Modified tea saponin-based green antibacterial separation membrane and preparation method thereof

Abstract

The application discloses a modified tea saponin-based green antibacterial separation membrane and a preparation method thereof, and belongs to the field of membrane separation technology and functional polymer materials. The method comprises the following steps: a functional monomer with reaction activity and amphiphilicity is prepared by chemically modifying natural tea saponin through a long-chain aliphatic compound or an unsaturated double bond monomer; a functional casting solution is constructed by adopting a copolymerization path (radical copolymerization of a reactive monomer and a matrix monomer) or an anchoring path (physical entanglement of long-chain modified tea saponin and a membrane matrix); a membrane is formed through an NIPS process; and a dense antibacterial layer is formed by using a tea saponin surface self-enrichment effect. The prepared membrane material has an antibacterial rate of > 99% on escherichia coli and staphylococcus aureus, an antibacterial component retention rate of > 90% after continuous operation for 500 hours, and high flux recovery rate and long-acting antibiofouling performance. The application solves the technical problems that natural tea saponin is easy to flow off and has poor compatibility with a traditional membrane matrix, and provides an intrinsic sterilization and physical screening cooperative separation membrane for green water treatment.

Description

Technical Field

[0001] This invention relates to the fields of membrane separation technology and functional polymer materials, specifically to a water treatment separation membrane prepared by modifying natural tea saponin, which has green and long-lasting antibacterial properties and anti-biofouling characteristics, and its preparation method. Background Technology

[0002] Traditional filtration membranes only physically trap bacteria, failing to kill them. This means trapped bacteria may penetrate membrane defects or proliferate downstream. Current antibacterial membrane preparation methods often employ physical blending of silver-loaded inorganic particles or chemical grafting of quaternary ammonium salts and antibiotics, posing risks of heavy metal release, high costs, and the development of drug resistance. Furthermore, bacteria (such as Escherichia coli and Staphylococcus aureus) easily adhere to the membrane surface, forming biofilms that drastically reduce membrane flux, increase operating pressure, and shorten membrane lifespan. Therefore, developing green, broad-spectrum, and biocompatible natural antifouling materials has become a hot topic.

[0003] Tea saponins, a major byproduct of the tea oil industry, possess natural biological activity due to their triterpenoid saponin structure. They can specifically bind to cholesterol and phospholipids on bacterial cell membranes, achieving efficient contact sterilization by interfering with membrane permeability. However, unmodified natural tea saponins have significant drawbacks in membrane preparation and application: chemical stability and leaching issues: their strong hydrophilicity leads to easy dissolution during water treatment, resulting in a short antibacterial duration; interface compatibility bottlenecks: natural tea saponins have poor compatibility with commonly used membrane matrices such as polysulfone (PSF) and polyvinylidene fluoride (PVDF), easily causing uncontrolled liquid-phase separation during casting and resulting in membrane defects.

[0004] Therefore, how to effectively and stably integrate the natural antibacterial and hydrophilic advantages of tea saponins into the separation membrane, and develop a green, long-lasting, and stable antibacterial separation membrane to solve the technical problems of easy loss of natural tea saponins and poor compatibility with the membrane matrix, is the key problem restricting its application. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing antibacterial separation membranes, such as easy loss of antibacterial components, short duration of bactericidal efficacy, and severe biofouling on the membrane surface, and provides a modified tea saponin-based green antibacterial separation membrane and its preparation method.

[0006] This invention utilizes molecular modification technology to transform natural tea saponins into monomers with polymerization activity or hydrophobic long-chain anchoring function. By employing copolymerization locking (forming chemical bonding structures) or long-chain entanglement (forming interface anchoring structures), tea saponin molecules with intrinsic bactericidal activity are firmly integrated into the membrane matrix. Furthermore, by leveraging the amphiphilic induction of surface self-enrichment effect of tea saponins, the membrane surface achieves highly efficient killing and deep purification of pathogenic bacteria such as Escherichia coli and Staphylococcus aureus. Simultaneously, it obtains a more durable hydrophilic modification effect and significantly improves the interfacial hydrophilicity and anti-biofouling ability of the separation membrane.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On the one hand, this invention proposes a modified tea saponin-based green antibacterial separation membrane, which is prepared from raw materials containing the following parts by weight of component A or component B. Component A (anchoring path): 10-25 parts of polymer membrane matrix resin; Modified tea saponin 0.5-5 parts; 0-10 parts of pore-forming agent; Solvent 60-80 parts; The modified tea saponin is an esterified or etherified product generated by the reaction of natural tea saponin with long-chain aliphatic compounds (C12-C22). Component B (copolymerization path): 10-25 parts of matrix monomer; Modified tea saponin 0.5-5 parts; Initiator 0.1-1 part; 60-100 parts solvent; The modified tea saponin is a copolymerized functional monomer generated by reacting natural tea saponin with a monomer containing unsaturated double bonds; and the component B forms an intrinsic antibacterial copolymer after copolymerization, which is then film-formed by a non-solvent-induced phase inversion method.

