A graphene porous membrane and a method for preparing the same

Abstract

The application discloses a graphene porous membrane and a preparation method thereof. A slurry is prepared by mixing graphene oxide powder, a composite pore-forming agent and deionized water in a specific proportion, film coating is performed, laser drilling pretreatment is performed, and a multi-stage heat treatment process is performed, so that the pore-forming agent is carbonized and dispersed, and the reduction and graphitization of the graphene oxide are simultaneously completed, thereby preparing the graphene porous membrane which has controllable pore structure and excellent mechanical properties. The material relies on the high heat conduction characteristics and the permeability advantages of the intrinsic graphene, realizes the synergistic optimization of the porosity and the mechanical strength, and effectively solves the structural defect problem caused by gas accumulation in the heat treatment process through the through channels constructed by laser drilling, thereby significantly improving the material structure stability. The graphene porous membrane can be widely applied to heat management, energy storage carriers, filtration and separation and other scenes, and provides a technical path for the low-cost and large-scale preparation of the graphene porous material.

Description

Technical Field

[0001] This invention relates to the field of graphene functional materials, specifically to a graphene porous membrane and its preparation method. Background Technology

[0002] Graphene porous membranes, combining the unique physicochemical properties of graphene with the advantages of high specific surface area and low bulk density of porous structures, have shown great application potential in fields such as thermal management, energy storage electrode substrates, and high-efficiency filtration. While current graphene porous membrane preparation technologies are becoming increasingly diverse, most methods still face core technological bottlenecks, such as low precision in pore structure control, complex preparation processes, and high production costs. Furthermore, they struggle to achieve a synergistic improvement in both the material's mechanical properties and functional characteristics, thus hindering their industrialization.

[0003] Template methods require the use of pore-forming agents, which are subsequently removed through high-temperature calcination and solvent washing. This not only increases the process and cost but may also leave residual impurities that affect membrane performance. Freeze-drying methods have demanding equipment requirements, extremely high energy consumption, and produce porous membranes with low mechanical strength, making them prone to structural collapse. Hydrothermal methods involve complex reaction conditions and uneven pore size distribution, making it difficult to prepare large-area films. Existing preparation processes often suffer from defects such as membrane layer delamination and pore aggregation due to poor gas dissipation, severely affecting the structural integrity and overall performance of graphene porous membranes and limiting their industrial application.

[0004] Therefore, developing a simple, cost-controllable, precisely tunable pore structure method for preparing graphene porous membranes that can achieve synergistic optimization of mechanical properties and functional characteristics has become a key requirement for breaking through existing technological bottlenecks and promoting the industrial application of graphene porous materials. Summary of the Invention

[0005] To address the problems of poor controllability of pore structure and insufficient structural stability in existing technologies, this invention provides a method for preparing graphene porous membranes. Through an innovative combination of a composite pore-forming system and laser-assisted drilling technology, precise control of pore-forming efficiency and pore distribution is achieved, while simplifying the preparation process and reducing production costs. A selectively pressurized gradient heat treatment process simultaneously completes pore formation, reduction, and graphitization, improving the overall material performance and resolving defects such as membrane layer delamination and wrinkles caused by poor gas dissipation. This method meets the performance requirements of graphene porous membranes for various applications and the requirements for large-scale production.

[0006] Specifically, the technical solution of the present invention includes the following steps: (1) A composite graphene oxide slurry is obtained by mixing and dispersing graphene oxide cake, alkaline reagent, pore-forming agent, and deionized water evenly; wherein the mass ratio of pore-forming agent to graphene oxide is 1-3:10, and the mass ratio of alkaline reagent to graphene oxide is 1-5:500; preferably 4-5:500. The alkaline reagent is one or more of ammonia, sodium hydroxide, or potassium hydroxide; the pore-forming agent is one or more of glycerol, polyvinyl alcohol, and polyethylene glycol; the graphene oxide cake has a solid content of 50 wt%; (2) Homogenize the composite graphene oxide slurry. The median diameter of the graphene oxide sheets after homogenization is 1-10 μm. (3) Degas the homogenized graphene oxide slurry, then coat it into a film, and dry it to obtain a graphene oxide film. (4) The graphene oxide film is perforated to construct gas escape channels and prevent bubbling and delamination during heat treatment. The pore size is 30-200 μm, preferably 50-200 μm, and the pore spacing is 2-5 mm; (5) The perforated graphene oxide film obtained in step (4) is subjected to gradient heat treatment, which has three stages: the first stage is 100-300℃, held for 10-20h, then heated to the second stage of 1000-1600℃ at a heating rate of 5-8℃ / min, held for 3-4h, and finally heated to the third stage of 2000-3100℃ at a heating rate of 3-5℃ / min, held for 2-3h.

