Graphene filtration membrane and method of making the same

Abstract

The application relates to the technical field of filtration, in particular to a graphene filter film and a preparation method thereof. The graphene filter film comprises a first non-woven fabric layer, a graphene layer and a second non-woven fabric layer arranged in sequence, the layers are embedded with each other at connecting positions, and the weight percentage of the graphene in the graphene layer is greater than or equal to 90%. The graphene filter film provided by the scheme can increase the contact area of graphene with the outside world, so that the adsorption and filtration effects of graphene can be better exerted.

Description

Technical Field

[0001] This invention relates to the field of filtration technology, and in particular to a graphene filter membrane and its preparation method. Background Technology

[0002] Filter membranes are all porous structures, and can be fiber membranes, mesh membranes, etc. Graphene filter membranes typically consist of graphene components and polymeric materials used for shaping. Because commonly used graphene raw materials are in the form of powders or slurries, which lack shape-forming properties, polymeric materials are needed to aid in shaping. These polymeric materials are mostly viscous, such as polyethylene, polypropylene, polyvinyl alcohol, and polyacrylonitrile. However, in filter membranes made from these polymeric materials and graphene, the graphene is often encapsulated by the polymeric material, preventing it from contacting the outside environment or allowing only a small portion to reach it, thus hindering the full realization of graphene's filtration function.

[0003] Chinese patent CN105483939B discloses a method for preparing porous graphene nanofiber membranes, which addresses the aforementioned problem by adding a pore-forming agent to the spinning solution. However, even with the addition of the pore-forming agent, the portion of graphene in contact with the external environment remains limited, thus failing to fully realize the filtration function of graphene. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a graphene filter membrane.

[0005] The graphene filter film comprises a first nonwoven fabric layer, a graphene layer, and a second nonwoven fabric layer arranged sequentially, with each layer interlocked at the connection points, and the graphene layer contains ≥90% graphene by weight.

[0006] Beneficial Effects: In existing graphene filter films, graphene is typically added as an additive to malleable polymers such as polyethylene and polypropylene to enhance their properties, such as strength and toughness. The graphene content is usually between 0.1% and 8%. Increasing the graphene content further causes the graphene sheets to agglomerate and reform into graphite. Because malleable polymers account for over 90% of the composition, the graphene is encapsulated and cannot fully exert its function. Adding pore-forming agents only allows a small amount of graphene to come into contact with the external environment. Furthermore, graphene slurries or dispersions themselves lack malleability; without the addition of malleable polymers, a structure with sufficient strength cannot be formed, making it difficult to withstand the impact of fluids.

[0007] The graphene filter membrane provided by this solution comprises two layers of nonwoven fabric and a graphene layer located between them, with the graphene layer containing ≥90% graphene by weight. By separating the graphene and the polymer material, and using the nonwoven fabric layers on both sides as the supporting structure for the middle graphene layer, the problem of graphene being encapsulated by the polymer material is overcome.

[0008] In this structure, the graphene content of the graphene layer is significantly higher, which not only highlights the role of graphene and allows graphene molecules to have more contact with the external environment, but the nonwoven fabric layers on both sides of the graphene layer also provide a substrate for the graphene layer to adhere. The naturally formed narrow gaps between the nonwoven fabric fibers create a porous structure for the filter membrane. The interwoven fibers also give the nonwoven fabric surface a greater roughness compared to metal or ordinary plastic surfaces, thereby increasing the surface area for graphene layer adhesion and allowing the layers to interlock at the joints, strengthening the interlayer connections. Using nonwoven fabric avoids post-processing of the support plate surface, such as perforation and sanding, which helps simplify the preparation method and steps. Since the gaps between nonwoven fibers are usually in the micrometer range, that is, mostly between 1μm and 100μm, and the lateral dimensions of graphene sheets are also mainly in the micrometer range, the nonwoven layer can act as a barrier to the graphene sheet. At the same time, the intermolecular forces of the graphene sheet can increase the binding force inside the graphene layer, thereby maintaining the stability of the graphene layer structure.

[0009] The raw material used to prepare the graphene layer is graphene slurry. This not only ensures the dispersibility of the graphene sheets and avoids agglomeration due to high concentration, but also allows the solvent to evaporate and the dissolving agent to dissolve on the nonwoven fabric surface after spraying, forming a graphene layer containing more than 90% graphene. Because the purity of graphene in the graphene slurry is mostly above 95%, some undissolved dispersant may inevitably remain after rinsing and drying, and a small amount of the embedded portion of the nonwoven fabric layer may also enter the graphene layer. Therefore, the graphene layer will contain less than 10% of other components.

