A method for preparing an ultrafiltration membrane based on surface segregation, an anti-pollution ultrafiltration membrane and application thereof

Abstract

The application relates to a method for preparing an ultrafiltration membrane based on surface segregation, an anti-pollution ultrafiltration membrane and application thereof, and the method comprises the following steps: coating a casting solution to a substrate surface, scraping an initial state membrane on the surface of the substrate to obtain a substrate with the initial state membrane; the casting solution comprises polyvinylidene fluoride, a hydrophilic polymer and perfluorosulfonic acid; and placing the substrate with the initial state membrane in a coagulation solution to solidify into a membrane; the coagulation solution contains polyethyleneimine and water. The casting solution is converted into a solid membrane through non-solvent induced phase transition, perfluorosulfonic acid and polyethyleneimine are enriched on the surface, the surface segregation of perfluorosulfonic acid is enhanced, and the prepared ultrafiltration membrane has persistent and stable anti-pollution performance and high flux recovery rate after cleaning.

Description

Technical Field

[0001] This invention belongs to the field of membrane materials, specifically relating to a method for preparing ultrafiltration membranes based on surface segregation, an antifouling ultrafiltration membrane, and its applications. Background Technology

[0002] Ultrafiltration is a filtration technology that utilizes tangential fluid flow driven by pressure. It separates substances based on their molecular weight differences, effectively removing large molecules such as suspended solids, colloids, proteins, and microorganisms to achieve solution purification, separation, and concentration. However, membrane fouling occurs during filtration, leading to a decrease in membrane permeate velocity and a significant reduction in solute retention rate. This degrades the membrane separation characteristics during ultrafiltration, becoming a bottleneck restricting the application of membrane separation technology in purification and separation fields.

[0003] To obtain membrane materials and separation membranes with better antifouling performance, hydrophilic antifouling materials (such as polyethylene glycol, polyoxyethylene polymers, or zwitterionic polymers) are often used to modify hydrophobic polymer porous membranes. For example, hydrophilic molecules are introduced into the membrane surface to improve the hydrophilicity of the ultrafiltration membrane surface and improve its antifouling performance. For example, CN102755844A discloses a method for preparing a surface ionization modified polysulfone ultrafiltration membrane. This method involves blending an amphiphilic block copolymer containing poly(dimethylaminoethyl methacrylate)-polysulfone-poly(dimethylaminoethyl methacrylate) with a polysulfone solution, and preparing a polysulfone ultrafiltration membrane by immersion precipitation phase inversion. After the polysulfone ultrafiltration membrane is subjected to surface quaternization treatment with a bromoacid solution, the membrane surface simultaneously carries both anions and cations, significantly improving the membrane's hydrophilicity and antifouling ability.

[0004] CN105727760A discloses an antifouling ultrafiltration membrane grafted with amino acids onto composite cellulose. This ultrafiltration membrane uses an ultrafiltration membrane composed of oxidized nanocellulose and cellulose acetate as the base membrane, which is activated in a solution containing a condensing agent and an amide to form a carbonyl activator, and then grafted with amino acids to prepare the antifouling ultrafiltration membrane. However, although this ultrafiltration membrane exhibits excellent antifouling performance, simple hydrophilic antifouling modification alone cannot meet the diverse needs for antifouled surfaces.

[0005] In recent years, polymer copolymers containing hydrophilic segments and nonpolar low surface energy segments have been frequently used to construct amphiphilic antifouling membranes. The surface of an amphiphilic antifouling membrane is chemically composed of randomly distributed hydrophilic and low surface energy microregions. The hydrophilic regions can tightly bind a significant number of water molecules to form a hydration layer, acting as a barrier to pollutant adsorption on the surface. The low surface energy regions reduce the interaction between the surface and polar pollutants, making it easier for pollutants to leave the surface. Based on the synergistic antifouling effect of the hydrophilic and low surface energy microregions, both reversible and irreversible fouling of pollutants on the membrane surface can be effectively reduced, further improving the membrane's application efficiency. For example, CN103755891A discloses an antifouling ultrafiltration membrane prepared by filling a polysiloxane amphiphilic surface modifier, which can effectively inhibit membrane fouling problems caused by proteins, polysaccharides, and microorganisms during the separation process.

