A preparation method of surface decontamination ultrafiltration membrane

Abstract

The present invention relates to the field of ultrafiltration membrane technology, and specifically discloses a method for preparing a surface decontamination ultrafiltration membrane. The method for preparing the surface decontamination ultrafiltration membrane comprises: preparing a sulfonated cross-linked base membrane; preparing a grafting liquid; preparing a zwitterionic grafted membrane; preparing a prepolymer solution; immersing the zwitterionic grafted membrane in the prepolymer solution, vacuum impregnation, curing, purging with nitrogen, and vacuum drying to obtain a surface decontamination ultrafiltration membrane. The present invention achieves a balance between anti-pollution, durability and adaptability through the synergy of molecular design and process. Specifically, the hydrophilicity enhanced by the sulfonic acid group of the surface decontamination ultrafiltration membrane reduces operating energy consumption, the zwitterionic layer inhibits the adsorption of pollutants and reduces the cleaning frequency, and the self-repairing characteristics of the dynamic network reduce maintenance costs, thereby providing a more economical and efficient solution for difficult water treatment scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafiltration membranes, in particular to a method for preparing a surface decontamination ultrafiltration membrane. Background Art

[0002] As a core component of modern separation technology, filter membranes play an irreplaceable role in water treatment, food industry, biomedicine and other fields. Their core function is to achieve efficient interception of pollutants through physical screening and charge repulsion mechanisms. However, in practical applications, membrane fouling has always been a key bottleneck restricting their performance and lifespan. Membrane fouling not only leads to flux attenuation and increased energy consumption, but also causes frequent chemical cleaning, causing damage to membrane materials and environmental burdens. When faced with complex pollutant systems, traditional ultrafiltration membranes often find it difficult to balance interception efficiency and long-term stability due to their single anti-fouling mechanism and insufficient self-cleaning ability. This makes the development of a new generation of anti-fouling ultrafiltration membranes a technical challenge that the industry urgently needs to overcome.

[0003] In actual operation, ultrafiltration membranes face two main types of pollution threats: first, organic pollutants, such as macromolecular substances such as proteins, polysaccharides, and oils, which easily form a dense gel layer on the membrane surface, obstructing the water flow channel; second, inorganic pollutants, such as calcium and magnesium ions combined with sulfates and carbonates to form a micron-sized scale layer. This type of sediment will irreversibly block the membrane pores. Existing technologies mostly rely on single hydrophilic modification or physical flushing methods, but hydrophilic coatings are easily affected by fluctuations in the chemical environment and become ineffective, and physical cleaning cannot completely remove deeply adsorbed pollutants. Even more seriously, frequent acid or alkaline washing will damage the membrane structure, resulting in a decrease in porosity and the loss of functional groups, forming a vicious cycle of "cleaning-pollution-re-cleaning."

[0004] The industry is in urgent need of an ultrafiltration membrane technology that can fundamentally achieve a breakthrough in the synergistic optimization of anti-pollution performance and self-cleaning capabilities. This technology must significantly improve the membrane material's tolerance to multiple pollutants without sacrificing retention efficiency, while reducing cleaning frequency and reliance on chemicals, thereby extending the life of the membrane components and reducing operation and maintenance costs. Solving this problem is not only related to the sustainable development of the water treatment industry, but also provides key support for the large-scale application of ultrafiltration technology in challenging water treatment scenarios (such as oily wastewater and high-salinity seawater desalination). Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing a surface decontamination ultrafiltration membrane.