[0010] Furthermore, the graphene layer contains medium-layer graphene and large-layer graphene. The lateral dimensions of the medium-layer graphene are 10 μm to 15 μm, and the lateral dimensions of the large-layer graphene are 20 μm to 30 μm. The ratio of medium-layer graphene to large-layer graphene is 1:1 to 5:1. Beneficial effects: Large-layer graphene has stronger intermolecular forces, allowing it to connect more medium-layer graphene, while the medium-layer graphene can maintain the dispersion of the large-layer graphene, thus ensuring good dispersibility and internal bonding after the graphene layer is formed.

[0011] Furthermore, both the first and second nonwoven layers contain polymeric fiber-forming materials, which are one or more of polyethylene, polypropylene, polyvinyl alcohol, polyacrylonitrile, polyester, polylactic acid, chitosan, and polyphenylene sulfide. Beneficial effects: Depending on the application requirements, the polymeric fiber-forming materials can be selected from commonly used components. When biodegradability is required, components such as polylactic acid and chitosan can be selected.

[0012] Furthermore, both the first and second nonwoven fabric layers contain graphene, with a polymer fiber material to graphene mass ratio of 90:10 to 99:1. Beneficial effects: Graphene not only increases the strength and toughness of the nonwoven fabric layers but also enhances the bonding force between the graphene layer and the nonwoven fabric layer. This is because when the graphene in the graphene layer comes into contact with the graphene in the nonwoven fabric layer, the intermolecular forces further tighten the interlayer bond.

[0013] Furthermore, the fibers in the first and second nonwoven layers are porous fibers. Beneficial effects: Porous fibers not only enhance the adsorption properties of the nonwoven layers but also increase the surface area for graphene layer embedding, thereby further strengthening the interlayer bonding and making the layered structure more stable.

[0014] Furthermore, both the first and second nonwoven layers contain oriented fibers with the same orientation, and the proportion of oriented fibers is >80% in both cases. Beneficial effects: Oriented fibers can reduce the gaps between fibers, strengthening the barrier effect on the graphene sheets; they can also enhance the tensile strength between the fiber ends, and placing the anchoring points of the nonwoven layer at the ends of the oriented fibers allows the nonwoven layer to withstand greater impact forces.

[0015] Furthermore, the angle between the projection of the oriented fibers of the first nonwoven layer and the oriented fibers of the second nonwoven layer is 30° to 90°. Beneficial effect: The oriented fibers of the two nonwoven layers can have different orientations. For example, when the angle is 90°, the left and right sides of the first nonwoven layer are fixed, and the top, bottom, or front and back sides of the second nonwoven layer are fixed, thereby enhancing the stress resistance of the graphene layer from four directions, allowing the graphene layer and the graphene filter membrane as a whole to withstand greater impact forces. When the angle is acute, such as 30° or 45°, the nonwoven layer can withstand tensile forces in different directions, making it suitable for filtration requirements where the fluid direction and strength are uncertain.

[0016] The present invention also provides a method for preparing the above-mentioned graphene filter film. The method includes the following steps: S1: preparing a spinning solution for forming a first nonwoven layer and a second nonwoven layer; S2: forming the first and second nonwoven layers on a substrate using a dry spinning method, and forming a graphene layer by spraying graphene slurry, such that the graphene layer is located between the first and second nonwoven layers, and the layers are interlocked at their joints; S3: drying, thereby obtaining the graphene filter film.

[0017] Beneficial effects: Compared to wet spinning, dry spinning eliminates the need for a coagulation bath, resulting in better fiber size uniformity and easier control over the curing process. Spraying graphene slurry utilizes the impact force of the liquid flow and the airflow it generates to act on the nonwoven fabric surface, helping to expel air from the surface pores. This allows the graphene slurry to adhere more fully to the rough surface of the nonwoven fabric due to inertia, avoiding the problem of incomplete air removal in ordinary coating methods.