[0007] Preferably, the pore-forming agent is glycerol. As a small-molecule alcohol pore-forming agent, glycerol has good compatibility with graphene oxide slurry, can be uniformly dispersed at the molecular level, resulting in uniform pore-forming sites and narrower pore size distribution; it decomposes completely without carbon residue or hydrocarbon byproducts, thus avoiding pore blockage, membrane contamination, and furnace carbon buildup, significantly improving the structural integrity and performance stability of the membrane material.

[0008] Further, step (5) is carried out under an inert atmosphere, which is one or more of nitrogen and argon; the gas flow rate of the inert atmosphere is 50-100 mL / min.

[0009] Further, the dispersion method in step (1) is as follows: first perform mechanical dispersion for 0.5-3 hours, and then perform nano-dispersion for 0.5-3 hours; the mechanical dispersion speed is 1000-5000 r / min, and the nano-dispersion uses a nano-disperser with a rotor frequency of 10-30 Hz.

[0010] Furthermore, in step (2), the homogenization pressure is 20-40 MPa, and the homogenization is performed 2-3 times.

[0011] Furthermore, the degassing method in step (3) is vacuum degassing, with a degassing time of 20-40 min and a vacuum degree of -0.08~-0.1 MPa.

[0012] Furthermore, in step (3), the coating thickness is 1000-3000μm, the coating speed is 10-30mm / s, the drying temperature is 40-70℃, and the drying time is 2-4 hours.

[0013] Generally, a coating method is used to form the film on a substrate. The substrate is quartz glass, polytetrafluoroethylene film, or polyethylene terephthalate (PET) film. Before use, the substrate is ultrasonically cleaned with anhydrous ethanol for 10-15 minutes and then dried for later use.

[0014] Furthermore, in step (4), pulsed laser drilling is used, with a laser power of 5-20W.

[0015] Furthermore, the first stage of gradient heat treatment in step (5) is carried out under a constant pressure of 20-40 kg.

[0016] In some embodiments, the steps of step (5) are as follows: 1. Under an inert gas atmosphere, uniform pressure treatment is applied to the graphene oxide film: The laser-drilled graphene oxide film is laid flat on a graphite carrier, and a graphite pressure plate of the same size is placed on top of the film surface. A constant pressure of 20-40 kg is applied by counterweights, with the pressure evenly distributed on the film surface. By pre-introducing laser-drilled channels and supplementing with uniform pressure throughout the process, structural defects such as bubbling, delamination, and rupture caused by rapid gas release in the early stage of heat treatment are actively suppressed. At the same time, the pressure and the drilling channels work synergistically to guide the gaseous products to slowly and orderly escape along a preset path, thereby significantly improving the uniformity and controllability of pore structure development. Subsequently, the film is kept at 100-300 °C for 10-20 hours to achieve deep removal of residual moisture and preliminary reduction of graphene oxide.

[0017] 2. Heat to 1000-1600℃ at a heating rate of 5-8℃ / min and hold for 3-4 hours to allow the pore-forming agent to completely decompose (glycerol decomposes to produce CO2 and H2O gases, while polyvinyl alcohol and polyethylene glycol decompose to produce CO2, H2O, and a small amount of hydrocarbon gases). The gases escape in an orderly manner along the channels formed by laser drilling, and at the same time, the membrane undergoes a carbonization reaction to form a porous graphene carbon membrane. The pore-forming agent is completely decomposed at this stage, and the gases escape along the laser drilling channels to form uniform and interconnected pores. After graphitization treatment, the membrane surface is smooth and intact, without blistering or delamination.