[0006] A method for preparing a surface decontamination ultrafiltration membrane comprises the following steps:

[0007] S1. Mix polyethersulfone and concentrated sulfuric acid, stir, add polyvinyl butyral, glutaraldehyde, and divinylbenzene, adjust the pH of the system, stir, cool, and vacuum dry, add N-methylpyrrolidone and polyvinylpyrrolidone, stir, ultrasonically degas, and let stand. Use a non-woven fabric as a support layer, scrape a wet film on a glass plate with a scraper, and soak it in deionized water to obtain a sulfonated cross-linked base membrane;

[0008] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, and ultrasonicating to obtain grafting solution 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonicating to obtain grafting solution 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonicating to obtain grafting solution 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting solution 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting solution 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting solution 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane;

[0009] S3. Mix polyethyleneimine and glyoxal, stir, and obtain a prepolymer solution; immerse the zwitterion grafted membrane in the prepolymer solution, vacuum impregnate, solidify, purge with nitrogen, and vacuum dry to obtain a surface decontamination ultrafiltration membrane.

[0010] Preferably, in step S1, the weight ratio of polyethersulfone, concentrated sulfuric acid, polyvinyl butyral, glutaraldehyde, divinylbenzene, N-methylpyrrolidone, and polyvinylpyrrolidone is 500:1500:25:15:2-3:1500:25.

[0011] Preferably, in step S1, polyethersulfone and concentrated sulfuric acid are mixed and stirred at a temperature of 45-55° C., a stirring time of 3-5 h, and a stirring speed of 400-600 rpm.

[0012] Preferably, in step S1, the pH value of the system is adjusted to 4 using an acetic acid solution with a mass fraction of 10%.

[0013] Preferably, in step S1, the pH of the system is adjusted and then stirred at a temperature of 55-65° C., a stirring time of 1-3 h, and a stirring speed of 200-400 rpm.

[0014] Preferably, in step S1, N-methylpyrrolidone and polyvinylpyrrolidone are added and stirred at a temperature of 55-65° C., a stirring time of 7-9 h, and a stirring speed of 200-400 rpm.

[0015] Preferably, in step S1, the ultrasonic degassing time is 0.3-0.7 h, and the standing time after ultrasonic degassing is 22-26 h.

[0016] Preferably, in step S2, the sulfobetaine is one of dodecyl sulfopropyl betaine, tetradecyl sulfopropyl betaine, cocamidopropyl hydroxysulfobetaine, and oleamidopropyl hydroxysulfobetaine.

[0017] Preferably, in step S2, the duration of the three ultrasonic treatments is 0.3-1 h, and the ultrasonic frequency is 40 kHz.

[0018] Preferably, in step S3, the weight ratio of polyethyleneimine to glyoxal is 3:2.

[0019] Preferably, in step S3, polyethyleneimine and glyoxal are mixed and stirred at a temperature of 55-65° C., a stirring time of 0.5-1.5 h, and a stirring speed of 300-500 rpm.

[0020] Preferably, in step S3, vacuum impregnation is performed by pumping the vacuum pump to -0.08-0.15 MPa and maintaining the pressure for 2-4 hours.

[0021] Preferably, in the step S3, curing is performed at a temperature of 55-65° C. and a curing time of 1-3 hours.

[0022] Preferably, in step S3, nitrogen is used for purging, the purging time is 5-15 minutes, and the nitrogen flow rate is 5-15 L / min.

[0023] Beneficial effects:

[0024] The surface decontamination ultrafiltration membrane provided by this invention achieves breakthroughs in pollution resistance, self-repairing ability, and long-term stability through innovative molecular structure and coordinated functional design. This addresses the core issues of traditional ultrafiltration membranes in complex water treatment, such as easy contamination, difficult cleaning, and short lifespan. Its innovations are primarily reflected in three aspects: a sulfonated cross-linked base membrane enhances hydrophilicity, a zwitterionic gradient grafting creates a charge-balancing barrier, and a dynamic imine bond network imparts self-repairing capabilities. The synergistic effect of these three factors enables the membrane to demonstrate excellent performance in highly polluted environments such as oily wastewater and high-salt solutions.