[0018] Furthermore, the method of inter-layer embedding at the connection is as follows: (1) First, a first nonwoven fabric layer is formed on the substrate. Before curing, graphene slurry is sprayed onto its upper surface to form a graphene layer. Then, a second nonwoven fabric layer is formed on the graphene layer. Or, (2) First, a first nonwoven fabric layer and a second nonwoven fabric layer are formed simultaneously. Before the first and second nonwoven fabric layers are cured, graphene slurry is sprayed and the layers are overlapped so that the graphene layer is located between the first and second nonwoven fabric layers. Or, (3) A water-soluble pore-forming agent is added to the spinning solution. After the first and second nonwoven fabric layers are cured, the water-soluble pore-forming agent is dissolved to form porous fibers. Then, graphene slurry is sprayed. Before the graphene slurry dries, the layers are overlapped so that the graphene layer is located between the first and second nonwoven fabric layers.

[0019] Beneficial effects: The first two methods involve spraying graphene slurry before the fiber is cured. At this time, the fiber still has a certain degree of deformability. After being impacted by airflow and liquid flow, it will deform in accordance with the surface, so that the graphene slurry can be embedded in the fiber.

[0020] The first method involves forming each layer sequentially. The fibers ejected from the spinning holes fall onto the graphene layer to form the second nonwoven layer. At this stage, the second nonwoven layer has a low degree of curing and can be fully embedded with the graphene layer at the connection points. Because the steps of forming each layer are performed separately, it takes a relatively long time.

[0021] The second method involves simultaneously forming two nonwoven fabric layers, which saves the time required to form the second nonwoven fabric layer in the first method. For graphene slurries with volatile solvents, the solvent evaporates rapidly after spraying, causing the graphene layer to dry quickly. Therefore, a graphene layer is first formed on one nonwoven fabric layer, and then the other uncured nonwoven fabric layer is bonded on top. Because the other nonwoven fabric layer is layered after the graphene slurry spraying is complete, the curing of the other nonwoven fabric layer needs to be slowed down by adjusting the substrate temperature. For graphene slurries with less volatile solvents (easily soluble in water), the graphene slurry can be sprayed onto two uncured nonwoven fabric layers simultaneously, and then bonded together to form a graphene layer between the two nonwoven fabric layers. The solvent can then be evaporated by raising the substrate surface temperature, or removed by rinsing or soaking with water, and dried to obtain the graphene filter film.

[0022] The third method involves first forming two nonwoven fabric layers with porous fibers using a pore-forming agent, and then embedding the graphene slurry into the pores of the porous fibers when spraying it.

[0023] All of the above methods make the interlayer bonding tighter, making the layered structure of the graphene filter film more robust.

[0024] Furthermore, the dry spinning method can be electrospinning, centrifugal spinning, or centrifugal electrospinning; the surface temperature of the substrate receiving the spun fibers can be adjusted; the substrate can be a pair of rollers, a platform, or two platforms hinged together.

[0025] Beneficial effects: Electrospinning can produce finer, more uniform fibers with a certain degree of consistency in fiber orientation, but its efficiency is lower. Centrifugal spinning, compared to electrospinning, can achieve even greater consistency in fiber orientation and higher spinning efficiency, but the fiber fineness is generally lower than that of electrospinning. Centrifugal electrospinning combines the advantages of both methods while overcoming their shortcomings, achieving fiber fineness, orientation, and spinning efficiency that fall between the two.

[0026] The surface of the platform or roller that serves as a carrier can be temperature-adjusted, thereby controlling the fiber coagulation process. For example, when the spinning solution is in a molten state, increasing the temperature can slow down the coagulation of the melt; when the spinning solution is a mixture made from a solution, decreasing the temperature can slow down the evaporation of the solvent, thereby slowing down the coagulation of the mixture. Attached Figure Description

[0027] Figure 1 An electron microscope image of oriented fibers formed by centrifugal spinning is shown.

[0028] Figure 2 A schematic diagram of the preparation method of the graphene filter film provided in Example 3 is shown.

[0029] Figure 3A schematic diagram of the preparation method of the graphene filter film provided in Example 4 is shown. Detailed Implementation

[0030] It should be understood that the terms "upper," "middle," "lower," "left," "right," "inner," "outer," and similar directional terms used in this specification are intended to facilitate understanding of the embodiments of this application, and are not intended to limit the scope of protection claimed by this application. For example, "above" can refer to a directly contacted area above, or a non-directly contacted area above, and other structures may also exist in between.

[0031] The following examples illustrate the solution of the present invention in detail.

