Graphene membrane filters for gas separation

Abstract

To provide an efficient gas selective filter using graphene membrane. The present invention relates to a carbon-supported, large-area, crack- and crevice-free graphene membrane useful for selective gas separation, its preparation method, and use. In particular, the present invention relates to a carbon-supported, crack- and crevice-free graphene membrane with good gas separation performance, especially high H permeance and H / CH selectivity.

Description

[Technical Field]

[0001] The present invention relates generally to the field of gas-selective separation filters, particularly those useful for the separation of gas mixtures, especially in the context of carbon capture resulting from the separation of H and N from CO and hydrocarbons, for example from gaseous waste or effluents. The present invention more particularly relates to filters employing atomically thick porous graphene membranes. [Background technology]

[0002] In the framework of addressing the global warming problem and the identified contributing factors, one of the options that has been developed is the reduction of greenhouse gas emissions by capturing carbon dioxide from gas streams and subsequent underground sequestration. Carbon capture and storage is a strategy to mitigate CO2 emissions from large-scale point sources, such as coal-fired power plants. Furthermore, effective CO2 / CH4 separation is also necessary for biogas processing, which mainly contains about 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 species, especially CO2. Polymer membranes have been applied in industrial gas separations for decades, and their gas selectivity has been commercialized to separate a variety of gases (Sanders et al., 2013, Polymer., 54, pp. 4729-4761). However, they face performance limitations due to the inherent selectivity-performance tradeoff (Park et al., 2017, Science 356) and physical aging, which primarily involves plasticization of the polymer film over time in the gas flow channels, affecting the filtration-free volume (Sanders et al., 2013, supra).

[0003] Atomically thick graphene films with molecularly selective nanopores represent the thinnest possible molecular barrier and can therefore be considered the ultimate membrane for molecular separation. Several molecular simulations have shown that two-dimensional nanopores in graphene can achieve unprecedented gas permeances on a scale larger than those achieved in 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-flux membranes could substantially reduce the membrane area required for the separation of a given volume of gas mixture, representing a novel solution to the long-standing problem of membrane scale-up in this field. Therefore, the chemical robustness and high mechanical strength of graphene lattices make them highly suitable for gas separation, even with porosities as high as 5%. Recently, several etching methods have been developed to drill subnanometer pores in graphene, which have shown promising sieving performance for liquids and dissolved ions. However, demonstration of gas sieving capabilities has been limited. Concrete evidence was only obtained by measuring the shrinkage rate of bilayer graphene microballoons in which pores were created in micromechanically exfoliated graphene by UV treatment (Koenig et al., 2012, Nat. Nanotechnol., 7, 728–732). Generally, the majority of liquid, ion, and gas transport studies have been performed in micron-sized graphene regions, which contributes to the limitations of micromechanical exfoliation and the occurrence of cracks and tears during the transfer of chemical vapor deposition (CVD)-derived graphene.

[0004] Indeed, CVD-assisted single-layer graphene is considered particularly suitable for fabricating large-area films due to the scalability of the CVD process (Polsen et al., 2015, Sci. Rep. 5, 10257). However, after CVD, one must transfer graphene from a nonporous catalytic metal foil (e.g., Cu) to a porous substrate to fabricate the film. Because conventional transfer methods invariably result in cracks and tears in the graphene film, thus far, suspended, crack- and crack-free single-layer graphene films have been limited in film area to a few micrometers (Suk et al., 2011, ACS Nano 5, 6916–6924). Among the several transfer techniques developed to date, wet transfer technology has been the most explored due to its versatility, enabling graphene transfer to a wide range of supports (Zhang et al., 2017, Adv. Mater. 29, 1–7). Briefly, graphene films are coated with a mechanically reinforcing 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. Finally, the suspended film is skimmed onto the top surface of a desired substrate, and the polymer film is dissolved away, exposing the graphene surface. However, when porous supports are used, significant cracks and tears develop in the graphene film, primarily due to strong capillary forces on the suspended graphene film during the solvent drying step (Lee et al., 2014, ACS Nano, 8, 2336-2344).

[0005] Celebi et al., 2014, Science, 344, 289-292, report a 2'500 μm thin film obtained by overcoating a graphene layer with another graphene layer to hide cracks in the individual layers. 2A bilayer graphene film has been reported. Using a focused ion beam (FIB), relatively large pores (>7.6 nm) were drilled in graphene, and the burst of gas transport was observed in this perforated bilayer graphene film. The burst of transport demonstrated gas selectivity expected by Knudsen diffusion (H / CO selectivity up to 4) and enormous H permeance (ca. 10 -2 molm -2 s -1 Pa -1 ) led to the development of nanoporous graphene films. Recently, Boutilier et al. (2017), ACS Nano, 11, pp. 5726-5736, reported the fabrication of centimeter-scale single-layer nanoporous graphene using a combination of ion bombardment and O2 plasma. However, the presence of cracks in the graphene film generated during transfer limited the separation selectivity to that expected from Knudsen diffusion (He / SF6 and H2 / CH4 separation selectivities of 8 and 3.2, respectively). Nevertheless, using transport modeling, they demonstrated the presence of nanopores in the film that sieve molecules and are highly suitable for gas separation. Graphene oxide (GO) films have a small H2 permeance (10 -7 molm -2 s -1 Pa -1 ), which has been successfully used for H2 / CO2 separation (Li et al., 2013, Science, 342, 95–98). However, the reproducible synthesis and stability of GO films are questionable due to difficulties in predicting the exact structure of GO flakes and unstable bent bonds in the GO lattice. Overall, demonstrating gas mixture separation from fully scaled single-layer graphene films remains elusive, as it requires the development of a) methods to transfer large areas of graphene to porous supports without generating cracks and tears, and b) methods to produce a narrow pore size distribution (PSD) in the graphene (Wang et al., 2017, Nat. Nanotechnol., 12, 509–522).