[0025] The sulfonation reaction introduces sulfonic acid groups into the polyethersulfone molecular chain, which is then cross-linked with dynamic acetal bonds to form a stable hydrophilic base membrane, which can not only reduce the attachment of pollutants, but also provide active sites for subsequent functional modifications. On this basis, sulfobetaine is gradient-grafted onto the membrane surface through free radical initiation. The sulfonic acid groups of the zwitterions and the quaternary ammonium groups form a charge balance layer, which uses hydration to repel pollutants such as proteins and oils. It is particularly suitable for scenarios such as milk protein separation in food processing wastewater and emulsified oil retention in oilfield reinjection water. Finally, the introduction of a dynamic imine bond network forms a reversible cross-linked structure. When pollutants accumulate on the membrane surface, acid washing can temporarily open the cross-linking points to release the pollutants. After cleaning, the network automatically reorganizes and restores its function. This feature greatly extends the service life of the membrane in working conditions that require frequent cleaning, such as electroplating wastewater treatment and seawater desalination pretreatment.

[0026] This multi-level design has multiple advantages in practical applications: the enhanced hydrophilicity of the sulfonic acid groups reduces operating energy consumption, the zwitterionic layer inhibits the adsorption of pollutants and reduces the frequency of cleaning, and the self-healing properties of the dynamic network reduce maintenance costs. For example, in the treatment of printing and dyeing wastewater, the charge barrier on the membrane surface can effectively intercept dye molecules, while the dynamic network protects the membrane structure during strong acid cleaning; in the biopharmaceutical field, the zwitterionic layer's ability to resist protein contamination combined with its self-healing properties ensures the stability of the membrane under frequent sterilization operations. Compared to the limitations of traditional membrane materials that only have anti-fouling properties or increased mechanical strength, this technology achieves a balance between anti-fouling, durability, and adaptability through the synergy of molecular design and process, providing a more economical and efficient solution for difficult water treatment scenarios. DETAILED DESCRIPTION

[0027] The present invention will be further explained below with reference to specific embodiments.

[0028] The polyethersulfone used below was purchased from Shandong Haoran Special Plastic Co., Ltd.

[0029] Example 1

[0030] A surface decontamination ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0031] S1, 500g polyether sulfone, 1500g concentrated sulfuric acid are mixed, at 55 ℃ of stirring for 5h, stirring speed is 600rpm (concentrated sulfuric acid hydrolyzes sulfone group to sulfonic acid group, enhances hydrophilicity), add 25g polyvinyl butyral, 15g glutaraldehyde, 3g divinylbenzene, adopting mass fraction to be 10% acetic acid solution adjustment system pH value is 4, at 65 ℃ of stirring for 3h, stirring speed is 400rpm (hydroxyl group of polyvinyl butyral and sulfonic acid group condense to generate acetal bond, and the aldehyde group of glutaraldehyde and the residual hydroxyl group of polyvinyl butyral are cross-linked to form dynamic network), cooling, vacuum drying, add 1500g N-Methyl pyrrolidone, 25g polyvinyl pyrrolidone, at 65 ℃ of stirring for 9h, stirring speed is 400rpm, ultrasonic deaeration 0.7h, leave standstill 26h, with non-woven fabric as supporting layer, on glass plate, scrape out wet film of thickness 250 μm with scraper, be placed in deionized water and soak, obtain sulfonated cross-linked base film;

[0032] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, letting it stand at 60°C for 1h, taking it out and rinsing it, immersing it in grafting liquid 2, letting it stand at 60°C for 1.5h, taking it out and rinsing it, immersing it in grafting liquid 3, letting it stand at 60°C for 2h, taking it out and rinsing it, and vacuum drying it to obtain a zwitterionic gradient grafted membrane;

[0033] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 65 ° C for 1.5 h, and stir at a speed of 500 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.15 MPa with a vacuum pump and maintain for 4 h, and cure at 65 ° C for 3 h (the amino group of polyethyleneimine and the aldehyde group of glyoxal form a dynamic imine bond; the imine bond can be reversibly broken during acid washing and reorganized after releasing pollutants), purge with nitrogen for 15 min at a nitrogen flow rate of 15 L / min, and vacuum dry to obtain a surface decontamination ultrafiltration membrane.

