Method for treating a graphene membrane and membrane obtained by the method

Abstract

The present invention concerns a method for producing a nanoporous 2D film, for example a graphene membrane. The method comprises exposing the non-porous 2D film to a reactive plasma and etching the 2D film so as to provide said nanoporous 2D film. In an embodiment, the method is a two-step method, comprising the initial deposition, by sputtering, of a protective layer comprising an inorganic oxide or nitride, before etching the 2D film. The nanoporous 2D films are useful for gas-separation.

Description

[0001]Method for Treating a Graphene Membrane and Membrane Obtained by the Method Technical Field 5 The present invention generally relates to 2D (two-dimensional) film treatment and fabrication, in particular graphene membranes. In some aspects, the invention provides a method for providing a graphene membrane comprising nanopores. In some aspects, the invention relates to membranes for gas separation. 10 Background Art and Problems Solved by the Invention Separation processes are of great economic importance as they account for 40%–90% of capital costs in the industry. In this context, membranes play a pivotal role in gas separation, water purification, solvent treatment, and biomedical applications due to their high energy 15 efficiency, low cost, robustness, reliability, and scalability. Gas separation is used, for example for CO2-separation in general, flue gas treatment, hydrogen recovery, for example from syngas, and natural gas purification applications. Graphene is considered as an ideal membrane material due to its atomic thickness and its 20 significantly higher permeability compared to the commercially existing membranes. This reduces the operational costs of the membranes due to a very negligible pressure drop across the membrane. However, graphene is not porous and impermeable to any gases, which requires artificial pore fabrication (etching) for membrane applications. 25 The perforation of graphene membranes is the subject of manifold efforts and research. For example, US 2013 / 0249147 A1 discloses a method for perforating a graphene membrane by exposing a stream of gas into plasma, and to direct the activated gas stream toward a graphene sheet, and perforating the graphene sheet with the activated gas stream. Indeed, it is known that oxygen can be added to an activated gas in order to etch the graphene sheet. However, it 30 is difficult to control pore size and overall porosity under such conditions. In gas separation applications, the two key performance parameters are selectivity (Sijor ^ij), and permeance Pi of the preferentially permeating gas (i). High permeance enables high gas P-0693-WO; 13 / 12 / 2024 flow rate and high amounts of gas that can be treated, and high selectivity means that the resulting separated gases are highly purified. Generally, there is a compromise to be taken between these two parameters: the higher the permeability, the lower the selectivity, and the higher the selectivity, the lower the permeability. This applies, in particular, but not only, to 5 gas separation by way of molecular sieving. In this context, WO 2022 / 136447 discloses, in Figure 2 panel A, different basic principles of gas separation, which are Knudsen diffusion, solution-diffusion, adsorptive separation, besides molecular sieving. In adsorptive separation, disclosed in WO 2022 / 136447, the 10 membrane needs to be regenerated once the adsorptive material on the membrane is saturated. While these membranes achieve a high ratio between selectivity and permeance, the regeneration step may be regarded as less desirous, for example when large amounts of gases need to be separated. 15 Under all these concepts, it is desirous to provide a graphene membrane with pores having a narrow distribution of pore size, and to have a controlled porosity, which means, an adjustable number of pores per surface area. In particular, it is an objective to provide graphene membranes having pores in the nanometer range, preferably the lower nanometer range. In some applications, mean pore sizes of below 20 nm and even lower are preferred. In some 20 cases, mean pore sizes of 1-20 nm or around 2-10 nm are preferred. Another important element is to be able to provide a fabrication method that is scalable and cost effective, allowing for the industrial preparation of the porous membranes. Many perforation methods developed in the lab, such as focused ion beam milling (FIB) and ion- 25 beam tracking, are not suitable for upscaling. Further regarding FIB, this technique does not allow to get pore sizes below 5 nm, and the resulting membranes have low selectivity. Treatments with reactive gases, UV or ozone plasma, on the other hand, allow for obtaining Angstrom-sized pores (< 1 nm), but result in low overall porosity and thus low permeance, and non-uniform pore sizes. 30 It is an objective of the present invention to provide porous graphene membranes with high porosity, mean pore sizes ranging from 1 nm up to micron, preferably from 3 nm to micron, and a narrow size-distribution. P-0693-WO; 13 / 12 / 2024 Further objectives and problems addressed by the present invention will become apparent from the description of the aspects and embodiments of the invention herein below. Summary of the Invention 5 Surprisingly, the present inventors provide methods for producing 2D films comprising nanopores. The pores are obtained by exposing the 2D film to a plasma comprising a reactive gas. In preferred embodiments, the plasma comprises components that are deposited on the 2D film, while or before the nanoholes are created. 10 In an aspect, the invention provides a method of treating a non-porous 2D film, the method comprising: providing a 2D film, and, exposing said 2D film to a plasma, wherein said plasma comprises components suitable to deposit an inorganic oxide or inorganic nitride on said 2D film. 15 In an aspect, the invention provides a method of treating a non-porous 2D film in order to prepare a 2D film comprising nanopores, the method comprising: providing a 2D film, and, exposing said 2D film to a plasma, wherein said plasma comprises components suitable to deposit an inorganic oxide or inorganic nitride on said 2D film. 20 Preferably, wherein exposing said non-porous 2D film to said plasma comprises depositing said inorganic oxide or inorganic nitride on said 2D film. Preferably, said 2D film at the beginning, before treatment according to the method of the 25 invention, is non-porous. In an aspect, the invention provides a method for producing a 2D film comprising nanopores, the method comprising: providing a 2D film, and, exposing said 2D film to a plasma to obtain said membrane comprising nanopores. 30 In an embodiment, a plasma suitable to create said nanoholes further comprises components that are deposited on said 2D film. P-0693-WO; 13 / 12 / 2024 In an aspect, the invention provides a single step method for producing 2D films comprising nanopores, wherein said non-porous 2D membrane is exposed directly to a plasma suitable to create said nanopores. 5 In another aspect, the invention provides a two-step method for producing 2D films comprising nanopores, wherein a non-porous 2D membrane is exposed to a first plasma that is not suitable to create said nanopores and then to a second plasma suitable to create said nanopores. 10 In another aspect, the invention provides a two-step method for producing 2D films comprising nanopores, wherein a non-porous 2D membrane is exposed to a first plasma suitable to deposit an inorganic oxide or inorganic nitride on said 2D film and subsequently to a second plasma suitable to create said nanopores. 15 In an aspect, the invention provides a nanoporous 2D film obtained by the method of the invention. In an aspect, the invention provides the use of the nanoporous 2D film of the invention in gas separation. 20 In an aspect, the invention provides a method for separating gases, the method comprising exposing a mixture of gases to the nanoporous 2D film of the present invention. Further aspects and preferred embodiments of the invention are defined herein below and in 25 the appended claims. Further features and advantages of the invention will become apparent to the person skilled in the art from the description of the preferred embodiments given below. 