[0006] Therefore, the development of new methods to fabricate crack- and crevice-free suspended graphene films possessing size-selective pores with narrow pore size distributions would be highly advantageous in terms of large-scale deployment of nanoporous 2D membranes, which have been hampered to date 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., 175-176, pp. 101-105 [Non-Patent Document 5] Koenig et al., 2012, Nat. Nanotechnol., 7, 728-32 [Non-patent document 6] Polsen et al., 2015, Sci. Rep. 5, 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 Summary of the Invention [Problem to be solved by the invention]

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

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

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

[0011] It would be advantageous to have a gas-selective filter that has stable gas separation performance over multiple separation cycles, especially over multiple heating and cooling cycles.

[0012] It would be advantageous to have a gas-selective filter that has stable gas separation performance, especially under high pressure (eg, transmembrane pressures of at least 7 bar) and over multiple separation cycles.

[0013] It would be advantageous to have atomically thick, large-area graphene films free of cracks and crevices for gas selective filters.

[0014] It would be advantageous to obtain atomically thick graphene films that are free of cracks and crevices and that present a production cost that is feasible for large-scale use.

[0015] Although it is possible to transfer fairly large areas of CVD monolayer graphene to porous supports, it would be advantageous to obtain atomically thick graphene membrane supports that do not compromise the gas filtration properties of graphene.

[0016] It would be advantageous to have a cost-effective method for preparing atomically thick, large-area graphene membranes free of cracks and crevices, useful for selective gas separation.

[0017] A fairly large area (e.g. 1 mm 2 It would be advantageous to have a method for transferring CVD monolayer graphene (above) to a support structure without cracks and crevices.

[0018] It would be advantageous to have an easily scalable method for tailoring the separation performance of graphene membranes according to target specifications (e.g., supply specifications, and purity and recovery requirements).

[0019] It is an object of the present invention to provide a gas selective filter comprising a graphene membrane and a method for preparing a gas selective filter comprising 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 has been 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] 1. A method for preparing a gas-selective separation filter, comprising: a) providing a graphene film on a sacrificial support layer; b) coating the graphene film with an organic precursor of a porous carbon substrate; c) subjecting the organic precursor to pyrolysis 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) placing the composite of the porous carbon substrate and the graphene film on a macroporous support structure; e) before or after step d), removing at least a portion of the sacrificial support layer and flowing a gas through the composite of the porous carbon substrate and the graphene film; Disclosed herein is a method comprising:

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

[0023] Also disclosed herein is the use of a gas-selective filter comprising a graphene membrane on a porous carbon substrate for separating gases, particularly for separating H, N, and / or CH from CO and from larger molecular weight hydrocarbons (e.g., C, H, C, H, C, H).

[0024] According to another aspect of the present invention, there is provided a method for improving the gas filtration performance of a nanoporous graphene membrane, comprising the steps of: (i) providing a graphene membrane on a porous support; (ii) treating the graphene film with ozone at a temperature of 25°C to 300°C, typically 25°C to 100°C, for 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; Further disclosed herein is a method comprising:

[0025] This method is (iii) storing the graphene film at 25°C to 200°C in an air environment or an inert environment.

[0026] In an advantageous embodiment, the H permeance of the graphene film is about 10-8 molm -2 s -1 Pa -1 from about 10 -4 molm -2 s -1 Pa -1 (e.g. 10 -7 From 10 -6 molm -2 s -1 Pa -1 )

[0027] In an advantageous embodiment, 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 an advantageous embodiment, the porous carbon substrate has a porosity greater than 10%, more particularly in the range of 20% to 70%, formed by pores having an average size (i.e., circular width or diameter of the localized pores) in the range of about 10 nm to about 1000 nm, preferably 10 nm to about 100 nm.

[0029] Porous carbon substrates according to embodiments of the present invention have an H2 permeance that is at least 10 times higher than that of graphene films, and typically more than 100 times higher.

[0030] The porous support structure may have pores with an average size in the range of 0.01 μm to 100 μm, such as in the range of 0.1 μm to 20 μm, and more particularly in the range of 1 μm to 10 μm.

[0031] The porous support structure may have a porosity in the range of 2% to 60%, preferably greater than 5%, e.g., 5% to 25%, so as to contribute a negligible or slight increase in resistance to gas flow through the filter, ensuring on the one hand sufficient structural strength and on the other hand good permeance (compared to graphene membranes).

[0032] The porous support structure may have a thickness in the range of 10 μm to 10000 μm, typically 20 μm to 100 μm (eg 50 μm).

[0033] Advantageously, the porous carbon substrate provides ideal support for the graphene layer, allowing for the removal of a sacrificial support layer and, inter alia, limiting thermal and mechanical stresses in the graphene layer during the transfer process, thereby allowing the graphene layer to be mounted on a mechanical support structure without inducing tears or cracks in the graphene layer. The porosity of the carbon substrate is easily configured due to its ideal properties, while avoiding excessive resistance to gas flow compared to graphene films and avoiding overly 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 for reducing the relative thermal expansion.

[0034] In an advantageous embodiment, removing at least a portion of the sacrificial support layer comprises etching said 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 carried out before the porous carbon support and graphene membrane are placed on the macroporous support structure to obtain a free-standing composite of the porous carbon substrate and graphene membrane suspended in the etching solution.

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

[0037] Although removal of the sacrificial layer by etching is preferred, other removal methods may also be practiced within the scope of the present invention, for example, electrochemical foaming techniques, whereby the graphene is exfoliated from the Pt support, allowing the Pt support to be reused.

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

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

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

[0041] In an advantageous embodiment, the graphene film is a chemical vapor deposition (CVD) graphene layer, particularly a CVD-derived substantially single layer graphene having a thickness of about 0.34 to 2 nm.

