Adjustable graphene-based membranes and methods of making the same

Abstract

A graphene-based film is provided, wherein the mechanical properties, thermal conductivity, electrical conductivity, and / or three-dimensional curvature of the film are adjusted according to the desired application of the film. Methods for accelerating the vacuum-assisted self-assembly (VASA) process for graphene-based films and methods for accelerating the process of removing liquid from graphene-based dispersions are also provided. The methods can include two reduction steps to minimize filtration time and substantially restore the electrical and thermal properties of the graphene-based film at low temperatures.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 489,335, filed April 24, 2017, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The following typically refers to graphene-based films whose physical properties can be adjusted during the manufacturing process. Background Technology

[0004] Graphene is a hydrophobic material in its pristine state. Therefore, modification is necessary to obtain stable, homogeneous dispersions of individual graphene sheets. Such dispersions are desirable for the controlled processing of graphene-based materials. For example, this can be achieved by coating a substrate with graphene material or incorporating graphene sheets into a polymer matrix. Among these modification methods, the oxidation of graphene sheets is a commonly used technique known in the art. This oxidation process occurs naturally during the exfoliation of graphene sheets using widely adopted methods (e.g., the method described by Hummers et al. in J. Am. Chem. Soc. 1958, 80, 1339 and its modifications).

[0005] The resulting graphene oxide comprises individual graphene sheets grafted with oxygen-containing groups (e.g., hydroxyl, carboxylic acids, and epoxides). With the introduction of hydrophilic groups, the sheets can be readily dispersed in water after gentle sonication. Vacuum filtration of such dispersions through a filter medium, as described by Dikin et al. in Nature 2007, 448, 7152, yields graphene oxide membranes with an extremely orderly layered structure. However, it has been found that the accumulation of graphene sheets during filtration can impede water flow through the filter medium. This results in dehydration times of up to several days for a 50 μm thick membrane. An example of such undesirable dehydration times can be found in U.S. Patent No. 8,709,213 to Compton et al.

[0006] It was also found that, due to various manufacturing factors, the above method produces films with inconsistent mechanical properties. Furthermore, films produced by this method do not possess the desired electrical or thermal properties of pristine graphene.

[0007] To restore these properties, graphene oxide materials can be chemically reduced via electromagnetic or thermal reduction processes. Thermal and electromagnetic methods typically lead to rapid degassing of the oxygen grafted onto the graphene sheet. Degassing causes delamination of the graphene-based film, ultimately resulting in a sharp decline in its mechanical properties. Furthermore, very high temperatures are required to impart the desired electrical conductivity to the film.

[0008] Therefore, one of the following objectives is to address at least one of the aforementioned shortcomings or defects. Summary of the Invention

[0009] It has been recognized that there is a need for a graphene-based film with tunable physical properties and a method for manufacturing such a graphene-based film. In one exemplary aspect, a graphene-based film is provided in which the mechanical properties, thermal conductivity, electrical conductivity, and / or three-dimensional curvature of the film are tuned according to the desired application of the film.

[0010] On the other hand, methods are provided for accelerating the vacuum-assisted self-assembly (VASA) process for graphene-based films and for accelerating the process of removing liquid from graphene-based dispersions.

[0011] On the other hand, the method involves two reduction steps to minimize filtration time and substantially restore the electrical and thermal properties of the graphene-based film at low temperatures.

[0012] It will be understood that the aspects and features described in the Summary of the Invention section are non-limiting, and additional features and embodiments are provided in the specification and drawings. Attached Figure Description

[0013] The embodiments will now be described by way of example only with reference to the accompanying drawings, wherein:

[0014] Figure 1A-1D A series of cross-sectional side views of the vacuum filtration process used to manufacture cellulose / graphene oxide (GO) composite membranes;

[0015] Figure 2 A cross-sectional side view of a pressure-assisted vacuum filtration process used to manufacture cellulose / GO composite membranes;

[0016] Figures 3A-3C A series of cross-sectional side views of the vacuum filtration process used to manufacture GO membranes;

[0017] Figures 4A-4C A series of cross-sectional side views of the vacuum filtration process used to manufacture gelled GO membranes;

