperature, the supply and sweep gas lines, as well as the membrane module, were heated inside the oven. Once a steady state was established (typically 30 minutes after changing the permeation conditions), the gas flow rate was calculated. The membrane temperature was varied between 25 and 250°C to study the effect of temperature on membrane permeance and the thermal stability of the membrane of the present invention. Single-component gas transport from eight different graphene membranes prepared as described in Example 1 and measured as described above yielded 5.2 × 10⁻⁶ H₂ / CH₄ and H₂ / CO₂. -9 ~7.2×10 -8 molm -2 s -1 Pa -1 The H2 permeance in the range of (15-215 gas permeation units, GPU) and the He / H2 selectivity in the ranges of 4.8-13.0, 3.1-7.2, and 0.7-2.0 at 25°C were revealed. The H2 permeance was 5.4 × 10⁻⁶. 10 individual defects / cm 2 Based on the defect density, 1.0 × 10-23 ~1.3 × 10 -22 mols -1 Pa -1 This corresponds to the minimum transmittance coefficient. This transmittance coefficient is consistent with that of the Bi-3.4Å film reported by Koenig et al. in 2012, where it is 4.5 × 10⁻¹⁰. -23 mols -1 Pa -1 The coefficients have been reported. Interestingly, the H2 / CO2 selectivity is higher than that of the Bi-3.4 film, which has been reported to have a selectivity of ca.1.5. One film (M8) exhibited the best molecular sieving performance, showing He / H2 selectivity greater than 1, which means that the average pore size in M8 was less than the dynamic diameter of H2 (0.289 nm).

[0097] The permeances of He, H2, CO2, and CH4 increased with temperature, indicating that transport was under an activated transport regime. At 150°C, the H2 permeance was 3.3 × 10⁻⁶. -8 ~4.1×10 -7 molm -2 s -1 Pa -1 With an increase in GPUs (100-1220), the H2 / CH4 and H2 / CO2 selectivity increased to 7.1-23.5 and 3.6-12.2, respectively (Figures 4a-4i). This H2 / CH4 separation performance by a single layer graphene with a very low porosity of 0.025% reaches the upper limit measured for polymer films (Robeson, 2008, above) (as a 1 μm thick selective skin layer of a polymer film). Using the absorption phase transport models described by Drahushuk et al., 2012, Langmuir, 28, pp. 16671-16678 and Yuan et al., 2017, ACS Nano 11, pp. 7974-7987, the mean activation energy of the gas can be extracted from the temperature-dependent gas flow rate.

[0098]

number

[0099]

number

[0100] Here, C O E is the pore density, act and ΔE sur These are the activation energies for pore rearrangement and gas-graphene interaction potential, respectively. act and A sur is the corresponding pre-exponential factor. T is temperature, and P A and P R These are the partial gas pressures on the supply side and the permeate side, respectively. Average E for He, H2, CO2, and CH4 act The activation energies (for all eight membranes) were 16.7±3.2, 20.2±2.7, 31.3±2.8, and 25.8±4.8 kJ / mol, respectively, and increased with the dynamic diameter. The activation energy at H2 was similar to that from hydrogen-functionalized pore-10 reported by Jiang et al., 2009, Nano Lett., 9, pp. 4019-402 (0.22 eV), indicating that the average pore in this study consists of a deficiency of 10 carbon atoms, consistent with previous STM findings (Agrawal et al., 2017, above). act However, the slightly lower C in CH4 compared to CO2 can be explained by the fact that CH4 rearrangements occur from fewer pores (average C in He, H2, CO2 and CH4). O A act A sur Each is 1.5 × 10 -5 , 2.6×10 -5 , 3.8×10 -6 and 1.3 × 10 -6 (was), A act A sur It is estimated that this does not change significantly in CO2 and CH4. High-resolution transmission electron microscopy (HRTEM) demonstrated that sub-nanometer pores are indeed present in CVD graphene. Statistical analysis of these pores revealed that the pore density is approximately 2.8 × 10⁻⁶. 11 cm -2This suggests that the scale is comparable to that predicted from the carbon amorphous trajectory. Overall, observations of activated transport and visualization of sub-nanometer pores indicate that higher H2 permeance can be obtained at higher temperatures (250–300°C), particularly in a non-oxidizing atmosphere.

