Method of preparing co2 selective pores in graphene & uses thereof

Abstract

The invention relates to a method for the preparation of porous single layer graphene (PG) useful for CO2 capture and porous single layer graphene membrane obtained therefrom.

Description

[0001] METHOD OF PREPARING CO2SELECTIVE PORES IN GRAPHENE & USES

[0002] THEREOF

[0003] Field of the Invention

[0004] The present invention pertains generally to the field of porous single-layer porous graphene (PG).

[0005] Background of the Invention

[0006] Nanoporous atomically thin membranes (NATM) have emerged as a promising platform for effectively separating molecules and ions, exploiting mass, size, and affinity differences (Drahushuk et al., 2012, Langmuir 28, 16671 16678; Koenig et al, 2012, Nat. Nanotechnol. 7, 728-732; O ’Hern et al., 2012, ACS Nano 6, 10130-10138, Cohen-Tanugi, et al., 2012 Nano Lett. 12, 3602-3608 ; Li et al., 2013, Science 342, 95-98).

[0007] Despite significant progress on the fundamental aspects of NATM including transport mechanism, pore incorporation, and membrane fabrication, this field faces an outstanding critical challenge on the scalability of NATM membranes. The most popular and studied NATM is single-layer PG. Successful incorporation of carbon dioxide (CO2)-selective pores in PG has led to attractive performance for carbon capture (Koenig et al. , 2012, supra; Huang et al., 2018, Nat. Commun. 9, 1 11; He et al., 2019, Energy Environ. Sci. 12, 3305-3312; Huang et al., 2021, Sci. Adv. 7, eahfOl 16).

[0008] This involves selective separation of CO2 from nitrogen (N2). It is crucial to develop high- performance carbon capture membranes that reduce the consumption and the associated cost of carbon capture from point-emission sources. Indeed, technoeconomic assessments of the capture process based on high-performance PG membranes indicate that the energy efficiency of capture can be significantly improved compared to the commercial amine-based absorption process (Soo, et al., 2024, J. CO2 Util. 81, 102727; Mota-Martinez et al., 2017, Sustain. Energy Fuels 1, 2078- 2090). This is mainly because the membrane processes do not require thermal energy but rather rely on electrical energy (Sholl etal., 2016, Nature 532, 435-437; Darunte et al, 2016, Curr. Opin. Chem. Eng. 12, 82-90).

[0009] This is also because PG membranes yield extremely high CO2 permeance thanks to its atom-thin selective layer. This minimizes the required membrane area and the capture process footprint, making capture based on PG membranes advantageous compared to the state-of-the-art membranes based on polymers (Du et al, 2012, Energy Environ. Sci. 5, 7306-7322; Han et al, 2021, J. Membr. Sci. 628, 119244), zeolites (Varoon Agrawal et al, 2011, Science 334, 72-75; Rangnekar et al., 2015, Chem. Soc. Rev. 44, 7128-7154), metal-organic frameworks Chen et al., 2023, Chem. Soc. Rev. 52, 4586- 4602; Babu et al., 2019, ACS Sustain. Chem. Eng. 7, 49-69), covalent-organic frameworks (Li et al., 2023, Chem. Soc. Rev. 52, 6294-6329; Patel et al., 2013, Nat. Commun. 4, 1357) and carbon molecular sieves (Huang et al., 2019, ACS AppL Mater. Interfaces 11, 16729- 16736; Rungta et al., 2017, Carbon 115, 237-248).

[0010] A low-footprint capture process is attractive to application in the transportation sector, especially the international shipping industry, responsible for 2-3% of global CO2 emissions.

[0011] The proof-of-concept study on the selective transport of CO2 from PG was demonstrated by Bunch and coworkers in 2012 (Koenig et al. , 2012, supra)

[0012] This was a fundamental study from a micron-sized exfoliated graphene with only a couple of pores responsible for gas transport. However, for practical membranes, one must prepare macroscopic films. For this, polycrystalline graphene, produced by chemical vapor deposition (CVD) on Cu foil, has become a standard material Li et al., 2009, Science 324, 1312-1314; Polsen et al., 2015, Sci. Rep. 5, 10257; Bae et al., 2010, Nat. NanotechnoL 5, 574-578).