30 Figure 1 shows, in panels A to E, SEM images of nanoporous graphene membranes obtained in accordance with embodiments of the present invention. The image in the top panels show 2x2 arrays of 0.8 µm SiNxpores covered with double layer of graphene, and the lower panel shows a magnified single 0.8 µm SiNx window showing the nanopores in the membrane. P-0693-WO; 13 / 12 / 2024 Figure 2 shows, in panels A-E, pore size distributions of the corresponding membranes shown in Figure 1, panels A-E. Figure 3 is a graph showing the permeation rates of different gases through the 2D film 5 according to an embodiment of the invention. Figure 4 is a graph showing the permeance of the 2D film according to the same embodiment as mentioned with respect to Fig.3 as a function of the kinetic diameter of gas molecules. 10 Figures 5-8 are TEM images of 2D films obtained according to different embodiments of the invention. Hereinafter, preferred embodiments of the device of the invention are described, in order to illustrate the invention, without any intention to limit the scope of the present invention. 15 Detailed Description of the Preferred Embodiments The present invention relates to methods for producing 2D film comprising nanopores. The method comprises exposing a preferably substantially non-porous film to a plasma. 20 2D materials in accordance with the invention have planar atomic structure. Generally, the 2D materials have an effective thickness of below 5 nm in a single layer. The "effective thickness" of a 2D material can be determined from images obtained from transmission electron microscope (TEM), atomic force microscope (AFM), low energy electron 25 microscopy (LEEM), and / or scanning tunneling microscope (STM). Effective thickness can also be determined by optical contrast, as disclosed in by Dan Bing et al, "Optical contrast for identifying the thickness of two-dimensional materials", Opt Commun, 406 (2018), 128-138. In an embodiment, the 2D film comprises and / or consists essentially of a material selected 30 from the group consisting of graphene, graphene oxide (GO), reduced graphene oxide (rGO), transition metal dichalcogenides (TMDs), and hexagonal boron nitride (hBN). In an embodiment, the 2D film is a membrane. P-0693-WO; 13 / 12 / 2024 In an embodiment, the 2D film comprises and / or consists essentially of graphene or of a graphene derivative. Derivatives of graphene include, for example, GO, rGO, graphdyine, graphyne, just to mention a few. 5 The 2D film of the invention preferably comprises one or several layers of a 2D material. In an embodiment, the 2D film may be provided in the form of a multilayer, for example a double or triple layer of graphene, GO, rGO, and so forth, including mixed double or triple layers, such as graphene-GO, graphene-rGO, GO-graphydine, and so forth. All combinations of multilayers, such as double and triple layers of different 2D films are encompassed as a 2D 10 film of the present invention. Multilayer 2D film may comprise two or more 2D films comprising and / or made of different materials. In a preferred embodiment, the 2D film is a graphene membrane. 15 The 2D film that is subjected to the treatments of the present invention is preferably non- porous initially. However, the invention does not exclude, including in the preferred embodiments below, the presence of pores in the 2D film before the treatment in accordance with the invention. In such a case the method of the invention preferably results in additional pores and / or larger pores. Furthermore, the 2D film may comprise pores for fixing the 2D 20 film in a frame or for other purposes. The term "nonporous" is thus intended to mean, for the purpose of the present specification "lacking the pores that are created by the method of the invention". In an embodiment, the method comprises treating a non-porous 2D film, preferably by 25 exposing said non-porous 2D film to a plasma. During said exposure to said plasma, nanopores may be formed directly, or may not yet be formed, depending on whether said nanopores are formed in a one-step procedure or in a two-step procedure. In the case of the two-step procedure, an inorganic oxide or inorganic nitride is deposited on said non-porous 2D film, preferably without any pores being generated. This layer may function as a 30 protective and / or masking layer. In the case of a one-step procedure, the nanopores are generated generally while at the same time an inorganic oxide or inorganic nitride is deposited. It is noted that the terms "one-step" and "two-step" are not intended to exclude additional P-0693-WO; 13 / 12 / 2024 steps, during, before and / or after the deposition of said inorganic oxide or inorganic nitride. These terms refer to a distinction wherein an inorganic oxide or inorganic nitride is either deposited while at the same time nanopores are created, or where a complete layer of an inorganic oxide or inorganic nitride is first deposited, followed by the generation of the pores in the substantially non-porous, coated 2D film comprising said inorganic oxide or nitride as a coating, mask and / or layer. In case of a two-step method, the two steps may be conducted in the same or in different apparatuses and / or devices. In an embodiment, exposing said non-porous 2D film to a plasma comprises depositing, by Physical Vapor Deposition (PVD), said inorganic oxide or inorganic nitride on said non- porous 2D film. The inorganic oxide or inorganic nitride may be deposited by any suitable sputtering or evaporation instrument. In a preferred embodiment, the inorganic oxide or inorganic nitride is deposited by sputter deposition in presence of a plasma. In a preferred embodiment, the method of the invention comprises: - providing a target comprising said inorganic oxide, inorganic nitride or a precursor thereof, and, - sputtering said inorganic oxide, inorganic nitride or said precursor from said target so as to obtain a plasma comprising said components. In a preferred embodiment, the said inorganic oxide or inorganic nitride is selected from the group consisting of oxides and nitrides of Si, Al, Ge, In, Sn, Mg, Ta, V, Ti, and Zr. In a preferred embodiment, said inorganic oxide is SiO2. In an embodiment, said components are suitable to deposit one selected from the group consisting of SiO2, Al2O3, AlSc, GeO2, In2O3, SnO2, MgO2, Ta2O5, TiO2, TiN, V2O5, ZrO2, and ZrOX, where x is in the range of >1 and <3. In accordance with the above, the inorganic oxide or nitride is preferably selected from SiO2, Al2O3, AlSc, GeO2, In2O3, SnO2, MgO2, Ta2O5, TiO2, TiN, V2O5, ZrO2, and ZrOX, where x is in the range of >1 and <3. In a preferred embodiment, said components are suitable to deposit SiO2 on said 2D film. In an embodiment, said plasma is a SiO2 plasma. P-0693-WO; 13 / 12 / 2024 The components for deposition may be provided as a target material in the sputtering instrument, wherein the components are ejected from the surface of the target after bombardment of the target by energetic particles, typically in the presence of an electric or magnetic field. The target material may be substantially the material that is deposited. In this case, the target may comprise directly the components of the material to be deposited, for example the target may be made of SiO2, or any of the other oxides and nitrides mentioned above. In other embodiments, the target may form the material that is deposited together with components in the plasma, such as oxygen. In this case, the target may comprise a precursor material, for example the inorganic material in elemental form, and the corresponding oxide and / or nitride is formed due to the presence of oxygen and nitrogen, and ionized forms thereof, that is pumped into the deposition chamber. In an embodiment, where the material to be deposited comprises SiO2, the target material comprises and / or consists essentially of SiO2. In a preferred embodiment, the target consists of SiO2, preferably with a purity of 99%, more preferably 99.999%. The size of the target will depend on the apparatus used. In a preferred embodiment, said plasma further comprises providing a reactive gas or reactive gas mixture, preferably comprising one or more selected from oxygen (O2), nitrogen (N2) and argon (Ar) gas, more preferably at least oxygen as a reactive gas, and most preferably at least oxygen and argon. In two step-embodiments, oxygen may be absent in the first step and / or during deposition of the inorganic oxide and / or nitride mask in the first step. In a preferred embodiment, the method comprises providing nanoholes in said non-porous 2D film by exposing said non-porous 2D film to a plasma and adding the reactive gas to said plasma at a rate suitable to generate said nanoholes in said 2D film, preferably at a rate of 5 sccm or higher. In a preferred embodiment, the method of the invention is a one-step method and / or a single step method for producing a 2D film comprising nanopores, wherein said non-porous membrane is exposed to said plasma comprising said components suitable to deposit an P-0693-WO; 13 / 12 / 2024 inorganic oxide or inorganic nitride on said 2D film, wherein said method comprises simultaneously adding said reactive gas to said plasma at a rate suitable to generate said nanoholes. 