[0018] 3. Continue heating at a rate of 3-5℃ / min to 2000-3100℃, and hold for 2-3 hours to complete the graphitization process. This will improve the graphitization degree of the porous carbon film, optimize its thermal conductivity and mechanical properties, and achieve the final shaping of the pore structure.

[0019] The present invention also provides a graphene porous membrane prepared by the above method. Its out-of-plane thermal conductivity is 7.6 W / (m·K), its in-plane thermal conductivity is 83 W / (m·K), and its peel strength is >2 N / cm. 2 Compression ratio >35% at 50 PSI.

[0020] The advantages of this invention are: the graphene porous membrane prepared by the method of this invention has uniform pore-forming sites and a narrower pore size distribution. Tests show that its out-of-plane thermal conductivity is 7.6 W / (m·K), its in-plane thermal conductivity is 83 W / (m·K), and its peel strength is >2 N / cm. 2 The compression ratio is >35% at 50 PSI. Compared with the traditional hydrazine hydrate foaming process, it completely avoids the use of toxic reducing agents, the treatment of hydrazine-containing waste liquid and complex post-processing procedures, and the overall preparation cost can be reduced by more than 5 times. At the same time, it significantly improves the environmental safety and process scalability of the production process. Attached Figure Description

[0021] Figure 1 Image of the graphene porous membrane prepared in Example 1.

[0022] Figure 2 The image shows a cross-sectional electron microscope image of the graphene porous membrane prepared in Example 1.

[0023] Figure 3 The image shows a cross-sectional electron microscope image of the graphene porous membrane prepared for Comparative Example 2. Detailed Implementation

[0024] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0025] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0026] The ammonia water described in this invention has a mass fraction of 25-28%. If sodium hydroxide or potassium hydroxide is used, it is in powder form with a purity of ≥98%.

[0027] The graphene oxide cake contains 50% solid graphene oxide and the remainder is moisture.

[0028] The “median flake size” described in this invention corresponds to D50 (the particle size value that accounts for 50% of the cumulative distribution) in particle characterization.

[0029] Rotor frequency refers to the rotational frequency of the rotor, so 10-30 Hz corresponds to 600-1800 r / min.

[0030] The embodiments of the present invention will be further described below with reference to several examples.

[0031] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0032] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] Example 1

[0034] (1) Take 100g of graphene oxide cake (graphene oxide solid content 50%), add 2g of ammonia water with a mass fraction of 25%, 15g of glycerol and 1L of deionized water to obtain composite graphene oxide slurry. (2) The composite graphene oxide slurry was first mechanically dispersed at a speed of 3000 r / min for 2 hours, and then nano-dispersed for 2 hours using a nano-disperser (rotor frequency 20 Hz) to complete the physical blending, ensuring that each component is uniformly dispersed and there is no agglomeration. (3) The composite graphene oxide slurry after physical blending was fed into a high-pressure homogenizer and homogenized twice at a pressure of 30 MPa to make the slurry system uniform and stable. The median sheet diameter of the slurry after homogenization was 6 μm. After homogenization, a vacuum degassing machine was used to remove air bubbles from the slurry at a vacuum of -0.09 MPa for 30 min to avoid defects in the subsequent film formation process. (4) The degassed composite graphene oxide slurry was coated onto the surface of a quartz glass substrate that had been ultrasonically cleaned with anhydrous ethanol for 12 min and dried by a scraping method. The scraping thickness was controlled at 2000 μm and the coating speed was 20 mm / s. After coating, it was pre-dried at 55℃ for 12 h to obtain the original graphene oxide film. (5) A pulsed laser was used to make equally spaced holes in the original graphene oxide film. The laser power was 12W, the hole diameter was 120μm, and the hole spacing was 3mm to construct a gas dissipation channel. (6) The laser-drilled graphene oxide film was sent to a heat treatment device under nitrogen protection throughout the process, with a gas flow rate of 80 mL / min. The following treatments were performed sequentially: 1) Pre-reduction: Under a nitrogen atmosphere, a uniform weight of 20 kg was applied to the film surface, the temperature was controlled at 200℃, and the temperature was maintained for 15 h to remove residual moisture and preliminarily reduce the graphene oxide; 2) Carbonization: After the pre-reduction was completed, the temperature was increased to 1400℃ at a heating rate of 6℃ / min and maintained for 3.5 h to completely reduce the glycerol content. The total decomposition produces CO2 and H2O gases, which are orderly dispersed along the channels formed by laser drilling. At the same time, the membrane undergoes a carbonization reaction to form a porous graphene carbon membrane; 3) Graphitization: After carbonization, the temperature is raised to 2800℃ at a rate of 4℃ / min and held for 2.5h to complete the graphitization process, thereby improving the graphitization degree of the porous carbon membrane, optimizing its thermal conductivity and mechanical properties, and achieving the final shaping of the pore structure; after the heat treatment, the membrane is naturally cooled to room temperature by the equipment to obtain the target product.