[0034] Example 2

[0035] A surface decontamination ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0036] S1, 500g polyethersulfone, 1500g concentrated sulfuric acid were mixed, stirred at 45 ° C for 3h, stirring speed was 400rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, stirred at 55 ° C for 1h, stirring speed was 200rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone, 25g polyvinylpyrrolidone were added, stirred at 55 ° C for 7h, stirring speed was 200rpm, ultrasonic degassing was performed for 0.3h, and the film was allowed to stand for 22h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and immersed in deionized water to obtain a sulfonated cross-linked base membrane;

[0037] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, letting it stand at 60°C for 1h, taking it out and rinsing it, immersing it in grafting liquid 2, letting it stand at 60°C for 1.5h, taking it out and rinsing it, immersing it in grafting liquid 3, letting it stand at 60°C for 2h, taking it out and rinsing it, and vacuum drying it to obtain a zwitterionic gradient grafted membrane;

[0038] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 55 ° C for 0.5 h, and stir at a speed of 300 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.08 MPa with a vacuum pump and maintain for 2 h, cure at 55 ° C for 1 h, purge with nitrogen for 5 min, and dry in vacuum to obtain a surface decontamination ultrafiltration membrane.

[0039] Example 3

[0040] A surface decontamination ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0041] S1, 500g polyethersulfone, 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, stirred at 60°C for 2h, stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone, 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and allowed to stand for 24h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and immersed in deionized water to obtain a sulfonated cross-linked base membrane;

[0042] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, letting it stand at 60°C for 1h, taking it out and rinsing it, immersing it in grafting liquid 2, letting it stand at 60°C for 1.5h, taking it out and rinsing it, immersing it in grafting liquid 3, letting it stand at 60°C for 2h, taking it out and rinsing it, and vacuum drying it to obtain a zwitterionic gradient grafted membrane;

[0043] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1 MPa with a vacuum pump and maintain for 3 h, cure at 60 ° C for 2 h, purge with nitrogen for 10 min, and dry in vacuum to obtain a surface decontamination ultrafiltration membrane.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 3 is that in step S1, the sulfonation reaction is eliminated.

[0046] An ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0047] S1, 500g polyethersulfone, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene, using a mass fraction of 10% acetic acid solution to adjust the system pH value to 4, stirring at 60 ° C for 2h, stirring at a speed of 300 rpm, cooling, vacuum drying, adding 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone, stirring at 60 ° C for 8h, stirring at a speed of 300 rpm, ultrasonic degassing for 0.5h, standing for 24h, using non-woven fabric as a support layer, scraping a wet film with a thickness of 250μm on a glass plate with a scraper, and soaking in deionized water to obtain preform 1;

[0048] S2, 20g of sulfobetaine was dissolved in 500g of deionized water, 2g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; 30g of sulfobetaine was dissolved in 500g of deionized water, 3g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; 50g of sulfobetaine was dissolved in 500g of deionized water, 5g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, the preform 1 was immersed in grafting liquid 1, allowed to stand at 60°C for 1h, taken out and rinsed, immersed in grafting liquid 2, allowed to stand at 60°C for 1.5h, taken out and rinsed, immersed in grafting liquid 3, allowed to stand at 60°C for 2h, taken out and rinsed, and vacuum dried to obtain a zwitterionic gradient grafted membrane;

[0049] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1 MPa with a vacuum pump and maintain for 3 h, cure at 60 ° C for 2 h, purge with nitrogen for 10 min, and dry in vacuum to obtain an ultrafiltration membrane.

[0050] Comparative Example 2

[0051] The difference between Comparative Example 2 and Example 3 is that in step S1, the dynamic crosslinking agent (polyvinyl butyral + glutaraldehyde) is replaced by epichlorohydrin static crosslinking.