[0018] Figure 5A Electron micrograph of a partially reduced GO film;

[0019] Figure 5B Electron micrograph of a partially reduced gelled GO membrane;

[0020] Figure 5C Electron micrographs of partially reduced cellulose / GO composite membranes; and

[0021] Figure 6 The analysis results represent the density and Young's modulus of graphene-based films with various compositions. Detailed Implementation

[0022] It should be understood that, for simplicity and clarity, reference numerals may be repeated in the drawings to indicate corresponding or similar elements where deemed appropriate. Furthermore, numerous specific details are set forth to provide a thorough understanding of the exemplary embodiments described herein. However, those skilled in the art will understand that the exemplary embodiments described herein can be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the exemplary embodiments described herein. Moreover, these descriptions should not be construed as limiting the scope of the exemplary embodiments described herein.

[0023] The graphene-based membranes described herein are composed of at least one of graphene oxide (GO) or reduced graphene oxide (rGO). In some embodiments, the membrane consists of GO or rGO and up to 60 wt% filler. The filler can consist of any number of materials, including but not limited to: natural polymers, synthetic polymers, inorganic fibers and carbon nanotubes, and any combination thereof. The filler should consist substantially of particles with an aspect ratio greater than 10. Non-limiting examples of such fillers include pulp (cellulose fibers), glass fibers, polyester fibers, and pyrolytic carbon nanofibers.

[0024] In some embodiments, the graphene-based film contains a chemical crosslinking agent. The chemical crosslinking agent provides chemical bonding between the individual GO sheets. Non-limiting examples of chemical crosslinking agents that can be incorporated into the film include sodium tetraborate and polymeric crosslinking agents (e.g., polycarbodiimide).

[0025] In some embodiments, the graphene-based film is physically crosslinked. The GO sheets can be chemically crosslinked or crosslinked via a physical crosslinking agent. Direct crosslinking can be achieved through physical bonds (e.g., hydroxyl or epoxy groups) between agents chemically bonded to adjacent GO layers and GO sheets within the same layer. Physical crosslinking agents are intercalated between GO layers, forming physical bonds with at least one GO sheet at a time. Non-limiting examples of physical crosslinking agents that can be introduced into the film include: small polar molecules, such as water, ethylene glycol, melamine, and dopamine; polymers, such as polyvinyl alcohol (PVA), polyethylene glycol (PEG), hydroxypropyl cellulose (HPMC), and carboxymethyl cellulose (CMC); and cationic molecules, such as Al. +3 Ca +2 and Mg +2 .

[0026] In some embodiments, the graphene-based membrane may further comprise at least one filter material layer. The filter material layer may consist of any number of materials, including but not limited to natural or synthetic polymers and aluminum. In some embodiments, the filter layer extends beyond the edge of the graphene-based material.

[0027] Graphene-based films can exhibit a wide range of physical properties that can be tunable through the manufacturing process. In some embodiments, graphene-based films exhibit relatively low electrical conductivity—less than 1 S / m. In other embodiments, graphene-based films exhibit relatively high electrical conductivity—greater than 4000 S / m. In some embodiments, the thermal conductivity is greater than 10 W / mK in a direction tangential to the plane formed by the film. A method for producing films capable of exhibiting a wide range of physical properties is disclosed below. Therefore, the upper or lower limit of the conductivity of the resulting film is not important in this invention. The technical significance of this invention lies in the ability to control or tune the film during the manufacturing process to obtain desired properties.

[0028] Furthermore, adding certain fillers can be used to reduce the density of the membrane. For example, a graphene-based membrane composed of GO and 40 wt% cellulose fibers can have a density of less than 1 g / cm³. 3 .

[0029] Graphene-based films can be formed to fit various shapes. Graphene-based films can be curved or substantially flat. The shape of the film is controlled during manufacturing to suit the intended application. Films can be made in various thicknesses. In some embodiments, multiple layers of films are stacked and subsequently bonded together to form a single film with a total thickness greater than the individual layers comprising that single film.

