Antibacterial nanofiltration membrane and preparation method thereof

Abstract

The application relates to the technical field of membranes, in particular to an antibacterial nanofiltration membrane and a preparation method thereof. The method comprises the following steps: polyethylene imine / tannic acid pretreatment is carried out on a polyethersulfone sulfone ultrafiltration membrane substrate; first interfacial polymerization of a water phase containing piperazine, guanidino butylamine sulfate and taurine and an organic phase containing trimesoyl chloride is sequentially carried out; secondary water phase back immersion is carried out by using a taurine solution; a cross-linking anchoring agent with 20%-22% maleimide double bonds is prepared; the cross-linking anchoring agent is used for anchoring-densification treatment together with trimesoyl chloride; and finally, acid / alkali alternation and heat curing are carried out. Through unique step design and function component synergy, a stable antibacterial and anti-pollution structure is constructed in the separation layer, and the problems of easy biological pollution and easy loss of antibacterial agents of traditional nanofiltration membranes are solved. The obtained membrane has long-acting antibacterial property, high flux recovery rate, high ion selectivity and excellent acid / alkali cycle stability.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, and in particular to an antibacterial nanofiltration membrane and its preparation method. Background Technology

[0002] Hospital wastewater is complex, containing not only conventional pollutants but also high concentrations of pathogenic microorganisms, residual antibiotics, and disinfectants, posing a significant challenge to advanced treatment and reuse technologies. Nanofiltration technology is considered a key process in this field due to its highly efficient retention of trace organic matter and multivalent ions. Among these, polyamide composite nanofiltration membranes are widely used due to their excellent separation performance; however, in actual operation, especially when treating hospital wastewater with high microbial loads over long periods, the membrane surface can easily become a breeding ground for bacteria.

[0003] The initial adhesion of bacteria to the membrane surface is the first step in biofilm formation. Since the surface of traditional polyamide separation layers is typically negatively charged and somewhat hydrophobic, it provides non-specific adsorption sites for negatively charged bacteria, further accelerating microbial colonization. Once a dense biofilm forms, it not only significantly increases membrane filtration resistance, leading to irreversible decline in water flux, but also exacerbates membrane material degradation due to biological metabolic activity, shortening membrane lifespan.

[0004] To suppress biofouling, researchers often modify nanofiltration membranes by surface grafting or coating with antibacterial agents. For example, broad-spectrum antibacterial agents such as silver ions and quaternary ammonium salts are introduced. However, these physically coated or simply blended antibacterial agents exhibit problems of easy leaching and deactivation during long-term operation, especially under the complex chemical environment of hospital wastewater (such as residual chlorine and oxidizing disinfectants) and dynamic hydraulic flushing. The rapid loss of antibacterial agents not only makes it difficult to maintain antibacterial performance, but more seriously, the pores or defects left after loss may damage the integrity of the polyamide separation layer, causing a decrease in selectivity and even becoming new pollution accumulation points.

[0005] On the other hand, to improve the fixation rate of antimicrobial agents, some studies have attempted to immobilize antimicrobial molecules through strong covalent bonding. However, excessive cross-linking or the introduction of excessively rigid antimicrobial segments often leads to the polyamide layer becoming brittle and hard. Under long-term pressure and pH fluctuations, interfacial stress concentration can easily induce microcracks, which also impair the long-term separation stability and mechanical durability of the membrane. Therefore, how to construct an antimicrobial structure within the nanofiltration membrane that has long-lasting antimicrobial activity, is firmly bonded to the substrate, and does not affect the inherent transport channels of the separation layer is the key to overcoming the current technological bottleneck. Existing technologies have not yet effectively solved the balance problem between antimicrobial function and separation stability, which restricts the further application of nanofiltration technology in high-standard hospital wastewater reuse. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose an antibacterial nanofiltration membrane and its preparation method, so as to solve the problems that existing polyamide nanofiltration membranes are prone to biofilm growth on their surface when treating hospital wastewater, which leads to performance degradation, and the surface-modified antibacterial agents are quickly lost due to poor interfacial stability, making it difficult to achieve both long-term antibacterial effect and separation stability.