[0006] However, in existing surface modification methods, the interaction between the coating layer and the membrane surface is weak, and the coating layer is easy to fall off the membrane surface, which leads to a weakening or disappearance of the modification effect. Surface grafting modification is prone to membrane pore blockage, resulting in a decrease in water flux, and the pore size distribution cannot be effectively controlled. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of severe pore blockage and difficult membrane pore modification in existing modification methods, and to improve the flux recovery rate of ultrafiltration membranes.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing an ultrafiltration membrane, the method comprising: S1. A casting solution is coated onto the surface of a substrate, and a nascent film is formed by scraping the surface of the substrate to obtain a substrate with a nascent film; the casting solution includes polyvinylidene fluoride, a hydrophilic polymer, and perfluorosulfonic acid; S2. The substrate with the initial film is placed in a coagulation solution to solidify into a film; the coagulation solution contains polyethyleneimine and water.

[0009] Optionally, the perfluorosulfonic acid content in the casting solution is 0.05-0.15 wt%, preferably 0.05-0.125 wt%; and / or the polyvinylidene fluoride content in the casting solution is 12-15 wt%; preferably, the hydrophilic polymer is selected from one or more of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone, preferably polyethylene glycol; preferably, the content of the hydrophilic polymer in the casting solution is 6-8 wt%; optionally, the number average molecular weight of the hydrophilic polymer is 1000-3000.

[0010] Optionally, the viscosity of the casting solution is 0.18-0.35 mPa·s.

[0011] Optionally, the casting solution is prepared by a method comprising the following steps: dissolving polyvinylidene fluoride, polyethylene glycol, and perfluorosulfonic acid in an organic solvent and stirring until homogeneous, and allowing the resulting solution to stand and degas until no obvious bubbles are present; optionally, the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; optionally, the conditions for standing and degassing include: a temperature of 55-65 °C and a time of 6-12 h.

[0012] Optionally, the thickness of the initial state film is 150-300 μm.

[0013] Optionally, the concentration of polyethyleneimine in the coagulation solution is 0.05-0.15 wt%; preferably, the temperature of the coagulation solution is 20-25 °C.

[0014] Optionally, the method further includes: placing the substrate with the initial film in the air for 10-30 seconds and then transferring it into the coagulation liquid for phase inversion to form a film.

[0015] Optionally, the method further includes: separating the solid film formed by curing from the substrate, and immersing the separated solid film in water; the immersion time of the solid film in water is 16-30 h, and the water temperature is 20-30℃.

[0016] A second aspect of the present invention provides an antifouling ultrafiltration membrane, which is prepared by the method described in the first aspect of the present invention; preferably, the pure water permeability of the antifouling ultrafiltration membrane is 340-367 L / (m³). 2 ·h·bar).

[0017] The third aspect of the present invention provides the application of the antifouling ultrafiltration membrane described in the second aspect of the present invention in water treatment.

[0018] Through the above technical solution, the present invention transfers the initial membrane formed by the casting solution into a coagulation solution containing polyethyleneimine for solidification. A solid membrane is generated through non-solvent-induced phase transformation, which allows the negatively charged perfluorosulfonic acid in the casting solution to react with the positively charged polyethyleneimine at the membrane-water interface through electrostatic interaction. This enriches the perfluorosulfonic acid and polyethyleneimine on the surface, enhancing the surface segregation of perfluorosulfonic acid. The resulting ultrafiltration membrane has durable, stable, and highly efficient antifouling properties, and a high flux recovery rate after cleaning.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] In existing technologies, to obtain membrane materials and separation membranes with better performance, the requirements for modification methods are stringent. While endowing the membrane with long-term antifouling ability, it is also necessary to take into account the impact on membrane permeation and retention performance. However, modification methods such as surface coating and surface grafting have drawbacks such as complex processes, severe pore blockage, and difficulty in modifying membrane pores. Surface segregation methods can simultaneously modify membrane pores and surfaces during phase transformation into membranes.

[0022] A first aspect of the present invention provides a method for preparing an ultrafiltration membrane, the method comprising: S1. A casting solution is coated onto the surface of a substrate, and a nascent film is formed by scraping the surface of the substrate to obtain a substrate with a nascent film; the casting solution includes polyvinylidene fluoride, a hydrophilic polymer, and perfluorosulfonic acid; S2. The substrate with the initial film is placed in a coagulation solution to solidify into a film; the coagulation solution contains polyethyleneimine and water.

