Preparation method of surface decontamination ultrafiltration membrane

Abstract

The invention relates to the technical field of ultrafiltration membranes, and particularly discloses a preparation method of a surface decontamination ultrafiltration membrane. The preparation method of the surface decontamination ultrafiltration membrane comprises the following steps: preparing a sulfonated cross-linked base membrane; preparing a grafting solution; preparing a zwitterionic grafted membrane; preparing a prepolymer solution; and immersing the zwitter-ion grafted membrane into the prepolymer solution, carrying out vacuum impregnation, curing, purging with nitrogen, and carrying out vacuum drying to obtain the surface-decontaminating ultrafiltration membrane. According to the invention, balance among pollution resistance, durability and adaptability is realized through cooperation of molecular design and process. Specifically, the operation energy consumption is reduced by improving the hydrophilicity of a sulfonic group of the surface decontamination ultrafiltration membrane, the cleaning frequency is reduced by inhibiting pollutant adsorption through a zwitterionic layer, and the maintenance cost is reduced by the self-repairing characteristic of a dynamic network, so that a more economical and efficient solution is provided for a high-difficulty water treatment scene.

Description

Technical Field

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

[0002] As the core component of modern separation technology, filter membrane plays an irreplaceable role in water treatment, food industry, biomedicine and other fields. Its core function is to achieve efficient interception of pollutants through physical screening and charge repulsion mechanism. However, in practical applications, membrane fouling is always the key bottleneck restricting its performance and life. Membrane fouling not only leads to flux attenuation and increased energy consumption, but also causes frequent chemical cleaning, resulting in damage to membrane materials and environmental burden. When facing complex pollutant systems, traditional ultrafiltration membranes often have difficulty balancing 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 problem that the industry urgently needs to break through.

[0003] In actual operation, ultrafiltration membranes are mainly faced with two 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 and block the water flow channel; second, inorganic pollutants, such as calcium and magnesium ions combined with sulfates and carbonates to form a micron-scale scaling layer. This type of sediment will irreversibly block the membrane pores. Existing technologies mostly rely on a single hydrophilic modification or physical flushing method, but the hydrophilic coating is easily affected by chemical environmental fluctuations and fails, and physical cleaning is difficult to completely remove deeply adsorbed pollutants. More seriously, frequent acid or alkaline washing will destroy the membrane structure, resulting in a decrease in porosity and loss of functional groups, forming a vicious cycle of "cleaning-pollution-re-cleaning".

[0004] The current industry is in urgent need of an ultrafiltration membrane technology that can fundamentally break through the coordinated optimization of anti-pollution performance and self-cleaning ability. This technology needs to significantly improve the tolerance of membrane materials to multiple pollutants without sacrificing interception efficiency, while reducing the frequency of cleaning and dependence on chemicals, thereby extending the service life of membrane components and reducing operation and maintenance costs. The solution to 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 difficult water quality treatment scenarios (such as oily wastewater and high-salt 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, mixing polyethersulfone and concentrated sulfuric acid, stirring, adding polyvinyl butyral, glutaraldehyde, and divinylbenzene, adjusting the pH of the system, stirring, cooling, vacuum drying, adding N-methylpyrrolidone and polyvinylpyrrolidone, stirring, ultrasonic degassing, standing, using non-woven fabric as a support layer, scraping a wet film on a glass plate with a scraper, and soaking 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 liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonicating to obtain grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonicating to obtain grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane;

[0009] S3, mixing polyethyleneimine and glyoxal, stirring to obtain a prepolymer solution; immersing the zwitterionic grafted membrane in the prepolymer solution, vacuum impregnating, curing, purging with nitrogen, and vacuum drying 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, the stirring temperature is 55-65° C., the stirring time is 1-3 h, and the stirring speed is 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, and the vacuum pump is pumped to -0.08--0.15 MPa and maintained for 2-4 hours.

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

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

[0023] Beneficial effects:

[0024] The surface decontamination ultrafiltration membrane provided by the present invention achieves breakthroughs in anti-pollution, self-repairing ability and long-term stability through molecular structure innovation and functional synergistic design, solving the core problems of traditional ultrafiltration membranes in complex water treatment, such as easy pollution, difficult cleaning and short life. Its innovations are mainly reflected in three aspects: sulfonated cross-linked base membrane enhances hydrophilicity, zwitterionic gradient grafting constructs a charge balance barrier, and dynamic imine bond network gives self-repairing ability. The synergistic effect of the three enables the membrane to show excellent performance in highly polluted scenes such as oily wastewater and high-salt solutions.