[0007] To achieve the above objectives, the present invention provides a method for preparing an antibacterial nanofiltration membrane, comprising the following steps:

[0008] (1) Interface layer pretreatment: Immerse the polyethersulfone ultrafiltration membrane substrate in a pretreatment solution prepared by deionized water, branched polyethyleneimine and tannic acid for 10-30 min, take it out and rinse it to obtain the pretreated substrate;

[0009] (2) First interface polymerization: The pretreated substrate is immersed in an aqueous phase containing piperazine, guanidinobutylamine sulfate, taurine, sodium bicarbonate and polysorbate 20 for 5-15 min, and the excess liquid is removed by rolling. Then it is immersed in an isoalkane organic phase containing trimesoyl chloride for 5-15 min, and the excess liquid is removed by rolling to obtain surface treated substrate B.

[0010] (3) Secondary aqueous phase immersion: Immerse the surface-treated substrate B in a water / isopropanol mixed solution containing taurine for 3-7 minutes, roll to remove excess liquid, and obtain surface-treated substrate C;

[0011] (4) Preparation of maleimide crosslinking anchoring agent: After reacting 4,4′-bismaleimide diphenylmethane with taurine and triethylamine in N,N-dimethylformamide, aminoguanidine bicarbonate is added to continue the reaction to obtain a crosslinking anchoring agent that retains part of the maleimide double bond;

[0012] (5) Anchoring-densification: The crosslinking anchoring agent is added to the isoalkane organic phase containing trimesoyl chloride, the surface-treated substrate C is immersed for 15-25 min and rolled to remove excess liquid, to obtain the surface-treated substrate D;

[0013] (6) Acid / alkali alternation and heat curing: The surface-treated substrate D is immersed in citric acid monohydrate solution and sodium bicarbonate solution in sequence, rinsed, and cured under hot air at 80-90°C for 5 minutes to obtain an antibacterial nanofiltration membrane.

[0014] Preferably, in step (1), the polyethyleneimine is branched and has a weight-average molecular weight of 24,000-26,000.

[0015] Preferably, in step (1), the polyethersulfone ultrafiltration membrane substrate has a size of 200mm×200mm, a molecular weight cutoff of 28-32kDa, and a thickness of 115-125μm.

[0016] Preferably, in step (1), the pretreatment solution is prepared by dissolving 1-3g of branched polyethyleneimine and 0.5-1.5g of tannic acid in 1000mL of deionized water.

[0017] Preferably, in step (2), the aqueous phase is prepared by adding 3-5g piperazine, 0.5-1.5g guanidinobutylamine sulfate, 3-7g taurine, 0.5-1.5g sodium bicarbonate and 0.5-1.5g polysorbate 20 per 1000mL of deionized water.

[0018] Preferably, the organic phase in step (2) is 0.5-1.5 g of pyromellitic chloride dissolved in 1000 mL of Isopar G.

[0019] Preferably, the mixed solution in step (3) is a mixture of 950 mL of deionized water and 50 mL of isopropanol, and 7-13 g of taurine is dissolved in it.

[0020] Preferably, in step (4), the mass ratio of 4,4′-bismaleimide diphenylmethane, taurine, triethylamine and aminoguanidine bicarbonate is 5:3:2:1.

[0021] Preferably, the amount of double bond retention in the crosslinking anchoring agent that retains part of the maleimide double bond in step (4) is 20%-22%.

[0022] Preferably, in step (5), 0.03-0.07g of crosslinking anchoring agent is pre-dissolved in 10mL of ethyl acetate and added to 1000mL of IsoparG, and 0.8-1.2g of trimesoyl chloride is added.

[0023] Preferably, in step (6), the acidic stage involves dissolving 1-3g of citric acid monohydrate in 2000mL of deionized water and immersing it for 1-3 minutes, while the alkaline stage involves dissolving 1-3g of sodium bicarbonate in 2000mL of deionized water and immersing it for 1-3 minutes.

[0024] The present invention also provides an antibacterial nanofiltration membrane, which is obtained by the above-described method for preparing the antibacterial nanofiltration membrane.