[0030] A low-temperature pathway for the efficient production of the aforementioned tunable graphene-based films is described. The graphene-based films are synthesized starting from at least one GO dispersion. The at least one GO dispersion consists of at least GO and a solvent. It should be understood that those skilled in the art will be able to select suitable solvents, and a variety of solvents can be used. Non-limiting examples of suitable solvents include: water, acetone, methanol, ethanol, 2-propanol, ethylene glycol, tetrahydrofuran, N,N-dimethylformaldehyde, chloroform, toluene, chlorobenzene, acetylacetone, diethyl ether, and other aqueous or non-aqueous solvents, and any combination thereof. The at least one GO dispersion should consist of 0.1 mg / mL to 50 mg / mL of GO.

[0031] In some embodiments, a weak base may be added to at least one GO dispersion to adjust the pH of the dispersion. GO is known to aggregate in a variety of solvents at low pH values. Adding a weak base increases the pH of the dispersion and reduces the aggregation rate. An appropriate amount of weak base may be added to adjust the pH of at least one GO dispersion to the range of 8 to 10, preferably 8 to 9, and most preferably 8.3 to 8.5.

[0032] To obtain a uniform dispersion, at least one GO dispersion is subjected to exfoliation for at least 5 minutes. In some embodiments, GO exfoliation is performed by immersing a vial containing the dispersion in an ultrasonic bath. In another embodiment, exfoliation can be performed by directly inserting an ultrasonic probe into the dispersion. These embodiments are merely two examples of how exfoliation can be performed and are not intended to limit the scope of the invention. Those skilled in the art can use any known exfoliation technique to disperse GO in at least one GO dispersion.

[0033] In some embodiments, at least one GO dispersion is partially reduced prior to film formation. Partial reduction is performed by briefly exposing the GO dispersion to a reducing agent at a high temperature. In a preferred embodiment, at least one GO dispersion is partially reduced by adding ascorbic acid, such that the dispersion contains 8 mM of ascorbic acid. The at least one dispersion is stirred for at least 5 minutes, then brought to a reaction temperature of 90°C, whereby the at least one dispersion is stirred again for an additional 5 minutes, and then cooled to room temperature.

[0034] The reducing agent used in the above process can be any amount of chemicals that can reduce graphene oxide. Examples of such reducing agents include, but are not limited to: acids containing halogens, such as HI, HBr, and HCl, and mixtures thereof; and organic acids, such as acetic acid, carbonic acid, formic acid, benzoic acid, and ascorbic acid.

[0035] The initial dispersion containing the reducing agent is stirred for more than 5 minutes to ensure thorough mixing. The reaction between graphene oxide and the reducing agent can be carried out at a temperature of 10°C or higher. Preferably, the reaction can be carried out at a temperature of 10°C to 120°C. It is worth noting that the reduction reaction of graphene oxide occurs efficiently at high temperatures. Therefore, the upper limit of the reaction temperature is not important in this invention. What is more important is the lower limit of the reaction temperature. However, lower reaction temperatures result in slower reaction rates.

[0036] In some embodiments, the at least one GO dispersion is viscous or gelled prior to membrane formation. It has been shown that gelling the GO dispersion reduces the dehydration time required during membrane formation. The GO in the gelled dispersion has a more cross-linked structure compared to the non-viscous dispersion. Thus, the GO forms a more porous and wrinkled membrane upon deposition, providing more channels for solvent flow. The at least one GO dispersion is gelled by exposing the dispersion to a high temperature for a period of time. Those skilled in the art can optimize the temperature and exposure time. For example, in one embodiment, a 5 mg / mL GO dispersion (in water) is gelled by heating the dispersion in an oven at 80°C for 72 hours.

[0037] In some embodiments, a filler is added to at least one GO dispersion. In some embodiments, the filler is another dispersion. In this embodiment, the filler previously described may be dispersed in a suitable solvent to form a filler dispersion. The filler, dispersed in a solvent or otherwise, is added to at least one GO dispersion so that the resulting film consists of less than 60 wt% filler. In other embodiments, at least one filler pre-coating is formed, and then the at least one GO dispersion is added on top to form a graphene-based film.