[0013] Yet, it is challenging to prepare a large-area PG membrane. One challenge concerns the lack of demonstration of CO2-selective pore incorporation in graphene over a large area. Pores in graphene are carbon vacancy defects incorporated by removing atoms from the basal plane. Chemical routes involving the gasification of the lattice by oxidation are intrinsically more scalable than carbon knockout routes using energetic beams. For oxidation, oxidative plasma Zhang et al., 2024, Adv. Funct. Mater. 34, 2307419), oxygen (O2) Yamada etal., 2014, J. Am. Chem. Soc. 136, 2232-2235; Wang et al., 2010, Nat. Chem. 2, 661-665), ultraviolet light / ozone (Ch) (Cheng et al., 2020, Nano Lett. 20, 5951-5959) or O3 (Huang et al., 2021, supra; Agrawal, et al., 2017, J. Phys. Chem. C 121, 14312-14321) have been demonstrated. However, they involved sophisticated setups that are challenging to scale up. The uniformity of pore incorporation over a large area is not demonstrated.

[0014] Oxidation of graphene in an O3 flow leads to the formation of energy-minimizing O-clusters on graphene (Vahdat etal., 2023, J. Phys. Chem. C 127, 22015-22022, Lee etal., 2009, J. Phys. Chem. C 113, 14225-14229). These clusters yield a pore at their core upon gasification (Huang et al., 2022, Adv. Mater. 34, 2206627).

[0015] It was recently reported a simplified process of decoupling pore nucleation and expansion involving exposing graphene to O3 followed by heat treatment or light exposure (Bondaz et al. 2023, JACS Au 3, 2844-2854). However, this approach has been limited to preparing small coupons. Implementing this concept for large-area PG requires developing a large-area reactor with a uniform reaction zone and the development of a dedicated protocol for incorporating uniform pores. Therefore, given that the global energy demand is growing faster than renewables, capturing CO2 from large point sources is becoming increasingly urgent. While the implementation of solid adsorbents for CO2 capture from flue gas mixtures is a viable solution, the development of highly efficient capture materials having long-term cyclability is still needed.

[0016] Summary of the Invention

[0017] A general object of this invention is to provide CO2 selective porous single layer graphene membranes and a cost-effective process for the preparation of the same.

[0018] It has been unexpectedly found that achieving a lateral flow of O3 over a graphene membrane surface with a velocity from about 0.08 cm s'1to 10 cm s’1, in particular 0.17 to 0.60 cm s’1allows to significantly increase the porosity of the obtained graphene membrane and an improved CO2 permeance and CO2 / N2 selectivity.

[0019] One of the specific objects of this invention is to provide a method for the preparation of singlelayer PG membranes, which are useful in CO2 separations from gas mixtures.

[0020] It is advantageous to provide a facile and scalable method for the incorporation of CO2-selective pores in graphene.

[0021] An object of this invention is to provide a single-layer PG membranes useful for CO2 capture.

[0022] It is advantageous to provide uniformly porous single-layer PG membranes for membrane surfaces more than 1 cm2, preferably from about 10 to 50 cm2.

[0023] It is advantageous to provide a large-area single-layer PG membrane with a high CO2 permeance, typically higher than 1000 GPU, for example from 1000 to 20000 GPU.

[0024] It is advantageous to provide a large-area (typically from about 1 cm2for about 50 cm2) singlelayer PG membrane with a high CO2 permeance with high CO2 / N2 selectivity (typically CO2 / N2 selectivity at 298 K higher than 15, in particular, higher than 20).

[0025] Objects of this invention have been achieved by providing a method preparation of a porous single layer graphene membrane as claimed, a porous single layer graphene membrane according to as claimed, use thereof and a gas filter as claimed.

[0026] Disclosed herein is a method for the preparation of a porous single layer graphene membrane, said method comprising the steps of: a) Providing a supported single-layer graphene in a reaction chamber, wherein the single-layer graphene is supported on a sacrificial support, preferably a Cu foil; b) Subj ecting said supported single-layer graphene to a lateral flow of O3 at a temperature from about 15°C to about 100°C, for example from about 80°C to about 85°C, wherein the velocity of the O3 flow is greater than or equal to 0.08 cm s’1, preferably greater than 0.15 cm s’1, and preferably less than 10 cm s’1, for instance in a range from 0.17 cm s’1to about 0.60 cm s’1, within a distance of 1 to 10 mm, preferably from 1 to 5 mm from the single layer graphene membrane surface; c) Cooling the reaction chamber to room temperature; d) Stopping the flow of O3; e) Removing the Os-treated supported single-layer graphene from the reaction chamber.