[0052] An ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0053] S1, 500g polyethersulfone and 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, stirring at a speed of 500rpm, 25g epichlorohydrin and 2.5g divinylbenzene were added, and the pH value of the system was adjusted to 10 with a mass fraction of 10% acetic acid solution. The mixture was stirred at 60°C for 2h, stirring at a speed of 300rpm, cooled, and vacuum-dried. 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, and the mixture was stirred at 60°C for 8h, stirring at a speed of 300rpm, ultrasonically degassed for 0.5h, and allowed to stand for 24h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and the film was immersed in deionized water to obtain preform 2;

[0054] S2, 20g of sulfobetaine was dissolved in 500g of deionized water, 2g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; 30g of sulfobetaine was dissolved in 500g of deionized water, 3g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; 50g of sulfobetaine was dissolved in 500g of deionized water, 5g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, preform 2 was immersed in grafting liquid 1, allowed to stand at 60°C for 1h, taken out and rinsed, immersed in grafting liquid 2, allowed to stand at 60°C for 1.5h, taken out and rinsed, immersed in grafting liquid 3, allowed to stand at 60°C for 2h, taken out and rinsed, and vacuum dried to obtain a zwitterionic gradient grafted membrane;

[0055] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1 MPa with a vacuum pump and maintain for 3 h, cure at 60 ° C for 2 h, purge with nitrogen for 10 min, and dry in vacuum to obtain an ultrafiltration membrane.

[0056] Comparative Example 3

[0057] The difference between Comparative Example 3 and Example 3 is that in step S2, no step-by-step gradient grafting is performed, and the grafting solution is directly immersed in one step.

[0058] An ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0059] S1, 500g polyethersulfone, 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, stirred at 60°C for 2h, stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone, 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and allowed to stand for 24h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and immersed in deionized water to obtain a sulfonated cross-linked base membrane;

[0060] S2. Dissolve 50 g of sulfobetaine in 500 g of deionized water, add 5 g of azobisisobutyronitrile, and ultrasonicate for 0.5 h at an ultrasonic frequency of 40 kHz to obtain preform 3; under nitrogen protection, immerse the sulfonated cross-linked base membrane in preform 3, stir at 60° C. for 5 h, rinse, and vacuum dry to obtain a zwitterionic grafted membrane;

[0061] S2. Dissolve 100 g of sulfobetaine in 1500 g of deionized water, add 10 g of ammonium persulfate, and ultrasonicate for 0.5 h at an ultrasonic frequency of 40 kHz to obtain a grafting solution; under nitrogen protection, immerse the sulfonated cross-linked base membrane in the grafting solution, stir at 60° C. for 4.5 h at a stirring speed of 200 rpm, rinse, and vacuum dry to obtain a zwitterionic grafted membrane;

[0062] S3. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1 MPa with a vacuum pump and maintain for 3 h, cure at 60 ° C for 2 h, purge with nitrogen for 10 min, and dry in vacuum to obtain an ultrafiltration membrane.

[0063] Comparative Example 4

[0064] The difference between Comparative Example 4 and Example 3 is that the sulfobetaine grafting is eliminated and only the sulfonated base membrane is retained.

[0065] An ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0066] S1, 500g polyethersulfone, 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, stirred at 60°C for 2h, stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone, 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and allowed to stand for 24h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and immersed in deionized water to obtain a sulfonated cross-linked base membrane;

[0067] S2. Mix 30 g of polyethyleneimine and 20 g of glyoxal, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain a prepolymer solution; immerse the sulfonated cross-linked base membrane in the prepolymer solution, vacuum pump to -0.1 MPa and maintain for 3 h, cure at 60 ° C for 2 h, blow with nitrogen for 10 min, nitrogen flow rate of 10 L / min, and vacuum dry to obtain an ultrafiltration membrane.

[0068] Comparative Example 5

[0069] The difference between Comparative Example 5 and Example 3 is that in step S3, glutaraldehyde is used to directly cross-link polyethyleneimine (static Schiff base bond) instead of dynamic imine bond.