[0038] Graphene-based membranes are formed using a vacuum-assisted self-assembly (VASA) process. In one embodiment, to produce a graphene-based membrane, a GO dispersion is continuously vacuum-assisted filtered through a filter, thereby assembling GO sheets onto the filter by directing the fluid flow of the GO dispersion through the filter. In another embodiment, a mixture of GO and packing material is continuously vacuum-assisted filtered through a filter, thereby assembling GO sheets and packing material onto the filter by directing the fluid flow of the mixture through the filter.

[0039] In another embodiment, the packing material is first subjected to continuous vacuum-assisted filtration through a filter, thereby assembling the packing material into a pre-coating on the filter by directing the fluid flow of the packing material dispersion through the filter. The GO dispersion is then added on top of the pre-coating, and continuous vacuum-assisted filtration is performed through the pre-coating and the filter, thereby dispersing the GO flakes throughout the pre-coating and forming a film together on the filter by the direct flow of the fluid of the GO dispersion through the filter.

[0040] Fillers are used for various purposes in the manufacture of graphene-based membranes and to improve their tunability. On one hand, high aspect ratio filler particles promote solvent flow through the membrane during membrane formation. When solvent flows through a filter, GO forms ordered stacks of sheets above the filter; these ordered stacks inhibit solvent outflow from the dispersion and lead to prolonged drying time. The addition of high aspect ratio filler particles provides a path for the solvent to flow through the membrane during formation. This can significantly reduce drying time and improve the efficiency of the manufacturing process.

[0041] On the other hand, the addition of fillers can change the mechanical properties of the resulting graphene-based film.

[0042] Now refer to Figure 1A-1DAn exemplary GO / cellulose filtration process is illustrated. The exemplary filtration apparatus 100 comprises a filter 108, a funnel 110, a flask 112, a resilient stopper 114, and an outlet 116. For simplicity, the funnel can be divided into an upper funnel body 110a, a lower funnel body 110b, and a nozzle 110c. The stopper 114 is inserted into the opening of the flask 112. The nozzle 110c is inserted into a hole in the center of the stopper 114, such that the nozzle 110c extends into the flask 112. When a vacuum is applied, the stopper 114 seals the area between the nozzle 110c and the sidewall at the opening of the flask 112. The filter 108 is placed in the funnel 110, defining the space above the filter 108 in the upper funnel body 110a and the space below the filter 108 in the lower funnel body 110b. The outlet 116 is connected to a vacuum, which is provided with reduced pressure in the flask 112 via a hose (not shown).

[0043] Although filter 108 is shown in a generally conical geometry, this is merely one of many possible shapes. Those skilled in the art will understand that the shape of filter 108 can be chosen for the intended application of the resulting graphene-based membrane. It should also be understood that the filtration device 100 shown in the figures is only one exemplary embodiment of such a device, and any number of vacuum filtration devices known in the art can be used.

[0044] Now refer to the specific details. Figure 1A A cellulose dispersion 102, consisting of cellulose fibers 104 and solvent 106, is added to the upper funnel body 110a. When a vacuum is applied, the interior of the flask 112 is maintained at a pressure lower than the atmospheric pressure present above the dispersion 102 in the funnel 110. This pressure gradient causes the solvent 106 to flow through the filter 108, where it exits the funnel 110 and is trapped in the flask 112 (e.g., ...). Figure 1B (As shown).

[0045] Figure 1B This illustrates how, after solvent 106 is discharged from funnel 110 and enters flask 112, a pre-coating 118 of cellulose fibers 104 is formed on top of filter 108. Then, in... Figure 1C In this process, a GO dispersion 122 of GO flakes 124 and solvent 126 is added to the upper funnel body 110a. When a vacuum is applied, the interior of the flask 112 will be maintained at a pressure lower than the atmospheric pressure present above the GO dispersion 122 in the funnel 110. The pressure gradient between the funnel 110 and the flask 112 will cause the solvent 126 to flow through the pre-coating 118 and the filter 108, where the solvent 126 flows through the pre-coating 118 and the filter 108 and is trapped in the flask 112 (e.g., as shown in the image). Figure 1D (As shown).