[0025] The beneficial effects of this invention are:

[0026] This invention constructs a stable structure with synergistic functions within the nanofiltration membrane separation layer through a unique interfacial polymerization and subsequent anchoring reaction design, thereby comprehensively improving the membrane's performance.

[0027] The nanofiltration membrane obtained by this invention exhibits significantly enhanced antimicrobial durability. The antimicrobial components stably present in the membrane separation layer can effectively act on contacting microorganisms for a long time. Even under long-term hydraulic scouring, its antimicrobial performance can still maintain a high level, effectively inhibiting the formation of biofilm and providing a guarantee for the long-term stable operation of the membrane in microbial enrichment environments.

[0028] This membrane exhibits excellent antifouling properties and easy cleaning characteristics. The membrane surface properties have been optimized, significantly reducing the initial adhesion of proteinaceous contaminants and bacteria. After fouling occurs, high-flux recovery can be achieved through simple physical cleaning, reducing the frequency and intensity of chemical cleaning, thus extending membrane lifespan and lowering operating and maintenance costs.

[0029] This invention achieves highly efficient antibacterial and antifouling effects while maintaining the nanofiltration membrane's high selective separation capability for salts. It maintains an extremely high rejection rate for divalent ions such as sulfate, while exhibiting some permeability to monovalent ions, demonstrating excellent selective separation characteristics and meeting the technical requirements for deep desalination and resource recovery.

[0030] This nanofiltration membrane exhibits excellent long-term operational stability and durability. Despite acid / alkali cleaning cycles or fluctuations in influent pH, the membrane maintains good structural integrity, separation performance, and functionality. This indicates that the membrane's internal functional structure is firmly integrated with the separation matrix, capable of withstanding certain chemical and physical shocks, and adapting to complex real-world water quality environments.

[0031] In summary, this invention successfully integrates long-lasting antibacterial properties, high-efficiency antifouling, highly selective separation, and excellent durability. The various functions work synergistically, rather than being simply additive, achieving a comprehensive improvement in membrane performance and providing an effective solution to the challenges of membrane fouling and biosafety in the advanced treatment of hazardous wastewater. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0033] Figure 1 The image shows the infrared spectrum of the antibacterial nanofiltration membrane surface coating powder sample in Example 2 of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Example 1

[0035] (1) Dissolve 1g of polyethyleneimine (branched type, weight average molecular weight of about 25,000, Sigma-Aldrich, catalog number P434400) and 0.5g of tannic acid in 1000mL of deionized water to obtain a pretreatment solution; completely immerse a polyethersulfone ultrafiltration membrane (size 200mm×200mm, molecular weight cutoff of about 30kDa, thickness of 120μm) for 10min, remove it and rinse it with deionized water to obtain a pretreated substrate;

[0036] (2) Preparation of aqueous phase: Add 3g piperazine, 0.5g guanidinobutylamine sulfate, 3g taurine, 0.5g sodium bicarbonate and 0.5g polysorbate 20 to 1000mL deionized water, stir for 5min, completely immerse the pretreated substrate for 5min, roll to remove the excess liquid to obtain surface treated substrate A. Preparation of organic phase: Dissolve 0.5g trimesoyl chloride in 1000mL of isoparaffinic alkane Mobil Isopar G solvent, then completely immerse surface treated substrate A for 5min, roll to remove the excess liquid to obtain surface treated substrate B.

[0037] (3) Dissolve 7g of taurine in a mixed solvent of 950mL deionized water and 50mL isopropanol, then completely immerse the surface-treated substrate B for 3min, roll it to remove the excess liquid, and obtain the surface-treated substrate C.

[0038] (4) Dissolve 5g of 4,4'-bismaleimide diphenylmethane in 500mL of N,N-dimethylformamide, add 3g of taurine and 2g of triethylamine, stir at 50°C for 120min; after cooling to room temperature, add 1g of aminoguanidine bicarbonate, stir for another 120min, and rotary evaporate to obtain maleimide crosslinking anchoring agent (quantitatively determined by 302nm UV to retain 21.1% of maleimide double bonds).

