Method for making porous grahene and for post-processing and / or functionalization thereof and graphene obtained using such methods

Abstract

Method for making a porous graphene layer of a thickness of less than 100 nm with pores having an average characteristic width as defined in the specification in the range of 1 - 1000 nm, comprising the following steps: providing a catalytically active substrate to catalyse the graphene formation under chemical vapour deposition conditions, said catalytically active substrate on its surface being provided with a plurality of catalytically inactive domains having a nanostructure essentially corresponding to the shape of the pores in the resultant porous graphene layer; chemical vapour deposition using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the porous graphene layer being formed in situ due to the presence of the catalytically inactive domains; wherein subsequent to the chemical vapor deposition, the porous graphene layer is functionalized using self-initiated photo-grafting polymerization.

Description

[0001] TITLE

[0002] METHOD FOR MAKING POROUS GRAHENE AND FOR POST-PROCESSING AND / OR FUNCTIONALIZATION THEREOF AND GRAPHENE OBTAINED USING SUCH METHODS

[0003] TECHNICAL FIELD

[0004] The present invention relates to a method for producing and / or post-processing porous (‘holey’) graphene membranes, in particular those that are waterproof yet highly breathable due to enhanced vapor transmission through the pores perforated within graphene layers. Furthermore, it relates to graphene membranes made using the method and uses of such membranes.

[0005] PRIOR ART

[0006] Waterproof membranes used in outdoor apparel are effective against high liquid static pressures (rain penetration resistance). However, in general they suffer from low vapor permeability to allow sufficient moisture vapor transport, breathability of the garments and user comfort.

[0007] Highly breathable membranes are also relevant to various technical textile applications including military uniforms for chemical protection, emergency responder uniforms, protective gloves and outdoor electronic circuit protective packaging. Membranes offering high efflux rates and / or selectivity also have a wide range of potential applications in separations and energy applications. They would also spark on many other potential areas of applications, unseen for the present absence of highly breathable membranes.

[0008] While GoreTex® is dominant in the waterproof membrane market, there are numerous alternative membrane providers manufacturing membranes from various polymers besides PTFE such as polyamide and polyurethanes. In each case, the membranes consist of a polymer film with small pores to enable passage of water vapor. The thickness of conventional membranes and limitations on pore area density limits the magnitude of vapor transport.

[0009] One proposed replacement material for applications where high vapor transmission and water sealing properties are required is porous graphene. Graphene, a two-dimensional, single-layer sheet of sp2 hybridized carbon atoms, has attracted world-wide attention and research interest, owing to its exceptional physical properties, including high electronic conductivity, thermal stability, and mechanical strength. The use of porous graphene membranes in fabric laminate structures has been proposed in the following documents: WO-A-2014084860 generally describes the fixation of a porous graphene layer onto a fibrous substrate backing. It describes the laminate assembly together with methods for constructing and assembling the laminate. It does not describe a method used to form the porous graphene layer.

[0010] US-A-2015273401 expands on the method described in WO-A-2014084860 with an assembly of a porous graphene membrane on a fabric substrate together with inclusion of selective membrane layers on the side of the graphene layer. The making of porous graphene membrane material is sketched to involve the growing of a contiguous monolayer and perforating the layer and a subsequent step.

[0011] WO-A-2015167145 discloses a graphene membrane and a method for manufacturing the same. The graphene membrane includes a graphene layer having a porous pattern including a plurality of pores having a size of 5 to 100nm and a supporter configured to support the graphene layer and including a plurality of pores having a greater size than the intended pores of the graphene layer. The proposed method involves the formation of block copolymer domains on the graphene surface to form a mask template. Subsequent exposure to ion beam irradiation is used to etch pores into the graphene layer.

[0012] KR-A-20120081935 and KR-A-101325575 propose to apply a thin metal film layer (Au or Ag) deposited onto surface of an existing graphene layer followed by an annealing step to form metal particle domains on the graphene surface. Further thermal steps lead to formation of pores at the contact to the metal domains via a catalytic oxidation.

[0013] CN-A-104261403 describes a preparation method for graphene film with a three- dimensional porous structure. Polystyrene domains are used as a sacrificial template for pore formation within a film layer formed from graphene oxide platelets as starting material. EP-A-2511002 proposes the growth of a graphene layer on an untreated copper substrate. The monolayer is subsequently solution coated with PMMA and then immersed in an etchant to remove the copper. The PMMA-layer carrying the graphene layer was attached to a PTMSP film and the PMMA layer removed using a solvent. In the resultant graphene layer a plurality of grains of graphene is present with pores as defects between the graphene grains. The patent describes the membrane properties for separation of various substances from liquids and gases.

[0014] CN-A-103241728 provides a method for preparing a graphene nanopore array, which comprises the following steps: 1) coating a carbon source solution on the surface of a porous anodic alumina (PAA) template; 2) pressing the PAA template with the carbon source coated on the surface of a metal base, peeling the PAA template, and ensuring that the carbon source is preserved on the surface of the metal base and the carbon source preserves a pattern which is consistent with that on the surface of the PAA template; and 3) performing annealing treatment on the obtained metal base in the presence of a mixed gas flow of hydrogen gas and argon gas, thus converting the carbon source into the graphene nanopore array. The nanopore array obtained by the invention is an interconnected nanopore array structure rather than a single nanopore or several nanopores; and the pore size of the nanopores can be regulated through the template effect of the PAA itself, and can be further regulated through growing and etching in the later stage.

[0015] TW-A-201439359 describes a method for forming a large-area graphene layer on a porous substrate by a chemical vapor deposition process. In a first step, carbon material is deposited onto a porous template using CVD. In a second step, the carbon material undergoes annealing and catalytic graphitization to convert the carbon to a graphene layer. In a third step, liquid exfoliation is used to reduce the number of graphene layers on the substrate.

[0016] CN-A-102583337 describes a preparation method for graphene material with porous structure. Porous magnesium oxide / silicon composite material is used as a template substrate. Chemical Vapor Deposition (CVD) is used to grow graphene directly on the porous template. The graphene layer retains the porous structure of the template substrate. The porous graphene layer is recovered by destructive etching of the magnesium oxide / silicon composite substrate.

[0017] US-A-2012241069 discloses how a graphene pattern is fabricated by forming a pattern of passivation material on a growth substrate. The pattern of passivation material defines an inverse pattern of exposed surface on the growth substrate. A carbon-containing gas is supplied to the inverse pattern of the exposed surface of the growth substrate, and patterned graphene is formed from the carbon. The passivation material does not facilitate graphene growth, while the inverse pattern of exposed surface of the growth substrate facilitates graphene growth.

[0018] US-A-2013160701 proposes methods for growing microstructured and nanostructured graphene by growing the microstructured and nanostructured graphene from the bottom-up directly in the desired pattern. The graphene structures can be grown via chemical vapor deposition (CVD) on substrates that are partially covered by a patterned graphene growth barrier which guides the growth of the graphene.

[0019] WO2017212039 proposes a method for making a porous graphene layer of a thickness of less than 100 nm with pores having an average size in the range of 5-900 nm, comprising the following steps: providing a catalytically active copper substrate catalyzing graphene formation under chemical vapor deposition conditions, said catalytically active substrate in or on its surface being provided with a plurality of catalytically inactive domains having a size essentially corresponding to the size of the pores in the resultant porous graphene layer; chemical vapor deposition using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the graphene layer in situ being formed due to the presence of the catalytically inactive domains.

[0020] WO2021121952 discloses a method for making a porous graphene layer of a thickness of less than 100 nm, comprising the following steps: providing a catalytically active substrate, said catalytically active substrate on its surface being provided with a plurality of catalytically inactive domains having a size essentially corresponding to the size of the pores in the resultant porous graphene layer; chemical vapour deposition and formation of the porous graphene layer on the surface of the catalytically active substrate; wherein the catalytically active substrate is a copper-nickel alloy substrate with a copper content in the range of 98 to less than 99.96 % by weight and a nickel content in the range of more than 0.04-2 % by weight, the copper and nickel contents complementing to 100% by weight of the catalytically active substrate.

[0021] In summary, the existing technology for the waterproof breathable membranes can be improved and there exists room for improvement and needs for breakthrough technology to gain vapor breathability (rapid gas phase transport) while maintaining the liquid barrier properties, and mechanical stability for the sake of customer comfort and protection of materials beneath the garment or packaging. Porous graphene membranes have been proposed for such applications, and also have been analyzed and compared with conventional breathable membranes and have been shown to exhibit better breathability. Steenackers et al. in J Am Chem Soc. 2011 Jul 13; 133(27): 10490-8. doi: 10.1021 / ja201052q. Epub 2011 Jun 20. PMID: 21639111 report that a critical bottleneck for the widespread use of single layer graphene is the absence of a facile method of chemical modification which does not diminish the outstanding properties of the two-dimensional sp(2) network. They report on the direct chemical modification of graphene by photopolymerization with styrene. They demonstrate that photopolymerization occurs at existing defect sites of the contiguous layers and that there is no detectable disruption of the basal plane conjugation of graphene. This method thus offers a route to define graphene functionality without degrading its electronic properties. Furthermore, they show that photopolymerization with styrene results in self-organized intercalative growth and delamination of few layer graphene. Under these reaction conditions, they find that a range of other vinyl monomers exhibits no reactivity with graphene. However, they demonstrate an alternative route by which the surface reactivity can be precisely tuned, and these monomers can be locally grafted via electron-beam-induced carbon deposition on the graphene surface. Li et al in Science, Vol 324, Issue 5932, pp. 1312-1314, DOI: 10.1126 / science.1171245 report that graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. They grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. They also developed graphene film transfer processes to arbitrary substrates, and dualgated field-effect transistors fabricated on silicon / silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.