[0046] Figure 1DThe diagram shows that after solvent 126 is discharged from funnel 110 and enters flask 112, a GO / cellulose membrane 130 is formed, consisting of cellulose fibers 104 and GO sheets 124. In this exemplary embodiment, solvent 106 from cellulose dispersion 102 is not removed from flask 112; therefore, solvent 126 from GO dispersion 122 mixes with cellulose solvent 106 upon entering flask 112, forming solvent mixture 128. After the filtration process is completed, solvent mixture 128 can be disposed of using safety measures known in the art.

[0047] In some embodiments, a positive pressure may be applied to the chamber above the formed membrane. Now refer to Figure 2 An exemplary pressure-assisted filtration process is illustrated. In this exemplary embodiment, compressed air is pumped via hose 152 in the direction of arrow 150. The compressed air flows through hose 152 into upper funnel body 110a. Cap 154 ​​seals funnel 110, causing the pressure in upper funnel body 110a above GO dispersion 122 to increase above atmospheric pressure. The pressure inside the funnel can be monitored using a standard pressure gauge 156. It has been found that applying this pressure improves the conformity of the resulting membrane to the filter shape.

[0048] In other embodiments, the flow rate of fluid exiting the formed membrane is increased by applying at least one of the following: ultrasound, heat, pulsed vacuum, and pulsed pressure.

[0049] In some embodiments, a vacuum is applied parallel to, rather than perpendicular to, the stack of sheets. In this embodiment, a parallel vacuum is applied when the membrane has sufficiently formed but is still wet. By applying a vacuum parallel to the stack of sheets, fluid will flow more easily from the membrane because the fluid will face less resistance from the GO sheets.

[0050] In some embodiments, an additional filler layer is added on top of the graphene substrate. The additional filler is continuously vacuum-assisted filtered through the formed membrane, thereby assembling the filler into layers on the formed membrane by directing the fluid of the filler dispersion through the lower membrane layer.

[0051] For embodiments without a pre-coating, the average pore size of the filter is less than 1 μm. Those skilled in the art will be able to select a suitable membrane filter; however, for embodiments without a pre-coating, ceramic frit filters known in the art are preferred. For embodiments with a pre-coating, larger pore sizes are permissible. For example, for embodiments with a cellulose fiber pre-coating, the average pore size of the filter is less than 5 μm. It should be understood that those skilled in the art will be able to select a suitable filter for the intended application. Those skilled in the art will know the size of the packing particles and select a filter that will restrict the passage of those particles.

[0052] In some embodiments, the filter becomes a component of the membrane after the vacuum filtration step. For example, GO sheets can be embedded in a cellulose pre-coating, and the final membrane is a combination of cellulose and GO. In another embodiment, a thin Al filter is used. After filtration, the thin Al filter is impregnated with GO sheets, and together they form a graphene-based membrane.

[0053] In other embodiments, an adhesive can be used to combine multiple films to form a generally single film. For example, a thin layer of Al can be adhered to a graphene-based film using an adhesive.

[0054] In some embodiments, the graphene-based membrane should then be transferred from the vacuum filtration apparatus to a hot press. The hot press is used to at least partially reduce the GO sheets and further dry the graphene-based membrane after filtration. The press is configured such that it presses the graphene-based membrane into the desired shape.

[0055] A press for pressing and heating graphene-based films includes a lower die and an upper die. The upper and lower dies are configured to conform to the desired shape of the graphene-based film. In one embodiment, the lower die has a protrusion projecting from its forming surface, and the upper die has a corresponding recess. In another embodiment, the upper die has a protrusion projecting from its forming surface, and the lower die has a corresponding recess. When it is desired that the graphene-based film be substantially flat, both the upper and lower dies form substantially flat plates. The film is placed on the lower die, and the two dies are brought into contact, applying pressure to both surfaces of the graphene-based film.