[0039] (5) First, pre-dissolve 0.03g of maleimide crosslinking anchoring agent in 10mL of ethyl acetate, then add it to 1000mL of isoparaffinic Mobil Isopar G solvent and add 0.8g of pyromellitic tricarboxylic acid chloride. Stir for 10min, immerse the surface-treated substrate C for 15min, roll to remove excess liquid, and obtain the surface-treated substrate D.

[0040] (6) Dissolve 1g of citric acid monohydrate in 2000mL of deionized water and immerse the surface-treated substrate D completely for 1min. Then dissolve 1g of sodium bicarbonate in 2000mL of deionized water and immerse it for another 1min. Finally, rinse with deionized water and cure under 80°C hot air for 5min to obtain an antibacterial nanofiltration membrane. Example 2

[0041] (1) Dissolve 2g of polyethyleneimine (branched type, weight average molecular weight of about 25,000, Sigma-Aldrich, catalog number P434400) and 1g of tannic acid in 1000mL of deionized water to obtain a pretreatment solution; completely immerse a polyethersulfone ultrafiltration membrane (size 200mm×200mm, molecular weight cutoff of about 30kDa, thickness of 120μm) for 20min, remove it and rinse it with deionized water to obtain a pretreated substrate;

[0042] (2) Preparation of aqueous phase: Add 4g piperazine, 1g guanidinobutylamine sulfate, 5g taurine, 1g sodium bicarbonate and 1g polysorbate 20 to 1000mL deionized water, stir for 10min, completely immerse the pretreated substrate for 10min, roll to remove the excess liquid to obtain surface treated substrate A. Preparation of organic phase: Dissolve 1g trimesoyl chloride in 1000mL of isoparaffinic alkane Mobil Isopar G solvent, then completely immerse surface treated substrate A for 10min, roll to remove the excess liquid to obtain surface treated substrate B.

[0043] (3) Dissolve 10g of taurine in a mixed solvent of 950mL deionized water and 50mL isopropanol, then completely immerse the surface-treated substrate B for 5min, roll it to remove the excess liquid, and obtain the surface-treated substrate C.

[0044] (4) Dissolve 5g of 4,4'-bismaleimide diphenylmethane in 500mL of N,N-dimethylformamide, add 3g of taurine and 2g of triethylamine, stir at 50°C for 120min; after cooling to room temperature, add 1g of aminoguanidine bicarbonate, stir for another 120min, and rotary evaporate to obtain maleimide crosslinking anchoring agent (quantitative determination by 302nm UV showed that 21.2% of maleimide double bonds were retained).

[0045] (5) First, pre-dissolve 0.05g of maleimide crosslinking anchoring agent in 10mL of ethyl acetate, then add it to 1000mL of isoparaffinic Mobil Isopar G solvent and add 1g of trimesoyl chloride. Stir for 10min, immerse the surface-treated substrate C for 20min, roll to remove excess liquid, and obtain the surface-treated substrate D.

[0046] (6) Dissolve 2g of citric acid monohydrate in 2000mL of deionized water and immerse the surface-treated substrate D completely for 2min. Then dissolve 2g of sodium bicarbonate in 2000mL of deionized water and immerse it for another 2min. Finally, rinse with deionized water and cure under 85°C hot air for 5min to obtain an antibacterial nanofiltration membrane. Example 3

[0047] (1) Dissolve 3g of polyethyleneimine (branched type, weight average molecular weight of about 25,000, Sigma-Aldrich, catalog number P434400) and 1.5g of tannic acid in 1000mL of deionized water to obtain a pretreatment solution; completely immerse a polyethersulfone ultrafiltration membrane (size 200mm×200mm, molecular weight cutoff of about 30kDa, thickness of 120μm) for 30min, remove it and rinse it with deionized water to obtain a pretreated substrate;

[0048] (2) Preparation of aqueous phase: Add 5g piperazine, 1.5g guanidinobutylamine sulfate, 7g taurine, 1.5g sodium bicarbonate and 1.5g polysorbate 20 to 1000mL deionized water, stir for 15min, completely immerse the pretreated substrate for 15min, roll to remove the excess liquid to obtain surface treated substrate A. Preparation of organic phase: Dissolve 1.5g trimesoyl chloride in 1000mL isoparaffinic solvent Mobil Isopar G, then completely immerse surface treated substrate A for 15min, roll to remove the excess liquid to obtain surface treated substrate B.

