A graphene filter plate and a preparation method thereof

Abstract

The application relates to the technical field of filtration, in particular to a graphene filter plate and a preparation method thereof. The graphene filter plate comprises a substrate, the substrate is provided with a filter hole, a graphene filter unit is arranged in the filter hole, and the graphene filter unit covers the filter hole. The graphene filter plate has a longer service life and can reduce maintenance cost.

Description

Technical Field

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

[0002] Graphene, due to its superior adsorption properties and ease of grafting and doping, is commonly used in the fabrication of filter membranes and filter plates. Whether used for air or water filtration, it needs to withstand significant air or water pressure and be relatively fixed within the device. Therefore, filter membranes are typically mounted on a porous substrate, with the substrate bearing the majority of the pressure; fixing the substrate secures the filter membrane relative to the device. However, graphene filter membranes immersed in water for extended periods are prone to swelling and detaching from the substrate, rendering them unusable for filtration. Graphene filter membranes used for air filtration, after prolonged use in high-humidity environments, also gradually swell due to the adsorption of large amounts of water vapor, leading to detachment from the substrate surface. In the prior art, thin plates are placed on both sides of the graphene layer to maintain its fixation, and the two plates are bonded together with an adhesive.

[0003] Chinese patent application CN214936252U discloses an automated device for complete seawater desalination based on graphene, including a porous graphene brine separator, such as... Figure 1 As shown, it consists of two 2mm thick polytetrafluoroethylene (PTFE) sheets sandwiching a porous graphene sheet. The PTFE sheets have square holes, and these holes are fitted with sieve-like structures to act as a strength support membrane for the porous graphene sheet filtration. The side length of each square hole is 3mm. The unperforated portions of the two sheets are bonded together using a small amount of water-resistant cyanoacrylate adhesive. The cyanoacrylate used in this design is essentially super glue (502 glue). While water-resistant super glue prevents water penetration, it lacks elasticity and toughness after drying and is brittle. Because the PTFE sheets deform under water impact, the super glue layer is inevitably affected. Due to its lack of toughness and brittleness, the bond between the two sheets is weak, and the graphene layer remains prone to detachment. Summary of the Invention

[0004] To address the problem of graphene filter membranes easily detaching in existing technologies, this invention provides a graphene filter plate.

[0005] The graphene filter plate includes a substrate with filter holes and graphene filter units inside the filter holes, the graphene filter units covering the filter holes.

[0006] Beneficial effects: Existing technologies often employ a method of directly coating a graphene layer onto the upper surface of a substrate. While simple to operate, this method only adheres to one side of the substrate, leading to easy detachment after swelling. Even after drying and shrinking, it is difficult to re-adhere to the substrate surface automatically, requiring recoating or the use of adhesives. However, adhesives are mostly polymeric materials, which also suffer from swelling issues. Even with waterproof adhesives, such as the water-resistant 502 glue mentioned in the background section, there is still the problem of fragility after deformation. Therefore, while existing graphene filter plates have low manufacturing costs, their maintenance costs are high.

[0007] The basic scheme of this invention places the graphene filter unit inside the filter pores. After the graphene filter unit swells, its volume expands, thus adhering more tightly to the inner wall of the filter pores, forming an interference fit. This increases the pressure on the inner wall of the filter pores and the static friction between them, thereby compensating for the weakened adhesion caused by swelling, making the graphene filter unit less likely to fall off even if it swells.

[0008] Compared to existing technologies, this solution transforms the problems that need to be overcome into a means of achieving beneficial results, extending the product's lifespan and reducing maintenance costs without the need for complex structures.

[0009] Furthermore, the graphene filter unit includes a filter section and a connecting section. The connecting section is provided on the inner wall of the filter pores, the filter section is located inside the connecting section, and the edge of the filter section is completely connected to the connecting section. Beneficial effects: Refining the structure of the graphene filter unit to include a connecting section and a filter section, the connecting section is used to fix the filter section to the substrate, while also reducing the thickness of the filter section, allowing fluid to pass through the filter section more quickly, and making it easier to remove accumulated impurities after filtration through backwashing, thus facilitating maintenance.

[0010] Furthermore, a recess is formed on the inner wall of the filter pore, and the connecting part is located in the recess. Beneficial effects: The connecting part can form an interlocking structure with the recess, and after swelling, it can form an interference fit with the recess, thereby increasing the stability of the graphene filter unit. This structure can also reduce the substrate thickness and lighten the substrate weight.

[0011] Furthermore, the connecting portion extends to the upper and / or lower surface of the substrate. Beneficial effects: Extending the connecting portion to the upper and / or lower surface of the substrate further prevents the graphene filter unit from detaching from the substrate, as the extended portion is subjected to the impact force of the fluid, thereby increasing its positive pressure on the substrate surface and making it adhere more tightly to the substrate surface. The extended portion also expands after swelling; for example, when the extended portion is annular, its inner diameter increases after swelling, tending to be pulled outwards. This helps maintain the shape of the connecting portion within the filter pores, making it less prone to wrinkling due to expansion, thus allowing for a suitable reduction in the thickness of the connecting portion. To avoid damage to the filter unit from long-term pressure in only one direction, the connecting portion can extend to both the upper and lower surfaces of the substrate, allowing for periodic changes in the filtration direction or reverse rinsing. This not only balances the stress on the filter unit but also removes some impurities, facilitating subsequent maintenance and purification, thereby extending the service life of the filter plate.