[0025] The sulfonation reaction introduces sulfonic acid groups into the polyethersulfone molecular chain, and forms a stable hydrophilic base membrane with dynamic acetal bond cross-linking, which can not only reduce the attachment of pollutants, but also provide active sites for subsequent functional modification. On this basis, sulfobetaine is gradiently grafted onto the membrane surface through free radical initiation, and the sulfonic acid group of the zwitterion and the quaternary ammonium group form a charge balance layer, which uses hydration to repel pollutants such as protein and oil. It is particularly suitable for milk protein separation in food processing wastewater and emulsified oil interception in oil field reinjection water. Finally, the introduction of a dynamic imine bond network forms a reversible cross-linking 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 to restore its function. This feature greatly extends the service life of the membrane in conditions that require frequent cleaning, such as electroplating wastewater treatment and seawater desalination pretreatment.

[0026] This multi-level design has the advantage of killing two birds with one stone in practical applications: the hydrophilicity enhanced by the sulfonic acid group 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 field of biopharmaceuticals, the ability of the zwitterionic layer to resist protein contamination combined with its self-healing properties ensures the stability of the membrane under frequent sterilization operations. Compared with the limitations of traditional membrane materials that only have anti-fouling properties or improved 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 in conjunction with 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 and 1500g concentrated sulfuric acid were mixed, stirred at 55°C for 5h, and the stirring speed was 600rpm (concentrated sulfuric acid hydrolyzed the sulfone group to a sulfonic acid group to enhance hydrophilicity), 25g polyvinyl butyral, 15g glutaraldehyde, and 3g divinylbenzene were added, and the pH value of the system was adjusted to 4 with a mass fraction of 10% acetic acid solution, and the mixture was stirred at 65°C for 3h, and the stirring speed was 400rpm (the hydroxyl group of polyvinyl butyral and the sulfonic acid group condensed to form an acetal bond, and the aldehyde group of glutaraldehyde and the remaining hydroxyl group of polyvinyl butyral were cross-linked to form a dynamic network), cooled, vacuum dried, 1500g N-methyl pyrrolidone and 25g polyvinyl pyrrolidone were added, stirred at 65°C for 9h, and the stirring speed was 400rpm, ultrasonic degassing was performed for 0.7h, and the mixture was allowed to stand for 26h. A wet film with a thickness of 250μm was scraped on a glass plate with a non-woven fabric as a supporting layer, and the film was immersed in deionized water to obtain a sulfonated cross-linked base film;

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

[0033] S3. Mix 30g of polyethyleneimine and 20g of glyoxal, stir at 65°C for 1.5h, and the stirring speed is 500rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.15MPa with a vacuum pump and maintain for 4h, and cure at 65°C for 3h (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 the pollutants are released and then reassembled), purge with nitrogen for 15min, the nitrogen flow rate is 15L / 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 and 1500g concentrated sulfuric acid were mixed, stirred at 45°C for 3h, the stirring speed was 400rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2g divinylbenzene were added, 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, the stirring speed was 200rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 55°C for 7h, the stirring speed was 200rpm, ultrasonic degassing was performed for 0.3h, and the mixture 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 the film was 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, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane;

[0038] S3. Mix 30g polyethyleneimine and 20g glyoxal, stir at 55°C for 0.5h, and the stirring speed is 300rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.08MPa with a vacuum pump and maintain for 2h, cure at 55°C for 1h, purge with nitrogen for 5min, and the nitrogen flow rate is 5L / min, and vacuum dry 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 and 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, the stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, 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, the stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, the stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and the mixture was 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 a sulfonated cross-linked base film;

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

[0043] S3. Mix 30g polyethyleneimine and 20g glyoxal, stir at 60°C for 1h at a stirring speed of 400rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1MPa with a vacuum pump and maintain for 3h, cure at 60°C for 2h, purge with nitrogen for 10min at a nitrogen flow rate of 10L / min, and vacuum dry 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 10% acetic acid solution to adjust the system pH value to 4, stirring at 60°C for 2h, stirring speed of 300rpm, cooling, vacuum drying, adding 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone, stirring at 60°C for 8h, stirring speed of 300rpm, 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, soaking in deionized water, to obtain preform 1;

[0048] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 3; under nitrogen protection, immersing preform 1 in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane;