[0035] The graphene porous membrane obtained by the above method, such as Figure 1 As shown, the membrane surface is fine, smooth, uniform, and intact, with no bulges or cracks visible to the naked eye. The graphene porous membrane obtained by the above method was observed under an electron microscope, and the resulting cross-sectional SEM image is shown below. Figure 2 As shown, a highly interconnected three-dimensional porous network is formed between the graphene sheets, with a pore connectivity rate ≥92%. The average pore size between layers is approximately 2.2 μm, exhibiting a narrow pore size distribution, with over 90% of the pores concentrated in the 1-3 μm range, and no obvious macropores or micropores. The cross-sectional porosity is approximately 52%, and the uniform overall pore distribution provides a stable and continuous channel for compression and rebound. Simultaneously, there is no obvious interlayer separation or sheet aggregation, demonstrating good structural integrity and excellent film-forming properties and structural stability. Tests show that its out-of-plane thermal conductivity is 7.6 W / (m·K), its in-plane thermal conductivity is 83 W / (m·K), and its peel strength is >2 N / cm. 2 The compression ratio is >35% at 50 PSI. The graphene porous membrane prepared by this process can achieve efficient foaming and pore formation simply by adding an environmentally friendly green foaming agent. Compared with the traditional hydrazine hydrate foaming process, it completely avoids the use of toxic reducing agents, the treatment of hydrazine-containing waste liquid and complex post-processing procedures, and the overall preparation cost can be reduced by more than 5 times. At the same time, it significantly improves the environmental safety and process scalability of the production process.

[0036] Example 2

[0037] (1) Take 100g of graphene oxide cake (graphene oxide solid content 50%), add 0.4g of sodium hydroxide powder, 10g of polyvinyl alcohol with a molecular weight of 1800 and 1.5L of deionized water, mix and react for 40min to obtain composite graphene oxide slurry. (2) The composite graphene oxide slurry was first mechanically dispersed at a speed of 2000 r / min for 1.5 h, and then nano-dispersed for 1.5 h using a nano-disperser (rotor frequency 15 Hz) to complete the physical blending, ensuring that each component is uniformly dispersed and there is no agglomeration. The composite graphene oxide slurry after physical blending was sent to a high-pressure homogenizer and homogenized twice at a pressure of 25 MPa to make the slurry system uniform and stable. The median sheet diameter of the homogenized slurry was 4 μm. (3) After homogenization, a vacuum degassing machine is used to remove air bubbles from the slurry under a vacuum of -0.08MPa for 25 minutes to avoid defects in the subsequent film formation process; (4) The degassed composite graphene oxide slurry was coated onto the surface of a polytetrafluoroethylene film substrate that had been ultrasonically cleaned with anhydrous ethanol for 10 min and dried by a scraping method. The scraping thickness was controlled at 1500 μm and the coating speed was 15 mm / s. After coating, it was pre-dried at 40℃ for 3.5 h to remove free water in the system and obtain the original graphene oxide film. (5) The graphene oxide film was perforated at equal intervals using a pulsed laser with a laser power of 10W, a perforation diameter of 100μm, and a perforation spacing of 2.5mm (2500μm) to construct a gas escape channel and prevent bubbling and delamination of the graphene film during heat treatment. (6) The graphene oxide film after laser perforation treatment is sent to the heat treatment equipment. Argon gas protection is used throughout the process, and the gas flow rate is 70 mL / min. The following treatments are performed in sequence: 1) Pre-reduction: Under the argon atmosphere, the graphene oxide film is uniformly pressed with a weight of 30 kg, the temperature is controlled at 180℃, and it is kept at this temperature for 12 h to remove residual moisture and preliminarily reduce the graphene oxide; 2) Carbonization: After the pre-reduction is completed, the temperature is increased to 1300℃ at a heating rate of 5.5℃ / min and kept at this temperature for 3 h to allow the polyvinyl alcohol to completely decompose and produce CO. 2. H2O and a small amount of hydrocarbon gas are emitted in an orderly manner along the channels formed by laser drilling, while the membrane undergoes a carbonization reaction to form a porous graphene carbon membrane; 3) Graphitization: After carbonization, the temperature is increased to 2600℃ at a rate of 3.5℃ / min and held for 2 hours to complete the graphitization process, thereby improving the graphitization degree of the porous carbon membrane, optimizing its thermal conductivity and mechanical properties, and achieving the final shaping of the pore structure; After the heat treatment is completed, the equipment is allowed to cool naturally to room temperature, and the graphene porous membrane is peeled off from the substrate to obtain the target product.

