A method for preparing a polysulfone nanofiltration membrane by surface thermal initiation polymerization cross-linking reaction of a porous membrane

Abstract

The application relates to a method for preparing a polysulfone nanofiltration membrane through a porous membrane surface thermal initiation polymerization crosslinking reaction, and belongs to the membrane separation technical field.The method comprises the following steps: 1) dissolving a polysulfone polymer and a thermal initiation polymerization small molecule in a suitable solvent, and preparing a homogeneous casting solution after adding an additive; 2) coating the casting solution on a substrate, immersing the substrate in a coagulation bath, and forming a polysulfone separation base film through non-solvent induced phase separation; and 3) heating the membrane embryo for a proper time length, and controlling the temperature to be slightly lower than the glass transition temperature of the polysulfone polymer, and meanwhile, the thermal initiation polymerization small molecule added in the step 1) can be polymerized to cause thermal crosslinking, so that a dense separation thin layer is formed on the surface of the polysulfone material, and a membrane embryo with nanofiltration separation performance is formed. The scheme is simple and easy to implement, the process design is ingenious, the selected polysulfone polymer material source is relatively wide, and the obtained polysulfone nanofiltration separation membrane has high permeability and retention rate.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically a method for preparing polysulfone nanofiltration membranes by thermally initiated polymerization and crosslinking reaction on the surface of porous membranes. Background Technology

[0002] The rapid industrialization and modernization of human society has brought about significant environmental problems; among them, the large-scale generation and discharge of industrial wastewater and domestic sewage pose serious threats to aquatic ecosystems. Traditional water treatment methods (such as sedimentation, adsorption, filtration, and chemical precipitation) are incomplete in removing pollutants from water bodies and consume a lot of energy, leading to intractable cost and environmental problems. Membrane technology, through its physical sieving effect, can precisely separate pollutants of different scales in water bodies, achieving efficient water treatment with low energy consumption. Its advantages, such as small footprint, no phase change, high separation precision, and ease of operation, are unmatched by traditional treatment methods. Currently, membrane separation technology is widely used in the field of water treatment, making a significant contribution to providing drinking water, maintaining water safety, and protecting ecosystems.

[0003] Based on filtration precision, membrane materials are classified into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. Among these, nanofiltration membranes, with pore sizes around 1 nanometer, are highly suitable for removing organic solvents and dyes from water, as well as for water softening. Polysulfone membrane materials possess strong rigidity, creep resistance, and dimensional stability. Their heat resistance, acid and alkali resistance, and hydrophilicity give them significant application potential in pharmaceuticals, food, and domestic drinking water purification. However, currently, polysulfone nanofiltration membrane products used in water treatment systems are mainly composite nanofiltration membranes, consisting of a support layer and an active separation layer. The former is primarily prepared by phase inversion, while the latter is mainly prepared by coating-crosslinking, multilayer self-assembly, and interfacial polymerization. Nanofiltration membranes prepared by coating-crosslinking have poor permeability and require cumbersome post-treatment steps; multilayer self-assembly requires intermolecular forces, limiting its application systems; and the most widely used interfacial polymerization method requires extremely large reagent quantities and is cumbersome. Furthermore, a distinct interface exists between the separation layer and the membrane body of the composite nanofiltration membrane, and this interface effect adversely affects the efficiency, accuracy, and durability of the membrane separation process. How to easily prepare stable, highly permeable polysulfone nanofiltration membrane products using green and environmentally friendly methods and apply them in the field of water treatment remains a pressing problem that needs to be solved. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, the present invention aims to provide a technical solution for preparing polysulfone-based nanofiltration membranes via thermally initiated polymerization and crosslinking reactions on the surface of porous membranes. This method utilizes the low glass transition temperature of the membrane surface to form a separation layer on the polysulfone membrane surface through thermal crosslinking, achieving nanofiltration separation performance. This preparation method is simple, environmentally friendly, and produces nanofiltration membranes with excellent performance, possessing the potential to replace traditional polysulfone-based nanofiltration membrane production methods.