[0023] Through the above technical solution, the present invention transfers the initial membrane formed by the casting solution into a coagulation solution containing polyethyleneimine for solidification. A solid membrane is generated through non-solvent-induced phase transformation, which allows the negatively charged perfluorosulfonic acid in the casting solution to react with the positively charged polyethyleneimine at the membrane-water interface through electrostatic interaction. This enriches the perfluorosulfonic acid and polyethyleneimine on the surface, enhancing the surface segregation of perfluorosulfonic acid. The resulting ultrafiltration membrane has durable, stable, and highly efficient antifouling properties, and a high flux recovery rate after cleaning.

[0024] The method provided by this invention utilizes the hydrophilicity-hydrophobicity difference between perfluorosulfonic acid and polyvinylidene fluoride (PVDF) substrate membrane, and the electrostatic interaction between perfluorosulfonic acid and polyethyleneimine, to enhance the surface segregation of perfluorosulfonic acid, thereby enriching perfluorosulfonic acid and polyethylene on the membrane surface in situ. This achieves in-situ modification of the ultrafiltration membrane, and simultaneously modifies the membrane surface and ultrafiltration membrane pores. Furthermore, the ultrafiltration membrane exhibits durable and stable antifouling properties.

[0025] In some embodiments of the present invention, the content of perfluorosulfonic acid in the casting solution is 0.05-0.15 wt%, for example, it can be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.075 wt%, 0.08 wt%, 0.09 wt%, 0.10 wt%, 0.11 wt%, 0.12 wt%, 0.125 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, or any value within the aforementioned range, or any range composed of values ​​within the aforementioned range. Controlling the content of perfluorosulfonic acid in the casting solution is beneficial to improving the hydrophobicity of the ultrafiltration membrane and enhancing its antifouling performance. To further improve the antifouling performance of the ultrafiltration membrane and improve its flux recovery rate, the content of perfluorosulfonic acid in the casting solution is 0.05-0.125 wt%.

[0026] In this invention, an ultrafiltration membrane is prepared using polyvinylidene fluoride (PVDF) as the host membrane, and polyethylene glycol is added to the casting solution to improve the membrane's hydrophilicity, thereby increasing the water permeation of the ultrafiltration membrane. In some embodiments, the PVDF content is 12-15 wt%.

[0027] In some embodiments of the present invention, the hydrophilic polymer may be selected from one or more of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone. Introducing a hydrophilic polymer can improve the antifouling properties of the ultrafiltration membrane.

[0028] In some embodiments of the present invention, the content of the hydrophilic polymer in the casting solution is 6-8 wt%. This improves the porosity and pure water flux of the ultrafiltration membrane, and enhances its hydrophilicity and antifouling properties.

[0029] In some preferred embodiments of the present invention, the hydrophilic polymer is polyethylene glycol.

[0030] In some specific embodiments of the present invention, the number average molecular weight of the polyethylene glycol can be 1000-3000. By adding a hydrophilic polymer with appropriate chain length and content, the blending of the hydrophilic polymer with polyvinylidene fluoride leads to delayed phase separation behavior during phase inversion, which is beneficial to enhancing the porosity of the ultrafiltration membrane sublayer structure, thereby improving the porosity and pure water flux of the ultrafiltration membrane.

[0031] In some embodiments of the present invention, the viscosity of the casting solution is 0.18-0.35 mPa·s. Thus, the casting solution has a suitable viscosity, resulting in good fluidity and good scraping properties, which is beneficial for obtaining a uniform and dense initial film.

[0032] In some embodiments of the present invention, the casting solution is prepared by a method comprising the following steps: dissolving polyvinylidene fluoride, polyethylene glycol and perfluorosulfonic acid in an organic solvent and stirring until homogeneous, and allowing the resulting solution to stand and degas until no obvious bubbles are present.

[0033] The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0034] In some preferred embodiments of the present invention, the dissolution temperature of the polyvinylidene fluoride, polyethylene glycol, and perfluorosulfonic acid in the organic solvent is 60-70 °C. Since the polyvinylidene fluoride substrate undergoes solvation during dissolution in the organic solvent, a suitable dissolution temperature is beneficial for forming a regular surface structure.

[0035] The static degassing conditions include a temperature of 55-65 ℃ and a time of 6-12 h. Static degassing of the casting solution effectively reduces air bubbles, thus preventing the formation of air bubbles in the initial membrane and affecting membrane quality.

[0036] In some embodiments of the present invention, the thickness of the initial state film is 150-300 μm.

[0037] In some embodiments of the present invention, the concentration of polyethyleneimine in the coagulation solution is 0.05-0.15 wt%, for example, it can be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.10 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, or any value within the aforementioned range, or any range composed of values ​​from the aforementioned range. Controlling the concentration of polyethyleneimine in the coagulation solution is beneficial for the uniform enrichment of polyethyleneimine on the membrane surface.