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

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

[0044] Other features and advantages of the invention will be apparent from the claims, detailed description and drawings. [Brief explanation of the drawings]

[0045] [Figure 1] FIG. 1 is a schematic diagram illustrating the preparation of a gas-selective filter with a graphene film by a carbon substrate-assisted transfer method according to an embodiment of the present invention. [Figure 2]FIG. 1 shows structural characterization of a graphene film supported on a porous carbon substrate according to an embodiment of the present invention, obtained in Example 1, whose components are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging, as described in Example 2. a-b) SEM image of a porous tungsten substrate, showing an array of 5 μm pores spanning an area of ​​1 mm on a tungsten foil (50 μm thick). c) SEM image of a carbon substrate on a graphene film according to an embodiment of the present invention on a porous tungsten support substrate. d) SEM image of a porous carbon substrate on top of the graphene. e) TEM image of a porous carbon substrate and a single-layer graphene film according to an embodiment of the present invention on a TEM grid. f) Diffraction pattern of graphene through a porous carbon substrate and a single-layer graphene film according to an embodiment of the present invention. g) Cross-sectional SEM image of a porous carbon substrate and a single-layer graphene film according to an embodiment of the present invention. h) Typical Raman spectrum from single-layer LPCVD graphene. [Figure 3] FIG. 1 shows a schematic diagram of the gas permeance test set-up described in Example 3. [Figure 4a] 1 is a graph reporting the results of gas separation performance of eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. a) H2 permeance as a function of temperature from a single gas permeance test. [Figure 4b] Figure 1 is a graph reporting the gas separation performance results of eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. b-d) Selectivity of different gases via a single gas permeance test; b) H2 / CH4. [Figure 4c] Figure 1 is a graph reporting the gas separation performance results of eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs through internal defects in the graphene. b-d) Selectivity of different gases via a single gas permeance test, c) H2 / CO2. [Figure 4d]Figure 10 is a graph reporting the gas separation performance results of eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. b-d) Selectivity of different gases via a single gas permeance test, d) He / H2. [Figure 4e] Figure 1 is a graph reporting the results of gas separation performance for eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in graphene. e) Extracted activation energy for gases with different kinetic diameters. [Figure 4f] 1 is a graph reporting the gas separation performance results of eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. f) H2 permeance as a function of temperature from a mixture gas permeance test. [Figure 4g] Figure 1 is a graph reporting the results of gas separation performance for eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. g-i) Separation factors for different gases via mixed gas permeance tests, g) H2 / CH4. [Figure 4h] Figure 1 is a graph reporting the results of gas separation performance for eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. g-i) Separation factors for different gases via mixed gas permeance tests, h) H2 / CO2. [Figure 4i] Figure 1 is a graph reporting the results of gas separation performance for eight CVD graphene membranes (M1-M8) according to an embodiment of the invention described in Example 3. Gas transport occurs from internal defects in the graphene. g) Separation factors for different gases via mixed gas permeance tests: i) He / H2; [Figure 5a] 1 is a graph reporting internal defect stability testing of graphene films of the present invention, as described in Example 3. a) H2 and CH4 permeance at three consecutive temperature cycles. [Figure 5b] 1 is a graph reporting the internal defect stability test of the graphene film of the 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] 1 is a graph reporting internal defect stability tests of graphene films of the 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] 1A-1C are graphs reporting the characterization of ozone-treated graphene films according to an embodiment of the invention, as described in Example 4. a) Raman spectra of O3-treated graphene films under different conditions. [Figure 6b] 10A-10C are graphs reporting the characterization of ozone-treated graphene films according to an embodiment of the invention, as described in Example 4. a) Histograms of ID / IG values ​​of O3-treated graphene films using different treatments. [Figure 6c] 10 is a graph reporting the characterization of ozone-treated graphene films according to an embodiment of the invention, as described in Example 4. c) CO bond content of O3-treated graphene films treated at different reaction temperatures and reaction times. [Figure 6d] 10 is a graph reporting the characterization of ozone-treated graphene films according to an embodiment of the invention, as described in Example 4. d) C=O bond content of O3-treated graphene films treated at different reaction temperatures and reaction times. [Figure 7a]1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration of the ozone treatment. a-b) Permeance of M2, a) H2 and CH4 treated with O3 for 2 minutes at 25°C. [Figure 7b] 1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration of the ozone treatment. a-b) M2 treated with O3 for 2 minutes at 25°C; b) H2 / CH4 and H2 / CO2 selectivity. [Figure 7c] 1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration of the ozone treatment. c-d) Permeance of M8 treated with O3 at 100°C for 2 minutes, c) H2 and CH4. [Figure 7d]1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration 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] 1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration of the ozone treatment. e-f) Permeance of M6 treated with O3 at 80°C for 1 minute; e) Permeance of H2 and CH4. [Figure 7f] 1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration 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]Figure 1 is a graph reporting the gas separation performance results of several ozone-treated graphene membranes according to the present invention, as described in Example 4. Briefly, graphene films, in which CVD-grown internal defects act as transport pathways, were treated with ozone at temperatures ranging from 25 to 100°C for periods of 1 to 10 minutes, leading to improvements in the gas separation performance of the membranes. The improvement in performance depends on the internal defects (average pore size, pore density), as well as the temperature and duration of the ozone treatment. g) Gas separation performance trajectories after different ozone treatments (data for M8 were obtained at 200°C, the other data were measured at 150°C; the light markers are the gas performance of the pristine graphene membranes, while the dark markers are the gas performance of graphene membranes functionalized from the corresponding membranes). DETAILED DESCRIPTION OF THE INVENTION

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

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

[0048] The expression "organic precursor of a porous substrate" refers to any organic agent that can form a film on the graphene surface and, after pyrolysis, can be converted into a porous carbon substrate having pores of about 10 nm to about 1000 nm. According to a particular embodiment, examples of organic precursors of porous structures include block copolymers, particularly amphiphilic block copolymers, more particularly block copolymers that, when coated as a thin film and dried, undergo phase separation into hydrophilic (e.g., polyvinylpyridine) and hydrophobic (e.g., polystyrene) domains, 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. According to a particular embodiment, block copolymers that are soluble in N,N-dimethylformamide are preferably used as organic precursors of the porous carbon structure according to the invention.