[0005] The method for preparing polysulfone nanofiltration membranes by thermally initiated polymerization and crosslinking reaction on the surface of porous membranes is characterized by comprising the following steps:

[0006] 1) Prepare the casting solution: 50-85 parts organic solvent, 14-30 parts polysulfone polymer, 1-10 parts thermally initiated polymerizing small molecules, and 0-10 parts additives. Dissolve the polysulfone polymer, thermally initiated polymerizing small molecules, and additives in the organic solvent to obtain a homogeneous casting solution.

[0007] 2) Preparation of polysulfone-based asymmetric ultrafiltration membrane preforms with porous surfaces by non-solvent-induced phase separation: The casting solution prepared in step 1) is uniformly coated on a flat substrate surface to a thickness of 100-300 μm. Then, it is quickly placed in a coagulation bath at 0-90℃ and left for 5-25 min. When the polymer has completely undergone phase separation and solidified and detached from the substrate, it is removed to obtain a polysulfone-based asymmetric ultrafiltration membrane preform with a uniformly porous surface. The air humidity is maintained at 55%±5% during the preparation process.

[0008] 3) Thermally Initiated Polymerization and Crosslinking: Under a specific atmosphere, the polysulfone membrane preform obtained in step 2), with a porous surface structure, is heated in a heating device at a temperature slightly below the glass transition temperature of polysulfone polymers for an appropriate duration. This temperature is precisely designed to induce the addition of thermally initiated polymers in step 1, leading to thermal crosslinking. During heating, the temperature is first increased from room temperature to 50°C below the target temperature within 30 minutes, and then increased to the target temperature at a rate of 1°C / min. By controlling the temperature and heating rate, only the molecular chains in and around the membrane surface layer are activated, keeping the membrane phase molecular chains in a glassy state. This provides sufficient space for the crosslinking reaction of the thermally initiated polymers on the membrane surface, allowing them to successfully crosslink and form a surface separation layer. Simultaneously, the small molecules in the membrane phase, due to space constraints, cannot crosslink, ensuring good permeability of the membrane material and resulting in a polysulfone nanofiltration membrane product with both excellent permeability and separation performance.

[0009] The method for preparing polysulfone nanofiltration membranes by thermally initiated polymerization crosslinking reaction on the surface of porous membranes is characterized in that, in step 1), the following components are present: 60-80 parts of organic solvent, 18-27 parts of polysulfone polymer, 1-8 parts of thermally initiated polymerized small molecules, and 2-8 parts of additives; preferably, 65-70 parts of organic solvent, 20-25 parts of polysulfone polymer, 4-6 parts of thermally initiated polymerized small molecules, and 5-7 parts of additives.

[0010] The organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0011] The polysulfone polymer mentioned is one of polysulfone and polyethersulfone. Polysulfone polymers are the most widely used polymer materials in water treatment filter membranes, exhibiting excellent separation performance, permeation performance, and mechanical properties. Furthermore, polysulfone polymers are already in mass production at low cost. The polysulfone nanofiltration membrane prepared by this invention is expected to meet the needs of various applications in water treatment.

[0012] The thermally initiated polymerizable small molecules are acrylamides, styrene, triphenylamines, triphosphazenes, triterpenoids, or other small molecules whose thermal initiation temperature matches the glass transition temperature of the polymer material. The small molecules selected in this invention should meet the following requirements: 1) They cannot undergo cross-linking reactions at room temperature and can be directly initiated by heating for polymerization and cross-linking reactions without the need for other initiation conditions or substances; 2) Their molecular size is within a suitable range; after the molecular chains on the surface of polysulfone polymers are activated, they possess the ability to undergo cross-linking; while when the molecular chains of polysulfone polymers are in the glassy state, they do not possess the ability to undergo large-scale thermal cross-linking and form a skin layer; 3) They can form a homogeneous system with polymers, additives, and solvents under heating and stirring conditions. This method can achieve the cross-linking reaction of such thermally initiated polymerizable small molecules only on the surface of polysulfone polymer ultrafiltration membranes, forming a separation skin layer with nanofiltration performance; while simultaneously maintaining the macroporous structure of the ultrafiltration membrane bulk phase, minimizing the loss of membrane permeability.