5 Without wishing to be bound by theory, it is hypothesized that said nanoholes are formed by etching in the presence of the plasma comprising said components of said inorganic oxide or nitride, and preferably one or both selected from oxygen and argon. In a preferred embodiment of the one-step method, said reactive gas is or comprises oxygen, 10 wherein oxygen is added at a rate of 5 to 80 sccm, preferably 8 to 60 sccm, more preferably 10 to 30, and wherein said membrane is exposed to said plasma for a duration that is sufficient to create said nanopores. Preferably, said duration is from 1 second to 10 minutes, more preferably from 2 seconds to 5 minutes, even more preferably from 3 seconds to 1 minute, and most preferably from 5 to 30 seconds. 15 The duration and / or time corresponds to the time during which power is applied, resulting formation of the plasma. The time as indicated in this specification generally includes ramping or start-up time, which is the time during which power is applied, but the system has not yet reached the set power. 20 Sccm stands for a gas flow of "standard cubic centimeters per minute". Preferably, gas flow rates are kept substantially constant at a value of the ranges indicated herein for the corresponding time. 25 In a preferred embodiment, in particular of the one-step method, oxygen is added at a rate of 10 to 50 sccm, preferably 11 to 40 sccm, more preferably 12 to 30 sccm, and most preferably 13 to 20 sccm. In a more preferred embodiment, in particular of the one-step method, oxygen is added at a 30 rate of 5 to 20 sccm, more preferably 5 to 15 sccm, and most preferably 5-10 sccm. Preferably, said gas or reaction gas also comprises argon. Argon is preferably provided at a rate of 50-200 sccm, preferably 60-170 sccm, more preferably 70-150 sccm, and most preferably 80-130 sccm. P-0693-WO; 13 / 12 / 2024 Preferably, oxygen and argon are provided simultaneously for the above indicated time intervals, in particular in the one-step method. In some embodiments, the reactive gas comprises nitrogen in addition to oxygen, or comprises nitrogen gas instead of oxygen. 5 Preferably, the sputtering instrument is used by applying a power 100-1'200 W, more preferably 400-1'100 W, and most preferably 300-1'050 W, and a frequency of 10-20 Mhz, preferably 12-17 Mhz, most preferably 13-15 Mhz, for example about 14 Mhz. 10 In a preferred embodiment, in particular of the one-step method, the applied power is 250- 750 W, more preferably 300-700W, and most preferably 400-600 W. In a preferred embodiment, the time of applying said power is in the range of 1 s to 1.5 mins, preferably 2 s to 1 min, more preferably 5 s to 45 s, and most preferably 9 s to 30 s. 15 Preferably, in case the depositing instrument requires ramping time, such ramping time is preferably included in the indicated durations. During ramping, some deposition takes generally place. The ramping time is the time the PVD depositing apparatus requires for reaching the set (applied) power. 20 In a more preferred embodiment, in particular of the one-step method, said time is 15-120 seconds, most preferably 30-90 seconds. The time, time periods and / or durations indicated in this specification correspond to the time 25 of applying the power, and generally coincide with the addition of oxygen to the plasma and / or with the presence of the plasma in the chamber. The above power inputs correspond to the energy that is put into the plasma and determines the amount of the target material that is sputtered. 30 Preferably, the sputtering instrument is equipped with a DC generator and an RF generator. While the operation of a sputtering instrument in a RF mode is herewith exemplified, the same output can be obtained in other modes, such as DC mode, combined DC RF mode, or pulsed DC mode, as long as the appropriate plasma is generated. P-0693-WO; 13 / 12 / 2024 In a particular embodiment, the sputtering instrument is a magnetron sputtering instrument, such as the Pfeiffer SPIDER600 instrument used in the examples. In such instruments, a magnetic field is used to control the plasma in such a way that it reacts with the target 5 material, not with the substrate (here the substrate is the 2D film). The 2D film, for example a graphene membrane, is preferably placed on a support during exposure to the plasma as described. Examples of suitable supports are silicon nitride supports, polymeric supports, such as plastic supports, supports of glass fibre, and cupper10 foils, just to make some examples. Plastic supports, include, for example, PET (polyethylene- terephthalate) and PI (polyimide) supports, or other preferably flexible plastics. In some embodiments, the support is itself porous, but comprises pores in the µm or mm range, for example pores having a size of from 300 nm to 100 µm, preferably 500 nm to 50 µm, most preferably 700 nm to 10 µm. 15 Under the conditions described above, nanopores of having the desired sizes and size- distribution are surprisingly obtained, as illustrated, for example, in Figure 1. As mentioned above, the method may comprise two steps, wherein the two separate steps may 20 be conducted in the same or in different devices. The two steps may be considered as separate in that one step may be conducted sequentially after the other. If the two steps are conducted in the same device, and no transfer between devices is thus necessary, one can envisage a fluent and / or flowing transition between the two steps. However, in the two-step method, the etching for the pore generation preferably starts after at least some masking inorganic oxide or 25 inorganic nitride has been deposited. The deposition of inorganic oxide or inorganic nitride may or may not continue during the step of pore generation. In accordance with the two-step method, an inorganic oxide or nitride layer is generally deposited first, without any pores being generated. The deposited layer may then function as a 30 protection in the subsequent etching of pores. In accordance with this embodiment, the conditions, such as the exposure time, flow of various gases, during deposition in the first step are preferably adjusted so that etching sufficient to generate pores does not or cannot not occur. P-0693-WO; 13 / 12 / 2024 In a preferred embodiment, the method of the invention comprises the two steps of: (1) depositing said inorganic oxide or inorganic nitride on said non-porous 2D film by exposing said non-porous 2D film to a first plasma comprising said components; and, (2) exposing said non-porous 2D film of step (1) to a second plasma comprising a reactive 5 gas suitable to generate nanoholes in said non-porous membrane. In a preferred embodiment, step (1) comprises not adding said reactive gas (in particular oxygen) or adding said reactive gas, preferably oxygen, to said plasma, at a rate that is insufficient to generate nanoholes in said non-porous 2D film. In an embodiment, oxygen 10 and / or nitrogen in addition to argon gas are added to form a plasma in the first step. In a preferred embodiment, only argon gas is added during the first step to generate the plasma. In a particular embodiment, the flow rate of argon of as described above for the one-step method. In a preferred embodiment, the flow of argon during the first step is 50-300, 15 preferably 70-250, more preferably 80-220, and most preferably 90-200 sccm. In the first step of the two-step method, the flow of oxygen