[0049] The expression "membrane performance" refers to the combination of membrane gas permeance and its gas selectivity. Typically, in the field of gas separation, -8 molm -2 s -1 Pa -1 An H2 permeance of 6 or more and an H2 / CH4 selectivity of 6 or more are considered to be good membrane performance.

[0050] Referring now to the drawings, and particularly to Figure 1 , an illustration of a method for preparing a gas-selective filter including a crack- and crevice-free single-layer graphene membrane according to an embodiment of the present invention is shown. The illustrated method for preparing the gas-selective filter generally includes providing a graphene membrane on a sacrificial support layer, coating the graphene membrane with an organic precursor of a porous carbon substrate, and subjecting the organic precursor to pyrolysis in an inert atmosphere to convert the organic precursor to the porous carbon substrate on the graphene membrane, the porous carbon substrate having a porosity ranging from 5% to 90% and an H permeance at least 10 times higher than that of graphene. Mounting the composite of the porous carbon substrate and graphene membrane on a macroporous structural support, and removing at least a portion of the sacrificial support layer to allow gas to flow through the composite of the porous carbon substrate and graphene membrane. The porous substrate may be flat or curved, e.g., tubular.

[0051] More specifically, the steps of the embodiment illustrated in FIG. 1 include: a) providing a CVD graphene film 3 (particularly a graphene monolayer) on a sacrificial support layer 2 to form a supported graphene film 1; b) coating the graphene membrane 3 with a solution containing an organic precursor of the 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 membrane; c) subjecting the film of organic precursor 4 to pyrolysis under an inert atmosphere so that the film of organic precursor 4 is converted into a porous carbon substrate 5 on the surface of the graphene membrane 3, the porous carbon layer having a porosity of about 5% to about 90%, typically 10% to 80%, preferably greater than 20%, typically less than 70%; d) placing the composite of the porous carbon substrate and the graphene film on the sacrificial support layer 2 obtained in step c) in an etching chamber 7 containing an etchant 8 to etch the sacrificial support layer 2, thereby obtaining a graphene film supported on the porous carbon substrate suspended in the etching solution; e) transferring the graphene membrane 9 supported on the carbon substrate obtained in step d) onto a macroporous support 10 to obtain a gas-selective filter sheet 11 (step f)) comprising a combined layer of the porous carbon substrate 5, the graphene membrane 3 and the macroporous support structure 10; Includes:

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

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

[0054] According to embodiments, the average size of the pores of the nanoporous graphene film is in the range of 0.2 nm to 0.5 nm, in particular 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 approximately 10 to 100 μm thick, in particular approximately 10 to 50 μm thick, for example approximately 25 μm thick.

[0056] According to one particular embodiment, the organic precursor of the porous carbon substrate is an amphiphilic block copolymer, in particular a block copolymer of polyvinylpyridine and polystyrene monomers, such as 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, so that the concentrations of turanose and block copolymer are 1-10% and 1-10% (w / w), respectively.

[0058] According to another particular embodiment, the coating solution used in step b) is treated at an elevated temperature, for example from about 50 to about 200°C (e.g., 180°C), before coating in order to anneal the film and induce phase separation of the hydrophilic and hydrophobic domains.

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

[0060] According to another particular embodiment, the pyrolysis in step c) is carried out at a temperature of about 400-1000° C., in particular at about 500° C., for about 1 hour.

[0061] According to another particular embodiment, the pyrolysis is carried out in step c) under a stream of H2 / Ar.

[0062] According to another particular 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 20-70%, resulting in a significant area of ​​graphene exposed (i.e., not covered by the porous carbon substrate 5).

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

[0064] According to another particular embodiment, the composite 9 of porous carbon substrate and graphene membrane obtained in step d) is rinsed (for example in deionized water) to remove residues.

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

[0066] According to another particular embodiment, the macroporous support structure 7 has a thickness of from 10 μm to about 10000 μm, typically from 20 μm to about 100 μm.

[0067] According to a further particular embodiment, the macroporous support structure 7 is selected from sintered ceramics (eg alumina, silica, etc.) and metals (stainless steel, Inconel, Hastelloy, etc.).

[0068] According to a further particular 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%-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 particular embodiment, the gas selective filter sheet 11 obtained in step f) has a molecular weight of about 10 -8 molm -2 s -1 Pa -1 from about 10 -4 molm -2 s -1 Pa -1 (e.g. 10 -7 From 10 -6 molm -2 s -1 Pa -1 ) H2 permeance.

[0070] According to another more particular embodiment, the gas-selective filter sheet 11 obtained in step f) has a H2 / CH4 selectivity of about 3 to about 1000 (eg, about 20).

[0071] According to another more specific embodiment, the gas filtration performance of the graphene membrane is improved by treating the supported graphene membrane with ozone under an inert atmosphere for a period of time ranging from about 1 ms to about 1 month, typically from about 30 s to about 60 minutes.

[0072] According to another further particular embodiment, the method according to the invention further comprises a step g) of functionalizing the graphene film by subjecting the gas-selective filter sheet 11 to a treatment with ozone under an inert atmosphere for a period of from about 1 ms to about 1 month, typically from about 30 s to about 60 min.

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

[0074] According to another more specific embodiment, gas filtration performance can be tailored through improved gas filtration performance using ozonation conditions to handle different feed specifications and purity and recovery requirements. For example, a separation process may require selective or more permeable membranes depending on the feed concentration, permeate purity (90%, 95%, 99%, etc., where higher purities require more selective membranes), overall recovery (80%, 90%, 95%), or cost (further cost savings are achieved by using more permeable membranes).

[0075] Typically, the functionalization step g) is carried out at a temperature of about 0-60° C. (eg, 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 60-150° C., preferably 80-100° C., to improve the H 2 permeance of the graphene film.

[0077] According to one particular aspect, a gas-selective filter according to the invention can be advantageously used for the separation of H from CH and from larger molecular weight hydrocarbons, or in the processing of synthesis gas (syngas) to remove impurities or to adjust the H / CO ratio for a particular downstream application.