[0013] The mass fraction of polysulfone polymer in the casting solution of this invention is 14-30 wt%. This solids content range ensures that the prepared nanofiltration membrane product achieves a usable balance between permeability and operational stability. When the solids content is above 30 wt%, the membrane's permeability to pure water will be so low that it cannot be used for water treatment, and the polymer will also be difficult to completely dissolve in the solvent to form a homogeneous casting solution; while when the solids content is below 14 wt%, the membrane's mechanical properties are extremely poor, and it cannot maintain a good macroscopic morphology after heat treatment, making it difficult to use in long-term water treatment processes.

[0014] The additive of this invention is either polyethylene glycol or polyvinylpyrrolidone. Experiments have shown that both additives can regulate the pore structure of membranes prepared by the solvent-inducing phase separation method and can be effectively removed by methods such as water washing, thus having no impact on subsequent thermal crosslinking reactions. In addition to the two additives mentioned above, any other additives that can effectively regulate the pore structure and are easily removed can also be added.

[0015] The method for preparing polysulfone nanofiltration membranes via thermally initiated polymerization and crosslinking reaction on porous membrane surfaces is characterized in that, in step 2), the coating thickness of the casting solution is 150-250 μm, preferably 200-220 μm. If the casting solution coating layer is too thick, the permeation performance of the polysulfone membrane preform will decrease, ultimately resulting in extremely low flux of the thermally crosslinked nanofiltration membrane; conversely, if the coating layer is too thin, the mechanical properties of the polysulfone membrane preform will be poor, making it difficult to apply to high-pressure separation processes after thermal crosslinking.

[0016] The method for preparing polysulfone nanofiltration membranes by thermally initiated polymerization and crosslinking reaction on the surface of porous membranes is characterized in that, in step 2), the coagulation bath is at least one of deionized water, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; the coagulation bath temperature is 10-80℃, preferably 20-60℃, more preferably 30-50℃; and the coagulation bath time is 5-25 min, preferably 10-20 min.

[0017] The drying method specified in this invention is one of the following: natural air drying at room temperature, drying at 30-80℃, and freeze drying (each lasting 1-48 hours). Different drying temperatures have different effects on the pore structure of polysulfone-based films; in practical applications, the appropriate method should be selected based on cost and other requirements.

[0018] The heating temperature set in this invention is within the range of -20°C to 0°C from the glass transition temperature of polysulfone polymers. For polymer materials, the molecular chains near the material surface have a lower glass transition temperature than the polymer bulk, and their chain segment movement will be "thawed" at a relatively lower temperature. This is the "surface effect" of polymer materials, which has been proven by numerous experiments and theories. In polysulfone polymer membranes, the surface of polysulfone ultrafiltration membranes prepared by the non-solvent-induced phase separation method has a pore structure with a diameter of about 10 nanometers. When heated slightly below the glass transition temperature, the chain segment movement of molecular chains near the surface becomes active, providing the temperature and space required for the cross-linking reaction of thermally initiated polymerization of small molecules, thereby forming a surface separation layer, which is the polysulfone nanofiltration membrane product prepared by the surface thermally initiated polymerization cross-linking method. However, since the temperature has not reached the glass transition temperature of polysulfone polymers, the small molecules in the polysulfone membrane material bulk will not undergo large-area cross-linking, and the macroporous structure formed during the non-solvent-induced phase separation membrane preparation will not change significantly, thus ensuring that the sacrifice of membrane material permeability by this method is minimized. If the processing temperature is too low, the segmental movement of the molecular chains on the membrane surface cannot be "thawed," making it difficult for a large-area, complete cross-linking reaction to occur on the membrane surface. Therefore, a surface separation skin cannot be formed, and the membrane's separation performance is not significantly improved. If the processing temperature is too high, the molecular chains within the entire membrane material will have extremely high mobility, triggering a thermal cross-linking polymerization reaction in the membrane phase, which has a significant negative impact on the membrane's permeability. Furthermore, excessively high processing temperatures will damage the membrane's mechanical properties, making it difficult to apply in practical water treatment scenarios.