[0032] Example 1 This invention provides a graphene filter film comprising a first nonwoven fabric layer, a graphene layer, and a second nonwoven fabric layer arranged sequentially. The layers are interlocked at their joints; that is, depressions or pores are formed on the surface of the nonwoven fabric fibers in contact with the graphene layer, and the graphene layer is embedded within these pores. Structurally, the nonwoven fabric layers also embed the graphene layer; therefore, the layers are indeed interlocked at their joints. The raw material used to prepare the graphene layer is an aqueous graphene slurry. The graphene purity in the aqueous graphene slurry is >98wt%, the concentration is 1.5wt%, the lateral dimension of the graphene sheets is 1μm to 50μm, and the dispersant is pyrene sulfonic acid with a concentration of 0.3wt%. The graphene weight percentage in the graphene layer is 95%. The fineness of the nonwoven fabric fibers is 10μm to 20μm. The thickness of both nonwoven fabric layers is 80μm to 100μm. The dimensions of both nonwoven fabric layers are 20cm x 20cm. The slurry containing graphene sheets within a certain size range was obtained through purchase, and its preparation method is existing technology in this field and will not be detailed here. The polymer fiber-forming material is low-density polyethylene. The fiber orientation of the two nonwoven layers is irregular.

[0033] Preparation method: A spinning solution is prepared by melting low-density polyethylene. Two nonwoven layers are prepared by electrospinning at a voltage of 30 kV and a collection distance of 10 cm. The spun threads fall onto the surface of a platform serving as a substrate, forming the first nonwoven layer. The upper surface of the platform is coated with polytetrafluoroethylene (PTFE) to facilitate the peeling of the nonwoven layer from the platform surface. The platform moves uniformly to the left at a speed of 1 cm / s, thus forming the first nonwoven layer from left to right on the platform surface. Before the upper surface of the first nonwoven layer is cured, a graphene aqueous slurry is sprayed onto it at a spraying pressure of 0.05 MPa, a spray gun distance of 250 mm, and a spray gun moving speed of 15 cm / s. Since the melting point of low-density polyethylene is 105℃~115℃, the water in the slurry evaporates rapidly, forming a graphene layer. Then, a second nonwoven layer is prepared by electrospinning, with the threads falling onto the upper surface of the graphene layer. After curing, it is rinsed with deionized water to remove most of the dispersant and other impurities. After drying, the graphene filter membrane is obtained.

[0034] Example 2 The difference between Example 2 and Example 1 lies in the composition of the polymer fiber-forming material, the composition and fiber orientation of the nonwoven fabric layers, and the preparation method. The polymer fiber-forming material is polypropylene. The nonwoven fabric layer is composed of polypropylene and graphene, with a mass ratio of 90:10 (including unavoidable impurities). The graphene layer contains 96% graphene by weight. Both nonwoven fabric layers contain more than 80% oriented fibers, which are fibers with the same orientation within the nonwoven fabric layer. The projection of the oriented fibers of the first nonwoven fabric layer onto the second nonwoven fabric layer is perpendicular to the oriented fibers of the second nonwoven fabric layer. The fineness of the nonwoven fabric fibers is 30μm to 40μm. The thickness of both nonwoven fabric layers is 90μm to 110μm. The dimensions of both nonwoven fabric layers are 20cm x 30cm.

[0035] The difference in the preparation method lies in the addition of graphene N-methylpyrrolidone slurry to the melted polypropylene in a specific ratio. The graphene purity is >98%, and the concentration is 1.5%. The dispersant is a perylene derivative with a concentration of 0.3%. After stirring, the mixture is ultrasonically treated for 10-20 minutes at a power of 100W to ensure uniform dispersion. The platform surface is heatable. An internal temperature control unit, consisting of a heating wire, is installed on the platform; the surface temperature can be adjusted by regulating the current. The platform moves uniformly to the left at a speed of 3 cm / s, thus forming the first nonwoven fabric layer on the platform surface from left to right. Since polypropylene has a melting point of 189℃ and softens at around 155℃, the platform surface temperature is adjusted accordingly. Before the upper surface of the first nonwoven fabric layer solidifies, an aqueous graphene slurry is sprayed on.