[0038] The resulting graphene porous membrane has a smooth surface without obvious bubbling, delamination, or cracking defects, and exhibits good membrane integrity. The pore connectivity is approximately 81%, with an average interlayer pore size of approximately 3.5 μm. The pore size distribution is relatively wide, with about 70% of the pores concentrated in the 2-5 μm range, and slight localized pore blockage is observed. The cross-sectional porosity is approximately 45%, and the three-dimensional pore network connectivity is slightly lower than in Example 1. The out-of-plane thermal conductivity is 6.2 W / (m·K), the in-plane thermal conductivity is 71 W / (m·K), and the peel strength is 1.6 N / cm. 2 At 50 PSI, the compression rate is 28%.

[0039] Example 3

[0040] (1) Take 100g of graphene oxide cake (graphene oxide solid content 50%), add 0.5g of potassium hydroxide powder, 15g of polyethylene glycol with a molecular weight of 400 and 1L of deionized water, mix and react for 35min to obtain composite graphene oxide slurry.

[0041] (2) The composite graphene oxide slurry was first mechanically dispersed at a speed of 1000 r / min for 0.5 h, and then nano-dispersed for 0.5 h using a nano-disperser (rotor frequency 15 Hz) to complete the physical blending, ensuring that each component is uniformly dispersed and there is no agglomeration. The composite graphene oxide slurry after physical blending was sent to a high-pressure homogenizer and homogenized twice at a pressure of 25 MPa to make the slurry system uniform and stable. The median sheet diameter of the homogenized slurry was 10 μm. (3) After homogenization, a vacuum degassing machine is used to remove air bubbles in the slurry under a vacuum of -0.1MPa for 40 minutes to avoid defects in the subsequent film formation process; (4) The degassed composite graphene oxide slurry was coated onto the surface of a polytetrafluoroethylene film substrate that had been ultrasonically cleaned with anhydrous ethanol for 10 min and dried by a scraping method. The scraping thickness was controlled at 1500 μm and the coating speed was 15 mm / s. After coating, it was pre-dried at 40℃ for 3.5 h to remove free water in the system and obtain the original graphene oxide film. (5) The graphene oxide film was perforated at equal intervals using a pulsed laser with a laser power of 10W, a perforation diameter of 50μm, and a perforation spacing of 2mm (2000μm) to construct a gas escape channel and prevent bubbling and delamination of the graphene film during heat treatment. (6) The graphene oxide film after laser perforation is sent to the heat treatment equipment. Argon gas protection is used throughout the process. The gas flow rate is 70 mL / min. The following treatments are performed in sequence: 1) Pre-reduction: Under the atmosphere of argon, the graphene oxide film is uniformly weighed 40 kg, the temperature is controlled at 100℃, and the temperature is held for 20 h to remove residual moisture and preliminarily reduce the graphene oxide; 2) Carbonization: After the pre-reduction, the temperature is raised to 1600℃ at a heating rate of 8℃ / min and held for 4 h to allow the polyethylene glycol to completely decompose and produce CO2, H2O and a small amount of hydrocarbon gas. The gas is orderly dispersed along the channel formed by laser perforation. At the same time, the film undergoes a carbonization reaction to form a porous graphene carbon film; 3) Graphitization: After the carbonization is completed, the temperature is raised to 3100℃ at a heating rate of 5℃ / min and held for 3 h to complete the graphitization treatment.