[0022] O'Hern et al in ACS Nano. 2012 Nov 27;6(11):10130-8. doi: 10.1021 / nn303869m. Epub 2012 Oct 9. PMID: 23030691 report graphene composite membranes with nominal areas more than 25 mm(2) fabricated by transfer of a single layer of CVD graphene onto a porous polycarbonate substrate. A combination of pressure-driven and diffusive transport measurements provides evidence of size-selective transport of molecules through the membrane, which is attributed to the low-frequency occurrence of intrinsic 1-15 nm diameter pores in the CVD graphene. Their results present the first step toward the realization of practical membranes that use graphene as the selective material.

[0023] SUMMARY OF THE INVENTION

[0024] Due to its excellent electrical, mechanical, and thermal properties, graphene is often dubbed as the wonder material since it was first isolated. To promote the use of graphene-based materials as a fundamental element in daily life applications, prior art on graphene modifications have been quite extensive over the years. However, the chemical stability of graphene makes it very difficult to covalently functionalize the surface without generating defects in the graphene structure (i.e. , transformation from sp2 to sp3 hybridized carbons) and disrupting the basal plane conjugation. Self-initiated photo-grafting polymerization (SI PGP) methods can be used to grow dense brushes of polymers (carpets) from pristine single-layer graphene to circumvent these issues. The pivotal challenge in the SI PGP process lies in the ability to selectively target and modify only the defect sites instead of the basal plane and vice versa due to their simultaneous presence on the graphene surface. Methods like plasma or UV treatment of pristine single-layer graphene with the presence of a photomask to specifically generate patterned defects on the graphene surface serving as the starting point for SIPGP lack precise control over the modification areas due to the resolution limitation associated with the processes, as photolithography techniques involving UV is diffraction limited.

[0025] Spatial selectivity during the modification of graphene can open a pathway to myriad membrane applications, specifically for chemical vapor-deposited (CVD) porous graphene. Widely cited as the ultimate membrane, porous graphene has gained tremendous interest in the last decade due to its potential in desalination, gas separation, and other membrane applications. However, the mechanical stability of CVD porous graphene is still a matter of contention, partly due to the defect sites at the pore edges. To this extent, chemical modification of the porous graphene along the pore edges may improve their durability, especially during its processing, which includes the transfer from a metal catalyst (used during CVD synthesis of the porous graphene) to the desired substrate. Here we address the question of spatial control of porous graphene. We have used CVD porous graphene produced in a bottom-up approach that exploits a self-assembly process (the invention however not being limited to such base manufacturing techniques) rather than traditional top-down approaches like focus ion / electron beam milling, chemical treatment of pristine graphene, and lithographic methods that utilize block copolymers. Compared to the porous graphene prepared by other techniques, the bottom-up route can produce porous graphene with very few defects in the basal plane, advantageously allowing only pre-defined defect areas. With a bottom-up fabrication process, we modified the porous graphene with SI PGP, seeking to exploit these reactive sites. The unique properties of these kinds of porous graphene ensure pre-defined defect areas represented by the edges of the pore. Here, we have conclusively outlined a simple route to modify the pore edges selectively, with the results demonstrating the possibility of fabricating polymer-reinforced porous graphene layers for state-of-the-art membranes.

[0026] Self-initiated photo-grafting polymerization (SI PGP) is shown to provide a simple one-step polymerization process that yields dense polymer carpets on various surfaces, including pristine graphene. Precise spatial selectivity of this process has not been recognized yet. In this context, we used SIPGP to selectively functionalize the edges of pores in chemical vapor-deposited porous graphene sheets. Well-defined areas represented by the pore edges formed during the graphene fabrication served as the reactive sites for the functionalization process. By polymerizing styrene monomers from the pore edges using a radical-mediated process, we were able to selectively graft most of the polymer chains along and from the pore edges of the graphene. This resulted in unique graphene pore edges decorated with a functional "halo" of polymer chains. We analyzed the surface profile of the functionalized pores using atomic force microscopy (AFM), which revealed the presence of open pores with a controllable thickness of polymer halo around them. The precise pore edge selectivity of the approach demonstrated here can be implemented for numerous membrane-based applications of porous graphene.

[0027] According to a first embodiment of the present invention, it relates to a method for making a porous graphene layer of a thickness of less than 100 nm with pores having an average characteristic width as defined in the specification in the range of 1 - 1000 nm.

[0028] The average characteristic width of the pores is defined and measured as follows:

[0029] As the shape of pore becomes elongated and uneven, resulting from the catalytically inactive domains (e.g. W nanostructures), it is challenging to obtain the pore diameter. The characteristic width was, therefore, chosen and defined as the widest width of pore rather than the diameter of the pore. The characteristic width of the pores was extracted by using image analysis software (Imaged) on scanning electron microscope (SEM) images. Porous graphene was transferred onto SiNx chip including hole with 4 pm in diameter to make a free-standing section suitable for clear image interpretation. Five representative SEM images of porous graphene were then, taken over 1.14 um2 to visualize the clear difference in the contrast between pore and surrounding graphene (e.g., black for pore and grey for graphene). As the characteristic width of pore is few tens of nm, high magnification SEM images were required. Afterward, based on the SEM image, the widest width of each pore opening was measured and the average of the measured widths subsequently calculated. The thickness of the porous graphene layer can be determined using Atomic Force Microscopy (AFM). AFM characterization of the material, for example via tapping-mode surface scanning, generates images of the surface height and thickness of the material.

[0030] The method comprises the following steps: providing a catalytically active substrate to catalyse the graphene formation under chemical vapour deposition conditions, said catalytically active substrate on its surface being provided with a plurality of catalytically inactive domains having a nanostructure essentially corresponding to the shape of the pores in the resultant porous graphene layer; chemical vapour deposition using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the porous graphene layer being formed in situ due to the presence of the catalytically inactive domains; wherein subsequent to the chemical vapor deposition, the porous graphene layer is functionalized using self-initiated photo-grafting polymerization.

[0031] Self-initiated photo-grafting polymerization (SI PGP) is an initiator-free grafting from surface polymerization technique that utilizes the monomer as the photosensitizer.

[0032] SI PGP can modify hydrogenated graphene and sp3 hybridized defects of graphene. UV light irradiation leads to the abstraction of hydrogen atoms from the graphene structure. The UV irradiation triggers homolytic bond scission, initiating surface-mediated free radical polymerization. Hydrogen atoms are found at the dangling bonds of graphene edges, even at ambient temperature. Porous graphene has disordered edges with a high density of C-H groups, making them conducive to polymerization. Polymerization occurs mainly at the pore edges of the graphene, forming distinct “rim-like” structures around the pores. Even after 24-hour polymerization period, the structural integrity of the pores is maintained, remaining open.

[0033] As pointed out above, the porous graphene layer does not necessarily have to be produced using that bottom-up process, but can also be a porous graphene layer having been obtained using a different method but with corresponding activated edges of the pores.

[0034] The self-initiated photo-grafting polymerization normally leads to functionalization of the porous graphene layer at the edges of said pores.

[0035] According to a first preferred embodiment of this method, the self-initiated photo-grafting polymerization is carried out in the gas or preferably in the liquid phase, before or after the porous graphene layer has been detached from the catalytically active substrate; the selfinitiated photo-grafting polymerization may be carried out before the porous graphene layer is attached to a final support layer, or it may be carried out with the porous graphene layer already attached to a final support layer..

[0036] According to yet another preferred embodiment, the self-initiated photo-grafting polymerization is carried out in the liquid phase, wherein the graphene layer is immersed in or coated or sprayed with at least one monomer (which may be the pure monomer or a monomer in a corresponding solvent or carrier, also possible is the use of pre-polymers) for the self-initiated photo-grafting polymerization, preferably under an inert gas atmosphere. Typically, self-initiated photo-grafting polymerization is initiated using ultraviolet irradiation, preferably using irradiation with a wavelength in the range of 250-500 nm, preferably in the range of 300-400 nm, and / or with a total power of 0.1-5 mW / cm2, preferably in the range of 0.5-2 mW / cm2.