[0027] Also disclosed herein is a single-layer PG membrane obtainable by a process according to the invention.

[0028] Also disclosed herein is a single-layer PG membrane of a size from about 1 to about 500 cm2, typically from 10 to 500 cm2wherein said single-layer PG membrane has a porosity in the range of 1011- 1013pore / cm2.

[0029] Also disclosed herein is the use of porous single layer graphene membrane according to the invention for CO2 removal from a gas mixture.

[0030] Also disclosed herein is gas filter for selective CO2 removal from a gas mixture comprising a porous single layer graphene according to the invention.

[0031] Other features and advantages of the invention will be apparent from the claims, detailed description, and figures.

[0032] Brief Description of the drawings

[0033] Figure 1 is an illustration of the effects of a method of oxidation of a single layer graphene membrane according to the invention, as described in Examples 1 and 2. A: Ozone oxidation reactor hosting a quartz semi-cylindrical block (12 cm in diameter). The inset is the side view of the reactor with the quartz block; B: Schematic illustration of the ozone functionalization setup containing the ozone oxidation reactor; C: COMSOL CFD simulation results from an unmodified reactor: extracted gas velocity 1 mm above the substrate in the middle of the reactor with a sample size of 6 x 16 cm2; D: COMSOL CFD simulation results from the modified reactor at the same sample position in C; E: Gas permeation results of as-synthesized graphene and PG membranes at 1 cm2and 50 cm2-scale. The permeance of PG is extracted from the membrane using the resistance model.

[0034] Figure 2 represents a COMSOL simulated gas flow profile: iso-surface plot of gas flow velocity in the reactor a) without and b) with a quartz block inside the reactor as described in Example 2.

[0035] Figure 3 represents that COMSOL CFD simulated gas velocity at the sample position in the scale- up reactor as described in Example 1.

[0036] Detailed description of embodiments of the invention

[0037] The uniformity of the oxidation of the graphene by ozone treatment can be documented by Raman mapping. Indeed, the peak intensity ratio of ID / IG indicates the defect density introduced in the graphene during the ozone oxidation and the uniformity of those defects can be characterized by Raman mapping of a relatively large surface of the graphene.

[0038] The pore density of the single-layer graphene can be quantified by high-resolution electron microscopy according to standard procedure.

[0039] The porosity of the graphene membrane can be characterized by gas permeance measurement as described herein.

[0040] The expression “CO2 removal” refers to any gas separation where CChis the target, such as natural gas sweetening, Direct Air Capture (DAC), Post-Combustion Capture (PCC), and the removal of CO2 from gas mixtures produced during incineration or cement / steel production.

[0041] Disclosed herein is a method for the preparation of a porous single layer graphene membrane, said method comprising the steps of: a) Providing a supported single-layer graphene in a reaction chamber, wherein the single-layer graphene is supported on a sacrificial support, preferably a Cu foil; f) Subj ecting said supported single-layer graphene to a lateral flow of O3 at a temperature from about 15°C to about 100°C, for example from about 80°C to about 85°C, wherein the velocity of the O3 flow is greater than or equal to 0.08 cm s’1, preferably greater than 0.15 cm s’1, and preferably less than 10 cm s’1, for instance in a range from 0.17 cm s’1to about 0.60 cm s’1, within a distance of 1 to 10 mm, preferably from 1 to 5 mm from the single layer graphene membrane surface; b) Cooling the reaction chamber to room temperature; c) Stopping the flow of O3; d) Removing the Os-treated supported single-layer graphene from the reaction chamber.

[0042] According to a particular embodiment, the reaction chamber is first purged with an inert gas or a reducing gas mixture (e.g. EE / Ar) before the O3 treatment step. According to a particular embodiment, the single-layer graphene is from about 10 to about 500 2 cm .

[0043] According to a particular embodiment, the provided supported single-layer graphene is an as synthesized chemical vapor deposition on a sacrificial support (e.g. Cu foil).

[0044] According to a particular embodiment, single-layer graphene is supported on a sacrificial support is placed on a solid in the reaction chamber (e.g. alumina support).

[0045] According to a particular embodiment, the single-layer graphene is subjected to the lateral flow of O3 for a period from about 0.1 to about 3 h.

[0046] According to a particular embodiment, the reaction chamber is cooled rapidly to room temperature to stop the reaction and before stopping the flow of O3. Typically, the temperature of the reaction chamber reaches room temperature within about 30 min.