[0078] The gas-selective filter according to the present invention can be used in combination with a dehydrogenation reactor as a membrane reactor (e.g., for producing olefins from alkanes) to remove H and improve the efficiency of the process and increase the overall conversion rate. Furthermore, the graphene membrane according to the present invention can be suitable for carbon capture (separation of H / CO, H / CH, CO / N, and CO / CH).

[0079] The remarkable stability of the observed temperatures of the gas selective filters according to the invention allows their use as a useful alternative to polymeric membranes, which have a short life cycle, especially at high pressures (5-20 bar) and high temperatures (100-250°C).

[0080] The invention described in the following examples is offered by way of illustration and not by way of limitation. [Example]

[0081] Example 1: Support-assisted transfer method of single-layer graphene to a porous substrate The method of the present invention for preparing crack- and crevice-free atomically thick graphene films, which comprises support-assisted transfer of single-layer graphene to a porous substrate, is illustrated in FIG. 1 and described in detail below.

[0082] Step a: Providing CVD graphene synthesized on a sacrificial support layer. Supported graphene films 1 were prepared as CVD graphene monolayers 3 supported on sacrificial support layers 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 min in a CO atmosphere to remove most of the organic contaminants. Then, 8 sccm of H was introduced to purge the CO and anneal the copper surface. Subsequently, 24 sccm of CH was added to initiate graphene crystallization. After graphene growth (30 min), the CH flow was switched off.

[0083] Step b: Coating the organic precursor of the porous carbon structure onto the graphene film on the sacrificial support layer As organic precursors for the porous carbon structures of the present invention, 0.2 g of turanose (Sigma-Aldrich) and an amphiphilic block copolymer (0.1 g of block copolymer, polystyrene-co-poly(4-vinylpyridine) (PS-P4VP) (Sigma-Aldrich)) were dissolved in N,N-dimethylformamide. Turanose helps control 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 domains of the block copolymer, then spin-coated on top of a graphene surface and dried at room temperature. The block copolymer film then undergoes phase separation into hydrophobic and hydrophilic domains upon drying, as previously described (Rodriguez et al., 2007, Adv. Funct. Mater., 17, pp. 2710-2716).

[0084] Step c: converting the polymer into a porous carbon layer by pyrolysis The dried copolymer film formed in step (b) on the surface of the graphene membrane is then pyrolyzed at 500°C for 1 hour under an inert atmosphere (H2 / Ar flow), causing the formation of a porous carbon substrate 5 on top of the graphene layer 3 and exposing a significant area (ca. 50%) of graphene.

[0085] Step d: removing the sacrificial support by etching The composite structure 6 formed by the graphene layer 3 sandwiched between the freshly produced porous carbon substrate 5 and the 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 NaSO in water) (d1) to etch the Cu sacrificial support layer 2 and obtain a free-standing, carbon-substrate-supported graphene membrane 9 suspended in the etching solution 8 (d2), which is then rinsed in deionized water to remove Cu etching residue (d3).

[0086] Step e: Transferring the composite of the porous carbon substrate and the graphene layer to a macroporous support Next, the graphene film 9 supported on the carbon substrate is transferred to a macroporous support 10 (e.g., 50 μm thick W foil with 5 μm pores, the pores having been previously incorporated 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 under the floating graphene film, so that 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 of obtaining a gas selective separation filter sheet A gas-selective filter sheet 11 comprising a graphene membrane 3 and a macroporous support structure 10 (e.g., W foil) on a porous carbon substrate 5 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 elements for integration into a filter unit for introduction into a gas flow device for separating gases. The filter unit can be, for example, a filter having a size of several cm, depending on the application and the gas flow rate to be processed. 2 For example, 1m from 2 The filter may comprise multiple large filter sheets arranged in a honeycomb configuration covering a surface area of ​​up to 1000 mm.

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

[0089] Scanning electron microscopy (SEM) was performed using an FEI Teneo SEM. No conductive coating was applied to the substrates prior to SEM. Transmission electron microscopy (TEM) imaging and electron diffraction of the carbon substrates and composite graphene / carbon substrates were performed on an FEI Tecnai G2 Spirit Twin using a 120 keV incident electron beam.

[0090] High-resolution TEM (HRTEM) was performed on free-standing graphene films (without carbon film) transferred to quantifoil TEM grids by conventional wet transfer techniques (Robeson et al., 2008, J. Memb. Sci., 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 over the region of interest. HRTEM images were post-processed using a combination of bandpass and Gaussian filters.

[0091] Raman characterization is performed using the wet transfer method 4 The experiments were performed on free-standing graphene (without a carbon film) transferred onto a SiO2 / Si wafer by NMR. Single-point data collection and mapping were performed using a Renishaw micro-Raman spectrometer (532 nm, 2.33 eV, 100x objective). Raman data analysis was performed using MATLAB. A least-squares curve-fitting tool (lsqnonlin) was used to subtract the background from the Raman data to calculate the D and G peak heights.

[0092] Examination of the supported graphene membrane obtained in Example 1 by optical and electron microscopy confirmed that the surface of the composite of the transferred porous carbon substrate and graphene membrane was free of visible cracks or fractures when compared with the surface of the macroporous substrate before transfer (Figures 2a-b) (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), as well as a TEM image of the graphene membrane 9 supported on the carbon substrate obtained after etching the Cu foil in step d1 and after transfer onto a TEM grid (before transfer onto the macroporous support) (Figure 2e), revealed that the carbon substrate exhibited pores with diameters of 20–30 nm after PSD (pore size distribution) analysis. Selected-area electron diffraction (SAED) (Figure 2f) of the graphene film 9 supported on the carbon substrate, obtained after etching the Cu foil in step d1 and collected on a TEM grid, exhibited typical diffraction peaks of suspended monolayer graphene, exhibiting periodicities of 0.213 and 0.123 nm (Meyer et al., 2007, Nature, 446, pp. 60–63). The carbon substrate exhibited broad ring shapes, characteristic of amorphous carbon substrates, contributing to the SAED (Figure 2f). No regions representing only the carbon substrate were found, indicating a strong bond between the graphene and the carbon substrate during the pyrolysis step. This is a crucial, unexpected feature, enabling the achievement of crack-free graphene transfer, as unbonded graphene layers would disintegrate and separate during the transfer process.