[0037] The self-initiated photo-grafting polymerization can be carried out using at least one monomer selected from the group consisting of: styrene, styrene derivatives (for example styrene sulfonate, p-methoxystyrene, 4-Methylstyrene, 4-hydroxystyrene and other compounds structurally derived and based on styrene), acrylate, methacrylate (and in each case derivatives thereof for example methyl acrylate, ethyl acrylate, butyl acrylate, hydroxyethyl methacrylate and other compounds derived and based on acrylate and methacrylate), as well as combinations and mixtures thereof, wherein preferably styrene is used. Possible alternative systems to styrene are methyl methacrylate (MMA), N,N- dimethylaminoethyl methacrylate (MAEMA), methacrylatoethyl trimethyl ammonium chloride (METAC), and 4-vinyl pyridine (4VP). Also bases are possible (for example, NiPAAM, PDMS, P3HT, PMMA).

[0038] The self-initiated photo-grafting polymerization can be carried out at a temperature in the range 10-40°C, preferably in the range of 15-30°C, preferably for a time span in the range of 0.5-30 h, preferably in the range of 2-24 h.

[0039] The self-initiated photo-grafting polymerization is preferably carried out with at least one monomer (or pre-polymer) providing reactivity for further functionalization, and subsequent to the self-initiated photo-grafting polymerization further functionalization can be carried out using that reactivity. The functional groups present in the monomers remain available for subsequent chemical reactions such as post-functionalization or cross-linking to further modify the properties of the material. Examples of such reactive groups may include hydroxyl groups (e.g. hydroxyethyl methacrylate), carboxylic acids (e.g methacrylic acid), epoxides (e.g. glycidyl methacrylate), amines (e.g. aminoethyl methacrylate), amide (Poly(N-isopropylacrylamide) and isocyanate (e.g. isocyantoethyl methacrylate) and azides (e.g. azidoethyl methacrylate).

[0040] The catalytically active substrate is preferably a copper-nickel alloy substrate with a copper content in the range of 98 to less than 99.96 % by weight and a nickel content in the range of more than 0.04 to 2% by weight, the copper and nickel contents complementing to 100% by weight of the catalytically active substrate.

[0041] Further preferably, the catalytically active substrate has a nickel content in the range of 0.06 - 1% by weight or 0.08 - 0.8% by weight complemented to 100% by weight by the copper content.

[0042] The catalytically active substrate can be prepared by applying, preferably using electrochemical plating, e-beam evaporation, PVD or sputtering, a nickel film of a thickness in the range of 10 nm to 2.2 pm preferably in the range of 25-300 or 20-500 nm, preferably in the range of 50-300 nm on a pure copper foil, preferably having a thickness in the range of 0.01-0.10mm, preferably in the range of 0.02-0.04 mm, in particular having a purity of more than 99.5%, and by annealing, preferably at a temperature in the range of 800- 1200°C, preferably in the range of 900-1100°C, in particular during a time span of 10 minutes-120minutes, preferably during a time span in the range of 30 minutes-90 minutes. The porous graphene layer normally has a thickness in the range of less than 50 nm, preferably in the range of 1-20 nm, in particular in the range of 5-15 nm or 7-12 nm.

[0043] The porous graphene layer can have an areal porosity, defined as the ratio of total area of pores to total projected area of the layer, so as the areal fraction of pore space in the total graphene layer, in the range of at least 10%, preferably at least 15%, more preferably of at least 20% or at least 25%, or at least 30% or at least 40%.

[0044] The catalytically active substrate can be provided on its surface with a plurality of catalytically inactive domains by applying, preferably using sputtering, e-beam evaporation or PVD, and essentially contiguous tungsten layer, preferably with a thickness in the range of more than 1 nm, preferably more than 3 nm, more preferably more than 5 nm, or in the range of 1-10 nm, preferably in the range of 5-10 nm, and by subsequently annealing at a pressure below normal pressure, preferably of less than 100 mTorr, in particular under a reducing atmosphere, preferably in the presence of an inert gas such as argon or nitrogen gas, combined with hydrogen gas, to convert the tungsten film into a plurality of catalytically inactive domains (2), wherein preferably the annealing takes place at a temperature in the range of 700-1100°C, more preferably in the range of 750-950°C or 800-900°C, typically during a time span in the range of 10-180 minutes, preferably in the range of 50-100 minutes.

[0045] The catalytically inactive domains can have an average characteristic width in the range of 1-1000 nm, preferably in the range of 10 - 100 nm, more preferably in the range of 10-50 nm, or having an average characteristic width in the range between 5-900 nm, preferably in the range of 10-200 nm, more preferably in the range of 10-100 nm.

[0046] The average characteristic width of the catalytically inactive domains can be determined as follows: Scanning electron microscopy (SEM) images of catalytically inactive domains formed on copper-nickel alloy are acquired. The characteristic width of each catalytically inactive domain is measured by utilizing the Imaged software. Given the elongated, noncircular morphology of the catalytically inactive domains, the characteristic width is defined as the maximum width of each domain measured perpendicular to the elongated axis of each domain.

[0047] Chemical vapour deposition can be implemented using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the graphene layer in situ being formed due to the presence of the catalytically inactive domains using methane gas as carbon source, preferably in the copresence of argon and hydrogen gas under reduced pressure, preferably below 50 Torr, preferably below 5 Torr, during a time span of preferably in the range of 10-120 minutes, preferably below 60 minutes, more preferably below 50 minutes, most preferably below 35 minutes, wherein this graphene layer deposition process preferably takes place during a time span allowing for the generation of a graphene layer of average thickness of more than 5 nm, preferably in the range of 8-12 nm.

[0048] The porous graphene layer can be removed from the catalytic substrate, and applied to a porous, preferably nonwoven or fabric supporting substrate, wherein the self-initiated photografting polymerization is carried out before or after the porous graphene layer has been detached from the catalytically active substrate and before or after being applied to said porous. The substrate is preferably a nonwoven or fabric supporting substrate, preferably in that for removal of the graphene layer first a carrier layer is applied to the graphene layer on the surface opposite to the catalytic substrate and the sandwich of this carrier layer is removed from the catalytic substrate.

[0049] Prior to removal of the graphene layer, the layered structure of the catalytic substrate with the catalytically inactive domains and the graphene layer can be subjected to a pre-leaching process weakening or removing the bond between the graphene layer and the catalytic substrate and / or wherein the catalytically inactive domains.

[0050] This pre-leaching step may include the formation of an oxide layer at least partially, preferably essentially completely between the graphene layer and the catalytic substrate and the removal of the catalytically inactive domains.

[0051] Preferably in the pre-leaching step the material is subjected to a basic or acidic environment, preferably in water, more preferably at a pH of less than 6 or more than 7, preferably more than 10, more preferably at a pH of more than 12, wherein most preferably an aqueous solution of 0.01-0.5 M NaOH is used, preferably for a time span in the range of 10-60 minutes at a temperature in the range of 40-60°C, optionally followed by rinsing with water and drying.

[0052] Subsequent to the chemical vapor deposition of the porous graphene layer the porous graphene layer can be removed from the substrate, in that the exposed porous graphene layer on the surface of the catalytically active substrate is subjected to an aqueous solution containing a dissolved oxidant, directly or indirectly followed by treatment of the exposed porous graphene layer on the surface of the catalytically active substrate with an aqueous persulfate solution, directly or indirectly followed by lamination and / or generation of a carrier layer onto the exposed porous graphene layer from the side opposite to the catalytically active substrate and mechanical separation of said carrier layer with the exposed porous graphene layer (5) from said catalytically active substrate.

[0053] The graphene layer can be removed, preferably after a pre-leaching step, from the substrate using electrochemical methods, by immersing the layered structure of the catalytic substrate and the graphene layer in an electrolyte and applying electrochemical potential to the substrate relative to a counterelectrode in the same electrolyte.

[0054] The graphene layer after or for removal from the catalytic substrate can be attached to a porous, preferably nonwoven or fabric supporting substrate, preferably having a characteristic filament diameter in the range of 200-2000 nm, preferably in the range of 300- 1000 nm, in particular with a standard deviation in the range of less than 500 nm, and / or having a characteristic pore size in the range of 500-50000 nm, preferably in the range of 1000-10000 nm, in particular with a standard deviation in the range of less than 1000 nm, wherein preferably the nonwoven or fabric supporting substrate is attached to the graphene layer using solvent induced bonding and / or heat bonding, wherein preferably adhesion to non-woven is effected using Isopropanol-mediated adhesion plus annealing and / or heat treatment.

[0055] According to another aspect of the present invention, it relates to a graphene layer, preferably on at least one supporting substrate, obtainable or obtained using a method as detailed above.

[0056] Preferably it has a thickness in the range of less than 50 nm, preferably in the range of 1- 20 nm, in particular in the range of 5-15 nm or 7-12 nm and / or it has an areal porosity in the range of at least 10%, preferably at least 15%, more preferably of at least 20% or at least 25% or at least 30% or at least 40%.