[0056] At a temperature greater than 50°C, a pressure greater than 5 MPa, most preferably greater than 10 MPa, is applied to the graphene-based film. It is noteworthy that the reduction reaction of graphene oxide occurs effectively at high temperatures. Therefore, the upper limit of the reaction temperature is not important in this invention. As mentioned above, the lower limit of the temperature is more important. The production process of this invention can be carried out at a relatively low temperature of 50°C. Therefore, this invention is advantageous for the mass production of reduced GO composite films or partially reduced GO composite films at low temperatures. For graphene-based films where pristine graphene properties are desired, temperatures above 150°C are preferred. For graphene-based films where pristine graphene properties are desired, temperatures above 200°C are more preferred.

[0057] Pressure was applied to reduce the effects of degassing during thermal reduction. It has been found that increasing pressure helps maintain mechanical properties, such as the Young's modulus of the resulting film. The applied pressure suppressed the volumetric expansion of the stacked GO sheets during heating.

[0058] In some embodiments, multiple graphene-based films can be combined to form a substantially single film. For example, graphene-based films prepared by the methods described above can be stacked and then pressed using a vapor press or hot press to form a substantially single film.

[0059] The following embodiments are provided to further illustrate the above principles, but are not limited thereto.

[0060] Example 1

[0061] Manufacturing of rGO membranes

[0062] The pH of the aqueous dispersion of GO tablets was adjusted to 8.4 by adding 20 μL of ammonia solution (20 wt%–30 wt%). A stable aqueous dispersion was prepared by exfoliating GO (1 mg / mL) through sonication at room temperature (sonication in a 483 W ultrasonic bath for 5 minutes). Partial reduction of the GO tablet dispersion was achieved by stirring continuously for 5 minutes at 90 °C with 8 mM ascorbic acid as a reducing agent. Ascorbic acid was added to the dispersion before stirring began, followed by stirring for 5 minutes before heating. Partial reduction of the graphene oxide tablets occurred in the solution, and the reaction was stopped by cooling the dispersion to room temperature. The cooled dispersion was immediately poured into a vacuum filter for dehydration.

[0063] The dispersion of partially reduced GO sheets was filtered through a ceramic frit filter with an average pore size of 500 nm, the surface of which mimicked the shape of the desired membrane. A vacuum was applied for 2–8 hours, or until no water remained. The formed filter was then transferred to a hot press, where the dehydrated graphene-based material was compressed using a mold shaped within the negative geometry of the filter medium. A pressure of 10 MPa was applied to the material at 200 °C for 15 minutes, while residual water evaporated, and the graphene oxide sheets were reduced.

[0064] The conductivity of the GO film obtained before hot pressing was 0.005 S / m. After a pressure-assisted thermal reduction process, the conductivity of the resulting rGO film was 4600 S / m – close to that of pristine graphene.

[0065] This embodiment illustrates how the above-described thermal reduction process can be used to adjust the conductivity of the resulting graphene-based film.

[0066] Example 2

[0067] Manufacturing of cellulose / rGO composite membranes with gelled GO

[0068] A dispersion of 5 mL of viscous / gelled GO tablets (5 mg / mL) was prepared by heating an aqueous GO dispersion in an oven at 80 °C for 3 days.

[0069] A second dispersion was prepared, comprising 8.33 mL (25 wt% cellulose composite) of 0.1 wt% cork kraft pulp.

[0070] In the first filtration step, kraft pulp is poured into the filtration apparatus, and a vacuum is applied to the filtrate side. The fully dehydrated pulp produces a pre-coating of tubular particles with a high aspect ratio. The filter medium is a metal mesh with a nominal porosity of 5 μm, the surface of which mimics the shape of the desired part.

[0071] In the second step, the gelled graphene oxide dispersion is added to the filtration device while maintaining a vacuum on the filtrate side. Compressed air is then introduced to pressurize the feed side, forcing the solvent through the filter medium. A vacuum is maintained until no water remains.

[0072] The formed filter media is transferred to a hot press, where the dehydrated graphene material is compressed using a mold shaped within the negative geometry of the filter media. A pressure of 10 MPa is applied to the material at 100°C for 15 minutes, while residual water evaporates and the graphene oxide sheets are partially reduced. In this embodiment, the electrical conductivity of the finished product is 0.6 S / m.