[0070] An ultrafiltration membrane and a preparation method thereof, comprising the following steps:

[0071] S1, 500g polyethersulfone, 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, stirred at 60°C for 2h, stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone, 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and allowed to stand for 24h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a support layer with a scraper, and immersed in deionized water to obtain a sulfonated cross-linked base membrane;

[0072] S2, 20g of sulfobetaine was dissolved in 500g of deionized water, 2g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 1; 30g of sulfobetaine was dissolved in 500g of deionized water, 3g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 2; 50g of sulfobetaine was dissolved in 500g of deionized water, 5g of ammonium persulfate was added, and the mixture was ultrasonically treated for 0.5h at an ultrasonic frequency of 40kHz to obtain grafting liquid 3; under nitrogen protection, the preform 1 was immersed in grafting liquid 1, allowed to stand at 60°C for 1h, taken out and rinsed, immersed in grafting liquid 2, allowed to stand at 60°C for 1.5h, taken out and rinsed, immersed in grafting liquid 3, allowed to stand at 60°C for 2h, taken out and rinsed, and vacuum dried to obtain a zwitterionic gradient grafted membrane;

[0073] S3. Mix 30 g of polyethyleneimine and 20 g of glutaraldehyde, stir at 60 ° C for 1 h, and stir at a speed of 400 rpm to obtain preform 4; immerse the zwitterionic grafted membrane in preform 4, evacuate to -0.1 MPa with a vacuum pump and maintain for 3 h, cure at 60 ° C for 2 h, purge with nitrogen for 10 min, and dry in vacuum to obtain an ultrafiltration membrane.

[0074] Performance Testing

[0075] Flux decay rate (anti-pollution performance verification): According to GB / T 32360-2015, the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were pre-pressed at 0.1 MPa and 25°C for 20 minutes to measure the initial pure water flux, J0. Simulated wastewater containing 1 g / L bovine serum albumin (BSA) and 0.1 g / L olive oil was circulated and filtered for 24 hours, and the post-pollution flux, J1, was measured and recorded. The results are shown in Table 1.

[0076] Calculation formula:

[0077] BSA retention rate (retention accuracy verification): According to GB / T 32360-2015 standard, a 1 g / L bovine serum albumin (BSA, Mw = 67 kDa) solution was prepared; the solution was filtered using the ultrafiltration membrane prepared in Examples 1-3 and Comparative Examples 1-5 at 0.1 MPa and 25°C, and the filtrate was collected and the concentration C was measured using an ultraviolet spectrophotometer (λ = 280 nm). 滤液 The data were recorded. The results are shown in Table 1.

[0078] Calculation formula:

[0079] Flux recovery rate (self-repair performance verification): According to the ASTM F2095-01 pressure decay method, the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were contaminated with a mixture containing emulsified oil (200 mg / L) and BSA (1 g / L) for 2 hours. After contamination, the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were rinsed with pure water for 30 minutes, and the flux J2 was then measured. The contaminated membranes of the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were immersed in pH = 2 HCl for 72 hours to release the contaminants (oil, BSA). They were transferred to pH = 10 NaOH for 48 hours to promote the recombination of dynamic imine bonds. The flux J2 after repair was measured and the data was recorded. The results are shown in Table 1.

[0080] Calculation formula:

[0081] Chemical Stability Retention Rate (Acid / Alkali Resistance Verification): In accordance with GB / T 32360-2015, the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were immersed in a pH = 2 (HCl) solution for 72 hours, rinsed with pure water three times for 0.5 hours each time, and then soaked in pure water overnight. The flux J3 was measured. The ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were immersed in a pH = 12 (NaOH) solution for 72 hours, rinsed with pure water three times for 0.5 hours each time, and then soaked in pure water overnight. The flux J4 was measured and the data were recorded. The results are shown in Table 1.