[0012] Furthermore, the upper surface of the filter section is inclined relative to the axial direction of the filter holes. Beneficial effects: The inclined arrangement of the filter section buffers the impact of the fluid, allowing for a larger filtration area within the same inner diameter filter holes. Because the pressure on the filter section is perpendicular to its surface, when the substrate is placed horizontally, this pressure does not coincide with the gravity of the fluid and its flow direction. This gravity can form an inertial force or impact force in the flow direction; that is, the filter section can disperse the impact force of the fluid. The dispersed force is mainly borne by the connecting part, which forms an acute angle with the filter section. By periodically changing the filtration direction, this lateral pressure can be distributed to the inner wall on the opposite side, thereby balancing the force on the inner wall and preventing damage from long-term pressure on only one side.

[0013] Furthermore, at least two filter sections are provided axially spaced within a single filter hole. Beneficial effect: This arrangement allows the fluid to pass sequentially through filter sections with different adsorption or filtration functions, improving purification quality and efficiency.

[0014] Furthermore, the raw materials used to prepare the graphene filter unit include graphene-based components, molding polymers, and water-soluble pore-forming agents. The graphene-based components include one or more of graphene, graphene oxide, and modified products of graphene oxide. Beneficial effects: Different graphene-based components are suitable for different fluids to be filtered; molding polymers make the filter unit easier to shape and easier to maintain its shape after swelling, avoiding wrinkles; pore-forming agents increase the contact area between graphene and the external environment, allowing graphene to better exert its function.

[0015] Furthermore, the molding polymer is one or more of polydopamine, chitosan, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene; the water-soluble pore-forming agent is polyethylene glycol and / or polyvinylpyrrolidone. Beneficial effects: Different molding polymers and pore-forming agents can be used in different application scenarios. For example, polydopamine and chitosan both have good hydrophilicity, which can promote the swelling of the filter unit; polyethylene components are hydrophobic, which helps maintain the shape of the filter unit and can reduce the thickness of the connection.

[0016] Furthermore, the substrate material is stainless steel or reinforced plastic. Beneficial effects: The substrate is used for the attachment and forming of the filter unit and to withstand external forces, requiring good tensile strength to resist the impact of strong airflow or liquid flow. Its material can be stainless steel, reinforced plastic, etc.

[0017] This invention also provides a method for preparing the above-mentioned graphene filter plate, comprising the following steps: Step 1: Preparing a first forming plate and a second forming plate using polyvinyl alcohol, wherein the shape of the upper surface of the first forming plate matches the shape of the lower surface of the graphene filter unit to be formed, and the shape of the lower surface of the second forming plate matches the shape of the upper surface of the graphene filter unit to be formed, and the length and width of the first forming plate, the second forming plate, and the substrate are all equal; Step 2: Preparing a slurry for forming the graphene filter unit; Step 3: Stacking the substrate on the first forming plate, wherein when the long side of the substrate and the first forming plate are aligned with each other and the wide side is aligned with each other, a gap for forming the graphene filter unit is reserved in the filter hole; Step 4: Pouring an excess of slurry onto the upper surface of the substrate, so that the slurry fills the gap. Step 5: Press the second forming plate downwards from the upper surface of the substrate until the lower surface of the second forming plate and the upper surface of the substrate are in contact. When the long side and the wide side of the second forming plate and the substrate are aligned, the slurry in the filter holes fills the gaps forming the graphene filter unit. Scrape off the extruded slurry along the edges of the substrate and the second forming plate. Step 6: Fix the graphene filter unit into shape. The fixing conditions depend on the properties of the slurry. Step 7: Put the graphene filter plate together with the first forming plate and the second forming plate into water at 90℃~95℃ to detach the first forming plate and the second forming plate from the graphene filter plate. Step 8: Rinse the demolded graphene filter plate with deionized water and dry it to obtain the final product.

[0018] Beneficial effects: The principle of preparing the graphene filter plate using a molded plate is as follows: the melting point of the molded plate is much higher than that of the molded polymer, so the molded plate will not deform when it comes into contact with the molten molded polymer; the melting temperature of the molded plate is lower than the softening temperature of the molded polymer, allowing the graphene filter plate to be demolded at the melting temperature of the molded plate after solidification. Specifically, polyvinyl alcohol has a melting point between 230℃ and 240℃, which is much higher than that of molded polymers such as polydopamine, chitosan, and polyethylene. It will not deform when it comes into contact with the molten state of these molded polymers and can be used to prepare molded plates; while polyvinyl alcohol can dissolve in water at 90℃ to 95℃, and this temperature is lower than the softening temperature of the molded polymer, thus facilitating the demolding of the graphene filter plate. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a graphene filter plate in the background art.

[0020] Figure 2 This is an isometric view of the graphene filter plate shown in Example 1.

[0021] Figure 3 This is a partial enlarged view of the graphene filter plate shown in Example 1.

[0022] Figure 4 This is a cross-sectional view of the graphene filter plate shown in Example 1 along the central axis of the filter holes.