[0019] The heat treatment temperature is within the glass transition temperature range of polysulfone polymers (-20℃ to 0℃), preferably -10℃ to 0℃, and more preferably within the glass transition temperature range of -5℃ to 0℃; the heat treatment atmosphere is at least one of air, nitrogen, and argon; the heat treatment time is 0.5-48 hours, preferably 1-24 hours, more preferably 2-12 hours, and most preferably 4-8 hours. The principle of preparing polysulfone nanofiltration membrane products through surface thermally initiated crosslinking reaction is to utilize the different glass transition temperatures of the membrane material's surface and interior. By controlling the heat treatment temperature at a suitable value, only the chain segment movement of surface molecular chains is activated, thereby achieving thermally initiated polymerization and crosslinking reactions of small molecules on the surface, forming a separation skin layer; while simultaneously maintaining the macroporous structure inside the membrane material. Therefore, the heat treatment of the membrane material requires not only a suitable temperature but also a suitable duration. A series of experiments on this system show that if the heating time is less than 0.5 hours, the molecular chain movement on the membrane surface cannot be fully activated, the thermal cross-linking reaction cannot be fully carried out, and thus a complete separation layer with nanofiltration separation performance cannot be obtained. If the heating time is more than 48 hours, it will damage the mechanical properties of the membrane and make the membrane preparation process too long, which is not conducive to the application of membrane materials in actual water treatment scenarios.

[0020] The aforementioned method for preparing polysulfone-based nanofiltration membranes via thermally initiated polymerization and crosslinking on the surface of porous membranes offers advantages over existing methods for preparing nanofiltration membranes used in water treatment. It is more environmentally friendly and simpler, and is expected to be widely applied in the water treatment field in the future. This method allows for control over the pore structure of the prepared polysulfone-based ultrafiltration membrane by altering the conditions during the solvent-initiated phase separation process, thereby optimizing the membrane structure and improving permeability. Subsequently, by selecting appropriate thermally initiated polymerization molecules, processing temperature, and time, good nanofiltration separation performance can be achieved while minimizing the sacrifice of permeability, resulting in polysulfone-based nanofiltration membrane products with excellent separation and high permeability. The parts mentioned in this application are by weight. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process for preparing polysulfone nanofiltration membrane products by surface thermally initiated polymerization according to the present invention. Detailed Implementation

[0022] The present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] 1) Dissolve 20g of polyethersulfone powder, 5g of acrylamide and 5g of polyethylene glycol 400 in a three-necked flask with 70g of N,N-dimethylformamide to form a homogeneous casting solution.

[0025] 2) Subsequently, a uniform casting solution was applied to a flat and clean glass plate surface to form a coating with a thickness of 200 μm. The plate was then quickly placed in a coagulation bath at 30 °C and left for 10 min. When the polymer completely underwent phase separation and solidified and detached from the substrate, the plate was removed to obtain a polysulfone-based asymmetric structure ultrafiltration membrane preform with a uniformly porous surface (the air humidity was maintained at 55% during the preparation process).

[0026] 3) The obtained polysulfone membrane preform was air-dried naturally in the air for 24 hours, and then heated in a tube furnace (nitrogen atmosphere); first, the temperature was raised from room temperature to 176°C in 30 minutes, and then the temperature was raised to 226°C at a heating rate of 1°C / min and held for 4 hours; the thermally initiated polymerization of small molecules on the membrane surface caused cross-linking to form a surface separation layer, resulting in a polysulfone nanofiltration membrane product with excellent performance.

[0027] Example 2:

[0028] 1) Dissolve 15 g of polyethersulfone powder, 5 g of acrylamide and 5 g of polyethylene glycol 400 in a three-necked flask with 75 g of N,N-dimethylformamide to form a homogeneous casting solution.