[0057] Furthermore, the present invention relates to a graphene layer on a substrate, in particular a piece of textile or apparel having at least one graphene layer made using a method according to the above and / or according to above, preferably in the form of a filtering or separation device or a water resistant and / or water repellent and / or breathable apparel.

[0058] According to yet another aspect of the present invention, it relates to the use of such a graphene layer as a semipermeable membrane, in various fields including electronics including batteries, medical applications, catalysis, separations, in particular for filtering, separation or textile applications in the field of apparel, or in the technical field, in particular for providing water barrier in electronics including batteries and / or mobile devices.

[0059] Further embodiments of the invention are laid down in the dependent claims.

[0060] BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0062] Fig. 1 shows an overview over the process;

[0063] Fig. 2 shows in (A) (i) a representative AFM image (scale bar = 50 nm, height range = 5 nm) of a porous graphene film transferred onto a silicon substrate; the schematic diagram shows the idealized representations of the edges of the graphene pores with both zigzag or armchair orientations, indicating dangling bonds containing hydrogen atoms; (ii) the Raman spectra of a single-layer region of the porous graphene com-pared to a non-porous pristine graphene; the ID / IG ratios of both graphene types are indicated in the plot; in (B) a schematical diagram depicting the SI PGP process on the porous graphene and the hypothesized model show the mechanism of the grafting process along the pore edges (hypothetical atomistic depiction); in (C) AFM images of selected regions of porous graphene at different stages of polymer grafting: (i) before, (ii) after 2hr, (iii) 4 hr, (iv) 6 hr, (v) 12 hr, and (vi) 24 hr of SI PGP with styrene monomers; all the scale bars are 50 nm; the height variation range is 20 nm; in (D) AFM surface profiles of single pores after varying times of polymerization; the surface profile of the pore morphology was carried out along the line shown in the AFM images (C i through vi); the selected images are representative of the samples as a whole (multiple analyses of various pores at different stages, see supporting Figure 13);

[0064] Fig. 3 shows in (A) a histogram from the AFM images (sampled area >30 average pore diameter) measured at varying grafting times; the presence of domains with height >8 nm increases with increasing time of polymerization; in (B) overview AFM images of porous graphene (i) before and after (ii) 4hr (iii) 6 hr, (iv) 8 hr, (v) 12 hr, and (vi) 24 hr of SI PGP of polystyrene; all the scale bars are 250 nm, and the height range is 20 nm; Additional histogram analysis Fig. 12;

[0065] Fig. 4 shows in (A) the influence of the polymerization time on average thickness (ha) of the porous graphene layer; in (B) changes in the root mean square roughness (Rrms) of the porous graphene layer with increasing polymerization time;

[0066] Fig. 5 shows a comparison of the influence of the SI PGP process on porous graphene surfaces vs non-porous graphene surfaces, wherein in (A) high-resolution AFM images of pores of porous graphene measured after (i) no polymerization and (ii) 4 hr of polymerization are shown; (iii) comparison of surface profiles of the pores measured along the straight lines indicated in the AFM images i-ii; in (B) high-resolution AFM images of non-porous graphene measured after (i) no polymerization and with (ii) 4 hr of polymerization; (iii) comparison of surface profiles of the basal plane of the graphene surface measured along the straight lines indicated in the AFM images i-ii; all the scale bars are 50 nm, and the height range is 20 nm; in (C) 3D AFM images of porous graphene obtained before and after SI PGP demonstrating regional specificity as polymer do-mains are observed mainly along the pore edges; in (D) 3D AFM images of porous graphene obtained before and after the SI PGP process showing the presence of an apparent “polymer carpet” on the graphene surface consistent with a random polymerization process; all the scale bars are 50 nm, and the height range is 16 nm; the schematic diagram highlights the remarkable differences between SI PGP on a surface with arbitrary defects and a surface with spatially resolved defects around pore edges; Fig. 6 shows a schematic diagram depicting the radius of curvature induced edge broadening during AFM measurements;

[0067] Fig. 7 shows in (A) overview AFM images of single layer / few layers porous graphene (i) before and after (ii) 4hr (iii) 6 hr, (iv) 12 hr, and (iv) 24 hr of SIPGP with styrene monomer; all the scale bars are 250 nm and the height range is 25 nm; in (B) surface profiles of two different areas (a, b) obtained from the images i-v showing evolution of height of the basal plane as well as the pore edges with increasing polymerization time;

[0068] Fig. 8 shows in (A) Raman spectra obtained for pristine graphene (lower), porous graphene type 1 (top), and porous graphene type 2 (middle); the ID / IG ratios clearly indicate the changes in the fractions of defects in the graphene with the intro-duction of pores for (i) single layer domains and (ii) multi-layer domains; in (B) SEM images (i) large-scale (scale bar = 20 pm), and (ii) small-scale (scale bar = 1 pm) showing the morphology of the copper where porous graphene type 2 is grown with CVD; the multi-layer domains of graphene are clearly visible in the SEM images; furthermore, the tungsten particles formed during the dewetting process which inhibit the growth of graphene is also visible in the SEM images; in (C) SEM images (i) large scale (scale bar = 20 pm), and (ii) small scale (scale bar = 1 pm) showing the morphology of the copper where porous graphene type 1 is grown with CVD; the multi-layer domains of graphene (in the large-scale image) and the tungsten particles (small-scale image) are clearly visible in the SEM images;

[0069] Fig. 9 shows in (A) the AFM images of a pore of a (i) unmodified, (ii) 2 hr, and (iii) 4 hr polymerized porous graphene; in (B) the evolution of the surface profiles of a pore with polymerization; the white dashed lines indicate the areas where the surface profiles were calculated. All the scale bars are 50 nm, and the height range is 15 nm;

[0070] Fig. 10 shows in (A) a histogram analysis of AFM images obtained at varying times of polymerization process of the pristine graphene without any pores; the unmodified graphene shows a peak at 0.93 nm indicating the presence of single layer graphene; the small tail observed in the histogram is attributed to the presence of localized PMMA residue from the transfer process of single layer graphene; with 4 hr of polymerization, we can observe a significant broadening of the peak with a shift towards higher thickness (from 0.93 nm to 2.5 nm), indicating a nonspecific covalent attachment of the polystyrene to the graphene film; further polymerization broadens the peak further with the maxima of the peak being at 6.4 nm; in B) overview AFM images of single layer non-porous graphene (i) before and after (ii) 4hr, and (iii) 12 hr of SIPGP with styrene monomer; all the scale bars are 250 nm, and the height range is 20 nm;

[0071] Fig. 11 shows the influence of defined defects on the grafting regions; in (A) AFM images of which focuses on the pores of type 1 porous graphene (i) with no SIPGP, (ii) with 4 hr of SIPGP process, and (iii) the surface profiles (measured along the white lines) highlight the changes in the pore morphology associated with the polymerization process; in (B) AFM images of the pores of type 2 porous graphene (i) with no polymerization, (ii) with 4 hr of SIPGP process, and (iii) the surface profiles of the pores (measured along the white lines shown in the images) demonstrate the propensity of the polymers to be grafted along the pores; in (C) AFM images of the non-porous graphene (i) with no polymerization, (ii) with 4 hr of SIPGP process, and (iii) the surface profiles of the modified and unmodified graphene (along the white lines drawn in the images) demonstrates the stochastic process of grafting in a surface with undefined defects; all scale bars are 50 nm, and the height range is 20 nm;

[0072] Fig. 12 shows in (A) the evolution of histogram with polymerization process for A1) porous graphene type 1 (left, from no SIPGP to 24 hr of SIPGP), A2) porous graphene type 2 (middle, from no SIPGP to 8 hr of SIPGP), and A3) non-porous graphene (right, from no SIPGP to 12 hr of SIPGP); in (B) large scale AFM images of porous graphene type 1 of (i) no SIPGP, (ii) 4 hr, (iii) 6 hr, (iv) 12 hr, and (v) 24 hr of SIPGP; in (C)large scale AFM images of porous graphene type 2 of (i) no SIPGP, (ii) 2 hr, (iii) 4 hr, and (iv) 8 hr of SIPGP; in (D) large scale AFM images of non-porous of (i) no SIPGP, (ii) 4 hr, and (iii) 12 hr of SIPGP; all scale bars are 500 nm, and the height range is 15 nm;

[0073] Fig. 13 shows in (A) surface profile analysis of the pores of porous graphene with increasing time of polymerization (0 - 24 hr); in (B) AFM images of focusing on the pores of porous graphene type 1 with (i) 0 hr, (ii) 4 hr, (iii) 6 hr, (iv) 12 hr, and (v) 24 hr of SIPGP; in (C) surface profile analysis of the pores of porous graphene with increasing time of polymerization (0 - 4 hr); in (D) AFM images of focusing on the pores of porous graphene type 2 with (i) 0 hr, (ii) 2 hr, and (iii) 4 hr of SIPGP; all the scale bars are 50 nm, and the height range is 20 nm;

[0074] Fig. 14 shows the hydrostatic pressure resistance of highly porous graphene with and without styrene polymerization for 24 hr on the SiNx chip...