[0101] The separation of gas mixtures is crucial for understanding the effects of competitive adsorption and diffusion through nanoporous graphene. However, to date, reports on the separation of gas mixtures through single-layer graphene films remain challenging. The transport of chemical species i from an n-component gas mixture through graphene nanopores can be modeled by the following equation.

[0102]

number

[0103]

number

[0104] The membrane of the present invention, including a large-area graphene membrane, enables the measurement of flow rates of He, H2, CO2, and CH4 from equimolar gas mixtures. Interestingly, the overall performance trend (permeance and separation factor) for mixture feeding was improved compared to that observed in the case of single-component feeding (Figures 4f-4i). However, the H2 permeance and corresponding activation energy using single components, particularly at membrane M2, were similar to those in the case of mixtures (E of mixture M2 with He, H2, CO2, and CH4). actwere 20.4, 19.9, 34.9, 28.8 kJ / mol). The H2 / CH4 selectivity improved from 5.7 (single component) to 10.8 (mixture) at 25 °C and from 11.2 (single component) to 12.2 (mixture) at 150 °C. Similarly, the H2 permeance did not change with M3, but the H2 / CH4 selectivity increased from 14.2 (single component) to 18.0 (mixture). For the other membranes (M1, M4, M5 and M6), the H2 permeance and H2 / CH4 selectivity did not change in the mixture case compared to the single component case. From these results, regarding the size sieving of light gases, the competitive adsorption (CH4 in contrast to H2) that does not lower the separation selectivity at least at moderate feed pressures (1 - 7 bar) is emphasized as an inherent feature of the single-layer graphene membranes of the present invention. This is advantageous for the separation of H2 from CH4 even with a high concentration of CH4.

[0105] Furthermore, the graphene membranes of the present invention showed exceptional thermal stability. Generally, all membranes were stable up to at least 150 °C. For example, the performance of membrane M2 tested under three consecutive temperature cycles from 25 °C to 150 °C did not change significantly (Figure 5a). From cycle 1 to cycle 3 at 150 °C, the H2 permeance decreased slightly (from 3.3×10 -8 to 2.3×10 -8 mol m -2 s -1 Pa -1 ), but the H2 / CH4 selectivity increased slightly (from 8.3 to 10.5). Furthermore, the graphene membranes were also stable up to at least 8 bar of mixture feed at 100 °C (Figure 5b & Figure 5c). The H2 permeance and H2 / CH4 separation factor did not change significantly when the feed pressure of the mixture increased from 2 to 8 bar and the permeate side pressure was maintained at 1 bar (Figure 5b - Figure 5c).

[0106] Overall, from such data, the method of the present invention enables the realization of an expandable transfer method assisted by a support, without cracks and thermally stable over a large area (about 1 mm 2It is confirmed that a suspended single-layer graphene film (size of ) is produced. The graphene film supported on a carbon substrate having an extremely low porosity of about 0.025% obtained in this way unexpectedly exhibited suitable gas separation performance where the carbon support coating did not unexpectedly bottleneck (H2 permeability up to 4.1×10 -7 molm -2 s -1 Pa -1 and H2 / CH4 selectivity up to 23).

[0107] The following table describes the permeability of the coated film alone.

[0108]

Table 1

[0109] The obtained H2 permeability and selectivity reached the performance of a 1μm thick state-of-the-art polymer film. More advantageously, the performance of the graphene film of the present invention supported on carbon was stable up to at least a moderate membrane differential pressure (7 bar) during multiple heating and cooling cycles. In the use of gas mixture supply, the H2 permeability or the H2 / CH4 separation selectivity did not decrease.

[0110] Example 4: Ozone treatment to further improve membrane performance As reported in Example 3, the porosity of the graphene film of the present invention that makes the H2 permeability approximately 3.3×10 -8 ~4.1×10 -7 molm -2 s -1 Pa -1 at 150°C was only 0.025%. Exposure of the graphene film to ozone has unexpectedly been found to be usable to further improve the gas separation performance of the graphene film, as demonstrated below.