[0049] (3) Dissolve 13g of taurine in a mixed solvent of 950mL deionized water and 50mL isopropanol, then completely immerse the surface-treated substrate B for 7min, roll it to remove the excess liquid, and obtain the surface-treated substrate C.

[0050] (4) Dissolve 5g of 4,4'-bismaleimide diphenylmethane in 500mL of N,N-dimethylformamide, add 3g of taurine and 2g of triethylamine, stir at 50°C for 120min; after cooling to room temperature, add 1g of aminoguanidine bicarbonate, stir for another 120min, and rotary evaporate to obtain maleimide crosslinking anchoring agent (quantitatively determined by 302nm UV to retain 20.9% of maleimide double bonds).

[0051] (5) First, pre-dissolve 0.07g of maleimide crosslinking anchoring agent in 10mL of ethyl acetate, then add it to 1000mL of isoparaffinic Mobil Isopar G solvent and add 1.2g of trimesoyl chloride. Stir for 10min, immerse the surface-treated substrate C for 25min, roll to remove excess liquid, and obtain the surface-treated substrate D.

[0052] (6) Dissolve 3g of citric acid monohydrate in 2000mL of deionized water and immerse the surface-treated substrate D completely for 3min. Then dissolve 3g of sodium bicarbonate in 2000mL of deionized water and immerse it for another 3min. Finally, rinse with deionized water and cure under 90°C hot air for 5min to obtain an antibacterial nanofiltration membrane.

[0053] Comparative Example 1:

[0054] The difference between Comparative Example 1 and Example 2 is that taurine is not added to the aqueous phase in step (2), while the other conditions are the same as in Example 2.

[0055] Comparative Example 2:

[0056] The difference between Comparative Example 2 and Example 2 is that guanidinobutylamine sulfate is not added to the aqueous phase in step (2), and the other conditions are the same as in Example 2.

[0057] Comparative Example 3:

[0058] The difference between Comparative Example 3 and Example 2 is that step (3) is omitted, while the other conditions are the same as in Example 2.

[0059] Comparative Example 4:

[0060] The difference between Comparative Example 4 and Example 2 is that maleimide crosslinking anchoring agent is not added to the organic phase in step (5), and the other conditions are the same as in Example 2.

[0061] Comparative Example 5:

[0062] The difference between Comparative Example 5 and Example 2 is that: in step (4) when preparing the maleimide crosslinking anchoring agent, the amount of aminoguanidine bicarbonate was adjusted to 2g (the other ratios, temperature and stirring time were the same), so that the amount of maleimide double bond retention measured by 302nm UV was 0, and the other conditions were the same as in Example 2.

[0063] Comparative Example 6:

[0064] The difference between Comparative Example 6 and Example 2 is that the pretreatment of the polyethyleneimine / tannic acid weak interface layer in step (1) is omitted (the substrate is only rinsed with deionized water before proceeding to step (2)); the other conditions are the same as in Example 2.

[0065] Comparative Example 7:

[0066] The difference between Comparative Example 7 and Example 2 is that step (6) only involves immersion in the "citric acid monohydrate acid segment" and omits the "sodium bicarbonate alkaline segment", while the other conditions are the same as in Example 2.

[0067] Performance testing:

[0068] Infrared spectroscopy: The coating on the surface of the substrate in Example 2 was scraped off with a scraper, dried, and then subjected to infrared spectroscopy scanning at a resolution of 4 cm⁻¹. -1 Range 4000-650cm -1 .

[0069] Surface Zeta potential: according to GB / T37617-2019, at 1 mmol·L⁻¹ -1 Potassium chloride solution, 25°C, pH 7.0, was measured three times on the same membrane and the average was taken. The results are shown in Table 1.