[0049] S3. Mix 30g polyethyleneimine and 20g glyoxal, stir at 60°C for 1h at a stirring speed of 400rpm to obtain a prepolymer solution; immerse the zwitterionic gradient grafted membrane in the prepolymer solution, evacuate to -0.1MPa with a vacuum pump and maintain for 3h, cure at 60°C for 2h, purge with nitrogen for 10min at a nitrogen flow rate of 10L / min, and vacuum dry 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, the stirring speed was 500rpm, 25g epichlorohydrin and 2.5g divinylbenzene were added, the pH value of the system was adjusted to 10 with a mass fraction of 10% acetic acid solution, stirred at 60°C for 2h, the stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, the stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and the mixture was 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, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 3; under nitrogen protection, immersing preform 2 in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane;

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

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

[0059] S1, 500g polyethersulfone and 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, the stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, 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, the stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, the stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and the mixture was 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 a sulfonated cross-linked base film;

[0060] S2, dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of azobisisobutyronitrile, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain preform 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane into preform 3, stirring at 60°C for 5h, rinsing, and vacuum drying to obtain a zwitterionic grafted membrane;

[0061] S2, dissolving 100g of sulfobetaine in 1500g of deionized water, adding 10g of ammonium persulfate, and ultrasonically treating for 0.5h at an ultrasonic frequency of 40kHz to obtain a grafting solution; under nitrogen protection, immersing the sulfonated cross-linked base membrane in the grafting solution, stirring at 60°C for 4.5h at a stirring speed of 200rpm, rinsing, and vacuum drying to obtain a zwitterionic grafted membrane;

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

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

[0066] S1, 500g polyethersulfone and 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, the stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, 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, the stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, the stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and the mixture was 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 a sulfonated cross-linked base film;

[0067] S2. Mix 30g polyethyleneimine and 20g glyoxal, stir at 60°C for 1h, and stir at 400rpm to obtain a prepolymer solution; immerse the sulfonated cross-linked base membrane in the prepolymer solution, pump the vacuum pump to -0.1MPa and maintain for 3h, cure at 60°C for 2h, blow with nitrogen for 10min, and dry in vacuum 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 and 1500g concentrated sulfuric acid were mixed, stirred at 50°C for 4h, the stirring speed was 500rpm, 25g polyvinyl butyral, 15g glutaraldehyde, 2.5g divinylbenzene were added, 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, the stirring speed was 300rpm, cooled, vacuum dried, 1500g N-methylpyrrolidone and 25g polyvinylpyrrolidone were added, stirred at 60°C for 8h, the stirring speed was 300rpm, ultrasonic degassing was performed for 0.5h, and the mixture was 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 a sulfonated cross-linked base film;

[0072] S2, dissolving 20g of sulfobetaine in 500g of deionized water, adding 2g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, ultrasonically treating for 0.5h, the ultrasonic frequency is 40kHz, and obtaining grafting liquid 3; under nitrogen protection, immersing preform 1 in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying 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 attenuation rate (anti-pollution verification): According to GB / T 32360-2015 standard, 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 min, and the initial pure water flux J0 was tested; simulated sewage containing 1 g / L bovine serum albumin (BSA) and 0.1 g / L olive oil was circulated and filtered for 24 h, and the post-pollution flux J1 was tested, and the data was 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, 1 g / L bovine serum albumin (BSA, Mw = 67 kDa) solution was prepared; the ultrafiltration membrane prepared in Examples 1-3 and Comparative Examples 1-5 was used for filtration at 0.1 MPa and 25°C, and the filtrate was collected and the concentration C was detected by ultraviolet spectrophotometer (λ = 280 nm). 滤液 . Record the data. 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 mixed solution containing emulsified oil (200 mg / L) and BSA (1 g / L) for 2 hours, rinsed with pure water for 30 minutes after contamination, and then the flux J2 was tested. The contaminated membranes of the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-5 were immersed in pH = 2HCl for 72 hours to release pollutants (grease, BSA). Transferred to pH = 10 NaOH for 48 hours to promote the recombination of dynamic imine bonds, tested the flux J2 after repair, and recorded the data. The results are shown in Table 1.