[0075] DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows the general principle of the present invention. On the left side in the upper row it is shown how porous graphene with predefined defects is reacted using SI PGP to lead the spatial specific polymerization at the edges of the pores, specifically to lead to a structure as indicated on the right.

[0076] On the other hand, in the bottom row on the left-hand side it is shown how pristine graphene which is not porous and has arbitrary defects leads to nonspecific weak polymerization.

[0077] When synthesizing porous graphene in a reductive process, the pores are structural defects that bear mainly hydrogen atoms. Due to the bottom-up fabrication process, the pores have numerous dangling bonds surrounding their edges, with the dominant species being aromatic C-H (Fig. 2 Ai).

[0078] The Raman analysis (see Fig. 2 Aii) of this type of porous graphene confirmed the emergence of both D and D' peaks with ID / IG and ID / ID ratios being 0.364 and 3.309, respectively. A D peak and the ID / ID ratio value of 3 are observed in the Raman spectra when disordered edges are present in graphene layers rather than vacancy-type defects or sp3 carbons. The dangling bonds at graphene edges contain hydrogen atoms at ambient temperature. Therefore, in this scenario, the pores can be rationalized as disordered graphene edges with abundant C-H groups.

[0079] SI PGP was used to functionalize the porous graphene surface (schematic diagram Fig. 2 B). The use of SI PGP to modify hydrogenated graphene as well as native sp3 hybridized defects of graphene is possible. Hydrogen can be abstracted upon UV light irradiation, and subsequent homolytic bond scission initiates surface-mediated free radical polymerization. Hence, instead of polymer carpets observed by prior art, domains of dense polymer brushes grafted along the pore edges due to constrained grafting areas are observed (schematic Fig. 2 B).

[0080] The morphologies of both modified and unmodified pores were investigated with a high- resolution atomic force microscope (AFM). Fig. 2 C shows the morphological changes of the pores after growing polystyrene chains. Interestingly, the pores remained open even after functionalization. Moreover, the presence of a distinct “rim-like” feature (some edge broadening is expected from AFM measurement, see below) in the surface profiles of single pores confirm that the polymerization is initiated most likely from the edge of the pores which is consistent with the model described above. The polymerization time was varied systematically from 2 to 24 hours to investigate the grafting process. From the AFM images, we can observe that the unmodified graphene surface is very flat with a height variation of 2-3 nm, measured by obtaining the height difference from the pore edge to the pore center. Prior works on AFM analysis of graphene reported the height of a single layer of graphene to be ca. 0.4 to 1 nm, the van der Waals distance being ~ 0.34 nm, thus indicating the possible presence of both domains of few layers of the graphene on the surface (see further below) and single layer domains. Corresponding with our model (Fig. 2 B), with 2 hours of polymerization, we can identify thicker domains in the magnitude of ca. 6 - 10 nm, predominantly along the edges of the pores, leading to a pore that is decorated with grafted polystyrene, thus creating a distinct “halo” around the pores. These regions became consistently thicker with increasing polymerization time (Fig. 2 D). The analysis of single pores after polymer grafting confirms the spatial selectivity, as mentioned above. As a next step, we investigated the influence of the photo-grafting process on the large-scale morphology of the porous graphene.

[0081] Fig. 3 shows the progress of the polymer grafting on the large-scale morphology of the porous graphene and corresponding histogram analysis. Within 4 hours of polymerization, we observed the presence of thicker domains predominantly along the pore edges while the graphene basal plane remains initially largely unaffected (dark background). However, after 6 h a thickness change on the basal plane was noticeable (see further below). The histogram analysis of the images on a large scale (30x average pore diameter) further elucidates the polymerization process. The histogram of unmodified porous graphene shows a bimodal distribution indicating the presence of the pores (i.e. reference height = 0 nm) and the other peak results from the height of the basal plane (i.e. height = 2.07 nm). In the pristine porous graphene, the peak originating from the graphene basal plane shows a narrow distribution which is indicative of a very flat surface. Within 4 hours of polymerization, we can still identify a graphene basal lamella peak at ca. 2.3 nm. Moreover, we can observe a distinct tail of events with heights > 10 nm, consistent with the presence of grafted polymer chains propagating from the pore edges over the basal plane, which is in line with previous observations, as we can clearly distinguish the basal plane from the modified pore edges. Further polymerization causes significant broadening of the surface height distribution profile with a noticeable shift in the curve towards increased height, suggesting the presence of thicker domains / areas with increased polymerization time. Interestingly, we also observe a shift in the peak observed for basal lamella indicating that with extended polymerization time, the polymer chains are grafted spatially. The histogram analysis of the AFM image obtained after 24 hr of polymerization shows the presence of two distinct levels: (i) a level at 8 nm resulting from the thickening of the basal plane and (ii) a peak at 15 nm thickness presumably from the polymers grafted along the pore edges.

[0082] Using the AFM images of functionalized and non-functionalized porous graphene, we calculated the average thickness (ha) and RMS roughness (Rrms) to quantify the overall change of the porous graphene surface. We plotted haand Rrms as a function of polymerization time to quantitively identify the kinetics of the polymerization process (see Fig. 4). We observed a seemingly linear increase in haand Rrms with increasing polymerization time until 4 hours. Then, a pseudo-plateau region emerged, after which haand Rrms increased again. Assuming a densely packed brush layer grafted to a surface, in an ideal scenario, the average thickness of the film should increase linearly with the reaction time. Initially, the length of an individual chain should increase with increasing polymerization time, demonstrated here through (i) the surface profile of a pore with increased polymerization time, (ii) the evolution of the histogram analysis with increased reaction time, and finally (iii) a linear increase in both haand Rrms with reaction time. However, we also need to consider the radius of curvature of a pore leading to a non-flat region of grafting. The pseudo-plateau region observed in the polymerized film might also be consistent with a change in the conformation of the grafted polymer and spatial growth of the grafted polymer in the basal plane of the graphene. Unlike a UV / plasma-treated graphene surface, in this case, the reactive sites for the grafting process are limited to defects that are present in the graphene during its fabrication process, and the possible areas are most likely the pore edges (Fig. 1A, and further below) and other defects in the basal plane resulting from either structural defects or defects at the grain boundaries or both. Hence, we can assume that the probability of grafting polymer is also limited to a few areas in the porous graphene surface, with pore edges being the most preferred ones, as evident from the AFM images presented here. Therefore, with prolonged polymerization time, the only possibility to attach additional monomer is to areas where the polymer is already grafted. The evolution of the film thickness with time potentially indicates a conformational transition in the polymer from stretched brushes to either coil or globule / tilted brushes, as notably, even with extended polymerization time, the pores remain open, and the polymer chains are grafted at areas around the pores. Nevertheless, the significance of this work lies in the selective grafting of polymer along the pore edges, especially at low polymerization times. The spatial selective modification of porous graphene demonstrated in this work indicates a method for the introduction of functional polymers at the pore edges, which is crucial in areas such as membrane applications.

[0083] To further resolve the spatial specificity of the graphene modification process with SIPGP, we compared the pore morphology of porous graphene with the basal plane of the pristine graphene surface both before and after the functionalization process. SIPGP, in all cases, was carried out with styrene as the monomer for 4 hours. The high contrast height images obtained through AFM demonstrate a clear distinction between the grafting zones of polystyrene in porous graphene as opposed to the pristine graphene without pores. In porous graphene, the grafted regions (light areas in the AFM images shown in Fig. 5A and light regions in Fig. 5C) are concentrated mainly around the pores (black areas). In non- porous pristine graphene, there is no selectivity in the grafted regions as the grafted polymers can be found randomly in the basal plane (background areas in the AFM image Fig. 5B and Fig. 5D). The thickness of the grafted polymer also varies significantly in non- porous graphene compared to porous graphene. In porous graphene surfaces, thicker polymer domains can be observed primarily around the pores (surface profiles Fig. 5A). In non-porous graphene, owing to the randomness of the process, the polymer domains are grafted indiscriminately in the basal plane with decreased thickness (surface profile Fig. 5B). There is higher reactivity of the graphene edges compared to the basal plane. Due to the higher reactivity of the pore edges, polymers are preferably grafted along the pore edges, leading to thicker domains. If pores are absent like in pristine graphene, no preferred region of grafting remains. Hence, the polymer is grafted randomly along the undefined defects in the graphene basal plane. This comparison further elucidates the importance of predefined defects in achieving areal specificity during the functionalization of graphene surfaces.