[0023] Figure 5 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 2.

[0024] Figure 6 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 3.

[0025] Figure 7 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 4.

[0026] Figure 8 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 5.

[0027] Figure 9 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 6.

[0028] Figure 10 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 7.

[0029] Figure 11 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 8.

[0030] Figure 12This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 9.

[0031] Figure 13 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 10.

[0032] Figure 14 This is a cross-sectional view along the central axis of the filter holes of the graphene filter plate shown in Example 2 before demolding. Detailed Implementation

[0033] List of reference numerals in the attached drawings: 1-substrate, 2-graphene filter unit, 21-connector, 23-filter, 31-first forming plate, 32-second forming plate.

[0034] 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 contacting upper surface or a non-directly contacting upper surface, and other structures may also exist in between. "Or" indicates a relationship of choosing one or both.

[0035] This invention provides a graphene filter plate, comprising a substrate 1, on which filter holes are provided, and graphene filter units 2 are disposed within the filter holes, the graphene filter units 2 covering the filter holes. The number of filter holes is n, where n is a positive integer greater than or equal to 1.

[0036] Preferably, the graphene filter unit 2 includes a connecting part 21 and a filter part 23. The connecting part 21 is provided on the inner wall of the filter hole, the filter part 23 is located inside the connecting part 21, and the edge of the filter part 23 is completely connected to the connecting part 21.

[0037] Preferably, the cross-section of the filter pore is circular, elliptical, or polygonal. The diameter of the circle, the side, short side, or minor axis of the polygon, or the length of the minor axis of the ellipse is b, where 1 mm ≤ b ≤ 3 cm. Preferably, the value of b is 1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, or 30 mm. Preferably, the length of the major axis, long side, or major axis of the filter pore is c, which can be set according to the size of the substrate. Since the length of b is limited, c can be appropriately increased to improve filtration efficiency and reduce the weight of the substrate. Preferably, 3 mm ≤ c ≤ 10 cm.

[0038] For graphene filter units, the dimensions before swelling can be defined as follows.

[0039] Preferably, when the cross-section of the filter hole is circular, the thickness of the connecting part is d, the radius of the filter hole is r, and 1 / 5r≤d≤2 / 3r.

[0040] Preferably, the thickness of the filter section is f, where f ≥ 0.1 mm, and f can be equal to the thickness of the substrate. Specifically, the thickness is 0.5 mm to 5 mm. More specifically, the thickness is 0.1 mm, 0.3 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm.

[0041] Preferably, the raw materials used to prepare the graphene filter unit include graphene-like components, molding polymers, and water-soluble pore-forming agents. The graphene-like components include one or more of graphene, graphene oxide, and modified products of graphene oxide. Different materials can be selected depending on the properties of the gas or liquid to be filtered. For example, when filtering out oleophilic components from a water-oil mixture, a filter unit containing graphene oxide and / or its modified products can be used, so that the oleophilic components are retained on one side of the filter unit, while only the hydrophilic components pass through. When filtering out hydrophilic components from a water-oil mixture, a filter unit containing graphene can be used, allowing the oleophilic components to pass through while retaining the hydrophilic components, thereby achieving separation. Since most oxygen atoms in graphene oxide form epoxy bonds with carbon atoms, and the hydrophilicity of epoxy bonds is less than that of hydroxyl, carboxyl, amino, and mercapto groups, graphene oxide mainly exhibits amphiphilic properties, being both hydrophilic and oleophilic. Further modification of graphene oxide to open the epoxy bonds and add hydrophilic groups such as hydroxyl, carboxyl, amino, and thiol groups can enhance hydrophilicity, thus adapting it to different application scenarios.

[0042] Preferably, the molding polymer is one or more polymers selected from polydopamine, chitosan, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene. To further improve the efficiency of filtering aqueous liquids or separating water and oil, hydrophilic polymers can be added. For example, polydopamine and chitosan have good hydrophilicity and biocompatibility, which can promote the swelling of the graphene filter unit in an aqueous environment. Hydrophobic polymers such as polyethylene can give the graphene filter unit a certain degree of rigidity and toughness, preventing wrinkles caused by the swelling of hydrophilic components even when the joints are thin, thus helping to maintain the structure of the joints.

[0043] Preferably, the weight ratio of graphene components to molding polymers in the slurry is (1-10):(1-50). More preferably, this weight ratio is (1-5):(5-30).

[0044] Preferably, the substrate is made of stainless steel or reinforced plastic. More preferably, the reinforced plastic can be one or more thermosetting plastics selected from phenolic resin, epoxy resin, and melamine-formaldehyde resin. All of these materials possess good toughness or rigidity, providing sufficient support for the graphene filter unit to withstand fluid impact within the filter pores.

[0045] The graphene filter unit can be configured with different structures depending on the application scenario. Correspondingly, the substrate can also have different structures. The following describes specific embodiments of the invention in detail with reference to the accompanying drawings, using a circular cross-section of the filter pores as an example.