gas is preferably below 100 sccm, preferably below 50 sccm, even more preferably below 20 sccm, and most preferably below 10 sccm, for example in the range of 1-10 sccm. In a preferred embodiment, there is no (zero) 20 oxygen flow during the first step and / or deposition step. The flow of nitrogen, if present is preferably in the range of 1-100 sccm, more preferably 2-50 sccm, even more preferably 5-40 sccm, and most preferably 10-20 sccm. There may be no nitrogen flow. Preferably, a power of 200-1'200 W of DC, more preferably 300-1'100 W, and most 25 preferably 500-1'050 W. Preferably, the above said with respect to RF power or other modes (DC, pulsed DC) also applies to this step. In a preferred embodiment, the applied power is of 500-2'000 W, more preferably 500- 1'500 W, most preferably 800-1'200 W. 30 During step (1), the plasma is preferably maintained and / or the power is applied for a duration of 10 s to 10 mins, more preferably from 15 s to 5 mins, even more preferably from 20 s to 2 min, and most preferably from 30 s to 1 min. P-0693-WO; 13 / 12 / 2024 The conditions and duration are preferably selected so as to deposit a layer of the inorganic oxide or nitride material on the 2D film. The thickness of the deposited material is preferably from 5-150 nm, more preferably 10-100 nm, and most preferably 20-60 nm. As mentioned above, pores are preferably not yet generated in the 2D film during this step. The O2 and / or N2, in as far as present, may be used as diluting gases in this case, assisting in the formation of the protective and / or masking inorganic oxide and / or nitride layer. In a preferred embodiment, in step (2), said reactive gas, preferably oxygen, is preferably added to said plasma at a rate of 30 sccm or higher, preferably 50 sccm or higher, more preferably 100 sccm or higher, and most preferably 200 sccm or higher. The flow rate is preferably also selected depending on the size of the chamber containing the plasma, with larger chambers preferably requiring higher flow rates. In larger chambers, such as those used in the example for the second step, the flow rate may be 200 sccm or higher, for example 300 sccm or higher. In particular, in step (2), the flow of oxygen is preferably higher than during step (1). More generally, a high energy O2plasma is preferably applied. Without wishing to be bound by theory, the present inventors hypothesize that the increased flow of oxygen into the plasma and / or the high energy oxygen plasma contributes to the generation of the nanopores in the 2D film that comprises the inorganic oxide and / or nitride coating deposited in step (1). In step (2), flow of O2 is preferably from 100-700 sccm, preferably 200-600sccm, and more preferably 300-500 sccm, most preferably 350-450 sccm. More preferably, in step (2), flow of O2 is from 20-400 sccm, preferably 30-350sccm, and more preferably 40-300 sccm, most preferably 50-200 sccm. The power is preferably in the range of 50-500 W RF, preferably 90-450W, more preferably 120-400 W, and most preferably 150-250 W, wherein the RF has the same frequency as described herein above. As above, other modes of generating the plasma, such as based on DC and pulsed DC, may also be used. More preferably, in step (2), power is preferably from 80-500 W, more preferably 90-450 W, most preferably 100-400 W. P-0693-WO; 13 / 12 / 2024 The duration (time) of plasma treatment during step (2) is preferably from 0.5-20 mins, preferably 1-15 mins, more preferably 2-10 mins, and most preferably 3-8 mins. More preferably, in step (2), the time of plasma treatment is preferably from 30-390 seconds, 5 more preferably 60-300 seconds. The method of the invention may comprise removing the protective and / or masking inorganic oxide and / or inorganic nitride layer. If the masking layer is removed, this is preferably a separate, further or final step. This step may be accomplished by exposing the coated, 10 nanoporous 2D film to an appropriate solution or solvent, for example to an acidic solution for removing an SiO2 layer that has been deposited in step (1) of the two-step method. The way the masking oxide and / or nitride films will be removed depends on the particular oxide and / or nitride that is used as a mask. 15 The step of removing deposited inorganic oxide and / or inorganic nitride may also be conducted in case of the one-step method, in which said inorganic oxide and / or inorganic nitride is deposited at the same time as the nanopores are generated. In some embodiments, the invention encompasses that the inorganic oxide and / or inorganic 20 nitride film is not removed and the membrane for gas separation comprises the graphene layer and the inorganic oxide and / or inorganic nitride film. Whether or not the mask is remove, the membrane may further comprise a support on which the graphene is deposited, as disclosed elsewhere in this specification. 25 In a preferred embodiment, the nanoporous 2D film obtained by the method of the invention comprises nanopores that have a mean pore width of ≤ 50 nm, preferably ≤ 30 nm, more preferably ≤ 20 nm, even more preferably ≤ 10 nm and most preferably ≤ 10 nm. In a particular embodiment, the mean pore with is ≤ 5 nm. 30 In a preferred embodiment, said 2D film comprising nanopores has a porosity of > 0.5%, preferably > 1%, more preferably > 3%, even more preferably > 4%, and most preferably > 5%, wherein said porosity is the surface of the membrane covered by the pores compared to the overall operational surface of the membrane. The surface of the membrane covered by the P-0693-WO; 13 / 12 / 2024 pores is a part of the overall operational surface, such that the porosity is a percentage (part of the overall operational surface). In an embodiment, the porosity is in the range of 2-25%, preferably 3-20%, more preferably 4-15%, for example 5-10%. Pore sizes and porosity may be determined from electron microscopy such as TEM and SEM electron microscopy images, such as TEM or SEM, and analysis of the pores in an automated manner. Preferably, a representative sample or area of the nanoporous 2D film is selected and statistically evaluated. Software for conducting image analysis for determining pore sizes and porosity include ImageJ, Fiji, QuPath, CellProfiler, Ilastik, Orbit, Icy, Cytomine, and PathML. For the analysis in the examples, ImageJ (version 1.5 and above) was used. Generally, such software uses TEM and SEM black and white images and, in case of SEM images, analyses pixels and defines dark areas as pores. Tutorials on ImageJ that can be used also for analyzing pore size distribution as shown in Fig.2 are available on YouTube, e.g. at (here for particle analysis). In an embodiment, the 2D film and / or membrane of the invention comprises more than 107, preferably more than 108, even more preferably more than 109, and most preferably more than 1010pores per cm2of the operational surface of the film. In an embodiment, the 2D film and / or membrane of the invention comprises 107to 1012pores per cm2, more preferably 108to 1011and most preferably 109to 1011or more pores per cm2, for example 3x109to 5x1010pores per cm2. The above pore sizes apply to the pores that are generated by the method of the present invention. Possible other pores that are present in the membrane for other reasons are not included in the above figures on mean pore size and porosity. The above pore sizes and / or porosity preferably apply to the operational or selective part of the 2D film, which is the part that is used for gas separation or intended for gas separation, and more specifically the part that will be exposed directly to a mixture of gases to be separated. The 2D may comprise a border region and / or other parts and areas of its total surface, which other parts may be used to fix the 2D film, for example in a frame, or which P-0693-WO; 13 / 12 / 2024 other parts may be used for other purposes. These other parts may have different (or no) pores and porosities, as these other parts are not related to the gas-separation properties of the membrane. Similarly, 5 The present invention also concerns the use of the nanoporous 2D films in gas separation and in a method for separating gases. The present invention also concerns the use of the nanoporous 2D films of the invention as a gas separation membrane and / or in the gas separation membrane. In particular, the 