[0084] Conclusions: We functionalized porous graphene layers containing predefined defects (pore edges) with polystyrene brushes by exploiting a one-step SI PGP process. AFM analysis showed that polystyrene was grafted selectively along the pore edges in the graphene layer while the pores remained open. The histogram and thickness analysis indicated thickness control over the grafted domains. The spatial specificity of the process was highlighted through comparative analysis with pristine graphene without any pores. Following a stochastic grafting process, the polymers were grafted randomly on the basal plane of the non-porous pristine graphene layers. In contrast, for porous graphene we observed grafted polymer domains concentrated around the pore edges. The spatial specificity realized in this study allows for the fabrication of polymer-reinforced graphene pores, offering potential to significantly improve the durability of porous graphene materials, especially during processing, enabling its practical applications. Further research will focus on extending this work toward membrane applications. Diverse polymer types with desired functionality (e.g., stimuli-responsive polymers) may also be grown along the pores by employing a similar pathway. This work emphasizes the potential of selective functionalization of porous graphene layers, which offers a useful tool towards fabricating the “ultimate” graphene-based membrane.

[0085] AFM analysis of polymerization of highly porous graphene:

[0086] The pore density and porosity were determined via SEM characterization. Pore density is defined as a number of pores to total projected area of the graphene layer. Porosity is defined as the ratio of total area of pores to total projected area of the graphene layer. Prolonged polymerization leads to a slight reduction in the pore density of highly porous graphene, attributable to the polystyrene accumulation over the pores. Despite this, the graphene maintains 10% areal porosity after a 24-hour-long polymerization.

[0087] Hydrostatic pressure of highly porous graphene: Hydrostatic pressure of highly porous graphene with and without styrene treatment was tested. Highly porous graphene and polymerized highly porous graphene were placed on SiNx chip for the measurement of hydrostatic pressure. The polymerized highly porous graphene exhibited a significant improvement of hydrostatic pressure up to >3.1 bar which is more than double the 1.4 bar measured for untreated samples (see Fig. 14). The measurement of hydrostatic pressure of the polymerized highly porous graphene on SiNx was stopped at 3.1 bar due to the SiNx broken above 3.1 bar.

[0088] Materials and Methods:

[0089] Bottom-up porous graphene fabrication method:

[0090] To synthesize porous graphene layers, a W / Cu planar catalyst is required. A 4-nm-thick W film was deposited atop a bare Cu foil (JX Metals Corporation, 99.9% purity) using sputtering (FHR Pentaco 100). This Cu foil requires no further treatment. Sputtering was conducted at a pressure of 0.002 mbar, utilizing 100 standard cubic centimetres per minute (seem) of Ar, and the 4-nm-thick W film was deposited for 30 seconds under 0.25 kW of DC plasma, along with 100 seem of Ar. Furthermore, to mitigate surface roughness, a Cu foil (Alfa Aesar 46986, 99.8% purity) underwent Ar-ion beam treatment for 10 minutes. Samples made with as received Cu-foil are referred to here as ‘Type T while samples made with Cu foil with Ar-ion beam treatment are referred to as ‘Type 2’. The sputtering process remained consistent with the aforementioned parameters.

[0091] Alternative: Preparation of Cu-Ni catalyst substrate: Cu foil catalyst (JX Metals Corporation, 99.9% purity) is provided; a Ni film with a varied thickness from 10 nm to 2.2 pm or 50 to 300 nm is deposited on as-received commercial Cu catalyst by sputtering in vacuum (e.g. FHR, Pentaco 100, Ni purity 99.95%3 x 10-3 mbar); pressure of the sputtering is about 0.006 mbar with 200 seem of Ar; the resulting film of Ni is deposited from 10 nm to 2.2 pm or 50 to 300 nm with DC plasma whose power is 0.25 kW; The bi-layered structure of Ni / Cu catalyst is then annealed at e.g. 1000 °C for e.g. 1 hour to convert to a binary metal alloy (Cu-Ni alloy) under low pressure (e.g. 200 mTorr) with e.g. 50 seem of H2 in a chemical vapor deposition (CVD) system (e.g. Graphene Square. Inc, TCVD-RF100CA). A thin film of W (thickness 1-10 nm) is deposited on the Cu-Ni alloy by sputtering in vacuum (e.g. FHR, Pentaco 100, W purity 99.95%) the pressure of the sputtering is e.g. 0.002 mbar with e.g. 100 seem of Ar; the thin film of W is deposited from 1 to 10 nm with e.g. 0.25 kW of DC plasma; a W / Cu-Ni alloy is mounted in the center of a 4-inch quartz tube chamber positioned in the furnace of the CVD system (e.g. Graphene Square. Inc, TCVD-RF100CA); the chamber is evacuated to reach a pressure of e.g. 45 mTorr and then purged with inert gas, e.g. N2 (e.g. 100 seem) for e.g. 5 min normally at room temperature; after purging, the chamber is put under vacuum (e.g. 45 mTorr) again and then the pressure is increased e.g. with a gas mixture of Ar and H2 (800 seem and 40 seem, respectively); to convert the W thin film into W nanostructures (NSs). The NSs are based variously on symmetric W nanoparticles and asymmetric W nanowalls with various degrees of interparticle agglomeration. The W / Cu-Ni alloy is carefully annealed at elevated temperature (e.g. 750- 950°C or 800-900°C) for an extended period of time, e.g. 1 hour including ramping with the continuous supply of e.g. 800 seem of Ar and 40 seem of H2 under 4 Torr.

[0092] The chemical vapor deposition (CVD) synthesis of porous graphene is outlined e.g. in WO2021121952, which is included in this disclosure for the making method.

[0093] Briefly, the prepared W / Cu catalyst was housed within a Cu envelope (Alfa Aesar 46986) for further processing. Following the placement of the W / Cu catalyst in the Cu envelope positioned at the centre of a low-pressure chemical vapor deposition (CVD) furnace, the sample underwent annealing for 30 minutes at 950 °C with a flow of 50 seem of H2. During this annealing process, the 4-nm-thick W film underwent dewetting, transforming into circular-shaped W nano-particles evenly distributed on the Cu surface. Subsequently, graphene synthesis was initiated at the same elevated temperature by introducing a mixture of 6 seem of CH4 and 50 seem of H2 at 800 mTorr for a duration of 15 minutes. The sample was then gradually cooled to room tempera-ture while maintaining a flow of 100 seem of H2.

[0094] The non-porous graphene samples were synthesized on a copper catalyst (product number: GHZ-Z-H-V2) purchased from JX Metals. During the synthesis of pristine graphene, the Cu foil does not require any surface treatment before the process. The Cu foil was placed at the centre of the CVD furnace for the synthesis. Before initiating the graphene growth, the Cu foil was annealed for 20 minutes at 1000 °C with 50 seem of H2 flow. Then, graphene was grown on the copper catalyst at a temperature of 1000 °C by introducing a mixture of 50 seem of CH4 and 10 seem of H2 flow. The growth time was limited to 45 minutes. After the growth process, the sample was gradually cooled to room temperature in an environment with 20 seem and 100 seem of H2 and Ar flow, respectively.

[0095] Functionalization of porous graphene with polystyrene:

[0096] All reactions were carried out with the graphene on the Cu foil catalyst substrate. As graphene grows on both sides of the copper foil, the graphene on the backside was removed by floating the copper foil with the backside on an aqueous 0.5M solution of (NH4)2S2C>8 for 10 minutes . The copper foil was then placed with the backside on a paper tissue and the backside was slid off by pulling the foil over the tissue. The copper foil with the remaining graphene on the other side was rinsed with deionized water and air dried. It was then used for polymerisation reactions. Monomers were inhibitor free, and oxygen was removed by applying two freeze-thaw cycles. The graphene sample was immersed in the monomer under argon atmosphere. Irradiation with UV fluorescent lamp with a spectral distribution between 300 and 400 nm (intensity maximum at A = 365 nm with a total power of 1 mW / cm2). It is to be noted that the power of the UV radiation is 5 times less than what is typically reported on the SI PGP of graphene. Polymerization and grafting reactions were performed with styrene as monomer. After UV irradiation, the samples were removed and thoroughly washed with toluene, ethyl acetate, and ethanol to remove physisorbed polymer and unreacted monomers.

[0097] Transfer of graphene:

[0098] To remove the polymer functionalized CVD graphene from the copper catalyst substrate, the copper foil was etched off during 3 hours by floating the sample, with the copper side facing down, on an aqueous 0.5M (NH4)2S20s solution. Furthermore, the (NH4)2S20s solution also assists in dissolving the W droplets present on the copper surface. Hence, during the etching process with (NH4)2S20s solution, W droplets are removed. After the total dissolution of the Cu foil and parallel removal of the W droplets, the functionalized graphene sheet remained floating on the (NH4)2S20s solution and could be observed by eye. The functionalized graphene sheet was then taken up by using a SiC>2 / Si wafer, was transferred to water and allowed to float for 1h. It was then picked up on a Si wafer with a 300 nm SiC>2 layer. The polymerized pristine graphene samples were also transferred to a Si wafer using an identical process described here. Unlike the polymerized samples, a thicker film of poly(methyl methacrylate) (PM MA) was spin-coated on the pristine graphene before transferring the graphene from the copper catalyst using the outlined etching process. For unpolymerized single-layer graphene, the PMMA layer acts as a supporting layer, which prevents it from disintegrating during the transfer process. After transferring the graphene onto a Si wafer, the PMMA layer was removed from the graphene by immersing the sample in an acetone bath for 1 hour.