[0038] In some embodiments of the present invention, the temperature of the coagulation liquid is 20-25 °C.

[0039] In some embodiments of the present invention, the method further includes: placing the substrate with the initial film in the air for 10-30 seconds and then transferring it into the coagulation liquid for phase inversion to form a film.

[0040] In some embodiments of the present invention, the method further includes: separating the solid membrane formed by curing from the substrate, and immersing the separated solid membrane in water; the solid membrane is immersed in water for 16-30 hours at a water temperature of 20-30 °C to remove impurities from the modified ultrafiltration membrane.

[0041] The method for preparing modified polyvinylidene fluoride ultrafiltration membranes based on surface segregation of the present invention has the advantages of simple process and easy operation, and the obtained ultrafiltration membrane has strong antifouling ability and high flux recovery rate.

[0042] A second aspect of the present invention provides an antifouling ultrafiltration membrane, which is prepared by the method described in the first aspect of the present invention.

[0043] In some embodiments of the present invention, the porosity of the antifouling ultrafiltration membrane is 80-88%, and the average pore size is 40-70 nm. The antifouling ultrafiltration membrane prepared by the method of the present invention has high porosity, and the membrane channels are not blocked during the preparation process.

[0044] In this invention, the membrane prepared by the method of this invention exhibits high water permeation flux and excellent antifouling performance. In some embodiments of this invention, the pure water permeability of the antifouling ultrafiltration membrane is 340-367 L / (m³). 2 ·h·bar).

[0045] The present invention also provides the application of the antifouling ultrafiltration membrane described in the second aspect of the present invention in water treatment.

[0046] The antifouling ultrafiltration membrane provided by this invention can reduce membrane fouling during oil and water treatment, and the membrane flux recovery rate is high after cleaning.

[0047] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0048] The hydrophilic polymer used in the examples and comparative examples is polyethylene glycol 2000; the polyvinylidene fluoride used is Solef 6020.

[0049] Example 1 This embodiment illustrates the method for preparing the antifouling ultrafiltration membrane of the present invention, including the following steps: S1. Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.05 parts by weight of perfluorosulfonic acid and dissolve them in 80.95 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution; the viscosity of the casting solution is 0.3 mPa·s. S2. The casting solution is allowed to stand at 60 °C for 6 hours to degas until there are no obvious bubbles. After the casting solution is cooled to room temperature, it is poured onto a glass plate and scraped to form a preliminary film. The thickness of the scraper is 240 μm. S3. After placing the glass plate with the initial film on its surface in the air for 20 seconds, it is placed in a 25 °C coagulation solution to solidify into a film. The coagulation solution is a polyethyleneimine aqueous solution with a mass fraction of 0.1 wt% and a pH value of 9. The solidified film is separated from the glass plate and soaked in deionized water for 24 hours to obtain a modified polyvinylidene fluoride ultrafiltration membrane, denoted as M1.

[0050] Example 2 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.04 parts by weight of perfluorosulfonic acid and dissolve them in 80.96 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0051] The resulting modified polyvinylidene fluoride ultrafiltration membrane is denoted as M2.

[0052] Example 3 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.075 parts by weight of perfluorosulfonic acid and dissolve them in 80.925 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0053] The modified polyvinylidene fluoride ultrafiltration membrane obtained is designated as M3.

[0054] Example 4 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.1 parts by weight of perfluorosulfonic acid and dissolve them in 80.9 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0055] The obtained modified polyvinylidene fluoride ultrafiltration membrane is designated as M4.

[0056] Example 5 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.125 parts by weight of perfluorosulfonic acid and dissolve them in 80.875 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0057] The resulting modified polyvinylidene fluoride ultrafiltration membrane is designated as M5.

[0058] Example 6 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.15 parts by weight of perfluorosulfonic acid and dissolve them in 80.85 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0059] The resulting modified polyvinylidene fluoride ultrafiltration membrane is designated as M6.

[0060] Example 7 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the preparation step of the homogeneous casting solution in step S1 includes: Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.165 parts by weight of perfluorosulfonic acid and dissolve them in 80.835 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution.

[0061] The obtained modified polyvinylidene fluoride ultrafiltration membrane is designated as M7.

[0062] Example 8 The method for preparing the ultrafiltration membrane in this embodiment is basically similar to that in Example 1, except that the mass fraction of polyethyleneimine in the coagulation solution in step S3 is 0.2 wt% polyethyleneimine aqueous solution, and the pH value of the coagulation solution is 10.