[0046] Example 1 Embodiment 1 of the present invention provides a graphene filter plate, such as Figures 2 to 4 As shown, the system includes a substrate 1 with multiple filter holes, each containing a graphene filter unit 2 that covers the filter hole. Specifically, the substrate measures 200mm x 200mm x 3mm, the filter holes have an inner diameter of 1.5mm, and are arranged in a square matrix. The axes of adjacent filter holes are spaced 5mm apart longitudinally and 5mm apart laterally. Each graphene filter unit is cylindrical with a cross-sectional diameter of 1.5mm and a height of 2mm. The upper and lower surfaces of each graphene filter unit 2 are perpendicular to the axial direction of the filter holes, and their distances from the upper surface to the substrate 1 are equal to their distances from the lower surface of the substrate 1, both being 0.5mm.

[0047] The raw materials used to prepare the graphene filter unit comprise, by weight percentage, 5% graphene, 3% polyethylene glycol (as a pore-forming agent), and 92% polydopamine. An aqueous graphene slurry is used, comprising 1.5% by weight. The substrate is made of stainless steel.

[0048] In the above structure, the height of the graphene filter unit is slightly smaller than the height of the filter pores. Because the graphene filter unit is cylindrical, its expanded volume after swelling is entirely used to form an interference fit, resulting in a high degree of interference fit. Even with a slight reduction in the height of the graphene filter unit, it can still be used for filtering fluids at normal flow rates. On the other hand, the graphene filter unit will elongate after swelling. Allowing some space allows the elongated graphene filter unit to remain within the filter pores, or only extend a small portion. When the fluid mass and flow velocity are both high, a large momentum is generated, manifesting as a strong inertial force or impact force. In this case, a graphene filter plate with a height equal to the substrate height can be used, or the substrate can be thickened to increase the contact area between the graphene filter unit and the filter pores, thus strengthening the connection.

[0049] The preparation method includes the following steps: Step 1: Prepare a first forming plate and a second forming plate using polyvinyl alcohol. The shape of the upper surface of the first forming plate matches the shape of the lower surface of the graphene filter unit to be formed, and the shape of the lower surface of the second forming plate matches the shape of the upper surface of the graphene filter unit to be formed. The length and width of the first forming plate, the second forming plate, and the substrate are all equal.

[0050] Specifically, the first forming plate has dimensions of 200mm x 200mm x 2mm. Its upper surface has cylindrical protrusions with a diameter of 1.5mm and a height of 0.5mm. These protrusions are arranged in a square matrix, with a 5mm interval between the axes of adjacent longitudinally aligned protrusions and a 5mm interval between the axes of adjacent transversely aligned protrusions. The axes of the cylindrical protrusions can coincide with the axes of their corresponding filter holes. Because the graphene filter plate has a symmetrical structure, the second forming plate is a mirror image of the first forming plate, with the axis of symmetry being the line connecting the midpoints of the two height sides of the substrate.

[0051] Preparation method of the molded plate: Polyvinyl alcohol (polyvinyl alcohol) type 17-99. Add 2% glycerol (emulsifier), 3% starch (plasticizer), and 3% sodium dodecyl sulfate (release agent) by weight to an aqueous solution of polyvinyl alcohol. After uniform mixing, pour the mixture into a stainless steel mold box. The mold box has recesses to form the protrusions on the molded plate. Smooth the upper surface of the mold box, and after drying, the molded plate is obtained. Drying methods can include room temperature drying, low temperature drying, or vacuum drying.

[0052] Step 2: Prepare the slurry for forming the graphene filter unit.

[0053] Specifically, according to the proportions, the graphene aqueous slurry, polyethylene glycol aqueous solution and polydopamine aqueous solution are mixed and stirred, ultrasonically treated for 10-20 minutes at a power of 100W to ensure uniform mixing, and then stirred and gradually heated to evaporate some of the water to obtain a viscous slurry.

[0054] Step 3: Stack the substrate on the first forming plate. When the long side of the substrate and the first forming plate are aligned with each other and the wide side is aligned with each other, a gap is reserved in the filter hole to form the graphene filter unit.

[0055] Specifically, the gap formed between the raised upper surface of the first forming plate and the inner wall of the filter hole of the substrate is used to form a graphene filter unit, and the unraised upper surface of the first forming plate is attached to the lower surface of the substrate.

[0056] Step 4: Pour an excess of slurry onto the upper surface of the substrate to fill the filter holes, and then scrape off the excess slurry along the upper surface of the substrate. Specifically, after pouring the excess slurry at once, let it stand for 10 to 20 seconds, or gently shake the substrate and the first forming plate as a whole for 10 to 20 seconds to allow the slurry to fill the reserved gaps.

[0057] Step 5: Press the second forming plate down from the upper surface of the substrate until the lower surface of the second forming plate and the upper surface of the substrate are in contact. When the long side of the second forming plate and the substrate are aligned with each other and the wide side is aligned with each other, the slurry in the filter hole fills the gaps that form the graphene filter unit. Scrape off the extruded slurry along the edges of the substrate and the second forming plate.

[0058] Specifically, because the lower surface of the second forming plate has protrusions, when the second forming plate is pressed downwards from the upper surface of the substrate, some slurry is squeezed out from the filter holes by the protrusions. The volume of the squeezed slurry is the volume of the protrusion. Rolling the second forming plate from one edge to the opposite edge repeatedly from its upper surface helps to achieve adhesion between the lower surface of the second forming plate and the upper surface of the substrate. This allows most of the squeezed slurry to flow out from the edges of the second forming plate and the substrate, which can then be scraped off. The result is as follows: Figure 14 The structure shown.