[0042] The resulting porous graphene film has an intact surface without structural damage, an out-of-plane thermal conductivity of 5.8 W / (m·K), an in-plane thermal conductivity of 67 W / (m·K), and a peel strength of 1.4 N / cm. 2 At 50 PSI, the compression rate is 25%.

[0043] Example 4

[0044] (1) Take 100g of graphene oxide cake (graphene oxide solid content 50%), add 0.5g of potassium hydroxide powder, 15g of glycerol and 1L of deionized water, mix and react for 35min to obtain composite graphene oxide slurry.

[0045] (2) The composite graphene oxide slurry was first mechanically dispersed at a speed of 5000 r / min for 1 h, and then nano-dispersed for 0.5 h using a nano-disperser (rotor frequency 30 Hz) to complete the physical blending, ensuring that each component is uniformly dispersed and there is no agglomeration. The composite graphene oxide slurry after physical blending was sent to a high-pressure homogenizer and homogenized twice at a pressure of 25 MPa to make the slurry system uniform and stable. The median sheet diameter of the homogenized slurry was 2 μm. (3) After homogenization, a vacuum degassing machine is used to remove air bubbles from the slurry under a vacuum of -0.08MPa for 20 minutes to avoid defects in the subsequent film formation process; (4) The degassed composite graphene oxide slurry was coated onto the surface of a polytetrafluoroethylene film substrate that had been ultrasonically cleaned with anhydrous ethanol for 10 min and dried by a scraping method. The scraping thickness was controlled at 1500 μm and the coating speed was 15 mm / s. After coating, it was pre-dried at 70°C for 2 h to remove free water in the system and obtain the original graphene oxide film. (5) The graphene oxide film was perforated at equal intervals using a pulsed laser with a laser power of 10W, a perforation diameter of 100μm, and a perforation spacing of 3mm (3000μm) to construct a gas escape channel and prevent bubbling and delamination of the graphene film during heat treatment. (6) The graphene oxide film after laser perforation is sent to the heat treatment equipment. Argon gas protection is used throughout the process. The gas flow rate is 70 mL / min. The following treatments are performed in sequence: 1) Pre-reduction: Under the argon atmosphere, the graphene oxide film is uniformly pressed with a weight of 20 kg, the temperature is controlled at 300℃, and the temperature is held for 10 h to remove residual moisture and preliminarily reduce the graphene oxide; 2) Carbonization: After the pre-reduction is completed, the temperature is raised to 1100℃ at a heating rate of 6℃ / min and held for 4 h to form a porous graphene carbon film; 3) Graphitization: After the carbonization is completed, the temperature is raised to 2000℃ at a heating rate of 3℃ / min and held for 3 h to complete the graphitization treatment.

[0046] There is no obvious interlayer separation or lamellar aggregation, and the structure is well-integrity, demonstrating good film-forming properties and structural stability.

[0047] Comparative Example 1 Unlike Example 1, glycerol was not added when preparing the graphene oxide slurry, but the other steps remained the same.

[0048] Comparative Example 2 Unlike Example 1, the graphene oxide film is not perforated, but the other steps remain the same.

[0049] Comparative Example 3 Unlike Example 1, the graphene oxide film was perforated with different pore sizes and spacings, while the other steps remained the same.

[0050] Comparative Example 1, without the addition of glycerol as a pore-forming agent, had a high overall membrane density and a cross-sectional porosity of only 12%. The membrane was hard, brittle, and lacked flexibility, failing to meet the functional requirements of porous structures for applications such as thermal management and energy storage. Comparative Example 2, without laser drilling pretreatment, experienced significant internal stress due to gas accumulation and poor dissipation during heat treatment, ultimately leading to membrane rupture. Its cross-sectional SEM results, as shown in Figure 3, revealed obvious internal delamination and severe damage to structural integrity.