[0099] Characterization methods:

[0100] Atomic Force Microscopy (AFM):

[0101] We have chosen atomic force microscopy as the primary characterization technique in this study since it provides information about the morphology and the thickness evolution of the samples with reaction time in a non-destructive way. We have used a Bruker Multimode 8- HR atomic force microscope to obtain the AFM images. All the images were obtained in tapping mode with Bruker RTESPA-150 AFM tips. The resonance frequency of the tips varied from 125 - 155 kHz and the nominal radius of curvature of the tips was 8 nm. The features measured in this study were » 8 nm, however, some edge broadening effects (ca. 10 nm) especially at the pore edges due to finite radius of curvature of the tip should be considered (see Fig. 6). The images were processed with WSxM software. For height and the roughness analysis, measured data was collected from at least three different regions of the samples. Images of sizes ranging exclusively from (500 x 500) nm2 and (3,000 x 3,000) nm2to were used to calculate the average height (ha) and roughness (Rrms) of both modified and unmodified films to account for the sub-micron size (< 100nm) pores of the graphene films. The error bars in haand Rrms indicate the heterogeneity of the polymer domains observed in the graphene films.

[0102] Raman Spectroscopy:

[0103] Raman spectra were recorded with a confocal Raman microscope (WITec alpha 500 / 300R+ ; WITec GmbH, Ulrn, Germany) using implemented Zeiss objectives (100* NA=0.95). The excitation wavelength of the Nd:YAG laser was 532 nm actuated at 5 mW. Signals were detected by a back-illuminated CCD camera after passing a 50-pm pinhole. The spectral resolution was 4 cm-1. Integration time for each Raman spectrum acquisition pixel was 0.2 s. The collected Raman spectra were processed using the software WITec Project Plus (WITec GmbH, Ulrn, Germany) to remove Cosmic ray occurrences, and to subtract the background.

[0104] Changes in the AFM thickness of the basal plane:

[0105] To demonstrate the changes in thickness in the basal lamella with increasing polymerization time, we used two separate surface profiles of the AFM images obtained at varying reaction times. The unmodified few layers of porous graphene showed a basal plane thickness of ca. 2.3 nm - 3.0 nm, similar to the histogram peak we observed from the histogram analysis. With 4 hrs of polymerization, we could still identify the basal plane at 2.3 nm - 3.0 nm. Additionally, we observed thick domains with heights > 10 nm, especially around the graphene pore edges. Further polymerization (6 hrs) led to a slight increase in the basal plane thickness (Fig. 7 iii(a-b)). Interestingly, polymerization times of 12 hrs and 24 hrs led to significant increases in the basal plane (> 5 nm in both cases, Fig. 7 iv(a-b) and Fig. 7 v(a-b)) indicating spatial growth of the polymers with time.

[0106] Reproducibility of the modification process in another type of porous graphene:

[0107] Raman spectra analysis and SEM images of graphene prepared using two different types of copper substrate:

[0108] To further investigate the feasibility of the process, we tested the influence of polymerization on another type of porous graphene. The porous graphene was grown in another type of copper substrate with a rougher surface structure (Fig. 8 B). The process is outlined in the materials and methods section in detail. Fig. 8 shows the comparison of the morphology of graphene on types of copper substrates and the comparison of Raman spectra between the two samples. We calculated ID / IG and ID / ID' ratios from the Raman spectra measured from the single layer domains of the two types of porous graphene as the ratios can help identify both the presence and the origin of defects, respectively. The ID / IG ratios were 0.364 for type 1 porous graphene, 0.427 for type 2 porous graphene, and 0.069 for non- porous graphene, with the ID / ID' ratios being 3.309 for type 1 porous graphene and 3.347 for type 2 porous graphene. The notable increase in the ID / IG ratios observed for porous graphene samples shows an increased presence of defects on porous graphene surfaces compared to graphene surfaces without pores. In addition, ID / ID' ratios for both graphene types were close to 3, indicating that the defects are due to disordered edges rather than the presence of vacancy-type defects or sp3 hybridized carbons. While the Raman spectra are comparable in both cases, the difference in their morphology comes from the observed pore density and the pore sizes. The tungsten particles, formed during the dewetting process of the deposited tungsten film, locally inhibit graphene growth, with pores forming at the areas where the tungsten particles were present. Hence, the sizes and density of the W particles directly reflects both the pore sizes and the density. The porous graphene used earlier (type 1 , average sizes = (1190.3 ± 831 .8) nm2) shows larger tungsten particles than the other porous graphene type (type 2, average sizes = (723.8 ± 602.1 nm2) nm2). Reciprocally, pore density seems to be higher in porous graphene type 2 compared to porous graphene type 1. Nevertheless, as the ID / IG ratios are comparable in both cases, we expect similar polymer growth kinetics in both graphene surfaces where the polymer should be grafted densely around the pore edges.

[0109] Influence of reaction time on pore morphology:

[0110] Polymerization of the graphene films was conducted for times between 2 - 8 hrs to investigate the influence of polymerization on this graphene film. Fig. 9 shows the evolution of the morphology of the graphene pore edges with increasing reaction time. From the surface profiles, we can clearly observe a thickening of pore edges that can be associated with the increasing reaction time. Consistent with the type 1 porous graphene, grafted polymer domains can be identified primarily along the pore edges in this type of graphene as well and the basal plane shows minimal presence of polymer domains compared to pore edges.

[0111] Influence of reaction time on large-scale porous graphene morphology:

[0112] Histogram analysis of the AFM images at varying polymerization time, is also consistent with the observed surface profiles (see Fig. 4). Until 2 hr polymerization time, we can identify the peak associated with the basal plane at ca. 2.5 nm. At 4 hours of polymerization time, we observe a slight shift in the peak at ca. 3.2 nm and additionally, we can clearly observe a distinct tail that is resulting from the grafted polystyrene chains. Further polymerization leads to a significant broadening of the peak associated with basal lamella implying the spatial polymerization process with increased polymerization. Hence, we can conclude that the growth kinetics of polystyrene in this graphene is also comparable to what we observed for type 1 graphene.

[0113] Influence of reaction time on average thickness and rms roughness of the layer:

[0114] From the AFM images we also calculated ha and Rrms in a similar way and the measured data was quite consistent until 12 hr of polymerization. The height analysis indicated a saturation in the thickness of the grafted polymer after 12 hrs of polymerization (see Fig. 5).

[0115] The morphology of the layer when carried out on a pristine graphene layer without pores compared to porous graphene:

[0116] Growth kinetics of SI PGP with styrene on non-porous graphene surfaces:

[0117] To understand the differences in the SI PGP process when it is carried out on a surface with arbitrary defects as opposed to porous graphene (see also Fig. 1), we used a pristine graphene surface for the SI PGP process with styrene monomer. SI PGP processing conditions and the transfer of graphene were identical to that used for porous graphene samples. In a pristine graphene with no pores, the “defects” are random. The defects can be structural in the basal plane or from the grain boundaries. Hence, the polymerization process should also be random resulting in a generalized increase in thickness of the basal plane. The large-scale AFM images (Fig. 10) of 4 hr and 12hr polymerized non-porous graphene suggest the stochastic nature of the grafting process where the grafting areas are not defined. Furthermore, unlike the porous graphene here, the basal plane thickening becomes evident even at 4 hr polymerization time. Consistent with previous works on SI PGP of graphene, we can identify a carpet of polymer on the graphene surface resulting in a significant basal plane thickening as evidenced by the histogram analysis shown in Fig. 10 (the peak of the histogram shifts from 0.94 nm (0 hr) to 6.4 nm (12 hr)). Furthermore, at any point (especially at low polymerization times), we could identify only one broad peak in the histogram rather than two distinct peaks associated with the basal plane and the grafting region observed for porous graphene type 1 and 2 (Fig. 3 and Fig. 4). This observation again emphasizes the specificity of the SI PGP process when carried out on graphene surfaces with pre-defined defects.

[0118] Comparison of grafted regions of polystyrene in both porous and non-porous films see Fig. 11.

[0119] Influence of UV light exposure and polymerization the graphene

[0120] To investigate the influence of both polymerization and UV exposure on the overall graphene quality (in terms of defect types / sites) we conducted Raman analysis of the graphene layer (both type 1 and 2) after varying SI PGP times (0 hr, 4 hr, and 24 hr) and after 24hr of only UV light exposure (type 1 graphene). The measured Raman spectra for both types are represented in Fig. 9. The Raman spectra showed no significant change in either ID / IG ratios or ID / ID' ratios. No significant deviations in the intensity ratios indicate that no additional defects are introduced during the process, and further, it alleviates the presence of physisorbed polymers on the graphene surface. This observation is consistent with Jordan and co-workers’ reported work.