[0070] Water contact angle: According to GB / T30693-2014, the static drip method was used, with a drip volume of 3µL, and the average of 5 points was collected. The results are shown in Table 1.

[0071] Antibacterial properties and antibacterial rinse resistance: According to GB / T37206-2018, Escherichia coli ATCC8739 and Staphylococcus aureus ATCC6538 were selected, with an inoculum size of (2.5±0.5)×10⁻⁶. 5 CFU·cm -2The antibacterial rate was maintained after rinsing with deionized water at 0.5 MPa for 24 hours at 35°C for 50 hours, followed by cross-flow rinsing with deionized water for 50 hours. The results are shown in Table 1.

[0072] Nanofiltration water flux and ion removal rate: Following GB / T34242-2017, at 25°C and an operating pressure of 0.50 MPa; the initial flux was recorded after the pure water flux stabilized for 30 minutes; the ion removal rate was determined using sodium sulfate and sodium chloride (2000 mg·L⁻¹ each). -1 According to the standard, the pure water flux / sodium sulfate removal rate / sodium chloride removal rate were calculated and recorded. The results are shown in Table 1.

[0073] Antifouling performance: Following the throughput test procedure of GB / T34242-2017, the contaminated solution was prepared with 1.0 g / L bovine serum albumin. -1 (25°C, 0.50MPa crossflow for 2h), the flux recovery rate (FRR) was measured after standard cleaning with deionized water for 10min. The results are shown in Table 1.

[0074] Acid and alkali resistance cycling: According to the acid and alkali resistance clause of GB / T34242-2017: hydrochloric acid solution pH 2 (25°C, 2h), deionized water rinsing, sodium hydroxide solution pH 11 (25°C, 2h), 5 cycles; record the sodium sulfate removal rate and pure water flux retention rate before and after the cycle, and the results are shown in Table 1.

[0075] Table 1 Performance Test Results

[0076] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Zeta potential (mV, pH7) −9.3 −6.8 −5.1 −10.7 −14.4 −12.6 −6.9 −7.5 −17.9 −7.9 Water contact angle (°) 44.9 41.7 39.6 47.2 43.8 49.5 42.1 45.6 54.3 43.2 Antibacterial rate of Escherichia coli (%) 99.2 99.6 99.4 97.9 36.4 93.8 99.2 98.5 96.8 99.0 Antibacterial rate against Staphylococcus aureus (%) 98.9 99.4 99.2 97.3 33.7 92.6 98.7 97.8 95.9 98.6 The antibacterial rate of Escherichia coli remained unchanged (50h, %). 95.1 98.7 97.9 92.4 30.5 80.2 90.3 84.8 72.6 88.6 Antibacterial rate against Staphylococcus aureus maintained (50h, %) 94.6 98.2 97.5 91.1 28.9 78.7 91.2 89.1 70.8 87.3 <![CDATA[Pure water flux (L·m -2 ·h -1 )]]> 66.3 63.4 54.2 64.8 61.7 66.1 64.2 58.7 78.4 62.9 Sodium sulfate removal rate (%) 97.6 98.4 99.1 97.5 98.2 96.8 98.1 98.1 92.3 97.9 Sodium chloride removal rate (%) 29.4 33.6 41.7 29.8 32.8 27.6 32.9 30.2 18.7 32.2 Post-contamination FRR (%) 92.1 94.6 92.3 88.9 93.9 86.7 93.1 92.0 80.4 92.6 Acid-base cycle flux maintained (%) 90.8 93.8 92.9 89.7 91.2 87.5 85.4 82.3 78.9 83.7 Acid-base cycle removal retention (%) 97.2 98.1 98.4 96.5 97.8 95.1 92.7 91.4 87.5 90.2

[0077] Data Analysis:

[0078] As can be seen from the data in Examples 1-3 in Table 1, this invention synergistically introduces guanidinium-containing cations and zwitterions during interfacial polymerization, stabilizes monomer diffusion with a weak polyethyleneimine / tannic acid interfacial layer, and then utilizes maleimide with retained double bonds to trigger secondary addition after acid / base alternation, resulting in a synergistic distribution of strong cation-containing antibacterial sites and surface zwitterionic hydration in the separation layer along the thickness direction. This configuration makes the surface potential close to neutral, ensures sufficient surface hydration, significantly limits the initial adhesion of proteins and bacteria, and facilitates flux recovery after membrane fouling. At the same time, the dense cross-linking and anchoring effect reduces structural relaxation caused by long-term rinsing and acid-base cycling, thereby maintaining high divalent salt retention while also considering monovalent salt selectivity and durability.