[0029] 2) Subsequently, a uniform casting solution was applied to a flat and clean glass plate surface to form a coating with a thickness of 150 μm. The plate was then quickly placed in a coagulation bath at 30 °C and left for 10 min. When the polymer completely underwent phase separation and solidified and detached from the substrate, the plate was removed to obtain a polysulfone-based asymmetric structure ultrafiltration membrane preform with a uniformly porous surface (the air humidity was maintained at 50% during the preparation process).

[0030] 3) The obtained polysulfone membrane preform was air-dried naturally in the air for 24 hours, and then heated in a tube furnace (air atmosphere); first, the temperature was raised from room temperature to 178°C in 30 minutes, and then the temperature was raised to 228°C at a heating rate of 1°C / min and held for 4 hours; the heat-induced polymerization of small molecules on the membrane surface crosslinked to form a surface separation layer, resulting in a polysulfone nanofiltration membrane product with excellent performance.

[0031] Example 3:

[0032] 1) Dissolve 14g of polysulfone powder and 1g of triphenylamine in 85g of N,N-dimethylacetamide in a three-necked flask to form a homogeneous casting solution.

[0033] 2) Subsequently, a uniform casting solution was applied to a flat and clean glass plate surface to form a coating with a thickness of 100 μm. The plate was then quickly placed in a coagulation bath at 0 °C and left for 25 min. When the polymer completely underwent phase separation and solidified and detached from the substrate, the plate was removed to obtain a polysulfone-based asymmetric structure ultrafiltration membrane preform with a uniformly porous surface (the air humidity was maintained at 58% during the preparation process).

[0034] 3) The obtained polysulfone membrane preform was air-dried naturally in the air for 24 hours, and then heated in a tube furnace (argon atmosphere); first, the temperature was raised from room temperature to 180°C in 30 minutes, and then the temperature was raised to 230°C at a heating rate of 1°C / min and held for 1 hour; the thermally initiated polymerization of small molecules on the membrane surface caused cross-linking to form a surface separation layer, resulting in a polysulfone nanofiltration membrane product with excellent performance.

[0035] Example 4:

[0036] 1) Dissolve 30g of polyethersulfone powder, 10g of styrene and 10g of polyvinylpyrrolidone in a three-necked flask with 50g of N-methylpyrrolidone to form a homogeneous casting solution.

[0037] 2) Subsequently, a uniform casting solution was applied to a flat and clean glass plate surface to form a coating with a thickness of 300 μm. The plate was then quickly placed in a coagulation bath at 90 °C and left for 5 min. When the polymer completely underwent phase separation and solidified and detached from the substrate, the plate was removed to obtain a polysulfone-based asymmetric structure ultrafiltration membrane preform with a uniformly porous surface (the air humidity was maintained at 60% during the preparation process).

[0038] 3) The obtained polysulfone membrane preform was air-dried naturally for 24 hours, and then heated in a tube furnace (air atmosphere). First, the temperature was raised from room temperature to 170°C within 30 minutes, and then the temperature was raised to 220°C at a heating rate of 1°C / min and held for 24 hours. The heat-induced crosslinking of the polymerized small molecules on the membrane surface forms a surface separation layer, resulting in a polysulfone nanofiltration membrane product with excellent performance.

[0039] The following experimental data further demonstrates the beneficial effects of the present invention, as shown in Table 1.

[0040]