[0121] Additional histogram analysis of large-scale area, see Fig. 12. Additional pore surface profile analysis, see Fig. 13.

Claims

CLAIMS1. Method for making a porous graphene layer of a thickness of less than 100 nm with pores having an average characteristic width as defined in the specification in the range of 1 - 1000 nm, comprising the following steps: providing a catalytically active substrate to catalyse the graphene formation under chemical vapour deposition conditions, said catalytically active substrate on its surface being provided with a plurality of catalytically inactive domains having a nanostructure essentially corresponding to the shape of the pores in the resultant porous graphene layer; chemical vapour deposition using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the porous graphene layer being formed in situ due to the presence of the catalytically inactive domains; wherein subsequent to the chemical vapor deposition, the porous graphene layer is functionalized using self-initiated photo-grafting polymerization.

2. Method according to claim 1 , wherein the self-initiated photo-grafting polymerization leads to functionalization of the porous graphene layer at the edges of said pores.

3. Method according to any of the preceding claims, wherein the self-initiated photo-grafting polymerization is carried out in the gas or in the liquid phase, before or after the porous graphene layer has been detached from the catalytically active substrate.

4. Method according to any of the preceding claims, wherein the self-initiated photo-grafting polymerization is carried out in the liquid phase, wherein the graphene layer is immersed in or coated or sprayed with at least one monomer for the self-initiated photografting polymerization, preferably under an inert gas atmosphere, and self-initiated photografting polymerization is initiated using ultraviolet irradiation, preferably using irradiation with a wavelength in the range of 250-500 nm, preferably in the range of 300-400 nm, and / or with a total power of 0.1-5 mW / cm2, preferably in the range of 0.5-2 mW / cm2.

5. Method according to any of the preceding claims, wherein the self-initiated photo-grafting polymerization is carried out using at least one monomer selected from the group consisting of: styrene, styrene derivatives, acrylate and derivatives thereof,methacrylate and derivatives thereof wherein preferably styrene is used.

6. Method according to any of the preceding claims, wherein the self-initiated photo-grafting polymerization is carried out at a temperature in the range 10-40°C, preferably in the range of 15-30°C, preferably for a time span in the range of 0.5 - 30h, preferably in the range of 2 - 24h.

7. Method according to any of the preceding claims, wherein the self-initiated photo-grafting polymerization is carried out with at least one monomer providing reactivity for further functionalization, and wherein subsequent to the self-initiated photo-grafting polymerization further functionalization is carried out using that reactivity.

8. Method according to any of the preceding claims, wherein the catalytically active substrate is a copper-nickel alloy substrate with a copper content in the range of 98 to less than 99.96 % by weight and a nickel content in the range of more than 0.04 to 2% by weight, the copper and nickel contents complementing to 100% by weight of the catalytically active substrate, wherein preferably the catalytically active substrate has a nickel content in the range of 0.06 - 1% by weight or 0.08 - 0.8% by weight complemented to 100% by weight by the copper content, and / or wherein the catalytically active substrate is prepared by applying, preferably using electrochemical plating, e-beam evaporation, PVD or sputtering, a nickel film of a thickness in the range of 10 nm to 2.2 pm preferably in the range of 25-300 or 20-500 nm, preferably in the range of 50-300 nm on a pure copper foil, preferably having a thickness in the range of 0.01-0.10mm, preferably in the range of 0.02-0.04 mm, in particular having a purity of more than 99.5%, and by annealing, preferably at a temperature in the range of 800-1200°C, preferably in the range of 900-1100°C, in particular during a time span of 10 minutes-120minutes, preferably during a time span in the range of 30 minutes-90 minutes.

9. Method according to any of the preceding claims, wherein the porous graphene layer has a thickness in the range of less than 50 nm, preferably in the range of 1-20 nm, in particular in the range of 5-15 nm or 7-12 nm, and / or wherein the porous graphene layer has an areal porosity in the range of at least 10%, preferably at least 15%, more preferably of at least 20% or at least 25%, or at least 30% or at least 40%.

10. Method according to any of the preceding claims, wherein the catalytically active substrate is provided on its surface with a plurality of catalytically inactive domains by applying, preferably using sputtering, e-beam evaporation or PVD, an essentially contiguous tungsten layer, preferably with a thickness in the range of more than 1 nm, preferably more than 3 nm, more preferably more than 5 nm, or in the range of 1-10 nm, preferably in the range of 5-10 nm, and by subsequently annealing at a pressure below normal pressure, preferably of less than 100 mTorr, in particular under a reducing atmosphere, preferably in the presence of an inert gas such as argon or nitrogen gas, combined with hydrogen gas, to convert the tungsten film into a plurality of catalytically inactive domains (2), wherein preferably the annealing takes place at a temperature in the range of 700-1100°C, more preferably in the range of 750-950°C or 800-900°C, typically during a time span in the range of 10-180 minutes, preferably in the range of 50-100 minutes, wherein preferably the catalytically inactive domains have an average characteristic width in the range of 1-1000 nm, preferably in the range of 10 - 100 nm, more preferably in the range of 10-50 nm, or having an average characteristic width in the range between 5-900 nm, preferably in the range of 10-200 nm, more preferably in the range of 10-100 nm.

11. Method according to any of the preceding claims, wherein chemical vapour deposition using a carbon source in the gas phase and formation of the porous graphene layer on the surface of the catalytically active substrate, the pores in the graphene layer in situ being formed due to the presence of the catalytically inactive domains using methane gas as carbon source, preferably in the copresence of argon and hydrogen gas under reduced pressure, preferably below 50 Torr, preferably below 5 Torr, during a time span of preferably in the range of 10-120 minutes, preferably below 60 minutes, more preferably below 50 minutes, most preferably below 35 minutes, wherein this graphene layer deposition process preferably takes place during a time span allowing for the generation of a graphene layer of average thickness of more than 5 nm, preferably in the range of 8-12 nm.

12. Method according to any of the preceding claims, wherein the porous graphene layer is removed from the catalytic substrate, and applied to a porous, preferably nonwoven or fabric supporting substrate, wherein the self-initiated photo-grafting polymerization is carried out before or after the porous graphene layer has been detached from the catalytically active substrate and before or after being applied to said porous,preferably nonwoven or fabric supporting substrate, preferably in that for removal of the graphene layer first a carrier layer is applied to the graphene layer on the surface opposite to the catalytic substrate and the sandwich of this carrier layer is removed from the catalytic substrate wherein preferably prior to removal of the graphene layer, the layered structure of the catalytic substrate with the catalytically inactive domains and the graphene layer are subjected to a pre-leaching process weakening or removing the bond between the graphene layer and the catalytic substrate and / or wherein the catalytically inactive domains, wherein preferably this pre-leaching step includes the formation of an oxide layer at least partially, preferably essentially completely between the graphene layer and the catalytic substrate and the removal of the catalytically inactive domains, and / or wherein preferably the pre-leaching step is subjected to a basic or acidic environment, preferably in water, more preferably at a pH of less than 6 or more than 7, preferably more than 10, more preferably at a pH of more than 12, wherein most preferably an aqueous solution of 0.01-0.5 M NaOH is used, preferably for a time span in the range of 10-60 minutes at a temperature in the range of 40-60°C, optionally followed by rinsing with water and drying, or wherein subsequent to the chemical vapor deposition of the porous graphene layerthe porous graphene layer is removed from the substrate, in that the exposed porous graphene layer on the surface of the catalytically active substrate is subjected to an aqueous solution containing a dissolved oxidant, directly or indirectly followed by treatment of the exposed porous graphene layer on the surface of the catalytically active substrate with an aqueous persulfate solution, directly or indirectly followed by lamination and / or generation of a carrier layer onto the exposed porous graphene layer from the side opposite to the catalytically active substrate and mechanical separation of said carrier layer with the exposed porous graphene layer (5) from said catalytically active substrate. or wherein the graphene layer is removed, preferably after a pre-leaching step, using electrochemical methods, by immersing the layered structure of the catalytic substrate with the catalytically inactive domains and the graphene layer in an electrolyte and applying electrochemical potential to the substrate relative to a counterelectrode in the same electrolyte.

13. Graphene layer, preferably on at least one supporting substrate, obtainable or obtained using a method according to any of the preceding claims,wherein it preferably has a thickness in the range of less than 50 nm, preferably in the range of 1-20 nm, in particular in the range of 5-15 nm or 7-12 nm and / or wherein it has an areal porosity in the range of at least 10%, preferably at least 15%, more preferably of at least 20% or at least 25% or at least 30% or at least 40%.

14. Piece of textile or apparel having at least one graphene layer made using a method according to any of the preceding claims 1-12 and / or according to claim 13, preferably in the form of a filtering or separation device or a water resistant and / or water repellent and / or breathable apparel.

15. Use of a graphene layer according to any of the preceding claims as a semipermeable membrane, in particular for filtering, separation or textile applications in the field of apparel, or in the technical field, in particular for providing water barrier in electronics including batteries and / or mobile devices.

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