[0063] The obtained modified polyvinylidene fluoride ultrafiltration membrane is designated as M8.

[0064] Comparative Example 1 The method for preparing ultrafiltration membranes in this comparative example includes the following steps: S1. Weigh 12 parts by weight of polyvinylidene fluoride and 7 parts by weight of polyethylene glycol 2000 and dissolve them in 81 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution. S2. The casting solution is allowed to stand at 60 °C for 6 hours to degas until there are no obvious bubbles. After the casting solution is cooled to room temperature, it is poured onto a glass plate and scraped to form a preliminary film. The thickness of the scraper is 240 μm. S3. After placing the glass plate with the initial film on its surface in the air for 20 seconds, it is placed in a 25°C coagulation solution to solidify into a film. The coagulation solution is deionized water. The solidified film is separated from the glass plate and soaked in deionized water for 24 hours to obtain a polyvinylidene fluoride ultrafiltration membrane, denoted as DM1.

[0065] Comparative Example 2 The method for preparing ultrafiltration membranes in this comparative example includes the following steps: S1. Weigh 12 parts by weight of polyvinylidene fluoride and 7 parts by weight of polyethylene glycol 2000 and dissolve them in 81 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution. S2. The casting solution is allowed to stand at 60 °C for 6 hours to degas until there are no obvious bubbles. After the casting solution is cooled to room temperature, it is poured onto a glass plate and scraped to form a preliminary film. The thickness of the scraper is 240 μm. S3. After placing the glass plate with the initial film on its surface in the air for 20 seconds, it is placed in a 25°C coagulation solution to solidify into a film. The coagulation solution is a polyethyleneimine aqueous solution with a mass fraction of 0.1 wt% and a pH value of 9. The solidified film is separated from the glass plate and soaked in deionized water for 24 hours to obtain a polyvinylidene fluoride ultrafiltration membrane, denoted as DM2.

[0066] Comparative Example 3 The method for preparing ultrafiltration membranes in this comparative example includes the following steps: S1. Weigh 12 parts by weight of polyvinylidene fluoride, 7 parts by weight of polyethylene glycol 2000 and 0.05 parts by weight of perfluorosulfonic acid and dissolve them in 80.95 parts by weight of N-methylpyrrolidone. Stir at 60 °C for 5 hours to prepare a homogeneous casting solution. S2. The casting solution is allowed to stand at 60 °C for 6 hours to degas until there are no obvious bubbles. After the casting solution is cooled to room temperature, it is poured onto a glass plate and scraped to form a preliminary film. The thickness of the scraper is 240 μm. S3. After placing the glass plate with the initial film on its surface in the air for 20 seconds, it is placed in a 25°C coagulation solution to solidify into a film. The coagulation solution is deionized water. The solidified film is separated from the glass plate and soaked in deionized water for 24 hours to obtain a polyvinylidene fluoride ultrafiltration membrane, denoted as DM3.

[0067] Test case The porosity and average pore size of the modified polyvinylidene fluoride ultrafiltration membranes M1-M8 prepared in Examples 1-8 and the polyvinylidene fluoride ultrafiltration membranes DM1-DM3 prepared in Comparative Examples 1-3 were measured, and the results are shown in Table 1.

[0068] The performance of the modified polyvinylidene fluoride (PVDF) ultrafiltration membranes M1-M8 prepared in Examples 1-8 and DM1-DM3 prepared in Comparative Examples 1-3 was evaluated using a cross-flow device. Evaluation included water permeate flux measurement and antifouling performance testing (including flux decay and flux recovery during separation). The effective membrane area of ​​the cross-flow device was 25 cm². 2 .

[0069] Preparation of simulated pollutant solution: 0.9 g of emulsified pump oil was added to 1000 mL of deionized water, and then 0.1 g of sodium dodecyl sulfate was added. The mixture was mechanically stirred for more than 12 h to form a surfactant-stabilized oil-in-water emulsion.

[0070] The testing methods include: Water permeation flux measurement: Under a pressure of 0.15 MPa, the polyvinylidene fluoride ultrafiltration membranes prepared in the examples and comparative examples were pressed with deionized water to obtain a stable flux for each membrane. Then, the water permeation flux (volume) of each ultrafiltration membrane was measured under a pressure of 0.10 MPa to obtain the initial flux; the results are shown in Table 1.