[0047] According to a particular embodiment, the lateral flow of O3 contains from about 1 to about 20 O3 wt% (O3 / O2), preferably between 8 and 20%.

[0048] According to a particular embodiment, the velocity of the O3 flow is from about 0.17 to about 0.60 cm s'1.

[0049] According to a particular embodiment, in the case of a sacrificial support containing Cu, the temperature of the reaction chamber is heated up to 500 - 800 °C (e.g. 600°C) for about 30 min to 10 h in a reducing atmosphere (e.g.th / Ar) after the O3 treatment step, when the flow of O3 was stopped and before the removing of the Os-treated supported single-layer graphene from the reaction chamber to reduce the oxidation of Cu, smoothen the Cu foil and to open pores in graphene.

[0050] According to a particular embodiment, the Os-treated supported single-layer graphene is then mechanically reinforced on a support (e.g., by a polymer film such as poly (trimethyl silyl propyne) and the sacrificial support is removed before using it as a membrane for gas separation.

[0051] According to another particular embodiment, is provided the use of the porous single layer graphene according to the invention for CO2 capture.

[0052] The invention having been described, the following examples are presented by way of illustration, and not limitation.

[0053] EXAMPLES

[0054] The method of the invention has been exemplified as follows with comparative examples shown below. Example 1: Method of treatment of a single layer graphene membrane

[0055] The method of the invention was applied to a single layer graphene membrane which has been obtained by a customized chemical vapor deposition (CVD) setup with a production capacity of about 0.1 m2per batch.

[0056] A tubular furnace (Nabertherm, 90 cm heating zone) hosting a 1.5 m long, 12 cm in diameter quartz tube onto which a 55 cm-long,l l cm large graphene substrate plate as synthesized was placed (Figure 1A). The quartz semi-cylindrical block placed in the reactor was designed to occupy and block the bottom half of the unnecessary space for the ozone reaction in order to achieve a laminar O3 flow close to the graphene membrane surface with a velocity from about 0.17 to 0.60 cm / s.

[0057] The reactor was connected to commercial O3 generator (Absolute Ozone, Atlas 60) and O3 (21 min' ') was produced and stabilized for at least 30 min to reach 8 wt%± 0.5 wt% (O3 / O2) as analyzed by a O3 monitor (2B Technologies, Model 106-H). An evacuation and gas delivery system was designed to rapidly exchange the gas environment (argon (Ar), hydrogen (H2), when needed, O3) and to attain control over the reaction time (Figure IB).

[0058] The temperature of the furnace was set to the oxidation temperature namely from about 80~85°C. The graphene membrane was subjected to the O3 flux (2 1 min'1) for 1 to about 3h.

[0059] The sample was kept under continuous ozone flow while the furnace was open for fast cooling. After 1 to 3 h, ozone was stopped and the reactor was exchanged with Ar. The sample was heated to 150°C for 1 h to open the pores in graphene and then annealed at 600°C under Tb / Ar for 3h to smoothen the surface of Cu foil.

[0060] The reduction in the cross-sectional area of the flow by the block, lead to a laminar O3 flow at a short distance after the inlet, leading as a consequence the O3 flow reaching the graphene surface as a laminar lateral flow (uniform gas velocity) (Figure 2).

[0061] A 2D plot of the gas velocity near the graphene surface (1 mm above the sample) reveals a significantly uniform flow profile (Figure ID). The velocity increased three-fold to 0.17 ± 0.02 cm s-1vo3,fast) compared to the same reactor without the reduction of the cross-section area. (Figure 1C)

[0062] Table 1 compares the gas permeance of single layer graphene membranes prepared under two different ozone gas velocities while keeping other conditions the same. The result shows that increasing gas velocity (mass transport) is more effective than increasing reaction temperature in having a larger pore density (CO2 permeance) while maintaining the pore size distribution (CO2 / N2 ideal selectivity).

[0063] Table 1 CO2 / N2 ideal selectivity means the ratio of CO 2 and N2 permeability measured when each gas is tested separately.

[0064] As a further comparison, the conditions for obtaining a single layer graphene membrane which was previously described (Bondaz et al. 2023, JACS Au 3, 2844- -2854) were used. In particular, the following conditions were used: Ozone concentration: 8 wt% O3 / O2; Reaction temperature: 85°C; Ozone flow rate: 1 1 / min; Reaction time: 1 h.