2D films 10 of the invention preferably form the separating part in gas separation methods and / or membranes. The gas separation membrane may comprise several layers. For example, the 2D film of the invention may be provided on a support or support substrate, which generally is also porous but has larger pores than the 2D film. The support may be the same support in which the 2D film is deposited before the generation of pores. Exemplary supports are 15 disclosed elsewhere in this specification. Furthermore, the gas separation membrane may comprise all or part of the inorganic oxide and / or nitride mask that is deposited on the 2D film, in particular if the latter is not removed after the generation of the nanopores in the 2D film. 20 The method of separating gases preferably comprises exposing a mixture of gases to the nanoporous 2D film of the present invention. Preferably, said nanoporous 2D film is a graphene membrane. The nanoporous 2D film preferably comprises first and second opposed, main sides, and the 25 film is exposed to a mixture of gases on a first side. A separated gas is preferably collected on the second side. The separated gas preferably selectively passes through the pores of said nanoporous 2D film, in particular, at a transfer rate that is higher than the transfer rate of one or more other gases that are present in said mixture of gases. The invention also encompasses that two or more gases of the gas mixture pass through the pores to be on the second side, 30 and / or one or more gases that do not pass through the pores to remain on the first side. In an embodiment, the membrane of the invention is suitable for gas separation by molecular sieving. P-0693-WO; 13 / 12 / 2024 In molecular sieving, molecules of the separated gas or gases are smaller than other gases of the mixture, and the nanopores in the 2D film let said smaller gas molecules pass through the pores, while other gas molecules are too large to pass through the pores. It is noted here that the above does not apply necessarily to all molecules of a given gas in a gas mixture. The 5 nanopores also have a certain size distribution, so that a 100% selectivity of gases is desired, but not always obtained. For there to be gas separation, the molecules of the separated gas preferably pass through the pores in the 2D film at a comparatively higher rate (higher permeance), and the gas or gases of the gas mixture that are retained may not be totally excluded from passing through the pores, but they preferably do so at a comparatively lower 10 rate. Parameters of the gas molecules of the gas to be separated and / or in the gas mixture, such as the kinetic diameter, the electronic density, the shape of the molecule, the mass of the gas all may have an impact on the permeance, such that the size of a molecule may not be the only 15 factor affecting separation of gases by way of molecular sieving. In a preferred embodiment, there is no pressure drop across the membrane during gas separation, although, in some embodiments, there may be a pressure drop, and the existence of a pressure drop, even if it is not preferred, is also encompassed by the present invention. In 20 an embodiment, the method comprises exposing said mixture of gases to an above-ambient pressure on a first side of said nanoporous 2D film and collecting a separated gas on a second side of said 2D film. In other embodiments, a vacuum may be created on the side of the collection of the separated gas while the gas on the mixture other side of the membrane is exposed to ambient pressure or to an above-ambient pressure. 25 The gas mixture subjected to gas separation by the method of the invention may comprise two or more gases, and the separated gas may comprise one or more gases. Generally, the separated gas contains less or lacks at least one type of gas that was present in the original gas mixture that was subjected to gas separation. 30 Examples of gas mixtures from which gases can be separated encompass flue gas. In this case, CO2is preferably separated from the flue gas mixture. In another embodiment, said gas mixture is syngas and said separated gas is or comprises H2. P-0693-WO; 13 / 12 / 2024 In yet another embodiment, the gas mixture is a biogas and the separated gas is or comprises methane (CH4). The nanoporous 2D film may also be used for nitrogen enrichment, wherein any gas mixture, for example air, comprising N2 is exposed to the nanoporous 2D film and the N2-enriched gas is collected at the side of the separated gas. The invention also provides a nanoporous gas separation membrane comprising the nanoporous 2D film of the invention. The 2D films of the invention may be used, independently, in one or more of the following exemplary methods and / or applications of gas separation: - The production (or separation) of Helium from natural gas, wherein the natural gas is a gas mixture comprising He and, for example, CH4, and the 2D film is used for separating Helium from said CH4. - The production (or separation) of hydrogen from methane, wherein a gas mixture (turquoise hydrogen) contains hydrogen and CH4, and the 2D film may be used for separating H2 from CH4 in the mixture. This encompasses hydrogen production by methane decomposition as disclosed, for example, in A.F. Abbas et al, Int. J. Hydrogen Energy, 35, 3, 2010, pp.1160-1190. - The treatment of biogas and / or the separation of CO2 from biogas (in particular from CH4), wherein the biogas is a gas mixture that may comprise said CO2 and CH4. - The treatment of flue gas. Here the gas mixture contains CO2and N2, and the 2D film is used for separating N2 from the gas mixture and / or from CO2. While certain of the preferred embodiments of the present invention have been described and specifically exemplified above, it is not intended that the invention be limited to such embodiments. Various modifications may be made thereto without departing from the scope and spirit of the present invention, as set forth in the following claims. Herein below, examples of the invention are disclosed. These examples are for illustration only and are not intended to limit the scope of the present invention. P-0693-WO; 13 / 12 / 2024 Examples Examples 1-5: Single step etching of pores into non-porous graphene membranes The aim in this approach is to etch pores on graphene membranes in single step. In this approach pores were generated using SiO2 plasma in combination with O2 plasma in a Sputtering instrument (Pfeiffer SPIDER600, at the EPFL, Lausanne). A double-layer graphene sample on a Silicon nitride support or copper foil was placed into the vacuum chamber with pressure of ~8x10-6mbar. Then, 98 sccm of Ar, 13 sccm of O2 was flown into the chamber and SiO2 plasma was formed by applying 1000W power (FR mode) to the SiO2 target. In this example, a disk shaped SiO2 target having a diameter of 200mm and a thickness of 6mm, with 99.999% purity (obtained from Codex International) is used. The gas and SiO2plasma form instantaneously. The duration of plasma was kept between 5 to 60 seconds. We also varied the gas flow, mainly O2, plasma power, and duration for optimization. The parameters of Examples 1-5 are shown in Table 1 below: Table 1: Parameters of graphene treatment in sputtering instrument Example Power (W) Ar flow rate (sccm) O2 flow rate (sccm) Exp. time (s) A 1000 98 13 10 B 1000 98 13 15 C 1000 98 13 20 D 250 98 13 20 E 100 98 13 20 Figure 1 panels A to D show SEM images of graphene membranes on SiNx substrate obtained in accordance with Examples A-D: the top images show a 2x2 array of 650 nm pores on SiNx covered with the double layer of graphene. See WO2022 / 136447 (p.33, line 7-p.34, line 2) for obtaining the graphene double or triple layer on porous SiNx substrate. Figure 2 panels A to D show the corresponding pore size distribution histograms of SEM images calculated using ImageJ software. Note: SEM images were digitally enhanced in order to better visualize the graphene holes. P-0693-WO; 13 / 12 / 2024 Table 2 below shows the porosity and the number of pores per cm2of the 2D films of Examples A-E: Table 2: Characterization of pores in 2D films of the invention Example Mean pore width (nm) Porosity (%) Pores / cm2A 20.7 6.5 1.35x1010B 12.8 7.3 4.45x1010C 28.2 3.6 3.8x109D 19.6 5.5 2.05x010E 10.4 0.95 9.23x109Surprisingly, the SiO2 plasma, in combination