[0008] Furthermore, the polymeric membrane matrix resin is selected from one or more of polysulfone (PSf), polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN); the matrix monomer is at least one of acrylonitrile and methyl methacrylate.

[0009] Furthermore, the long-chain aliphatic compound is selected from one of dodecyl succinic anhydride, octadecenyl succinic anhydride (ASA), stearoyl chloride, lauroyl chloride, and erucic acid chloride; the monomer containing unsaturated double bonds is selected from one of maleic anhydride and glycidyl methacrylate. The introduction of this long-chain aliphatic compound increases the hydrophobicity of tea saponin, improving its compatibility with the hydrophobic membrane matrix; on the other hand, the provided long carbon chain can anchor tea saponin to the membrane matrix through intermolecular physical entanglement. The introduction of the monomer containing unsaturated double bonds provides reaction sites for tea saponin to participate in the copolymerization reaction, enabling it to be fixed to the polymer backbone through covalent bonds.

[0010] Furthermore, the modified tea saponin is fixed to the membrane substrate through covalent bonding (copolymerization path) or long-chain molecular entanglement (anchoring path), and the modified tea saponin can migrate directionally to the membrane surface during the non-solvent-induced phase inversion (NIPS) film formation process, accumulate on the membrane surface, and form an antibacterial functional layer.

[0011] This invention also proposes a method for preparing the modified tea saponin-based green antibacterial separation membrane as described above, comprising the following steps: S1: Preparation of modified tea saponin: Natural tea saponin is reacted with long-chain aliphatic compounds (such as long-chain compounds containing acyl chlorides, acid anhydrides or isocyanates) or monomers containing unsaturated double bonds (such as maleic anhydride, glycidyl methacrylate) in an organic solvent to obtain functional monomers with a degree of substitution (DS) of 0.3-1.5, which are then obtained as modified tea saponin. S2: Casting solution preparation: prepared by one of the following methods: Method 1 (Anchoring Path): If the modified tea saponin in step S1 is obtained by reacting natural tea saponin with long-chain aliphatic compounds, the casting solution preparation steps are as follows: Dissolve the modified tea saponin, polymer membrane matrix resin, and pore-forming agent obtained in step S1 in a solvent, stir at 50-80℃ until uniform, let stand to degas, and prepare the casting solution. Method 2 (Copolymerization Path): If the modified tea saponin in step S1 is obtained by reacting natural tea saponin with a monomer containing unsaturated double bonds, the casting solution preparation steps are as follows: The modified tea saponin containing unsaturated double bonds and the matrix monomer are copolymerized in solution under the action of an initiator to obtain the intrinsic antibacterial copolymer of modified tea saponin. Then, the copolymer is dissolved in a solvent to prepare the casting solution. S3: Using the non-solvent induced phase inversion method (NIPS), the casting solution from step S2 is scraped into a liquid film, and then immersed in a coagulation bath for phase exchange and solidification to obtain the green antibacterial separation membrane.

[0012] Furthermore, in step S2, the porogen is polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), or polyethylene glycol (PEG); the solvent is THF, DMF, or NMP. The initiator is ammonium persulfate (APS), azobisisobutyronitrile (AIBN), or benzoyl peroxide (BPO).

[0013] Furthermore, in step S2, the modified tea saponin is mixed with the polymer membrane matrix resin only through physical blending, and the carbon chain length of the long-chain aliphatic compound is C18-C22.

[0014] Furthermore, in step S3, the coagulation bath temperature is 20-40℃, the phase transformation time is 5-30 min, and the film thickness is 100-300 μm.

[0015] Furthermore, the green antibacterial separation membrane exhibits an inhibition rate of >99% against Escherichia coli or Staphylococcus aureus; after 500 hours of continuous operation, the peak intensity retention rate of the characteristic elements or groups of tea saponin on the membrane surface is greater than 90%.