[0065] The gas velocity was analyzed under these conditions in the scale-up reactor as described in Figure

[0066] 1C and ID by COMSOL Computational fluid dynamics (CFD) simulation depending on the sample position in the scale-up reactor. As shown in Figure 3, the calculated average gas velocity is 0.038

[0067] ± 0.004 cm / s. The gas permeance of two graphene membranes prepared under the conditions mentioned for the comparative work can be found in Table 2 below. The transmembrane pressure difference between the feed and the permeate is 1 bar. The low permeance confirms that the pore density on those comparative graphene membranes is small when a low gas velocity is used in the comparative set up, and the reproducibility is poor as indicated by two membranes prepared from two batches.

[0068] Table 2

[0069] These data support that the ozone velocity near the graphene surface drastically impacts the pore density of the obtained single-layer graphene and therefore its gas sieving properties. The set-up earlier described (Bondaz et al. 2023, supra) could not achieve such velocities as shown in the simulation of Figure 3.

[0070] Example 2: Characterization of the porosity of the single layer graphene membranes treated by a method of the invention

[0071] The single layer graphene membrane obtained in Example 1 was then characterized for its porosity through the measurements of its CO2 permeance as described below. The 50 cm2PG membrane in the 5 x 10 cm2membrane module yielded an attractive CO2 permeance of 11799 GPU, and CO2 / N2 selectivity of 15.9

[0072] The resulting graphene membrane showed a significantly improved in the porosity of graphene, reflected by a drastically improved CO2 permeance compared to the same reactor without the reduction of the cross-section area. The average CO2 permeance from the 1-cm-scale membranes improved from 2’850 GPU to 13’ 105 GPU, with only a slightly compromised CO2 / N2 selectivity from 19.3 to 15.1.

[0073] The varying gas velocity in different parts of the reactor has been avoided by the present reactor design which also allowed increase the velocity near the graphene surface. Indeed, in standard settings the gas flow is the highest in the center of the reactor and decreases at the edges of the reactor, leading to a gas velocity near graphene was 0.06 ± 0.04 cm s'1(vO3iSiow), indicating an uneven flow. Therefore, a high standard deviation in velocity is not desired for obtaining uniformly porous graphene in scaled-up samples. The gas velocity is obtained from the COMSOL CFD simulations and the iso-surface curve of gas velocity inside the furnace as shown on Figure 2. Since the reaction temperature is relatively low (about 80°C), the effect of temperature on the gas flow profile is neglected.

[0074] The O3 velocity in the experimental setup was simulated by the COMSOL computational fluid dynamics package using an identical reactor geometry as described below. The gas velocity over the graphene samples was extracted from a 6x16 cm2area, 1 mm above the substrate at the center of the furnace. The average gas velocity was 0.17 ± 0.02 cm / s under a feed flow rate of 2 1 / min.

[0075] When all other conditions remain the same (temperature, reaction time, and ozone concentration), increasing ozone velocity to 0.17 cm / s leads to a significant improvement in the gas permeance of the graphene membrane while the CO2 / N2 selectivity is not compromised too much (values not lower than 15). For example, 1-cm-scale graphene membranes under fast ozone velocity e.g. 0.17 cm / s exhibit an average CO2 permeance of 13’ 105 ± 637 GPU and a CO2 / N2 ideal selectivity of 15.1 ± 1.1, while at slow velocity (lower than 0.06 cm / s), the average CO2 permeance is 2850 ± 330 GPU and CO2 / N2 selectivity is 19.3± 1.5.

[0076] Gas permeation measurement

[0077] Single-component gas permeation measurement was performed using a constant-volume, variablepressure method. In the experimental setup, the membrane was placed in a customized permeation cell where the top side of the membrane was installed with a feed and retentate tube for delivering the pure gas, and the bottom side was connected to a pump to collect the permeate. Once the permeate volume is isolated from the pump, the pressure of the volume will increase due to the gas permeation through the membrane. The gas permeance of the membrane can be obtained from the pressure change rate in the isolated permeate volume. Before the measurement, the membrane module was sealed with an impermeable Cu foil to measure the system leak rate. The leak rate was negligible (~ 1 GPU). The permeance was calculated by the following equation: where J, is the flow rate of the gas component i, A is the membrane area, R is the ideal gas constant, is the pressure difference of gas component i from the feed and the permeate side, dP and — is the pressure change in the constant permeate volume. Different feed gases were used to probe the permeation performance of the membrane. For each gas measurement, a sufficient gas flow controlled by a mass flow controller (MFC) was supplied to the feed side of the membrane. For membranes that have a high flux, the permeate flux was measured using a bubble flow meter according to the following equation: where — is the permeate flow rate (ml s' ) at the ambient condition (25 °C and 1 bar). A forced air convection oven was equipped to measure the gas permeance at elevated temperatures. All membrane data were collected after heating the membrane to 130 °C for 1 h followed by cooling to 25 °C. This allowed the removal of any atmospheric contaminations in the sample.