[0111] The effect of ozone treatment on a graphene film supported on a carbon substrate of the present invention was investigated at various temperatures (25°C to 100°C) and times (1 minute to 7 minutes). The treatment was performed in situ in the transmission setting (Figure 3), and O3 was guided from the transmission side to prevent oxidation of the mechanically reinforced carbon-supported film. Gas transport before and after O3 treatment was compared immediately after treatment and as a function of temperature. The release of graphene as a function of ozone exposure was studied by micro-Raman spectroscopy (Figures 6a-6b) and X-ray photoelectron spectroscopy (XPS, Figures 5c-5d), as detailed below.

[0112] Raman characterization was performed on the independent graphene film (without carbon film) of the present invention, which was transferred to an SiO2 / Si wafer by a wet transfer method (Robeson, 2008, above). Single-point data acquisition and mapping were performed using a Renishaw micro-Raman spectrometer (532 nm, 2.33 eV, 100 × objective). Raman data analysis was performed using MATLAB. Background was subtracted from the Raman data using the least-squares curve fitting tool (lsqnonlin) to calculate the D and G peak heights.

[0113] X-ray photoelectron spectroscopy (XPS) analysis was performed on an independent graphene film (without carbon film) of the embodiment of the present invention, also on a Cu foil, using a Mg Kα X-ray source (1253.6 eV) and a Phoibos 100 (SPECS) hemispherical electron analyzer, together with a multi-channel tron ​​detector. XPS spectra were recorded in fixed analyzer transmission (FAT) mode, using a pass energy of 90 eV for inspection and 20 eV for narrow scans. Since the sample did not show electrostatic charge, the bond energies are presented without correction (bond energies of CC: 284.4 eV, CO: 285.7 eV, C=O: 286.8 eV, OC=O: 288.5 eV). Since the carbonyl group (C=O) is part of (OC=O), OC=O was counted as C=O as a summary of the functional group. XPS spectra were processed using CasaXPS with background removal by the Shirley method.

[0114] The relative intensity of the D peak increased relative to the G peak, which represents the degree of damage in graphene (I D / I G (It increased from 0.07 to 4.0), but the intensity of the 2D peak decreased with increasing reaction time and temperature, which is due to sp in graphene. 3 -The hybridization sites increased after ozone treatment (Yuan et al., 2013, ACS Nano, 7, pp. 4233-4241). From the binding energy distribution of ozone-functionalized graphene, CO and C=O were shown to be the main functional groups in graphene after ozone functionalization. Interestingly, the number density of C=O groups was higher than that of CO groups, even in the case of mild functionalization (25°C, 2 min). The increasing number density of functional groups with reaction temperature and time (Figures 6c-d) is consistent with the results of Raman spectroscopy. At 100°C, the overall coverage of CO and C=O groups was as high as 35%, 56%, and 65% for exposure times of 2, 5, and 7 minutes, respectively.

[0115] Interestingly, after ozone treatment, the separation performance of all graphene membranes was significantly improved by either an increase in H2 permeance, an increase in H2 / CH4 selectivity, or an improvement in both permeance and selectivity.

[0116] When O3 treatment is performed at 25°C for 2 minutes, the H2 permeance is 1.9 × 10⁻⁶. -7 From 1.2 × 10 -7 molm -2 s -1 Pa -1 Although it decreased, the H2 / CH4 and H2 / CO2 selectivity increased from 10.0 to 15.0 and from 5.1 to 6.4, respectively, at 150°C (M2, Figures 6a-6b), indicating pore contraction. Interestingly, E act-app (E act +ΔE sur (defined as) and C0A act A sur Both decreased after pore functionalization with O3 treatment. act-app The change in E act (Higher activation energy due to pore contraction) and ΔE sur Due to the relative changes in (the bond energy increases due to the functionalized pores), it is difficult to interpret, and in CH4, C0A act A sur It decreased to 1 / 20th (5.7 × 10⁻¹⁰ -7 From 2.8 × 10 -8 ), it is clearly indicated that after ozone treatment, the number of pores available for CH4 rearrangement is small. This can be explained, without being bound by any theory, by the fact that the edges of the functionalized pores, whose size has contracted, block larger gas molecules from passing through the functionalized pores, leading to higher gas selectivity.