[0073] Example 3

[0074] Manufacturing of carbon nanofiber / rGO composite membranes

[0075] Divide 100 mL of 0.5 wt% GO solution into two vials. Add 8.3 mL of 0.1 M sodium tetraborate (anhydrous) solution to the first vial and stir the resulting dispersion for 5 minutes.

[0076] Partial reduction of the GO tablet dispersion in the second vial was achieved by stirring continuously for 5 minutes at 90°C with 70 mg ascorbic acid as a reducing agent. Ascorbic acid was added to the dispersion before stirring began, followed by stirring for 5 minutes before heating. Partial reduction of the graphene oxide tablets occurred in solution, and the reaction was stopped by cooling the dispersion to room temperature.

[0077] The two dispersions were then combined with 20 mL of a dispersion containing 1 wt% pyrolytic carbon nanofibers. The resulting dispersion was poured into the pressure chamber of a filtration apparatus, wherein the pressure chamber and the vacuum chamber were separated by a porous frit having a functional shape. A relative pressure of 120 Psi was applied on the feed side and a partial vacuum of 0.5 Atm was applied on the filtrate side to dehydrate the mixture.

[0078] After complete dehydration, the solids in the mixture deposit on the surface of the molten ingot, thus mimicking its shape. The pressure gradient is then removed, and the molten ingot is transferred to a hydraulic press, where a female mold heated to 200°C and a pressure of 20 MPa are applied to the dehydrated solids. A 200 μm thick, 25 cm long sample is obtained. 2 The composite membrane contains graphene sheets intercalated with carbon nanofibers.

[0079] Now refer to Figure 6 The graph shows the analytical results of density and Young's modulus of graphene-based films with various compositions. The x-axis of the graph shows the various film compositions. Figure 6 All graphene-based films shown in the figure underwent thermal reduction treatment at 90°C and 10 MPa. Figure 6 This indicates that Young's modulus increases with membrane density. Furthermore, the addition of filler (cellulose in this example) leads to a decrease in density, thereby reducing Young's modulus. Using gelled GO further reduces membrane density, thus decreasing Young's modulus.

[0080] Figure 6 It provides some examples of how the physical properties of graphene films can be controlled to suit specific applications.

[0081] The present invention has been described in detail above with reference to certain embodiments, but those skilled in the art will understand that the present invention is not limited to these embodiments and changes, modifications, etc. can be made without departing from the scope of the appended claims.

Claims

1. A method for forming a graphene-based film, the method comprising: a) Obtaining a dispersion comprising graphene material dispersed in a solvent, the graphene material having at least one of graphene oxide and reduced graphene oxide; b) Filtering the dispersion through a funnel-supported filter membrane having a three-dimensional tortuous shape, the filtration comprising the solvent flowing through the filter membrane to form the graphene-based membrane having a three-dimensional tortuous shape mimicking the three-dimensional tortuous shape of the filter membrane. The filtration of the dispersion is performed by pressure-assisted vacuum filtration, which includes... Compressed air is pumped to apply a positive pressure, greater than atmospheric pressure, to the feed side of the filter membrane. A vacuum is applied to the filtrate side of the filter membrane, the vacuum being lower than atmospheric pressure.

2. A method for forming a graphene-based film, the method comprising: a) Obtaining a dispersion comprising graphene material dispersed in a solvent, the graphene material having at least one of graphene oxide and reduced graphene oxide; b) Forming a pre-coating of the filler by filtering the filler dispersion through a filter membrane; as well as c) Filtering the dispersion through the filter membrane, the filtration comprising passing a solvent through the filter membrane to form the graphene-based membrane on the filter membrane, wherein the filter membrane is supported by a funnel having a three-dimensional tortuous shape, the filtration comprising passing the solvent through the filter membrane to form the graphene-based membrane having a three-dimensional tortuous shape simulating the three-dimensional tortuous shape of the filter membrane. The filtration of the dispersion is performed by pressure-assisted vacuum filtration, which includes... Compressed air is pumped to apply a positive pressure, greater than atmospheric pressure, to the feed side of the filter membrane. A vacuum is applied to the filtrate side of the filter membrane, the vacuum being lower than atmospheric pressure.