[0036] Example 3 like Figure 2As shown, the difference between Example 3 and Example 2 lies in the composition of the polymer fiber-forming material, the fiber orientation of the two nonwoven fabric layers, the composition of the graphene layer, and the preparation method. The polymer fiber-forming material is polyphenylene sulfide. The graphene layer contains medium-layer graphene and large-layer graphene. The transverse dimension of the medium-layer graphene is 10μm to 15μm, and the transverse dimension of the large-layer graphene is 20μm to 30μm, with a ratio of 1:1. The projection of the oriented fibers of the first nonwoven fabric layer onto the oriented fibers of the second nonwoven fabric layer forms a 45° angle. The fineness of the nonwoven fibers is 40μm to 50μm. The thickness of both nonwoven fabric layers is 110μm to 130μm. Both nonwoven fabric layers are 20cm wide, and their length can be cut as needed. The roller is 24cm high and 20cm in diameter. Figure 1 An electron microscope image of oriented fibers formed by centrifugal spinning is shown.

[0037] The difference in the preparation method lies in the spinning method, which is centrifugal spinning, with a collection distance of 8 cm and a rotation speed of 6000-7000 rpm, accelerating uniformly at 50 rpm. A pair of rotating rollers (including a first roller 31 and a second roller 32) serve as the substrate for forming the first nonwoven layer 11 and the second nonwoven layer 12, simultaneously receiving yarn on the surfaces of the two opposing rollers. A heating wire, acting as a temperature control unit 35, is located below the surface of the rollers receiving the yarn. This heating element heats that portion of the surface while leaving the remaining surface unheated, allowing the formed nonwoven layer to gradually cool as the rollers continue to rotate, with the cooling rate slowed by heat transfer from the roller surfaces. When the initially formed edges of the two nonwoven layers rotate to pass through the line connecting the center points of the two rollers, graphene slurry is sprayed downwards from above between the rollers, covering the upper surfaces of the two nonwoven layers to form the graphene layer 2. After the two nonwoven fabric layers detach from the roller surface, the formed graphene filter film is immersed in deionized water for 10-20 minutes, or rinsed with deionized water and dried. Since the melting point of polyphenylene sulfide is 285℃~300℃, the surface temperature at the roller receiving the yarn is adjusted accordingly, and graphene slurry is sprayed on the upper surface of the nonwoven fabric layer before it solidifies.

[0038] Example 4 like Figure 3As shown, the difference between Example 4 and Example 3 lies in the composition of the polymer fiber-forming material, the fiber orientation of the two nonwoven layers, the composition of the nonwoven layer and the graphene layer, and the preparation method. The polymer fiber-forming material is polylactic acid (PLA). In the nonwoven layer, the mass ratio of PLA to graphene is 93:7. In the graphene layer, the ratio of medium-sheet graphene to large-sheet graphene is 5:3. The projection of the oriented fibers of the first nonwoven layer onto the second nonwoven layer forms a 30° angle with the oriented fibers of the second nonwoven layer. The fineness of the nonwoven fibers is 60μm to 70μm. The thickness of both nonwoven layers is 130μm to 160μm. The dimensions of both nonwoven layers are 25cm x 50cm.

[0039] The difference in the preparation method lies in the spinning method, which is a centrifugal electrospinning method with a collection distance of 8 cm, a voltage of 30 kV, and a rotation speed of 5000-6000 rpm, accelerating uniformly at 50 rpm. The substrate consists of two hinged platform-shaped stainless steel plates (a first steel plate 41 and a second steel plate 42 connected by a hinge shaft 44), on which the filaments are simultaneously received, and the surfaces of the steel plates can be heated. Heating wires 45 are installed inside the steel plates as a temperature control unit. The steel plates move uniformly to the left at a speed of 10 cm / s, thereby forming a first nonwoven fabric layer 11 from left to right on the surface of the first steel plate 41, and simultaneously forming a second nonwoven fabric layer 12 from left to right on the surface of the second steel plate 42. Since polylactic acid has a melting point of 176°C, the platform surface temperature is adjusted accordingly. Before the upper surfaces of the first nonwoven layer 11 and the second nonwoven layer 12 are cured, for example, before the preparation of the two nonwoven layers is completed, a graphene aqueous slurry can be sprayed onto the upper surface of the first nonwoven layer 21 to form a graphene layer 2. Then, the incompletely cured second nonwoven layer is folded over by the hinged second steel plate 42, so that the layers can be interlocked at the joint. After cooling, the folded stainless steel plate is opened, and the product is rinsed and dried.