with added O2 at a relatively low flow rate results in the controlled and tunable creation of nanoholes in the graphene membrane. The size distribution of the nanoholes is in the lower nanosized range, which renders the membranes suitable in gas separations applications. It appears that in this configuration the SiO2 components in the plasma have a protective effect, preventing rapid etching of the graphene membrane. An oxygen flow rate of at least 10 sccm is required or preferred. If the flow rate is lower, no pore formation is observed. There is too much variation when high power (1000 W) is used, such that lower RF power inputs are preferred. Example 6: Two step method for generation of pores in graphene membranes The aim in this approach is to obtain more controlled pore generation method in 2 steps. In the 1ststep SiO2 plasma is deposited onto the graphene sample using the combination of Ar, O2 and / or N2 plasma in a Sputtering instrument (SPIDER600, EPFL CMi cleanrooms). The graphene sample on a Silicon nitride support or copper foil was placed into the vacuum chamber with pressure of ~8x10-6mbar. Then, 98 sccm of Ar, 5-10 sccm of O2 and 10-20 sccm of N2was flown into the chamber. The SiO2plasma was formed by applying 1000W of power (RF mode) to the SiO2 target. The gas and SiO2 plasma form instantaneously and the duration of plasma was kept between 60-90 seconds. We varied the gas flows O2 and N2 and duration for optimization. Here SiO2is deposited, and the SiO2layer will serve as a sacrificial mask to etch graphene in a second step. The SiO2 may have some porosity and may also be P-0693-WO; 13 / 12 / 2024 mesoporous. Graphene is not etched in this case due to low flow rate of O2. The O2 and N2 plasma in this case are used as diluting gases to form the silica mask. Graphene is etched in the 2ndstep by using high energy O2 plasma in a Tepla Gigabatch 300 plasma stripper. The parameters are as follows: 400 sccm of O2flow at 200W DC RF power and duration of 5 minutes. Finally, the silica mask is removed by using 1% HF solution for 5 minutes. Observations: This method is repeatable and can provide even smaller pores. etching of into Without wishing to be bound by theory, a mechanistic explanation for the creation of pores in the non-porous graphene membrane is provided. The SiO2target is stationary on top of the chamber of the sputtering instrument, and substrates are located at the bottom. Argon is pumped into the system and RF is applied to generate plasma. Argon plasma etches the SiO2 target by atomizing it, which with the help of gravity sets on the substrate. Deposition rate is how fast these particles are setting on the substrate (which here may be the initially non- porous 2D film), usually measured at nm / min. Mixing different gases in the process such as O2 or N2 results in the creation of plasma of these gases and a partial reaction with SiO2 particles. For instance, if O2is also pumped along with Ar, the deposited SiO2layer will have higher O2 content and lower density. Similarly, pumping N2 will result in partial formation of SiNx along with SiO2 resulting in higher density film. - The process can be controlled by way of the parameters of power, Ar flow rate, N2 flow rate, O2 flow rate, throttle valve (if present), DC bias, and sputtering time (time of applying RF power), as follows: Power: Directly influences the strength of the formed plasma, higher power more plasma, lower power less plasma thus less SiO2 particles, less deposition rate. - Ar flow rate: In these experiments, Ar is used for etching the SiO2target. At low Ar flow rates, fewer SiO2particles are formed, thus a slow deposition rate. At high Ar flow rates, the density of film is quite high with quick deposition. - N2 flow rate: The addition of nitrogen results in reactive plasma that converts some of P-0693-WO; 13 / 12 / 2024 the SiO2 into SiNx with higher density, this is mainly required for achieving denser film on the substate. - O2 flow rates: The addition of O2 gas forms O2 plasma that reacts with graphene and results in pores, as well as the reaction with SiO2 resulting in less dense SiO2 film, it also reduces the deposition rate. - Throttle valve: In the sputtering instrument used (see above), a throttle valve is present between the vacuum pump and the chamber. It controls the vacuum level within the deposition chamber with 3 positions: open, center, and closed. Open position means lower pressure in the chamber (higher vacuum). - DC bias: DC bias can be applied onto the substrate to direct plasma better which results in denser films and higher deposition rate. - Time: This is how long the RF is applied; the system is set to reach set power within 30s with a linear ramp. For instance, set power is 1000W it will take 30s until the system has reached set power and stabilizes after that. The ramping time is included in the time parameter. on graphene membrane In the single step approach, pores in graphene pores are formed directly using Ar and O2 simultaneously. In this case, as well as in Example 8 below, surface of the graphene is coated with SiO2, which is later removed by immersing in 1% HF solution for 5 minutes. Observations regarding each process are given below. Observations on control - Power: We tested 200-1000W, at low power levels (<300W) there are not enough SiO2 particles to mask resulting in almost complete etching of the graphene. Therefore, higher power with a short duration is better for generating smaller pores. The optimal power level was determined to be as 500W. - Ar flow: We varied flow between 25 to 200 sccm (200 sccm is the system maximum). At low argon levels (<75 sccm) again there is not enough SiO2 to mask and graphene is etched completely. Higher flow rates (125) result in less O2plasma density which means no pores are formed or porosity decreases. The optimal Ar flow rate was determined as ~100 sccm. - N2 flow: We observed there is no effect of N2 plasma as it does not etch graphene, P-0693-WO; 13 / 12 / 2024 however, it reacts with SiO2, resulting in worse porosity. We concluded it is better not to add N2. - O2 flow: We tested 5-15 sccm flow. O2 is the main component that is responsible for the formation of pores. However, at high flow rates (>10 sccm) even at low power levels (200-300W) graphene is etched almost completely. Of course, duration (time) also plays an important role. The optimal parameter was determined as 5 sccm with the corresponding time of the 60s. This is a more controlled process. - Throttle valve: The throttle valve was varied between closed, open, and center positions. We observed that when it is closed position, graphene is etched much quicker as plasma has higher density. There is no difference between open and center positions. The optimal was to keep it open during the graphene pore etching process. - DC bias: There are two positions, either it is on or off. When it is on 200V of voltage difference is applied on the substate. However, we did not see any effect when it was on, therefore, it was left off. - Source rotation: It was a set parameter, and we could not control it. There is no clear effect of this parameter on the process. - Time: Time is the main control parameter. The ramp duration was 30s and we counted this as well. There are two options: either a short period of 10-30s with high power or longer etching with lower power. We concluded that 60s, including ramping time, is the optimal parameter with lower power levels, it yields a more controlled procedure. The following parameter values were determined to be optimal for direct pore formation on graphene with the sputtering instrument used (see Examples 1-5): - Distance between source and target: 35 mm - Power: 500 Watts - Source: RF @13,56 MHz - Argon: 100 sccm - O2: 5 sccm - Duration: 60s - Ramping to full power: 30s (could not be controlled) - Throttle valve: Fully open Using the optimized parameter values above, and using the equipment of Examples 1-5, porous graphene films were obtained. The non-porous 2D films used to start the process were P-0693-WO; 13 / 12 / 2024 3-layer graphene films deposited on a porous SiNx substrate as disclosed in WO2022 / 136447, but with the method comprising the transfer of a third graphene membrane in the same manner to obtain the 3-layers. After simultaneous SiO2deposition and pore generation using the optimized