[0093] Interestingly, even macroscopic folding, as shown in Figure 2b, did not destroy the membrane, making the method highly promising for potential scale-up of single-layer graphene membranes.

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

[0095] Example 3: Porosity and gas separation performance of graphene membranes supported on carbon substrates Using scanning tunneling microscopy (STM), we showed that CVD-derived graphene has an ultralow density of 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 approximately equal to the carbon amorphization trajectory (Cancado et al., 2011, Nano Lett., 11, pp. 3190-3196) (I of 0.07 ± 0.02). D / I G , Figure 2h) to obtain a porosity of 5.4 × 10, which corresponds to a porosity of 0.025%. 10 defects / cm 2 This represents an upper limit for gas-permeable nanopores, due to the pore size distribution in graphene, which is composed of small pores that do not allow gas to pass through, such as those created by missing fewer than six carbon atoms, as well as larger pores suitable for gas separation.

[0096] The gas permeation of the graphene membranes achieved in Example 1 was tested in a gas permeation test, as described below, and is illustrated in Figure 3. The permeance through the graphene membranes was significantly lower than that of the carbon and W supports, indicating that the graphene membranes were free of cracks or fissures. Prior to testing, the membranes were heated to 150 °C to remove contaminants on the graphene surface. In a homemade permeation cell, the membrane was sealed directly to the top surface of the W support using a metal face seal to ensure leak-tight measurements of gas transport. Typically, the feed side (pure gas feed or mixture feed) was pressurized to 1.6–7.0 bar, while the permeate side, connected to a pre-calibrated mass spectrometer (MS), was maintained at 1 bar with an argon sweep. A mass flow controller (MFC) regulated the feed gas flow rate, and the feed pressure was controlled by adjusting a backpressure regulator installed downstream. In another MFC, the flow rate of Ar as a sweep gas was controlled, which delivered the permeate gas to a calibrated mass spectrometer (MS) for real-time analysis of the permeate concentration. For the mixture permeation test, an equimolar gas mixture was used on the feed side. The feed and sweep gas lines, as well as the membrane module, were heated inside an oven to ensure uniformity in temperature. Once a steady state was established (typically 30 minutes after changing the permeation conditions), the gas flow rates were calculated. The membrane temperature was varied from 25 to 250 °C to study the effect of temperature on the membrane permeance and the thermal stability of the membranes 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 a 5.2 × 10 saturation for H2 / CH4, H2 / CO2, and HCl / CO2. -9 ~7.2×10 -8 molm -2 s -1 Pa -1 The H permeance ranged from 15 to 215 gas permeance units (GPU) and the He / H selectivity ranged from 4.8 to 13.0, 3.1 to 7.2, and 0.7 to 2.0 at 25 °C, respectively. The H permeance was 5.4 × 10 10 defects / cm 2 Based on the defect density of 1.0×10-23 ~1.3×10 -22 mols -1 Pa -1 This corresponds to a minimum permeability coefficient of 4.5 × 10 for the Bi-3.4 Å film reported by Koenig et al., 2012, supra, where -23 mols -1 Pa -1 A coefficient of 0.289 nm has been reported. Interestingly, the H2 / CO2 selectivity is higher than that from the Bi-3.4 membrane, which reported a selectivity of ca. 1.5. One membrane (M8) exhibited the best molecular sieving performance, exhibiting a He / H2 selectivity of greater than 1, which means that the average pore size in M8 was less than the kinetic diameter of H2 (0.289 nm).

[0097] The permeance of He, H, CO, and CH increased with temperature, indicating that the transport was in the activated transport regime. At 150 °C, the H permeance was 3.3 × 10 -8 ~4.1×10 -7 molm -2 s -1 Pa -1 The H2 / CH4 and H2 / CO2 selectivities increased from 7.1 to 23.5 and 3.6 to 12.2, respectively (Figures 4a-i). This H2 / CH4 separation performance with single-layer graphene, with a very low porosity of 0.025%, reaches the upper limit measured in polymer membranes (Robeson, 2008, supra) (as a 1 μm-thick selective skin layer of a polymer membrane). Using the transport model for the absorbing phase described in Drahushuk et al. (2012) Langmuir 28, pp. 16671-16678 and Yuan et al. (2017) ACS Nano 11, pp. 7974-7987, the average activation energy of the gas can be extracted from the temperature-dependent gas flow rate.

[0098]

number

[0099]

number

[0100] where C O is the pore density and E act and ΔE sur are the activation energies for the pore rearrangement and gas-graphene interaction potential, respectively. A act and A sur is the corresponding pre-exponential factor, T is the temperature, and P A and P R are the gas partial pressures on the feed and permeate sides, respectively. Average E for He, H2, CO2, and CH4 act The activation energies for the eight films 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 kinetic diameter. The activation energy for H2 was similar to that (0.22 eV) from hydrogen-functionalized pore-10 reported by Jiang et al., 2009, Nano Lett., 9, pp. 4019-402, indicating that the average pore in this study is composed of 10 missing carbon atoms, consistent with previous STM studies (Agrawal et al., 2017, supra). E act The slightly lower C for CH4 compared to CO2 can be explained by the rearrangement of CH4 occurring from a smaller number of pores (average C for He, H2, CO2, and CH4). O A act A sur are 1.5 × 10 -5 , 2.6×10 -5 , 3.8×10 -6 and 1.3 × 10 -6 was), A act A sur is estimated not to change significantly with CO2 and CH4. High-resolution transmission electron microscopy (HRTEM) demonstrated that sub-nanometer pores do indeed exist in CVD graphene. Statistical analysis of these pores indicates a pore density of approximately 2.8 × 10 11 cm -2This suggests that the H permeance is within a range of similar magnitude to that predicted from the carbon amorphization trajectory. Overall, the observation of activated transport and the visualization of sub-nanometer pores indicate that higher H permeance can be obtained at elevated temperatures (250-300 °C), especially in non-oxidizing atmospheres.