[0059] Step 6: Fix the graphene filter unit into shape.

[0060] Specifically, a vacuum drying method is used, and the temperature can be set to the same as the operating temperature of the above steps to ensure that the shape of the graphene filter unit does not change. Since there will inevitably be a narrow gap between the substrate and the forming plate, the moisture in the filter pores will be extracted through the gap under the pressure of the vacuum, thereby solidifying the graphene filter unit.

[0061] Step 7: Place the graphene filter plate, along with the first and second forming plates, into water at 90℃~95℃ to detach the first and second forming plates from the graphene filter plate.

[0062] Specifically, type 17-99 polyvinyl alcohol is soluble in water at 90℃~95℃, thus allowing the molded plate to be demolded. Because sodium dodecyl sulfate is added to the molded plate as a release agent, and moisture can enter along the gap between the substrate and the molded plate, it is not necessary to wait until the molded plate is completely dissolved before removing the graphene filter plate; the molded plate can be peeled off after 5min~10min.

[0063] Step 8: Rinse the demolded graphene filter plate with deionized water and dry it.

[0064] Example 2 like Figure 5As shown, Embodiment 2 provides a graphene filter plate, which differs from Embodiment 1 in the size of the substrate and the structure and composition of the graphene filter unit. Specifically, the substrate size is 300mm x 300mm x 5mm, and the inner diameter of the filter pores is 5mm. The graphene filter unit includes a connecting part 21 and a filter part 23. The connecting part 21 is a hollow cylinder with a cross-section of two concentric circles. The difference in radii between the two circles is the thickness of the connecting part, which is 1.5mm. The thickness of the filter part 23 is 1mm. The connecting part 21 completely covers the inner wall of the filter pores, and the distance from the upper surface of the filter part 23 to the upper surface of the substrate is equal to the distance from its lower surface to the lower surface of the substrate. The raw materials used to prepare the graphene filter unit include 7% graphene and 93% chitosan. The chitosan is an aqueous solution.

[0065] Preferably, when the coefficient of swelling of the graphene filter unit is greater than 0.5, to avoid excessive expansion of the connection and the formation of wrinkles, through holes can be provided on the connection to relieve some pressure and maintain the shape of the connection. A coefficient of swelling of 0.5 means that when immersed in water for a long time without restraint, the volume can increase by half after expansion, that is, increase to 1.5 times the original volume.

[0066] When subjected to fluid impact, the connecting portion 21 downstream of the filter section 23 experiences a thrust from the filter section 23, with the force directed towards the inner wall of the filter orifice. This increases the pressure between the connecting portion 21 and the inner wall of the filter orifice, and consequently, the static friction. Conversely, the connecting portion 21 upstream of the filter section 23 experiences a pull force from the filter section 23, with the force directed towards the filter section. This decreases the pressure between the connecting portion 21 and the inner wall of the filter orifice, and consequently, the static friction. Therefore, when both the fluid velocity and mass are high, the filter section 23 can be positioned on the inner wall near the upstream opening of the filter orifice, thereby reducing the connecting portion 21 subjected to the pull force of the filter section 23 and increasing the connecting portion 21 subjected to the thrust force of the filter section 23. This method is commonly used for unidirectional filtration; reverse filtration can be used for rinsing or filtration at lower flow rates.

[0067] The difference in the preparation method lies in the structure of the forming plate, which is also different due to the different structures of the graphene filter units. The cylindrical protrusions on the forming plate have a diameter of 2 mm and a height of 2 mm. After the forming plate is superimposed on the substrate, the outer wall of the cylindrical protrusion and the inner wall of the filter hole form a 1.5 mm wide gap, which is used to form the connection part.

[0068] Example 3 like Figure 6As shown, Embodiment 3 provides a graphene filter plate, which differs from Embodiment 2 in the size of the substrate and the structure and composition of the graphene filter unit. Specifically, the substrate size is 350mm x 350mm x 7mm, and the inner diameter of the filter pores is 5mm. The thickness of both the connecting portion 21 and the filter portion 23 is 0.8mm. The angle between the upper surface of the filter portion 23 and the axial direction of the filter pores is 45°. Preferably, this angle can also be 60°, 70°, 75°, 80°, etc. The raw materials used to prepare the graphene filter unit include 5% graphene, 15% polydopamine, and 80% high-density polyethylene.

[0069] Compared to Embodiment 2, the filter section 23 in this structure has a larger area and can withstand a faster flow rate because the inclined filter section 23 can distribute some of the pressure to one side of the inner wall. Periodically changing the filtration direction can balance the force on the opposite side of the inner wall.

[0070] The differences in the preparation methods are as follows: 1) Polydopamine is dissolved in N,N-dimethylformamide (DMF) slurry containing graphene. High-density polyethylene is softened and melted at 125–135°C, and then the slurry is added, stirred, and ultrasonically treated to ensure uniform mixing. 2) Since the filter element in the graphene filter unit is at a 45° angle, the upper surface of the cylindrical protrusion of the forming plate is also set to be inclined at 45°. The inclined direction of the upper surface of the cylindrical protrusion of the second forming plate matches that of the first forming plate, thus forming the filter section. 3) The graphene filter unit solidifies and forms after cooling.