[0041] Table 1 shows that the nanofiltration membrane product exhibits high water permeability, with an external pressure water flux exceeding 60 liters / (m²*h) (4 bar, 25°C); simultaneously, it achieves a vitamin B12 rejection rate exceeding 95% (tested with water as the solvent); the product demonstrates excellent operational stability, with a permeability decrease of less than 20% after 48 hours of continuous testing at external pressure, and a vitamin B12 rejection rate still exceeding 90%. In summary, this invention utilizes a simple, environmentally friendly, and easily scalable process to prepare a polysulfone nanofiltration membrane product with excellent permeability and separation performance, overcoming numerous technical shortcomings of interfacial polymerization methods, such as difficult solvent recovery, large amounts of organic pollutants, cumbersome methods, interfacial effects affecting the long-term application of membrane materials, and difficulties in large-scale preparation. Furthermore, this invention, based on the fundamental physical phenomenon of "surface effect," fully applies the differences in glass transition behavior to nanofiltration membrane preparation, demonstrating strong innovation and providing inspiration for subsequent research in this field.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polysulfone-based nanofiltration membrane by surface thermal-initiated polymerization crosslinking reaction of a porous membrane, characterized in that It comprises the following steps: 1) configuring casting solution: 50-85 parts of organic solvent, 14-30 parts of polysulfone polymer, 1-10 parts of thermal initiation polymerization small molecule, 2-10 parts of additive, dissolving polysulfone polymer, thermal initiation polymerization small molecule and additive with organic solvent to obtain homogeneous casting solution; The thermal initiation polymerization small molecule is acrylamide, styrene, triphenylamine, triphosphazene, triptycene or other small molecules with matching thermal initiation temperature and polymer material glass transition temperature; The additive is one of polyethylene glycol and polyvinylpyrrolidone; 2) preparing surface porous polysulfone asymmetric structure ultrafiltration membrane embryo by non-solvent induced phase separation method: uniformly coating the casting solution prepared in 1) on the flat substrate surface, the coating thickness is 100-300 μm, then quickly placing it in a coagulation bath at 0-90 ℃ and staying for 5-25 min, when the polymer completely phase separates and solidifies and falls off from the substrate, it is taken out, thus obtaining a polysulfone asymmetric structure ultrafiltration membrane embryo with surface uniform pore structure, and the air humidity is kept at 55%±5% during the preparation process; 3) thermal initiation polymerization crosslinking: under a certain atmosphere, the polysulfone membrane embryo with surface porous structure obtained in 2) is heated in a heating device, the temperature is controlled at a value slightly lower than the glass transition temperature of the polysulfone polymer, and heating is performed for an appropriate time; at the same time, the temperature can just cause the thermal initiation polymerization small molecule added in step 1) to polymerize and cause thermal crosslinking; when the temperature is raised, the temperature is first raised from room temperature to a value 50 ℃ lower than the target temperature within 30 min, then the temperature is raised to the target value at a rate of 1 ℃ / min, and the reaction is completed to obtain a polysulfone nanofiltration membrane; The heat treatment temperature is in the range of -20 ℃-0 ℃ of the glass transition temperature of the polysulfone polymer, the heat treatment atmosphere is at least one of air, nitrogen and argon, and the heat treatment time is 0.5-48 hours.

2. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction for preparing a polysulfone-based nanofiltration membrane is characterized by In step 1), the organic solvent is 65-70 parts, the polysulfone polymer is 20-25 parts, the thermal initiation polymerization small molecule is 4-6 parts, and the additive is 5-7 parts.

3. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 100 °C. In step 1), the polysulfone polymer is one of polysulfone and polyethersulfone.

4. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 100 °C. In step 1), the organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

5. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 80 °C for 1-3 hours. In step 2), the casting solution coating thickness is 150-250 μm.

6. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 80 °C. In step 2), the casting solution coating thickness is 200-220 μm.

7. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 80 °C for 1-3 hours. In step 2), the coagulation bath is at least one of deionized water, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; the coagulation bath temperature is 10-80 ℃, and the coagulation bath time is 5-25 min.

8. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 80 °C. In step 2), the coagulation bath temperature is 30-50 ℃, and the coagulation bath time is 10-20 min.

9. The method for preparing polysulfone nanofiltration membranes by thermally initiated polymerization and crosslinking reaction on the surface of porous membranes as described in claim 1, characterized in that... In step 3), the heat treatment temperature is in the range of -10 ℃-0 ℃ of the glass transition temperature of the polysulfone polymer, and the heat treatment time is 1-24 hours.

10. The method of claim 1, wherein the porous membrane surface thermal-initiated polymerization crosslinking reaction is performed at a temperature of 60- 100 °C. In step 3), the heat treatment temperature is in the range of -5 ℃-0 ℃ of the glass transition temperature of the polysulfone polymer, and the heat treatment time is 4-8 hours.

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