[0101] Separation of gas mixtures is important for understanding the effects of competitive adsorption and diffusion through nanoporous graphene. However, to date, reporting gas mixture separation through single-layer graphene membranes has remained challenging. The transport of species i from an n-component gas mixture through a graphene nanopore can be modeled by the following equation:

[0102]

number

[0103]

number

[0104] The membranes of the present invention, including large-area graphene films, allow for the measurement of He, H, CO, and CH fluxes from equimolar gas mixtures. Interestingly, the overall performance trends (permeance and separation factor) for the mixture feed improved compared to those observed for the single-component feed cases (Figures 4f-i). However, the H permeance and corresponding activation energies using the single components, especially for membrane M2, were similar to the mixture case (E for M2 mixtures with He, H, CO, and CH). actwere 20.4, 19.9, 34.9, and 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 was unchanged for 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 remained unchanged in the mixture case compared to the single component case. These results highlight the unique feature of the single-layer graphene membranes of the present invention for size sieving of light gases, where competitive adsorption (CH4 versus H2) does not degrade separation selectivity, at least at moderate feed pressures (1-7 bar). This favors the separation of H2 from CH4 even at high concentrations of CH4.

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

[0106] Overall, such data demonstrate that the method of the present invention enables the realization of a support-assisted, scalable transfer process to produce crack- and tear-free, thermally stable, large-area (approximately 1 mm²) 2This study demonstrates the feasibility of fabricating suspended monolayer graphene membranes with a size of approximately 100 nm. The resulting graphene membranes supported on carbon substrates with an extremely low porosity of approximately 0.025% unexpectedly exhibited favorable gas sieving performance (4.1 × 10 nm), which was not affected by the carbon support coating. -7 molm -2 s -1 Pa -1 H2 permeance up to 23, and H2 / CH4 selectivity up to 23).

[0107] The table below lists the permeance of the coated film alone.

[0108] [Table 1]

[0109] The obtained H permeance and selectivity approached the performance of state-of-the-art polymer membranes with a thickness of 1 μm. Even more advantageously, the performance of the carbon-supported graphene membrane of the present invention was stable up to at least moderate transmembrane pressures (7 bar) during multiple heating and cooling cycles. The use of a gas mixture feed did not result in a decrease in H permeance or H / CH separation selectivity.

[0110] Example 4: Ozone treatment to further improve membrane performance As reported in Example 3, the H permeance at 150 °C was approximately 3.3 × 10 -8 ~4.1×10 -7 molm -2 s -1 Pa -1 The porosity of the graphene membrane of the present invention was only 0.025%. It has been unexpectedly discovered that exposure of graphene membranes to ozone can be used to further tailor the gas separation performance of graphene membranes, as demonstrated below.

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

[0112] Raman characterization was performed on freestanding graphene films of the present invention (without the carbon film) transferred to SiO2 / Si wafers by a wet transfer method (Robeson, 2008, supra). Single-point data collection and mapping were performed using a Renishaw micro-Raman spectrometer (532 nm, 2.33 eV, 100x objective). Analysis of the Raman data was performed using MATLAB. A least-squares curve-fitting tool (lsqnonlin) was used to subtract the background from the Raman data to calculate the D and G peak heights.

[0113] X-ray photoelectron spectroscopy (XPS) analysis was performed on free-standing graphene films (without the carbon film) of embodiments of the present invention, also on Cu foil, using a Mg Kα X-ray source (1253.6 eV) and a Phoibos 100 (SPECS) hemispherical electron analyzer with a multichannel tron ​​detector. XPS spectra were recorded in fixed analyzer transmission (FAT) mode using a pass energy of 90 eV for scanning and 20 eV for narrow scans. Because the sample did not exhibit electrostatic charging, bond energies are presented uncorrected (bond energies for C-C: 284.4 eV, C-O: 285.7 eV, C=O: 286.8 eV, and O-C=O: 288.5 eV). Because the carbonyl group (C=O) is part of (O-C=O), O-C=O was counted as C=O in the functional group summary. XPS spectra were processed by CasaXPS with background subtraction by the Shirley method.

[0114] The relative intensity of the D peak increased with respect to the G peak, which indicates the degree of disorder in graphene (I D / I G increased from 0.07 to 4.0), but the 2D peak decreased in intensity with increasing reaction time and temperature, which indicates that the sp 3 This indicates that the number of C═O hybridization sites increased after ozone treatment (Yuan et al., 2013, ACS Nano, 7, pp. 4233–4241). The bond energy distribution of ozone-functionalized graphene indicated that CO and C═O were the predominant 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 mildly functionalized case (25°C, 2 min). The increase in the number density of functional groups with reaction temperature and time (Figures 6c–d) is consistent with the Raman spectroscopy results. 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 min, respectively.

[0115] Interestingly, after ozone treatment, the separation performance of all graphene membranes improved significantly, either by increasing H2 permeance, or by increasing H2 / CH4 selectivity, or by improving permeance and selectivity.

[0116] When O3 treatment was performed for 2 minutes at 25°C, the H2 permeance was 1.9 x 10 -7 to 1.2 × 10 -7 molm -2 s -1 Pa -1 The selectivities of H2 / CH4 and H2 / CO2 increased from 10.0 to 15.0 and from 5.1 to 6.4, respectively, at 150 °C (M2, Figures 6a-b), indicating pore shrinkage. act-app (E act +ΔE sur ) and C0A act A sur Both of these decreased after pore functionalization with O3 treatment. act-app The change in E act (higher activation energy due to pore shrinkage) and ΔE sur (the binding energy increases with functionalized pores) and for CH4, the COA act A sur is reduced to one-twentieth of the original value (5.7 × 10 -7 to 2.8 x 10 -8 ), clearly indicating that fewer pores are available for CH rearrangement after ozone treatment. Without being bound by any theory, this can be explained by the fact that the edges of the functionalized pores, which have contracted in size, block larger gas molecules from passing through the functionalized pores, leading to higher gas selectivity.