[0071] Example 4 like Figure 7 As shown, Embodiment 4 provides a graphene filter plate, which differs from Embodiment 2 in the size of the substrate and the structure and composition of the graphene filter unit. Specifically, the substrate size is 350mm x 350mm x 7mm, and the inner diameter of the filter pore is 5mm. The thickness of both the connecting part 21 and the filter part 23 is 1mm. Two filter parts 23 are provided axially in each filter pore. The distance from the upper surface of the upper filter part 23 to the upper surface of the substrate 1 is equal to the distance from the lower surface of the lower filter part 23 to the lower surface of the substrate 1, both being 0.5mm. The raw materials used to prepare the connecting part and the upper filter part include 10% graphene oxide, 20% polydopamine, and 70% high-density polyethylene. The raw materials used to prepare the lower filter part include 6% graphene, 4% polyvinylpyrrolidone (as a pore-forming agent), 20% polydopamine, and 70% high-density polyethylene.

[0072] This structure allows fluid to pass sequentially through two filter sections 23. These two filter sections 23 can have different pore sizes; for example, the upper filter section 23 may have a larger pore size, while the lower filter section 23 may have a smaller pore size. This allows the upper section to filter or adsorb coarse residue, while the lower section can filter or adsorb fine residue, preventing the lower section from becoming clogged by coarse residue and hindering subsequent filtration. Preferably, the two filter sections 23 can be configured to filter or adsorb different substances; for example, the upper section may filter or adsorb oleophilic substances, while the lower section may filter or adsorb hydrophilic substances. This integrates two functions, improving the quality and efficiency of filtration. Preferably, three or more filter sections can be provided in the filter holes, thereby integrating a multi-step filtration production line.

[0073] The difference in the preparation method is that the upper or lower filter part is first formed by using a first forming plate (the diameter of the protrusion is 3mm and the height is 5.5mm) and a second forming plate (the diameter of the protrusion is 3mm and the height is 0.5mm). After curing and demolding, a cylindrical forming block (the diameter is 3mm and the height is 4mm) of the same material as the forming plate is placed in the filter hole. Then, the lower or upper filter part is formed by using a third forming plate (the size of the protrusion is the same as that of the second forming plate).

[0074] Example 5 like Figure 8 As shown, Embodiment 5 provides a graphene filter plate, which differs from Embodiment 2 in the size, structure, and material of the substrate, and the structure and composition of the graphene filter unit. Specifically, the substrate has dimensions of 400mm x 400mm x 4mm, an inner diameter of the filter pores of 7mm, and an annular recess on the inner wall of the filter pores. The depth below the opening of the recess (i.e., the distance from the opening to the bottom wall) is 1mm, the distance from the upper wall to the lower wall (i.e., the height) is 2mm, and the distance from the center point of the bottom wall to the upper surface of the substrate 1 is equal to the distance to the lower surface of the substrate 1. The thickness of the connecting part 21 is 1mm, and the height is 2mm. The thickness of the filter part 23 is 0.8mm. The substrate material is phenolic resin. Specifically, the substrate material is type 2130 phenolic resin. The raw materials used to prepare the graphene filter unit 2 include 15% graphene oxide, 15% polydopamine, and 70% high-density polyethylene.

[0075] Preferably, the recesses can be set discontinuously, i.e., spaced apart, and the connecting parts are also set accordingly at intervals. After the filter part swells, it forms an interference fit with the inner wall of the filter hole, i.e., there is no gap between the filter part and the inner wall of the filter hole. This can reduce the amount of connecting material and substrate used.

[0076] In this structure, the connecting portion 21 is located in a recess on the inner wall of the filter pore. The recess is open on only one side. The connecting portion can not only engage with the recess, but also form an interference fit after swelling. This reduces the thickness of the filter portion 21 and strengthens the connection between the graphene filter unit and the substrate. The thickness of the connecting portion 21 is greater than that of the filter portion 23, allowing the connecting portion 21 to have a larger expansion volume after swelling.

[0077] In the preparation method, the substrate with the recess can be prepared by the following method: A stainless steel mold box is used, with a double cylindrical protrusion inside. The first cylinder in the middle has a diameter of 7 mm and a height of 4 mm. A second cylinder, with a diameter of 9 mm and a height of 2 mm, is coaxially arranged on the outer side of the first cylinder. The distance from the upper surface of the second cylinder to the upper surface of the first cylinder is equal to the distance from the lower surface of the second cylinder to the lower surface of the first cylinder. 7%–9% (by weight) of NL curing agent is added to liquid phenolic resin, mixed evenly, and then poured into the mold box. The mixture is leveled along the upper surface of the first cylinder, cured at room temperature (around 20°C), and then demolded. The diameter of the cylindrical protrusion in the molded plate is 7 mm and the height is 1.6 mm.