[0078] Computational fluid dynamics (CFD) simulation

[0079] CFD simulations on the gas profile in the tubular furnace were performed using a COMSOL Multiphysics®6.1 package. The model geometry was created in the software as shown in Figure 2 which shows a cross-section view of the ozone reactor with the colored surface indicating different gas flow speeds, while the gray area represents the reactor wall. The semi-cylindrical block occupies half of the unnecessary volume of the reactor leading to an overall higher gas velocity above the sample. O2 was selected as the fluid material. A laminar flow study was applied to the model, with a gas inlet and outlet specified on the left and right ends of the reactor. Other domains of the model were all defined as wall boundaries. The boundary condition for the inlet was set as a fully developed flow with a flow rate of 2 1 min'1, and that for the outlet was set as a static pressure of 0 Pa. The results were analyzed by COMSOL.

[0080] The present method for oxidation of graphene can form the basis of roll-to-roll production of graphene membranes where various steps of graphene processing are comparable.

Claims

Claims1. A method for the preparation of a porous single-layer graphene membrane, said method comprising the steps of:- Providing a supported single-layer graphene in a reaction chamber, wherein the single-layer graphene is supported on a sacrificial support, preferably a Cu foil;Subjecting said supported single-layer graphene to a lateral flow of O3 at a temperature from about 15°C to about 100°C, for example from about 80°C to about 85°C, wherein the velocity of the O3 flow is greater than or equal to 0.08 cm s’1, preferably greater than 0.15 cm s’1, and preferably less than 10 cm s’1, for instance in a range from 0.17 cm s’1to about 0.60 cm s’1, within a distance of 1 to 10 mm, preferably from 1 to 5 mm from the single layer graphene membrane surface;Cooling the reaction chamber to room temperature;Stopping the flow of O3;- Removing the Os-treated supported single-layer graphene from the reaction chamber.

2. A method according to claim 1, wherein the reaction chamber is first purged with an inert gas or a reducing gas mixture before the O3 treatment step.

3. A method according to any one of the preceding claims, wherein the size of single layer graphene is from about 10 to about 500 cm2.

4. A method according to any one of the preceding claims, wherein the single layer graphene is subjected to the flow of O3 for a period from about 0.1 to about 3 h.

5. A method according to any one of the preceding claims, wherein the flow of O3 contains from about 1 to about 20 O3 wt% (O3 / O2), preferably 8 to about 20 O3 wt% (O3 / O2).

6. A method according to any one of the preceding claims, wherein the velocity of the O3 flow is from about 0.17 to about 0.60 cm s’1.

7. A method according to any one of the preceding claims, wherein the reaction chamber is cooled within 30 minutes to room temperature to stop the reaction and before stopping the flow of O3.

8. A method according to any one of the preceding claims, wherein the provided supported singlelayer graphene is an as synthesized chemical vapor deposition on a sacrificial support (e.g. Cu foil).

9. A method according to any one of the preceding claims, wherein the temperature of the reaction chamber is heated up to 500 - 800 °C (e.g. 600°C) for about 30 min to 10 h after the O3 treatment step, when the flow of O3 was stopped.

10. A method according to any one of the preceding claims, further comprising a step of removing the Os-treated supported single-layer graphene from the sacrificial support.

11. A porous single-layer graphene membrane obtainable by a method according to the preceding claim.

12. A porous single-layer graphene membrane according to claim 11, wherein said porous singlelayer graphene membrane has a size from about 1 to about 500 cm2.

13. A porous single-layer graphene membrane of a size from about 1 to about 500 cm2, wherein said porous single layer graphene membrane has a porosity in the range of 1011- 1013pore / cm2as measured by high-resolution electron microscopy.

14. Use of a porous single layer graphene according to claims 11 or 12 for the preparation of a gas filter.

15. A gas filter for selective CO2 removal from a gas mixture comprising a porous single layer graphene according to claims 11 or 12.

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