[0016] The present invention relates to the preparation of a modified tea saponin antibacterial component: Natural tea saponin is chemically modified using monomers containing unsaturated double bonds or long-chain aliphatic monomers. By adjusting the reactant ratio and process conditions, the degree of substitution (DS) of the hydroxyl groups on the sugar ring of tea saponin is precisely controlled, thus preparing an antibacterial functional component with an amphiphilic structure and retained biological activity.

[0017] The construction pathway of the functionalized separation membrane of this invention: Based on the binding mode of modified tea saponin with the membrane matrix, this invention provides the following two preparation pathways: Pathway 1: Reactive copolymer intrinsic antibacterial film Modified tea saponin containing unsaturated double bonds was used as a reactive functional monomer. It was mixed with matrix monomers (including but not limited to unsaturated monomers such as acrylonitrile and methyl methacrylate) and solution copolymerized under the action of an initiator. The modified tea saponin was covalently anchored to the polymer backbone, forming an intrinsic antibacterial copolymer. The copolymer was then dissolved in an organic solvent to prepare a casting solution, and a film was formed using the immersion precipitation phase inversion (NIPS) method. This approach achieves permanent non-dissolution of the antibacterial component.

[0018] This preparation route involves first reacting natural tea saponins with acryloyl chloride, isocyanate, and maleic anhydride containing unsaturated double bonds to prepare tea saponin monomers containing unsaturated double bonds. These tea saponin monomers do not require long chains, but must contain double bonds. Then, the tea saponin monomers containing unsaturated double bonds are copolymerized with matrix monomers (including but not limited to acrylonitrile, methyl methacrylate, etc.). The copolymerized copolymer is then directly formed into a film.

[0019] Pathway 2: Long-chain anchored self-enriched antibacterial blend membrane Modified tea saponins containing long-chain hydrophobic groups (C12-C22) are used as hydrophobic anchoring monomers, and are co-dissolved with polymeric membrane matrix resins (including but not limited to polysulfone, polyethersulfone, polyvinylidene fluoride, etc.) in organic solvents. Utilizing the amphiphilic characteristics of modified tea saponins (the hydrophobic long chains are compatible with the matrix, and the hydrophilic sugar rings face the membrane surface / pore walls), surface segregation and self-enrichment are induced during phase inversion to the membrane surface. The long-chain aliphatic groups achieve long-term anchoring through physical entanglement with matrix segments, constructing a separation membrane with long-lasting contact sterilization function.

[0020] This preparation route involves reacting tea saponin with long-chain compounds containing acyl chlorides, acid anhydrides, or isocyanates, which do not require double bonds. The resulting long-chain modified tea saponin is then blended with a film-forming matrix, such as polysulfone, polyethersulfone, or polyvinylidene fluoride, to form a film.

[0021] This is equivalent to two approaches: one is to form a film from a single copolymer, and the other is to form a film by blending it as a functional additive.

[0022] The film-forming process of this invention is as follows: the casting solution prepared by the above method is allowed to stand at 20-80°C to remove bubbles, and then a liquid film is formed on the support by a scraping or spinning process. After a short period of air pre-evaporation (0-120 seconds), it is immersed in a coagulation bath composed of deionized water or a mixture of water and non-solvent (temperature 20-40°C). By utilizing the bidirectional diffusion of solvent and non-solvent, liquid-liquid phase separation occurs, and the film is solidified into a separation membrane with a porous structure.

[0023] This invention also proposes the application of the modified tea saponin-based green antibacterial separation membrane as described above, or the separation membrane prepared by the method described above, in the field of deep water treatment purification or wastewater reuse.

[0024] Compared with the prior art, the modified tea saponin-based antibacterial separation membrane and its preparation method provided by the present invention have the following outstanding advantages and beneficial effects: 1. Combining efficient retention and active sterilization functions, this invention enhances water quality safety. It overcomes the limitations of traditional membranes that "only filter and do not sterilize," utilizing the unique mechanism of tea saponins in disrupting bacterial cell membranes to achieve rapid and efficient contact sterilization of retained bacteria. Experiments show that the membrane of this invention exhibits an inhibition rate of over 99% against both Escherichia coli and Staphylococcus aureus, providing a reliable safety barrier for advanced drinking water treatment.