[0117] In contrast, ozone treatment at 100 °C increases the gas permeance by up to three times, while the gas selectivity remains similar to that obtained from the internal defects (Figures 6c-d). act-app did not change significantly after functionalization, but COA act A surThe increase in the PSD of the graphene membrane indicates an increase in the pore density. Considering that the coverage of CO and C=O groups increases with high-temperature treatment, these functional groups likely aggregate, releasing carbon from the graphene lattice and forming new pores in the gas phase, such as CO and / or CO2, in this process. Functionalization-based performance improvement depends on the PSD of the internal defects in graphene. For example, graphene membranes exhibiting excellent separation performance (narrow PSD) due to internal defects maintained their separation performance even 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 (Fig. 6g). The overall trajectory trend clearly demonstrated that the gas separation performance of the graphene membrane of the present invention can be tailored 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–f). HRTEM images of functionalized graphene reveal a higher number density of subnanometer pores in the graphene after 2 min of ozone treatment at 80 °C (pore density of 2.8 × 10 11 to 4.2 x 10 11 cm -2 Evidence showed that selectivity was maintained despite the increase in permeance (increased to 100%). In the case of membrane M5, the increase in separation selectivity as well as permeance was achieved after 1 min of ozonation at 80 °C. The authors hypothesize that in the case of membrane M5, the new pores had a narrower PSD.

[0120] Higher selectivity is obtained when ozonation is carried out at room temperature (eg, 25° C.), but the permeance is reduced.

[0121] Therefore, since both permeance and selectivity determine membrane performance, these results confirm that the gas separation performance of gas-selective filters using graphene membranes according to embodiments of the present invention can be further improved by ozone functionalization, depending on feed specifications and purity and recovery requirements. After the synthesis process according to the present invention, improvements in H permeance (up to 300%) and H / CH selectivity (up to 150%) are possible.

[0122] Thus, controlled temperature-dependent functionalization of the graphene lattice with ozone-derived epoxy and carbonyl groups can be used to open gas-selective pores or compress existing pores in CVD-derived graphene, which will be useful for the gas filtration performance of tailoring gas-selective filters using graphene membranes according to the present invention. [Explanation of symbols]

[0123] 1. Supported graphene membranes 2. Sacrificial supporters 3. CVD graphene film 4. Organic precursor films 5. Porous carbon substrate 6 Composite structure 7. Etching chamber 8 Etchant 9. Graphene films supported on carbon substrates 10 Macroporous Support 11 Gas Selective Filter Sheet

Claims

1. A gas-selective separation filter comprising: a nanoporous graphene membrane having a thickness of about 0.34 to 2 nm and a porosity greater than 0.001%; ​​a porous carbon substrate having a graphene membrane thereon, the porous carbon substrate having a porosity in the range of 5% to 90%; and a porous support structure on which the graphene membrane and the porous carbon substrate are mechanically supported.

2. 2. The gas-selective separation filter of claim 1, wherein the pores of the nanoporous graphene membrane have an average size of about 0.2 nm to about 0.5 nm, preferably about 0.25 nm to 0.3 nm.

3. 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%, preferably greater than 20%, and contains pores with an average size in the range of about 10 to 1000 nm, preferably in the range of about 10 to 100 nm.

4. 4. A 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%, preferably greater than 5%, the porosity being formed by pores having an average size in the range of 0.01 μm to 100 μm, preferably in the range of 0.1 μm to 20 μm, for example in the range of 1 μm to 10 μm, and a thickness in the range of 10 μm to 10,000 μm, typically in the range of 20 μm to 100 μm.

5. 1. A method for preparing a gas-selective separation filter, comprising: a) providing a graphene film on a sacrificial support layer; b) coating the graphene film with an organic precursor of a porous carbon substrate; c) subjecting the organic precursor to pyrolysis to convert the organic precursor onto the porous carbon substrate on the graphene film, wherein the porous carbon substrate has a porosity of 5% to 90%; d) placing the composite of the porous carbon substrate and the graphene film on a macroporous support structure; e) removing at least a portion of the sacrificial support layer before or after step d); A method comprising:

6. The method of claim 5 , wherein in step e), removing at least a portion of the sacrificial support layer comprises etching a portion of the sacrificial support layer.

7. 7. The method of claim 6, wherein the etching step is performed before step d) to obtain a free-standing composite of porous carbon substrate and graphene film suspended in the etching solution.

8. 8. The method of claim 5, wherein in step e), the composite of the porous carbon substrate and the graphene film is placed on the macroporous support structure by a wet transfer process in a liquid bath.

9. 9. The method according to claim 5, wherein in step b) the organic precursor is in a solution, for example a solution of turanose and the block copolymer polystyrene-co-poly(4-vinylpyridine) (PS-P4VP) dissolved in N,N-dimethylformamide, and the solution is dried until a film of the organic precursor is formed on the surface of the graphene film.

10. 10. The method of any one of claims 5 to 9, wherein the organic precursor of the porous structure is an amphiphilic block copolymer, such as a block copolymer of polyvinylpyridine and polystyrene monomers, such as the block copolymer polystyrene-co-poly(4-vinylpyridine) (PS-P4VP).

11. 11. The method according to any one of claims 5 to 10, wherein in step c) pyrolysis is carried out at a temperature in the range of from 400°C to 1000°C for about 0.25 to about 1.5 hours.

12. In step c), the pyrolysis is carried out by H ２ 12. The process according to claim 5, wherein the process is carried out under a stream of Ar.

13. 13. The method of any one of claims 5 to 12, further comprising treating the graphene film with ozone under an inert atmosphere for a time period from about 1 ms to about 1 month, typically from about 30 seconds to about 60 minutes.

14. 14. The method of any one of claims 5 to 13, further comprising treating the graphene film with ozone at a temperature between about 25°C and 200°C, more preferably between 25°C and about 120°C.

15. For separating gases, especially CO ２ From H ２ or CH ４ 5. Use of the gas-selective separation filter according to any one of claims 1 to 4 for separating:

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