[0079] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, omitting zwitterions in the initial aqueous phase leads to insufficient surface hydration, resulting in a simultaneous decrease in flux recovery and antibacterial retention after contamination. The main reason is the absence of zwitterions during the initial interfacial condensation stage, which reduces the density and continuity of hydrophilic groups near the surface, making it difficult to form a stable hydration layer. Although subsequent introduction can partially compensate for this, the embedding depth and covalent ratio are limited, weakening the synergistic effect.

[0080] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, the initial antibacterial activity decreased significantly when guanidinium-containing cations were absent, but the antifouling activity remained good. This is because zwitterions mainly provide hydration and anti-adhesion, while the contact bactericidal sites come from guanidinium-containing cations. When cation sites are absent, even if bacteria do not easily adhere, they are difficult to inactivate quickly, and residual viable bacteria increase after rinsing, making it difficult to achieve long-lasting antibacterial activity.

[0081] As can be seen from the data in Example 2 and Comparative Example 3 in Table 1, omitting the secondary aqueous phase leads to insufficient enrichment of amphoteric molecules on the surface, resulting in a simultaneous decrease in hydrophilicity and antifouling properties. The main reason is that in the "back and forth" time series, the secondary aqueous phase is used to enrich amphoteric molecules and embed them near the surface; the absence of this step leads to fragmentation of the amphoteric layer, insufficient regulation of interfacial energy and surface free energy, resulting in a phenomenon where, although the flux is high, the selectivity and antifouling properties are compromised and exacerbated.

[0082] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, when no maleimide crosslinking anchoring agent was added, the initial indicators were similar, but the durability decreased significantly. The main reason is that no subsequent Michael addition occurred, the free amines in the membrane and the terminal sites were not captured a second time, and the separation layer relaxed and micro-decomposed after long-term rinsing and acid-base cycling, resulting in a simultaneous decrease in antibacterial retention and cycling retention.

[0083] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, when the maleimide double bonds are completely deactivated, the initial removal rate does not increase significantly and the flux is actually lower. The main reason is the increase in volume fraction caused by the inert framework and the local pore blockage. Subsequent acid-base cycles also fail to achieve re-densification due to the lack of reactive double bonds, resulting in more significant degradation in durability.

[0084] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, when pretreatment is omitted, the throughput is abnormally high, but the selectivity and durability are significantly reduced. The main reason is the lack of fine control over interfacial tension and monomer diffusion by polyethyleneimine / tannic acid. Interfacial polymerization is more prone to forming defects and non-uniform micropores, exhibiting the characteristics of high throughput / low rejection / low FRR.

[0085] As can be seen from the data in Example 2 and Comparative Example 7 in Table 1, when only the acid segment is treated without the alkali segment to promote the reaction, the initial performance is acceptable, but the antibacterial and acid / alkali resistance are significantly insufficient. The main reason is that the alkali segment is beneficial for activating Michael addition and stabilizing the zwitterionic dissociation state; the lack of the alkali segment leads to insufficient anchoring reaction, and after long-term rinsing or pH cycling, the surface rearrangement and swelling are aggravated, and the synergistic effect is weakened.

[0086] from Figure 1 It can be seen that the sample is at 1653cm. -1 Strong amide I absorption was observed at 1542 cm⁻¹. -1 The presence of amide II characteristics indicates that the release layer has a typical polyamide structure; 1775 / 1715cm -1 The imide carbon double peaks and 1670 cm⁻¹ -1 The guanidinium shoulder peaks together indicate the presence of maleimide anchoring structure and guanidinium group; 1203 and 1038 cm⁻¹ -1 The double strong peaks at S=O confirm the successful introduction of the amphoteric taurine group; 3390 cm⁻¹ -1 The broad peak is attributed to N–H / O–H hydrogen bond absorption.