[0078] Example 6 like Figure 9 As shown, Example 6 provides a graphene filter plate, which differs from Example 5 in the size and structure of the substrate, and the structure and composition of the graphene filter unit. Specifically, the substrate has dimensions of 500mm x 500mm x 4mm, and the inner diameter of the filter pores is 10mm. The bottom wall height of the recess is 2mm, and the height of the opening is 0.8mm. The thickness of the connecting portion 21 is 1mm, and its shape matches the recess, i.e., the height of the end away from the filter portion is 2mm, and the height of the end connected to the filter portion is 0.8mm. The raw materials used to prepare the graphene filter unit 2 include 20% graphene oxide, 20% polydopamine, and 60% low-density polyethylene.

[0079] The snap-fit ​​connection of this structure is more robust than that in Example 5, and therefore can withstand higher flow rates.

[0080] The preparation method is the same as in Example 6, but the dimensions can be adjusted accordingly based on the structure.

[0081] Example 7 like Figure 10As shown, Example 7 provides a graphene filter plate, which differs from Example 6 in the structure and material of the substrate, and the structure and composition of the graphene filter unit. Specifically, the upper wall of the recess in substrate 1 extends to the upper surface of substrate 1, so that the connecting part 21 only forms an engaging connection with the lower wall of the recess. The height of the recess is 3 mm. The height of the connecting part 21 is 2.5 mm. The filter part 23 is connected to the lower end of the connecting part 21, so that it can withstand a large flow rate during reverse filtration. The substrate material is epoxy resin. The raw materials used to prepare the graphene filter unit 2 include 20% graphene oxide, 5% polyethylene glycol, 15% polydopamine, and 60% low-density polyethylene.

[0082] This structure features a thin substrate, a simple and easy-to-process recessed structure, a large contact area at the connection part, a thin filter part, and the ability to perform bidirectional filtration.

[0083] The differences in the preparation methods are as follows: 1) The mold box used to form the substrate also has double cylindrical protrusions. The first cylinder has a diameter of 10mm and a height of 1mm. The second cylinder is coaxial with the first cylinder, and its lower surface is attached to the upper surface of the first cylinder. The second cylinder has a diameter of 12mm and a height of 3mm. Liquid epoxy resin is poured into the mold box, smoothed along the upper surface of the second cylinder, heated and cured, and then cooled and demolded. 2) The upper surface of the first forming plate has double cylindrical protrusions. The first cylinder has a diameter of 12mm and a height of 0.5mm. The second cylinder is coaxial with the first cylinder, and its lower surface is attached to the upper surface of the first cylinder. The second cylinder has a diameter of 1mm and a height of 1.5mm. The cylindrical protrusion on the lower surface of the second forming plate has a diameter of 10mm and a height of 1mm.

[0084] Example 8 like Figure 11 As shown, Example 8 provides a graphene filter plate, which differs from Example 2 in the size, structure, and material of the substrate, and the structure and composition of the graphene filter unit. Specifically, the substrate size is 400mm x 400mm x 6mm. A recess is provided at the upper opening of the filter hole, and its arrangement is the same as in Example 7, except that the height is different, which is 1mm. The connecting part 21 extends into the recess, and the upper surface of the connecting part 21 is flush with the upper surface of the substrate 1. There is a 0.3mm gap between the outer side wall of the connecting part and the inner side wall of the recess, which facilitates the expansion of the connecting part after swelling in the recess. The thickness of the non-extended portion of the connecting part 21 is 1mm. The thickness of the filter part 23 is 0.8mm, and the distance from its lower surface to the lower surface of the substrate 1 is 1mm. The substrate material is melamine-formaldehyde resin. The raw materials used to prepare the graphene filter unit include 25% graphene oxide, 5% polyethylene glycol, 10% polydopamine, and 60% linear low-density polyethylene.

[0085] In this structure, the connecting part 21 completely covers the inner wall of the filter hole in the axial direction, including a recess in the inner wall. The recess is relatively small and mainly serves a one-way interlocking function. The filter part is located in the middle and lower section of the filter hole, which facilitates reverse filtration. The gap between the connecting part and the recess also prevents the connecting part in the recess from sliding out of the recess under the reverse pressure due to expansion and the lack of a gap during reverse filtration.

[0086] The difference in the preparation method is that, in addition to the cylindrical protrusions on the upper surface of the first forming plate, there are also coaxial annular protrusions on its outer side, with an inner diameter of 6.4 mm, a height of 1 mm, and a thickness of 0.3 mm. Liquid melamine-formaldehyde resin is poured into the mold box, smoothed along the upper surface of the cylinder, heated to cure, and then cooled and demolded.

[0087] Example 9 like Figure 12 As shown, Example 9 provides a graphene filter plate, which differs from Example 8 in the size and structure of the substrate, and the structure and composition of the graphene filter unit. Specifically, the substrate size is 400mm x 400mm x 3mm. The lower surface of the filter section 23 is flush with the lower surface of the substrate 1. The connecting section 21 extends from the inner wall of the filter hole to the upper surface of the substrate 1, with an extension height of 0.8mm and a thickness of 0.8mm for the portion in contact with the upper surface. The raw materials used to prepare the graphene filter unit include 30% graphene oxide, 5% polyethylene glycol, 10% polydopamine, and 55% medium-density polyethylene.