parameter values above, the silica mask is may be removed by using 1% HF solution for 5 minutes. The pores generated using these parameters are almost angstrom-sized and it is difficult to discern them on conventional TEM images. We tested the membranes for determining permeation. membrane obtained with Gas permeation measurements on graphene membranes were carried out using a custom-made membrane system, previously described (WO2022 / 136447, page 34, lines 16-27, Fig.8). The system consists of 3 mass flow controllers (Alicat Scientific) controlling the feed gas, electronic differential pressure controller (DPC) (Alicat Scientific), mass flow meters (Alicat Scientific) and finally a gas chromatograph (GC) (Perkin Elmer Clarus 590 GC). The membrane was contained in a specially designed holder made of transparent Plexiglas. Membranes in 15x15 mm size were held between two O-rings to prevent any leakage during the measurements. Before each measurement, the system was flushed with a measured gas for several minutes. The permeance of gases was calculated by plotting transmembrane pressure (bar) versus flux (sccm / m2). During the mixed gas measurements, the composition of permeate was determined using GC analysis. Membranes were tested for any leak before the measurement. The method is described in more detail in WO2022 / 136447, page 34, line 29- page 35, line 26 (Mixed gas separation measurements and Permeance calculation). The flow rates are shown in Figure 3. As can be seen N2 and CH4 have much lower permeation rates compared to CO2, H2, and He. The permeance values were calculated as shown in Table 3. P-0693-WO; 13 / 12 / 2024 Table 3: Permeance values of the membrane of an embodiment with respect to selected gases. Gas Kinetic Diameter (nm) Permeance, GPU (1 GPU = 3.35x10-10mol s-1Pa-1m-2He 0.26 29'761.2 H2 0.289 29'474.3 CO2 0.33 21'011.2 N20.346 2'371.6 CH40.364 778.0 Figure 4 shows the permeance as a function of the kinetic diameter in nm, as used in Table 3 above. The electronic density of N2 may explain the substantially lower permeance of N2 compared to CO2, which has an only slightly larger kinetic diameter than N2. The gas separation mechanism is molecular sieving. These results suggest that the membranes of the invention can be used in particular for the gas separation applications as shown in Table 4 below. Table 4: Gas separation applications for the membrane of the invention. Gas Pair Selectivity Application He / CH438.2 Helium production from natural gas H2 / CH4 37.9 Hydrogen production from methane (turquoise hydrogen) CO2 / CH4 27.0 Biogas treatment CO2 / N2 8.9 Flue gas treatment Example 9: Optimization of two step deposition-etching generation of pores on graphene membrane The second approach is a two-step process, where first SiO2 is deposited, and graphene is removed by pure O2 plasma in the second step. The goal of the two-step method is to improve repeatability and reliability, render possible the transfer of the method to other instruments, and in particular rendering the technology suitable for larger or industrial scale production. P-0693-WO; 13 / 12 / 2024 For the first step (SiO2deposition), the parameters that were controlled and varied for optimization are power, Ar flow, N2 flow, O2 flow, Throttle valve position, DC bias and time, wherein time refers to the period during which the power in RF mode is applied. As a main outcome, the parameters used in the first step of SiO2 film deposition had an influence on the structure of the SiO2 film, which in turn affected the suitability of the film in subsequent graphene etching. SiO2films with comparatively low density and / or high porosity were found to be advantageous, as the low density and / or high porosity of the SiO2 film facilitates graphene etching in the subsequent step. O2 flow during the deposition step resulted in etching of graphene and was omitted in the first step. N2 flow results in the creation of SiNx which, together with SiO2, results in a dense layer. Therefore, N2was not used in the context of SiO2 deposition. The sputtering device also had the parameter of source rotation, which was set automatically between 30-50%, and which could not be controlled. The inventors found that power and time were relevant parameters that allowed controlling the density and structure of the SiO2 film. The optimal power level was determined to be 1'000W, the maximum on the possible range of 200-1'000W, and the time was a single period of 10-90s, preferably 10-30s (e.g.10s, 20s or 30s) for obtaining angstrom-sized pores in the subsequent pore generation step. With the apparatus used, there is a linear ramp or start delay of 30 seconds, that could not be controlled, and which is included in the above time periods. Therefore, in case of a duration of 20 seconds, only 2 / 3 of the set power is reached when the process is stopped. The high-power applied during a short time resulted in a desired, porous SiO2 deposition. The optimal Argon flow rate is between 100-200 sccm. The throttle valve was kept open during the SiO2 deposition, DC bias was kept off, and the distance to the target was 35 mm. For the second, graphene etching step, the following parameters were found to be optimal (Tepla Gigabatch 300 plasma stripper, see Example 6): - Power: 100-400W - O2 flow: 50-200 sccm - Vacuum level: 0.100-400 mbar - Time: 60-300 sec. P-0693-WO; 13 / 12 / 2024 Example 10-12: Specific examples of two-step deposition etching to obtain graphene membranes with pores. The time of applying power during the deposition step in these examples was increased to about 60- Examples 10-13 The 3-layer 2D graphene membrane was transferred to PET and PI substrates using the same method as described for the transfer to SiNx. The parameters shown in Table 5 were used for the SiO2 deposition: Table 5: Parameters of the mask-deposition on nanoporous graphene membranes using the Pfeiffer SPIDER600 sputtering instrument Parameter Example 10 Example 11 Example 12 Example 13 Power (W) 500 1000 500 1000 Ar flow (sccm) 50 100 100 100 O2flow (sccm) 0 0 0 0 Valve Open Open Open Open DC bias Off Off Off Off Time* (s) 60 60 90 20 Rotation (%) 50 30 50 30 Figure no. 5 6 7 8 *including ramping time (60s) Afterwards, the membranes comprising the SiO2 film were treated with O2 plasma using 200W; O2 flow: 50 sccm, vacuum level: 0.400 mbar; time: 120 seconds (Tepla Gigabatch 300 plasma stripper), for the generation of pores in the graphene membrane. At the end, the silica mask were removed in all Examples 10-13 exposure to 1% HF solution for 5 minutes. P-0693-WO; 13 / 12 / 2024 Figure 5 is a TEM image of the membrane according to Example 1, on a PET support after removal of the SiO2mask. It can be seen that a uniform, granular layer 1 of SiO2is deposited. The nanopores are discernible as bright points of the granular surface. The larger dark dots 2 are impurities, which can be disregarded. This membrane is less suitable for gas separation, as pores are formed less efficiently. In Figure 6 it can be seen that the SiO2 layer has an overall structured surface with brighter lines between thicker deposits. The structure could be described as scaled. The brighter lines define areas or crevices where graphene etching is efficient and where pore formation is favored during plasma etching. In Figure 7, the longer deposition time (90 s) results in a homogenous and denser layer of SiO2. In Figure 8, which shows an example with a short time of exposure (power), bright spots and crevices defining pores are well visible. The examples show that optimization of the method of the invention is possible and that graphene membranes with nanosized pores can be obtained on other supports. The parameters that were optimized here depend on several factors, such as the sputtering instrument used for the deposition (see Examples 1-5), and further on the selected inorganic oxide and / or nitride mask hat is deposited (here SiO2) and / or the plasma to which the 2D film is exposed. Depending on the components in the plasma and / or the inorganic oxide or inorganic nitride that is deposited, the parameters are expected to vary and may be optimized as disclosed herein. For example, in case components suitable to deposit Al2O3are present in the plasma, and Al2O3 is deposited, the parameters will need to be adjusted accordingly. P-0693-WO; 13 / 12 / 2024