[0087] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing an antibacterial nanofiltration membrane, characterized in that, Includes the following steps: (1) Interface layer pretreatment: Immerse the polyethersulfone ultrafiltration membrane substrate in a pretreatment solution prepared by deionized water, branched polyethyleneimine and tannic acid for 10-30 min, take it out and rinse it to obtain the pretreated substrate; (2) First interface polymerization: The pretreated substrate is immersed in an aqueous phase containing piperazine, guanidinobutylamine sulfate, taurine, sodium bicarbonate and polysorbate 20 for 5-15 min, and the excess liquid is removed by rolling. Then it is immersed in an isoalkane organic phase containing trimesoyl chloride for 5-15 min, and the excess liquid is removed by rolling to obtain surface treated substrate B. (3) Secondary aqueous phase immersion: Immerse the surface-treated substrate B in a water / isopropanol mixed solution containing taurine for 3-7 minutes, roll to remove excess liquid, and obtain surface-treated substrate C; (4) Preparation of maleimide crosslinking anchoring agent: After reacting 4,4′-bismaleimide diphenylmethane with taurine and triethylamine in N,N-dimethylformamide, aminoguanidine bicarbonate is added to continue the reaction to obtain a crosslinking anchoring agent that retains part of the maleimide double bond; (5) Anchoring-densification: The crosslinking anchoring agent is added to the isoalkane organic phase containing trimesoyl chloride, the surface-treated substrate C is immersed for 15-25 min and rolled to remove excess liquid, to obtain the surface-treated substrate D; (6) Acid / alkali alternation and heat curing: The surface-treated substrate D is immersed in citric acid monohydrate solution and sodium bicarbonate solution in sequence, rinsed, and cured under hot air at 80-90°C for 5 min to obtain an antibacterial nanofiltration membrane; In step (2), the aqueous phase is prepared by adding 3-5g piperazine, 0.5-1.5g guanidinobutylamine sulfate, 3-7g taurine, 0.5-1.5g sodium bicarbonate and 0.5-1.5g polysorbate 20 to every 1000mL of deionized water; the organic phase in step (2) is prepared by dissolving 0.5-1.5g of trimesoyl chloride in 1000mL of IsoparG; the mixed solution in step (3) is prepared by mixing 950mL of deionized water and 50mL of isopropanol and dissolving 7-13g of taurine; the double bond retention of the crosslinking anchoring agent that retains part of the maleimide double bond in step (4) is 20%-22%; in step (5), 0.03-0.07g of crosslinking anchoring agent is pre-dissolved in 10mL of ethyl acetate and added to 1000mL of IsoparG, along with 0.8-1.2g of trimesoyl chloride.

2. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (1), the polyethyleneimine is branched and has a weight-average molecular weight of 24,000-26,000.

3. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (1), the polyethersulfone ultrafiltration membrane substrate has a size of 200mm×200mm, a molecular weight cutoff of 28-32kDa, and a thickness of 115-125μm.

4. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (1), the pretreatment solution is prepared by dissolving 1-3g of branched polyethyleneimine and 0.5-1.5g of tannic acid in 1000mL of deionized water.

5. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (4), the mass ratio of 4,4′-bismaleimide diphenylmethane, taurine, triethylamine and aminoguanidine bicarbonate is 5:3:2:

1.

6. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (6), the acidic step involves dissolving 1-3g of citric acid monohydrate in 2000mL of deionized water and immersing it for 1-3 minutes.

7. The method for preparing the antibacterial nanofiltration membrane according to claim 1, characterized in that, In step (6), the alkaline step involves dissolving 1-3g of sodium bicarbonate in 2000mL of deionized water and immersing it for 1-3 minutes.

8. An antibacterial nanofiltration membrane, characterized in that, It is obtained by the method for preparing the antibacterial nanofiltration membrane according to any one of claims 1-7.

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