[0088] When subjected to pressure after swelling, the filter section with the above structure is prone to sliding out of the downstream outlet of the filter hole due to the swelling and elongation of the connecting part and the enlargement of the filter section. However, due to the locking action of the connecting part on the upper surface of the substrate, the filter section is stuck to the outside of the downstream outlet. Since both ends of the graphene filter unit have locking connections, it is not easily detached from the substrate.

[0089] The difference in the preparation method is that the upper surface of the first forming plate has a cylindrical recessed hole with a diameter of 6.6 mm and a depth of 0.8 mm, and the thickness of the first forming plate is 2 mm in the portion without protrusions or recesses. A cylindrical protrusion with a diameter of 3 mm and a height of 2.8 mm is coaxially arranged inside the cylindrical recessed hole. After filling the space between the first forming plate and the substrate with slurry, excess slurry is scraped off along the surface of the substrate, or a second forming plate with a flat lower surface is attached to the surface of the substrate and then slowly pulled out to one side along that surface. It is then dried at room temperature, or vacuum conditions can be set.

[0090] Example 10 like Figure 13As shown, Embodiment Ten provides a graphene filter plate, which differs from Embodiment Nine in the size, structure, and material of the substrate, and the structure and composition of the graphene filter unit. Specifically, the substrate size is 400mm x 400mm x 6mm. The filter portion 23 has a thickness of 0.8mm and is connected to the extension of the connecting portion 21 on the upper surface of the substrate 1. The distance from the lower end of the connecting portion 21 to the lower surface of the substrate is 1mm. The substrate material is stainless steel. The raw materials used to prepare the graphene filter unit include 20% graphene oxide, 5% polyethylene glycol, 5% polydopamine, and 70% medium-density polyethylene.

[0091] Preferably, the connecting portion 21 can extend to the lower surface of the substrate to facilitate bidirectional filtration.

[0092] The difference in the preparation method is that the first forming plate is provided with only cylindrical concave holes, and the lower surface of the second forming plate is provided with double cylinders. The diameter of the first cylinder is 5mm and the height is 1mm. The second cylinder is coaxial with the first cylinder, and the lower surface of the second cylinder is attached to the upper surface of the first cylinder. The diameter of the second cylinder is 3mm and the height is 5mm.

[0093] 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 method for preparing a graphene filter plate, characterized in that, Includes the following steps: Step 1: Prepare a first forming plate and a second forming plate using polyvinyl alcohol. The shape of the upper surface of the first forming plate matches the shape of the lower surface of the graphene filter unit to be formed, and the shape of the lower surface of the second forming plate matches the shape of the upper surface of the graphene filter unit to be formed. The length and width of the first forming plate, the second forming plate, and the substrate are all equal. Step 2: Prepare the slurry for forming the graphene filter unit. Step 3: Stack the substrate onto the first forming plate. When the long sides of the substrate and the first forming plate are aligned with each other and the wide sides are aligned with each other, gaps are reserved in the filter holes to form graphene filter units. Step 4: Pour excess slurry onto the upper surface of the substrate to fill the filter holes, then scrape off the excess slurry along the upper surface of the substrate. Step 5: Press the second forming plate downwards from the upper surface of the substrate until the lower surface of the second forming plate and the upper surface of the substrate are in contact. When the long sides of the second forming plate and the substrate are aligned with each other and the wide sides are aligned with each other, the slurry in the filter holes fills the gaps that form the graphene filter unit. Scrape off the extruded slurry along the edges of the substrate and the second forming plate. Step 6: Fix the graphene filter unit into shape. The conditions for fixing and shaping depend on the properties of the slurry. Step 7: Place the graphene filter plate, along with the first and second forming plates, into water at 90℃~95℃ to detach the first and second forming plates from the graphene filter plate. Step 8: Rinse the demolded graphene filter plate with deionized water and dry it.

2. The graphene filter plate prepared by the method of preparation of graphene filter plate according to claim 1, characterized in that, The device includes a substrate with filter holes and a graphene filter unit within the filter holes, the graphene filter unit covering the filter holes; the graphene filter unit includes a filter part and a connecting part, the connecting part is provided on the inner wall of the filter hole, the filter part is located inside the connecting part, and the edge of the filter part is completely connected to the connecting part; a recess is provided on the inner wall of the filter hole, and the connecting part is located in the recess.

3. The graphene filter plate according to claim 2, characterized in that, The connecting portion extends to the upper and / or lower surface of the substrate.

4. The graphene filter plate according to claim 2, characterized in that, The upper surface of the filter section is inclined relative to the axial direction of the filter holes.

5. The graphene filter plate according to claim 2, characterized in that, At least two filter sections are provided axially spaced in a filter hole.

6. The graphene filter plate according to claim 2, characterized in that, The raw materials used to prepare graphene filter units include graphene-like components, molding polymers, and water-soluble pore-forming agents. The graphene-like components include one or more of graphene, graphene oxide, and modified products of graphene oxide.

7. The graphene filter plate according to claim 6, characterized in that, The molding polymer is one or more of polydopamine, chitosan, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene; the water-soluble pore-forming agent is polyethylene glycol and / or polyvinylpyrrolidone.

8. The graphene filter plate according to claim 2, characterized in that, The substrate is made of stainless steel or reinforced plastic.

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