[0040] Example 5 Example 5 differs from Example 4 in the composition of the polymer fiber-forming material, the nonwoven fabric layer, the graphene layer, and the preparation method. The polymer fiber-forming material is chitosan. Chitosan is soluble in trifluoroacetic acid (boiling point 72.4℃). In the nonwoven fabric layer, the mass ratio of chitosan to graphene is 95:5. In the graphene layer, the ratio of medium-sheet graphene to large-sheet graphene is 2:1. The graphene weight percentage in the graphene layer is 94%. The fineness of the nonwoven fabric fibers is 80μm–100μm. The thickness of both nonwoven fabric layers is 160μm–200μm. The dimensions of both nonwoven fabric layers are 30cm x 60cm.

[0041] The difference in the preparation method lies in adjusting the current of the heating wire inside the steel plate to maintain the surface temperature of the steel plate between 20℃ and 40℃, thereby controlling the evaporation rate of trifluoroacetic acid. The steel plate moves uniformly to the left at a speed of 18 cm / s. Before curing, an ethanol slurry of graphene is sprayed onto the surface of the nonwoven fabric layer. The graphene purity is >98%, the concentration is 1.5%, and the dispersant is a perylene derivative with a concentration of 0.2%. Both ethanol and trifluoroacetic acid are volatile; increasing the temperature can accelerate their evaporation rate.

[0042] Example 6 Example 6 differs from Example 5 in the composition of the polymer fiber-forming material, the nonwoven fabric layer, the graphene layer, and the preparation method. The polymer fiber-forming material is polyacrylonitrile. The nonwoven fabric layer comprises polyacrylonitrile, graphene, and polyvinyl alcohol as a pore-forming agent, in a mass ratio of 95:4:1. In the graphene layer, the ratio of medium-sheet graphene to large-sheet graphene is 3:1. The graphene weight percentage in the graphene layer is 92%. The polyvinyl alcohol is type 17-99, which can also be used as a polymer fiber-forming material. Because it is soluble in water at 90℃~95℃, it can also be used as a pore-forming agent. The fineness of the nonwoven fabric fibers is 110μm~130μm. The thickness of both nonwoven fabric layers is 200μm~250μm. The dimensions of both nonwoven fabric layers are 30cm x 70cm.

[0043] The difference in the preparation method lies in the following: polyacrylonitrile is dissolved in N,N-dimethylformamide, and then uniformly mixed with an N,N-dimethylformamide slurry of graphene (graphene purity >98%, concentration 1.5%, perylene derivative dispersant, concentration 0.3%). A steel plate moves uniformly to the left at a speed of 25 cm / s. After forming two nonwoven layers, the surface of the stainless steel plate is heated to volatilize the N,N-dimethylformamide (boiling point 153℃), causing the nonwoven layer to solidify. Then, the two nonwoven layers are immersed in water at 90℃~95℃ for 20min~30min to dissolve the polyvinyl alcohol, and dried to obtain a nonwoven layer containing porous fibers. A graphene-ethanol slurry is then sprayed onto the upper surface of one of the nonwoven layers. Before the graphene layer dries, the steel plate with the other nonwoven layer is folded over, allowing the graphene layer to embed into the pores of the fibers in the other nonwoven layer.

[0044] Example 7 The difference between Example 7 and Example 6 lies in the composition of the polymer fiber-forming material, the composition of the nonwoven fabric layer and the graphene layer, and the preparation method. The polymer fiber-forming material is polyethylene terephthalate (PET), a polyester. The nonwoven fabric layer comprises PET, isophthalic acid, graphene, and polyvinylpyrrolidone (PVP) as a pore-forming agent, in a mass ratio of 92:5:2:1. In the graphene layer, the ratio of medium-sheet graphene to large-sheet graphene is 5:1. The fineness of the nonwoven fibers is 150 μm to 180 μm. The thickness of both nonwoven fabric layers is 300 μm to 350 μm. The dimensions of both nonwoven fabric layers are 30 cm x 80 cm.

[0045] The difference in the preparation methods lies in the fact that polyethylene terephthalate has a melting point of 250℃~255℃, while polyvinylpyrrolidone (PVP) has a melting point of 130℃ and a boiling point of 217.6℃, meaning the former's melting point is higher than the latter's boiling point. To prevent the latter from evaporating due to boiling after being added to the molten polyethylene terephthalate as a pore-forming agent, the polyethylene terephthalate needs to be modified. For example, isophthalic acid can be added to lower the melting point of the mixture to below 200℃. PPVP is soluble in water at room temperature, so after the nonwoven fabric layer cools and solidifies, it can be soaked in room temperature water, rinsed, and dried before being sprayed with graphene water-based slurry. The steel plate moves uniformly to the left at a speed of 33 cm / s.