Claims

Claims 1. A method for treating a non-porous 2D film in order to prepare a 2D film comprising nanopores, the method comprising: - providing a 2D film, and, - exposing said non-porous 2D film to a plasma, wherein said plasma comprises components suitable to deposit an inorganic oxide or inorganic nitride on said 2D film.

2. The method of claim 1, wherein exposing said non-porous 2D film to said plasma comprises depositing by Physical Vapor Deposition (PVD) said inorganic oxide or inorganic nitride on said non-porous 2D film.

3. The method of claim 1 or claim 2, wherein said method comprises: - providing a target comprising said inorganic oxide, inorganic nitride or a precursor thereof, and, - sputtering said inorganic oxide, inorganic nitride or said precursor from said target so as to obtain a plasma comprising said components.

4. The method of any one of the preceding claims, wherein said inorganic oxide or inorganic nitride is selected from the group consisting of oxides and nitrides of Si, Al, Ge, In, Sn, Mg, Ta, V, Ti, and Zr.

5. The method of any one of the preceding claims, wherein said components are suitable to deposit one selected from the group consisting of SiO2, Al2O3, AlSc, GeO2, In2O3, SnO2, MgO2, Ta2O5, TiO2, TiN, V2O5, ZrO2, and ZrOX, where x is in the range of >1 and <3.

7. The method of any one of the preceding claims, wherein said 2D film comprises or essentially consists of graphene, graphene oxide (GO), transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), preferably graphene.

8. The method of any one of the preceding claims, wherein said components are suitable to deposit SiO2on said 2D film. P-0693-WO; 13 / 12 / 20249. The method of any one of the preceding claims, wherein said plasma further comprises providing a reactive gas, preferably comprising one or more selected from oxygen (O2), nitrogen (N2) and argon gas, more preferably oxygen as a reactive gas. 5 10. The method of claim 9, which comprises providing nanoholes in said non-porous 2D film by exposing said non-porous 2D film to a plasma and adding the reactive gas to said plasma at a rate suitable to generate said nanoholes in said 2D film, preferably at a rate of 5 sccm or higher.

11. The method of any one of the preceding claims, which is a one-step method for producing a 2D film comprising nanopores, wherein said non-porous membrane is exposed to said plasma comprising said components suitable to deposit an inorganic oxide or inorganic nitride on said 2D film, wherein said method comprises simultaneously adding said reactive gas to said plasma at a rate suitable to generate said nanoholes.

12. The method of claim 11, wherein said reactive gas is oxygen which is added at a rate of 5 to 50 sccm, and wherein said membrane is exposed to said plasma for a duration that is sufficient to create said nanopores, wherein said duration is preferably from 1 second to 10 minutes, more preferably from 2 seconds to 5 minutes, even more preferably from 3 seconds to 1 minute, and most preferably from 5 to 30 seconds.

13. The method of any one of claims 1-9, which comprises the two separate steps of: (3) depositing said inorganic oxide or inorganic nitride on said non-porous 2D film by exposing said non-porous 2D film to a first plasma comprising said components; and, (4) exposing said non-porous 2D film of step (1) to a second plasma comprising a reactive gas suitable to generate nanoholes in said non-porous membrane.

14. The method of claim 13, wherein, in step (2), said reactive gas, preferably oxygen, is preferably added to said plasma at a rate of 100 sccm or higher, preferably 200 sccm or higher, more preferably 300 sccm or higher.

15. The method of any one of claims 13 and 14, wherein step (1) comprises adding said reactive gas, preferably oxygen, to said plasma, at a rate that is insufficient to generate nanoholes in said non-porous 2D film. P-0693-WO; 13 / 12 / 202416. The method of any one of the preceding claims, wherein said nanopores have a mean pore width of ≤ 50 nm, preferably ≤ 30 nm, more preferably ≤ 20 nm, and most preferably ≤ 10 nm.

17. The method of any one of the preceding claims, wherein said 2D film comprising nanopores has a porosity of > 0.5%, preferably > 1%, more preferably > 3%, even more preferably > 4%, and most preferably > 5%, wherein said porosity is the surface of the membrane covered by the pores compared to the overall operational surface of the membrane.

18. The 2D film obtained by any one of the preceding claims.

19. The use of the 2D film of any one of the preceding claims in gas separation.

20. A method for separating gases, the method comprising exposing a mixture of gases to the 2D film of any one of the preceding claims.

21. The method of claim 20, which comprises exposing said mixture of gases to an above- ambient pressure on a first side of said 2D film and collecting a separated gas on a second side of said 2D film.

22. The method of any one of claims 20 and 21, wherein said gas mixture is flue gas and said separated gas is CO2, or wherein said gas mixture is syngas and said separated gas is H2, or wherein the gas mixture is biogas and the separated gas is methane (CH4), or wherein the method is for nitrogen enrichment, wherein the mixture of gases contains N2mixed with other gases, and N2 is separated to be at a higher concentration on the side of the separated gas.

23. A gas separation membrane comprising a 2D film comprising nanopores, wherein: - said nanopores have a mean pore width of ≤ 50 nm, preferably ≤ 30 nm, more preferably ≤ 20 nm, even more preferably ≤ 15 nm, and most preferably ≤ 10 nm; - said membrane comprising nanopores has a porosity of > 0.5%, preferably > 1%, more preferably > 3%, even more preferably > 3%, and most preferably > 5%, wherein said porosity is preferably the surface of the membrane covered by the pores compared to the overall operational surface of the membrane. P-0693-WO; 13 / 12 / 2024

Images