[0025] 2. The antibacterial components are stably immobilized, exhibiting excellent long-lasting effects and chemical stability. This invention fundamentally solves the problem of easy loss of small molecules from natural products through molecular anchoring strategies such as covalent bonding (path one) or long-chain strong physical entanglement (path two). Continuous water flow or ultrasonic scouring tests (such as 500 hours of high-pressure water flow scouring in Example 2) show that the retention rate of the antibacterial activity characteristic peaks on the membrane surface is greater than 90%, and the antibacterial performance is durable and stable, far exceeding that of membranes prepared by simple physical blending methods.

[0026] 3. Improved hydrophilicity and significantly enhanced resistance to biofouling. The hydroxyl groups abundant in the modified tea saponin molecules accumulate on the membrane surface, effectively reducing the membrane's contact angle and improving surface hydrophilicity. The hydrophilic surface significantly inhibits the adhesion of pollutants such as proteins and polysaccharides, as well as bacteria. Simultaneously, bacteria attached to the surface are promptly killed, preventing them from multiplying and forming a biofilm. This synergistic effect results in a flux recovery rate (FRR) that is more than 35% higher than that of pure polymer membranes (as in Example 3), significantly reducing the cleaning frequency and operating energy consumption of the membrane module, and extending the membrane's service life.

[0027] 4. Environmentally Friendly Throughout the Entire Life Cycle. The core antibacterial component used in this invention is derived from tea saponin, a natural byproduct of tea oil, which is widely available, biodegradable, and renewable. This avoids the use of heavy metal ions such as silver and copper, or synthetic bactericides such as quaternary ammonium salts and antibiotics, eliminating the environmental and health risks associated with heavy metal leakage or the induction of drug-resistant bacteria. The prepared separation membrane does not leach any toxic or harmful substances during water production, and its environmental impact after disposal is minimal.

[0028] 5. Wide process window, compatible with existing membrane production lines, and easy to industrialize. Both preparation routes of this invention employ conventional solution copolymerization or physical blending processes, with subsequent film formation using the mature NIPS method. All equipment used is standard equipment from existing membrane production lines, requiring no additional large-scale investment. By adjusting the degree of substitution, amount, and ratio of modified tea saponin to the matrix resin, the structure and properties of the membrane can be flexibly controlled to meet the needs of different application scenarios.

[0029] In summary, this invention utilizes tea saponin as its intrinsic antibacterial core, achieving a high degree of synergy between antibacterial purification and anti-biofouling. The prepared separation membrane possesses both excellent mechanical strength and durable interfacial hydrophilicity, and the process route is mature with widely available raw materials. The widespread application of this invention will significantly reduce the cleaning frequency of membrane modules and the consumption of chemical reagents. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the molecular structure of natural tea saponin (TS), showing its triterpenoid saponin core skeleton and multiple sugar groups and hydroxyl groups.

[0031] Figure 2This is a schematic diagram of the structure of tea saponin modified with dodecyl succinic anhydride (DDSA) in one embodiment of the present invention, showing that long-chain alkyl groups are linked to the tea saponin molecule via ester bonds.

[0032] Figure 3 The infrared spectrum of maleic anhydride (MAH) modified tea saponin (TS-MAH) in one embodiment of the present invention is used to characterize the success of the chemical modification. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Example 1: Reactive copolymer intrinsic antibacterial membrane (P(AN-co-TS) copolymer membrane)

[0035] In this embodiment, modified tea saponin is embedded into the polyacrylonitrile backbone via covalent bonds to achieve permanent non-dissolution of antibacterial function.

[0036] 1. Preparation of polymerizable tea saponin monomer (TS-MAH): 100 g of vacuum-dried natural tea saponin and 300 g of anhydrous N,N-dimethylformamide (DMF) were added to a reaction flask equipped with a stirrer and condenser, and stirred until dissolved. 35 g of maleic anhydride (MAH) and 1.2 g of triethylamine catalyst were added. Under nitrogen protection, the mixture was heated to 65 °C and refluxed for 8 hours. After the reaction was complete, the reaction solution was poured into a large amount of ice water to precipitate. The precipitate was washed three times with an ethanol / water mixture and dried under vacuum at 50 °C to constant weight to obtain the polymerizable tea saponin monomer TS-MAH. Its degree of substitution (DS) was determined to be approximately 1.1 by acid-base titration, meaning that an average of 1.1 maleic anhydride groups were grafted onto each tea saponin molecule. (See attached reference.) Figure 3 infrared spectrum, Figure 3 The TS-MAH curve at 1730 cm -1 and 1210 cm -1 The presence of characteristic absorption peaks of anhydride in the vicinity confirms the successful grafting of maleic anhydride.