3. A method for forming a graphene-based film, the method comprising: a) Obtaining a dispersion comprising graphene material dispersed in a solvent, the graphene material having at least one of graphene oxide and reduced graphene oxide; b) Filtering high aspect ratio filler particles dispersed in the solvent through a filter membrane; as well as c) Filtering the dispersion through the filter membrane, the filtration comprising passing a solvent through the filter membrane to form the graphene-based membrane on the filter membrane, wherein the filter membrane is supported by a funnel having a three-dimensional tortuous shape, the filtration comprising passing the solvent through the filter membrane to form the graphene-based membrane having a three-dimensional tortuous shape simulating the three-dimensional tortuous shape of the filter membrane. The filtration of the dispersion is performed by pressure-assisted vacuum filtration, which includes... Compressed air is pumped to apply a positive pressure, greater than atmospheric pressure, to the feed side of the filter membrane. A vacuum is applied to the filtrate side of the filter membrane, the vacuum being lower than atmospheric pressure.

4. A method for forming a graphene-based film, the method comprising: a) Obtaining a dispersion comprising graphene material dispersed in a solvent, the graphene material having at least one of graphene oxide and reduced graphene oxide; b) Gel the dispersion; as well as c) Filtering the dispersion through a filter membrane, the filtration comprising passing a solvent through the filter membrane to form the graphene-based membrane on the filter membrane, wherein the filter membrane is supported by a funnel having a three-dimensional tortuous shape, the filtration comprising passing the solvent through the filter membrane to form the graphene-based membrane having a three-dimensional tortuous shape simulating the three-dimensional tortuous shape of the filter membrane. The filtration of the dispersion is performed by pressure-assisted vacuum filtration, which includes... Compressed air is pumped to apply a positive pressure, greater than atmospheric pressure, to the feed side of the filter membrane. A vacuum is applied to the filtrate side of the filter membrane, the vacuum being lower than atmospheric pressure.

5. A method for forming a graphene-based film, the method comprising: a) Obtaining a dispersion comprising graphene material dispersed in a solvent, the graphene material having at least one of graphene oxide and reduced graphene oxide; b) Filtering the dispersion through a filter membrane, the filtration comprising passing a solvent through the filter membrane to form the graphene-based membrane on the filter membrane, wherein the filter membrane is supported by a funnel having a three-dimensional tortuous shape, the filtration comprising passing the solvent through the filter membrane to form the graphene-based membrane having a three-dimensional tortuous shape simulating the three-dimensional tortuous shape of the filter membrane. The filtration of the dispersion is performed by pressure-assisted vacuum filtration, which includes... Compressed air is pumped to apply a positive pressure, greater than atmospheric pressure, to the feed side of the filter membrane. A vacuum is applied to the filtrate side of the filter membrane, the vacuum being lower than atmospheric pressure; as well as c) Apply pressure-assisted thermal reduction to the graphene-based film.

6. The method according to any one of claims 1 to 5, characterized in that, The bending shape of the filter membrane is a conical geometry, and the bending shape of the graphene-based membrane is a corresponding conical geometry.

7. The method according to any one of claims 1 to 5, characterized in that, The bending shape of the filter membrane is a truncated conical geometry, and the bending shape of the graphene-based membrane is a corresponding truncated conical geometry.

8. The method according to any one of claims 1 to 5, characterized in that, The graphene-based film is composed of graphene oxide or reduced graphene oxide and up to 60 wt% filler.

9. The method according to any one of claims 1 to 5, characterized in that, The filter membrane is selected from natural polymers, synthetic polymers, inorganic fibers, and any combination thereof.

10. The method according to claim 9, characterized in that, The filter membrane is made of carbon nanotubes.

11. The method according to any one of claims 1 to 5, characterized in that, The method further includes stripping the dispersion to obtain a uniform dispersion.

12. The method according to any one of claims 1 to 5, characterized in that, The filter membrane is a ceramic with a pore size greater than 10µm.

13. The method according to any one of claims 1 to 5, characterized in that, The filter membrane is a polymer with a pore size greater than 10µm.

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