[0080] Calculation formula:

[0081] Chemical stability retention rate (acid / alkaline resistance verification): According to GB / T 32360-2015 standard, 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 3 times, each time for 0.5 hours, and then immersed in pure water overnight, and the flux J3 was tested; 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 3 times, each time for 0.5 hours, and then immersed in pure water overnight, and the flux J4 was tested, and the data was 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 grafted layer

[0092] Sulfobetaine (-SO3 - 、-N + The ammonium persulfate is used as an initiator to generate active sites at 60°C, so that the carboxyl group of sulfobetaine forms hydrogen bonds with the sulfonic acid group of PES, and the grafting density decreases gradually from the surface to the inside. 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-). The imine bonds are hydrolyzed and broken during acid washing, the membrane pores expand, and the trapped pollutants are released; during alkaline washing, the amine groups and aldehyde groups re-condense to close the pores. This layer covers the membrane surface, which not only traps pollutants through screening, but also achieves reversible regulation of membrane pores through dynamic bonds to avoid permanent blockage. Reaction formula:

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

[0097] The hydrophilicity of the sulfonic acid group reduces the adsorption of pollutants, and the zwitterionic charge barrier repels charged pollutants. The dynamic acetal bond and imine bond can be reversibly broken and recombined under acid / base conditions to achieve 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, and the membrane flux decays rapidly; zwitterionic grafting relies on sulfonic acid groups as reaction sites, the grafting rate of the unsulfonated base membrane is reduced, and a charge repulsion layer cannot be formed.

[0101] (2) Comparative Example 2

[0102] Mechanism: Epichlorohydrin is used to replace the dynamic crosslinker to form a rigid epoxy bond (-O-CH2-CH(OH)-O-). This irreversible crosslinking fixes the pore size of the basement membrane and makes it unable to respond to acid-base changes. At the same time, epoxy crosslinking hinders the uniform distribution of sulfonic acid groups, weakens the charge repulsion effect, and makes it easier for microorganisms to attach.

[0103] (3) Comparative Example 3

[0104] Mechanism: When immersed in the grafting liquid once, in the absence of 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 to avoid 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 zwitterions is missing. Although the sulfonic acid group provides hydrophilicity, it cannot repel negatively charged pollutants (such as humic acid), while the zwitterion layer of Example 3 is hydrophilic. - / -N + The charge is reversed, causing the humic acid to be repelled when the pH changes.

[0107] (5) Comparative Example 5

[0108] Mechanism: Glutaraldehyde is used to directly cross-link polyethyleneimine to form an irreversible Schiff base bond (-C=N-). This bond cannot be reassembled after hydrolysis during acid washing, resulting in permanent enlargement of the membrane pores. For example, when treating high-concentration proteins, the first acid wash can release pollutants, but the enlarged membrane pores cannot be closed in subsequent operations, and small molecular pollutants (such as bacterial fragments) enter the membrane and block the support layer. The dynamic imine bond of Example 3 is reassembled after alkaline washing to maintain the controllability of the pore size.

[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. Under the concept 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, mixing polyethersulfone and concentrated sulfuric acid, stirring, adding polyvinyl butyral, glutaraldehyde, and divinylbenzene, adjusting the pH of the system, stirring, cooling, vacuum drying, adding N-methylpyrrolidone and polyvinylpyrrolidone, stirring, ultrasonic degassing, standing, using non-woven fabric as a support layer, scraping a wet film on a glass plate with a scraper, and soaking 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 liquid 1; dissolving 30g of sulfobetaine in 500g of deionized water, adding 3g of ammonium persulfate, and ultrasonicating to obtain grafting liquid 2; dissolving 50g of sulfobetaine in 500g of deionized water, adding 5g of ammonium persulfate, and ultrasonicating to obtain grafting liquid 3; under nitrogen protection, immersing the sulfonated cross-linked base membrane in grafting liquid 1, standing at 60°C for 1h, taking out and rinsing, immersing in grafting liquid 2, standing at 60°C for 1.5h, taking out and rinsing, immersing in grafting liquid 3, standing at 60°C for 2h, taking out and rinsing, and vacuum drying to obtain a zwitterionic gradient grafted membrane; S3, mixing polyethyleneimine and glyoxal, stirring to obtain a prepolymer solution; immersing the zwitterionic grafted membrane in the prepolymer solution, vacuum impregnating, curing, purging with nitrogen, and vacuum drying to obtain a surface decontamination ultrafiltration membrane.

2. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In the 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 the 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 the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: 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 duration of the three ultrasonic treatments is 0.3-1 h, 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 the step S3, the weight ratio of polyethyleneimine to glyoxal is 3:

2.

7. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In the step S3, vacuum impregnation is performed, and the vacuum pump is pumped to -0.08--0.15 MPa and maintained for 2-4 hours.

8. The method for preparing the surface decontamination ultrafiltration membrane according to claim 1, characterized in that: In the step S3, nitrogen is used for purging, the purging time is 5-15 minutes, and the nitrogen flow rate is 5-15 L / min.

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