[0117] In contrast, ozone treatment at 100°C increased the gas permeance by up to three times, but the gas selectivity remained the same as that obtained from internal defects (Figures 6c-6d). Here, E act-app The COA for gas did not change significantly after functionalization, but act A surThis increased by indicating an increase in pore density scale. Given that high-temperature treatment increases the coverage of CO and C=O groups, these functional groups are likely to aggregate, and in this process, carbon is released from the graphene lattice in a gaseous phase such as CO and / or CO2, forming new pores. Functionalization based on performance improvement depends on the PSD of internal defects in graphene. For example, graphene films exhibiting excellent separation performance due to internal defects (narrow PSD) also exhibited separation performance after ozone treatment at 80°C.

[0118] The separation performance trajectory was established by comparing the separation selectivity and hydrogen permeance before and after ozone treatment (Figure 6g). The overall trajectory trend clearly demonstrated that the gas separation performance of the graphene membrane of the present invention can be improved by ozone treatment.

[0119] Higher gas permeance (3-fold increase) can be achieved by generating new nanopores through ozone treatment at 80-100°C (Figures 6c-6f). HRTEM images of functionalized graphene show that after ozone treatment at 80°C for 2 minutes, the number density of subnanometer pores in the graphene is higher (pore density is 2.8 × 10⁻⁶). 11 From 4.2 × 10 11 cm -2 Evidence was shown that while the permeance increased, selectivity was maintained. In the case of membrane M5, the increase in separation selectivity and permeance was achieved after ozone treatment at 80°C for 1 minute. The authors hypothesize that in the case of membrane M5, the new pores had narrower PSDs.

[0120] Higher selectivity can be achieved by performing ozone treatment at room temperature (e.g., 25°C), but permeance will decrease.

[0121] Therefore, since both permeance and selectivity determine membrane performance, these results support the fact that the gas separation performance of a gas selective filter using a graphene membrane according to embodiments of the present invention can be further improved by ozone functionalization, depending on the supply standards and purity and recovery rate requirements. After the synthesis treatment according to the present invention, improvements in H2 permeance (up to 300%) and H2 / CH4 selectivity (up to 150%) are possible.

[0122] Therefore, by using ozone-derived epoxy and carbonyl groups for functionalization of the graphene lattice that depends on the control temperature, gas-selective pores can be created in CVD-derived graphene, or existing pores can be compressed. This is useful for improving the gas filtration performance of a gas-selective filter using a graphene membrane according to the present invention. [Explanation of Symbols]

[0123] 1. Supported graphene membrane 2. Supporters of the Victims 3 CVD graphene film 4. Film of organic precursor 5. Porous carbon substrate 6 Composite structure 7 Etching Chamber 8 Etchant 9. Graphene film supported on a carbon substrate 10 Macroporous support 11 Gas Selection Filter Sheet

Claims

1. The invention comprises a nanoporous graphene film having a thickness of 0.34 to 2 nm and a porosity of more than 0.001%, a porous carbon substrate supporting the graphene film having a porosity in the range of 5% to 90%, and a porous support structure in which the graphene film and the porous carbon substrate are mechanically supported such that the graphene film is positioned between the porous carbon substrate and the porous support structure. The pores of the nanoporous graphene film have an average size of 0.2 nm to 0.5 nm, and the porous carbon substrate is H of the graphene film. ２ H is higher than transmittance. ２ It has transmittance, A gas selective separation filter wherein the porous carbon substrate contains pores having an average size in the range of 10 to 100 nm.

2. The gas selective separation filter according to claim 1, wherein the pores of the nanoporous graphene membrane have an average size of 0.25 nm to 0.3 nm.

3. The gas selective separation filter according to claim 1 or 2, wherein the porous carbon substrate has a porosity in the range of 10% to 80% and includes pores having an average size in the range of 10 to 1000 nm.

4. The gas selective separation filter according to claim 3, wherein the porous carbon substrate having pores having an average size in the range of 10 to 100 nm is obtained by in situ thermal decomposition of an organic precursor of the porous carbon substrate coated on the graphene film in an inert atmosphere.

5. The gas selective separation filter according to any one of claims 1 to 3, wherein the porous support structure has a porosity in the range of 2% to 60%, the pores have an average size in the range of 0.01 μm to 100 μm, and a thickness in the range of 10 μm to 10,000 μm.

6. Use of a gas selective separation filter according to any one of claims 1 to 5 for separating gases.

7. CO ２ From H ２ or CH ４ Use of a gas selective separation filter according to any one of claims 1 to 5 for separating the gases.

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