[0082] Calculation formula:

[0083]

[0084] Table 1 Performance test results

[0085]

[0086] The following is a detailed analysis of the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5:

[0087] (1) Sulfonated cross-linked base membrane layer

[0088] Polyethersulfone (PES) reacts with concentrated sulfuric acid to introduce sulfonic acid groups (-SO3H) into the molecular chain. The hydrophilicity of the sulfonic acid groups is significantly improved, and the contact angle is reduced, so that the base membrane can quickly adsorb water molecules to form a hydration layer, reducing the adhesion of pollutants. Subsequently, polyvinyl pyrrolidone (PVP) is added as a porogen, and polyvinyl butyral (PVB) is cross-linked with glutaraldehyde under acidic conditions through dynamic acetal bonds (-OCO-). This dynamic bond is pH responsive: it is partially hydrolyzed during acid washing, and the pore size of the base membrane shrinks to enhance mechanical strength; it is re-cross-linked during alkaline washing to restore the pore size. This layer serves as a supporting skeleton, with both compressive resistance and self-healing ability. Reaction formula:

[0089] ①PES+H2SO4→PES-SO3H;

[0090] ②PVB-OH+OHC-(CH2)3-CHO→ H+ PVB-OCO-+H2O.

[0091] (2) Zwitterionic grafting layer

[0092] Sultaine (-SO3 - 、-N + The sulfobetaine (sulfobetaine) is grafted onto the surface of the base membrane through free radicals. Ammonium persulfate acts as an initiator, generating active sites at 60°C, causing the carboxyl groups of sulfobetaine to form hydrogen bonds with the sulfonic acid groups of PES. The grafting density decreases gradually from the surface to the interior. This gradient structure forms a charge barrier: the high density of zwitterions on the surface prevents the adsorption of large molecules (such as proteins) through electrostatic repulsion, while the lower grafting density inside allows small molecules (such as water) to pass quickly, while maintaining a gradient pore size of 3-15nm to prevent deep contamination. Reaction formula:

[0093] PES-SO3H+ammonium persulfate → free radical initiated grafting → PES-g-(sulfobetaine)

[0094] (3) Dynamic imine bond cross-linking layer

[0095] Polyethyleneimine (PEI) and glyoxal form a cross-linked network through reversible imine bonds (-C=N-). During acid washes, the imine bonds hydrolyze and break, expanding the membrane pores and releasing trapped pollutants. During alkaline washes, the amine groups and aldehyde groups recondense to close the pores. This layer covers the membrane surface, trapping pollutants through screening and enabling reversible control of membrane pores through dynamic bonds to prevent permanent clogging. Reaction formula:

[0096] PEI-NH2+OHC-CHO→PEI-N=CH-CH=N-PEI+H2O

[0097] The hydrophilicity of the sulfonic acid groups reduces contaminant adsorption, while the zwitterionic charge barrier repels charged contaminants. The dynamic acetal and imine bonds reversibly break and reform under acid / base conditions, enabling pore size regulation.

[0098] Mechanism analysis of performance defects of comparative examples 1-5:

[0099] (1) Comparative Example 1

[0100] Mechanism: After the sulfonation is cancelled, the original polyethersulfone is highly hydrophobic and easily adsorbs hydrophobic pollutants such as oils and proteins, causing the membrane flux to decay rapidly; zwitterionic grafting relies on sulfonic acid groups as reaction sites, and the grafting rate of the unsulfonated base membrane is reduced, making it impossible to form a charge repulsion layer.

[0101] (2) Comparative Example 2

[0102] Mechanism: Epichlorohydrin replaces the dynamic crosslinker, forming rigid epoxy bonds (-O-CH2-CH(OH)-O-). This irreversible crosslinking fixes the basement membrane's pore size, rendering it insensitive to changes in acidity and alkalinity. Furthermore, the epoxy crosslinking hinders the uniform distribution of sulfonic acid groups, weakening the charge repulsion effect and making it easier for microorganisms to attach.