[0071] Anti-fouling performance test: After the water permeation flux measurement was completed, the deionized water was replaced with the prepared simulated pollutant solution, and the measurement was carried out at a pressure of 0.10 MPa. The volume of the permeate was recorded. The permeation flux of the simulated pollutant solution was recorded at 60 min. Then, the membrane was cleaned with deionized water for 30 minutes to remove contaminants from the pipes and membrane surface. The permeate flux of the cleaned membrane was tested under the same test conditions as the initial flux to obtain the recovery water flux. The flux recovery rate and irreversible flux decay rate of each membrane were calculated respectively.

[0072] Table 1

[0073] As can be seen from the data in the table above, the modified antifouling membrane prepared by the method of the present invention exhibits excellent separation performance and antifouling effect when used for oil-water separation. While maintaining a high level of permeate flux, the flux recovery rate is significantly improved.

[0074] In Example 4, the best flux recovery rate was observed when the perfluorosulfonic acid content in the casting solution was 0.1 wt%, and the initial water permeation flux was 367 L·m⁻¹ when used for oil-water separation. -2 ·h -1 It decreased to 128 L·m during oil-water emulsion separation. -2 ·h -1 After rinsing the membrane surface with water for 30 minutes, the flux recovery rate can reach 98.1%.

[0075] The data in the table above also reveals that when the perfluorosulfonic acid content in the casting solution is too low, less perfluorosulfonic acid accumulates on the main membrane surface and binds with polyethyleneimine, resulting in a significant decrease in water flux during water emulsion separation and a reduced flux recovery rate after rinsing. Conversely, when the amount of perfluorosulfonic acid is excessive, the hydrophilicity of the membrane surface decreases significantly, leading to a lower flux recovery rate. The method of this invention utilizes the electrostatic interaction between perfluorosulfonic acid and polyethyleneimine, allowing both perfluorosulfonic acid and polyethyleneimine to accumulate in situ on the membrane surface without clogging the membrane pores or altering the membrane's pore structure.

[0076] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0077] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0078] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing an ultrafiltration membrane, characterized in that, The method includes: S1. A casting solution is coated onto the surface of a substrate, and a nascent film is formed by scraping the surface of the substrate to obtain a substrate with a nascent film; the casting solution includes polyvinylidene fluoride, a hydrophilic polymer, and perfluorosulfonic acid; S2. The substrate with the initial film is placed in a coagulation solution to solidify into a film; the coagulation solution contains polyethyleneimine and water.

2. The method according to claim 1, wherein, The perfluorosulfonic acid content in the casting solution is 0.05-0.15 wt%, preferably 0.05-0.125 wt%. And / or the polyvinylidene fluoride content in the casting solution is 12-15 wt%; Preferably, the hydrophilic polymer is selected from one or more of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone, with polyethylene glycol being the most preferred. Preferably, the hydrophilic polymer in the casting solution is 6-8 wt%. Optionally, the number-average molecular weight of the hydrophilic polymer is 1000-3000.

3. The method according to claim 1, wherein, The viscosity of the casting solution is 0.18-0.35 mPa·s.

4. The method according to claim 1, wherein, The casting solution is prepared by a method including the following steps: dissolving polyvinylidene fluoride, polyethylene glycol and perfluorosulfonic acid in an organic solvent and stirring until uniform, and then allowing the resulting solution to stand and degas until there are no obvious bubbles; Optionally, the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; Optionally, the static degassing conditions include a temperature of 55-65 ℃ and a time of 6-12 h.

5. The method according to claim 1, wherein, The initial film has a thickness of 150-300 μm.

6. The method according to claim 1, wherein, The concentration of polyethyleneimine in the coagulated solution is 0.05-0.15 wt%. Preferably, the temperature of the coagulated liquid is 20-25 °C.

7. The method according to claim 1, wherein, The method further includes: placing the substrate with the initial film in the air for 10-30 seconds and then transferring it into the coagulation liquid to perform phase transformation into a film.

8. The method according to claim 1, wherein, The method further includes: separating the solid film formed by curing from the substrate, and immersing the separated solid film in water; The solid membrane is immersed in water for 16-30 hours at a temperature of 20-30 °C.

9. An antifouling ultrafiltration membrane, characterized in that, The antifouling ultrafiltration membrane is prepared by the method described in any one of claims 1-8; Preferably, the pure water permeability of the antifouling ultrafiltration membrane is 340-367 L / (m³). 2 ·h·bar).

10. The application of the antifouling ultrafiltration membrane according to claim 9 in water treatment.

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