[0051] The out-of-plane / in-plane thermal conductivity of the sample obtained in Comparative Example 3 was tested. The data obtained are shown in the table below. The above results further verify that the selection of pore-forming agents must be reasonably matched with the pore size and spacing of the membrane. Changes in the pore size and spacing parameters of graphene membranes directly affect the thermal conductivity of the material. If the pore size is too small and the pore spacing is too large, gas cannot escape smoothly, the interlayer bonding density of the membrane decreases, the heat conduction pathway is blocked, and the thermal conductivity decreases accordingly. If the pore size is too large and the pore spacing is too small, excessive structural defects will be generated inside the membrane material, which will also degrade the thermal conductivity.

[0052] Glycerol, as a pore-forming agent, exhibits a significant synergistic effect with laser drilling. Glycerol provides uniform pore-forming sites at the molecular level, undergoes complete decomposition at high temperatures without residue or clogging of pores, ensuring narrow pore size distribution and high pore connectivity. Laser drilling pre-creates smooth gas escape channels, effectively avoiding defects such as membrane rupture and delamination caused by gas accumulation during heat treatment, thus ensuring structural stability. The synergistic effect of these two agents allows for the simultaneous optimization of high porosity, high structural stability, excellent thermal conductivity, and mechanical properties in graphene porous membranes.

[0053] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a graphene porous membrane, characterized in that, It includes the following steps: (1) A composite graphene oxide slurry is obtained by mixing and dispersing graphene oxide cake, alkaline reagent, pore-forming agent and deionized water evenly; wherein the mass ratio of pore-forming agent to graphene oxide is 1-3:10, and the mass ratio of alkaline reagent to graphene oxide is 1-5:500; the alkaline reagent is one or more of ammonia, sodium hydroxide or potassium hydroxide; the pore-forming agent is one or more of glycerol, polyvinyl alcohol, and polyethylene glycol. (2) Homogenize the composite graphene oxide slurry. The median diameter of the graphene oxide sheets after homogenization is 1-10 μm. (3) Degas the homogenized graphene oxide slurry, then coat it into a film, and dry it to obtain a graphene oxide film. (4) The graphene oxide film is perforated with a pore size of 30-200 μm and a pore spacing of 2-5 mm; (5) The perforated graphene oxide film obtained in step (4) is subjected to gradient heat treatment, which has three stages: the first stage is 100-300℃, held for 10-20h, then heated to the second stage of 1000-1600℃ at a heating rate of 5-8℃ / min, held for 3-4h, and finally heated to the third stage of 2000-3100℃ at a heating rate of 3-5℃ / min, held for 2-3h.

2. The method according to claim 1, characterized in that, The pore-forming agent is glycerol.

3. The method according to claim 1, characterized in that, Step (5) is carried out under an inert atmosphere, which is one or more of nitrogen and argon; the gas flow rate of the inert atmosphere is 50-100 mL / min.

4. The method according to claim 1, characterized in that, The dispersion method in step (1) is as follows: first perform mechanical dispersion for 0.5-3h, then perform nano-dispersion for 0.5-3h; the mechanical dispersion speed is 1000-5000r / min, and the nano-dispersion uses a nano-disperser with a rotor frequency of 10-30Hz.

5. The method according to claim 1, characterized in that, In step (2), the homogenization pressure is 20-40 MPa, and the homogenization is performed 2-3 times.

6. The method according to claim 1, characterized in that, In step (3), the degassing method is vacuum degassing, the degassing time is 20-40 min, and the vacuum degree is -0.08~-0.1 MPa.

7. The method according to claim 1, characterized in that, In step (3), the coating thickness is 1000-3000μm, the coating speed is 10-30mm / s, the drying temperature is 40-70℃, and the drying time is 2-12 hours.

8. The method according to claim 1, characterized in that, In step (4), a pulsed laser is used for drilling, with a laser power of 5-20W.

9. The method according to claim 1, characterized in that, The first stage of gradient heat treatment in step (5) is carried out under a pressure of 20-40 kg.

10. A graphene porous membrane prepared by the method of claim 1.

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