[0103] (3) Comparative Example 3

[0104] Mechanism: When immersed in the grafting solution once and lacking a gradient charge barrier, small molecular pollutants (such as colloidal silica) can easily penetrate the surface layer and accumulate in the middle layer. The gradient structure of Example 3 directly intercepts the colloid through high-density surface grafting, avoiding deep contamination.

[0105] (4) Comparative Example 4

[0106] Mechanism: Only the sulfonated membrane and the dynamic imine layer are retained, and the charge balancing function of the zwitterion is lost. Although the sulfonic acid group provides hydrophilicity, it cannot repel negatively charged pollutants (such as humic acid). The zwitterion layer of Example 3 is through -SO3 - / -N + The charge is reversed, causing humic acid to be repelled when the pH changes.

[0107] (5) Comparative Example 5

[0108] Mechanism: Glutaraldehyde is used to directly crosslink polyethyleneimine to form irreversible Schiff base bonds (-C=N-). These bonds break upon hydrolysis during acid wash and cannot be reformed, resulting in permanent enlargement of the membrane pores. For example, when processing high-concentration proteins, the initial acid wash releases contaminants, but subsequent runs of the enlarged membrane pores fail to close, allowing small contaminants (such as bacterial fragments) to enter the membrane and clog the support layer. The dynamic imine bonds in Example 3, however, reform after alkaline wash, maintaining pore size controllability.

[0109] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A method for preparing a surface decontamination ultrafiltration membrane, characterized in that: The steps include: S1. Mix polyethersulfone and concentrated sulfuric acid, stir, add polyvinyl butyral, glutaraldehyde, and divinylbenzene, adjust the pH of the system, stir, cool, and vacuum dry, add N-methylpyrrolidone and polyvinylpyrrolidone, stir, ultrasonically degas, and let stand. Use a non-woven fabric as a support layer, scrape a wet film on a glass plate with a scraper, and soak it in deionized water to obtain a sulfonated cross-linked base membrane; S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, and ultrasonicating to obtain grafting solution 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonicating to obtain grafting solution 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonicating to obtain grafting solution 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting solution 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting solution 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting solution 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane; S3. Mix polyethyleneimine and glyoxal, stir, and obtain a prepolymer solution; immerse the zwitterion grafted membrane in the prepolymer solution, vacuum impregnate, solidify, purge with nitrogen, and vacuum dry to obtain a surface decontamination ultrafiltration membrane.

2. The method for preparing a surface decontamination ultrafiltration membrane according to claim 1, wherein: In step S1, the weight ratio of polyethersulfone, concentrated sulfuric acid, polyvinyl butyral, glutaraldehyde, divinylbenzene, N-methylpyrrolidone, and polyvinylpyrrolidone is 100:300:5:3:300:

5.

3. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In step S1, the pH value of the system is adjusted to 4 using an acetic acid solution with a mass fraction of 10%.

4. The method for preparing a surface decontamination ultrafiltration membrane according to claim 1, wherein: In the step S2, the sulfobetaine is one of dodecyl sulfopropyl betaine, tetradecyl sulfopropyl betaine, cocamidopropyl hydroxysulfobetaine, and oleamidopropyl hydroxysulfobetaine.

5. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In step S2, the three ultrasonic treatments are performed for 0.3-1 h each, and the ultrasonic frequency is 40 kHz.

6. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In step S3, the weight ratio of polyethyleneimine to glyoxal is 3:

2.

7. The method for preparing a surface decontamination ultrafiltration membrane according to claim 1, wherein: In the step S3, vacuum impregnation is performed by pumping the vacuum pump to -0.08-0.15 MPa and maintaining the pressure for 2-4 hours.

8. The method for preparing a surface decontamination ultrafiltration membrane according to claim 1, wherein: In the step S3, nitrogen is purged for 5-15 minutes at a nitrogen flow rate of 5-15 L / min.

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