[0046] For nonwoven fabrics, the disordered or oriented fiber orientation is a matter of existing technology and can be achieved by existing methods.

[0047] Preferably, the graphene layer completely or partially covers the gaps between the fibers. After the solvent in the graphene slurry evaporates, micron-sized gaps are formed between the graphene sheets, allowing fluids such as air and liquids to pass through.

[0048] Preferably, the diameter of the spinning hole is 10μm to 200μm. Fibers spun from spinning holes with this diameter are finer and can be made into thinner nonwoven fabrics.

[0049] Preferably, the first nonwoven layer and the second nonwoven layer are fused together at the edges to make the connection between the layers stronger.

[0050] The embodiments of the present invention have been described in detail above. These are merely preferred embodiments, and the present invention is not limited to the above embodiments. It should be noted that those skilled in the art can make various changes and improvements without departing from the inventive concept and within the scope of their knowledge. These should also be considered to fall within the protection scope of the present invention, and will not affect the patentability and implementation effect of the present invention. The technologies, shapes, and structural parts omitted in the description of the present invention are all well-known technologies.

Claims

1. A graphene filter membrane, characterized in that, It includes a first nonwoven fabric layer, a graphene layer, and a second nonwoven fabric layer arranged sequentially, with each layer interlocked at the connection points, and the graphene layer contains ≥90% graphene by weight. The graphene filter membrane is prepared by the following method: S1: Prepare the spinning solution for forming the first and second nonwoven fabric layers; S2: A first nonwoven fabric layer and a second nonwoven fabric layer are formed on the substrate by dry spinning, and a graphene layer is formed by spraying graphene slurry, so that the graphene layer is located between the first nonwoven fabric layer and the second nonwoven fabric layer, and the layers are inter-embedded at the connection points. S3: Drying, to obtain the graphene filter membrane; The implementation method for embedding the layers at the connection points is as follows: (1) First, a first nonwoven fabric layer is formed on the substrate. Before curing, graphene slurry is sprayed onto its surface to form a graphene layer. Then, a second nonwoven fabric layer is formed on the graphene layer; or, (2) First, the first nonwoven fabric layer and the second nonwoven fabric layer are formed simultaneously. Before the first nonwoven fabric layer and the second nonwoven fabric layer are cured, graphene slurry is sprayed and the layers are overlapped so that the graphene layer is located between the first nonwoven fabric layer and the second nonwoven fabric layer.

2. The graphene filter membrane according to claim 1, characterized in that, The graphene layer contains medium-sized graphene and large-sized graphene. The lateral dimensions of the medium-sized graphene are 10 μm to 15 μm, and the lateral dimensions of the large-sized graphene are 20 μm to 30 μm. The ratio of medium-sized graphene to large-sized graphene is 1:1 to 5:

1.

3. The graphene filter membrane according to claim 1, characterized in that, Both the first and second nonwoven fabric layers contain polymer fiber-forming materials, which are one or more of polyethylene, polypropylene, polyvinyl alcohol, polyacrylonitrile, polyester, polylactic acid, chitosan, and polyphenylene sulfide.

4. The graphene filter membrane according to claim 3, characterized in that, The first and second nonwoven fabric layers also contain graphene, with the mass ratio of polymer fiber material to graphene being 90:10 to 99:

1.

5. The graphene filter membrane according to claim 1, characterized in that, The fibers in the first and second nonwoven layers are porous fibers.

6. The graphene filter membrane according to claim 1, characterized in that, Both the first and second nonwoven fabric layers contain oriented fibers with the same orientation, and the proportion of oriented fibers is >80% in both layers.

7. The graphene filter membrane according to claim 6, characterized in that, The angle between the projection of the oriented fibers of the first nonwoven layer and the oriented fibers of the second nonwoven layer is 30° to 90°.

8. The graphene filter membrane according to claim 1, characterized in that, The dry spinning method is electrospinning, centrifugal spinning, or centrifugal electrospinning; the surface temperature of the substrate receiving the spun fibers is adjustable; the substrate is a pair of rollers or at least one platform.

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