[0037] 2. Synthesis of copolymer P(AN-co-TS): 92 g of acrylonitrile (AN) and 8 g of the above-mentioned TS-MAH monomer were dissolved in 400 g of dimethyl sulfoxide (DMSO) (the tea saponin component accounted for 8% of the total monomer mass), and 0.4 g of ammonium persulfate was added as an initiator. After purging with nitrogen for 30 minutes to remove oxygen, the reaction was carried out in a constant temperature water bath at 70°C for 16 hours. After the reaction was completed, a viscous polymer copolymer P(AN-co-TS) solution was obtained.

[0038] 3. Preparation of casting solution and film formation: The copolymer solution was diluted with DMSO to adjust the solid content to 18%, and allowed to stand at 60°C for 24 hours to remove bubbles, thus obtaining the casting solution. At room temperature (25°C) and 50% humidity, the casting solution was uniformly coated onto a clean glass plate using a 200 μm doctor blade. Air pre-evaporation was allowed for 25 seconds, followed by rapid immersion in a 35°C deionized water coagulation bath. After complete curing, the membrane was removed and rinsed with deionized water for 24 hours to remove residual solvent, yielding the intrinsic antibacterial ultrafiltration membrane.

[0039] 4. Performance Characterization: Antibacterial properties: The obtained membrane has a log reduction value of >4.0 against Escherichia coli, corresponding to a kill rate of >99.99%.

[0040] Physical properties: The tensile strength of the film was 4.5 MPa and the elongation at break was 15% when tested with a universal testing machine. This is 15% higher than that of pure PAN film (tensile strength 3.9 MPa) prepared under the same conditions, indicating that the introduction of tea saponin has a reinforcing effect on the polymer matrix.

[0041] Example 2: Long-lasting anchored self-enriching blend membrane (LC-TS / PSf blend membrane)

[0042] This embodiment utilizes the hydrophobic anchoring effect and surface segregation effect of the ultra-long C22 carbon chain to construct a low-cost, high-performance blended antibacterial membrane.

[0043] 1. Preparation of long-chain hydrophobic modified tea saponin (LC-TS): 100 g of tea saponin and 350 g of anhydrous DMF were added to a reaction vessel and stirred until dissolved. Then, 1.0 g of 4-dimethylaminopyridine (DMAP) was added as a catalyst. Under ice-water bath cooling (10 °C), 12 g of erucic acid chloride (C22 long-chain fatty acid acyl chloride) was slowly added dropwise. After the addition was complete, the temperature was raised to 80 °C and the reaction continued for 8 hours. After the reaction was completed, some solvent was removed by vacuum distillation, the product was precipitated with acetone, washed three times with acetone, and dried under vacuum at 50 °C to obtain the long-chain modified monomer LC-TS. The degree of substitution (DS) was calculated to be 0.45 by 1H NMR spectroscopy.

[0044] 2. Preparation of self-enriched casting solution: By weight, 18 parts polysulfone (PSf), 4 parts LC-TS (approximately 22% of the mass of PSf), 5 parts polyvinylpyrrolidone (PVP, pore-forming agent), and 73 parts N-methylpyrrolidone (NMP) were taken. Each component was added sequentially to a reaction flask, and the mixture was mechanically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand at 60°C for 24 hours to remove bubbles, yielding a uniform and transparent casting solution.

[0045] 3. Film formation process: The casting method was employed, with a doctor blade gap set to 200 μm. Under conditions of room temperature and 60% humidity, the casting solution was coated onto a nonwoven support layer, pre-evaporated in air for 60 seconds, and then immersed in a 25°C deionized water coagulation bath. Due to the amphiphilic nature of LC-TS, its long hydrophobic chain (C22) is compatible with the PSf matrix, while the hydrophilic tea saponin heads tend to face the aqueous phase. Therefore, during phase transformation, LC-TS spontaneously migrates and accumulates on the membrane surface and pore surfaces (surface segregation). Simultaneously, the C22 segments form strong physical entanglements with the PSf molecular chains, creating a stable anchoring structure.

[0046] 4. Performance Characterization: Durability test: After 500 hours of high-pressure cross-flow filtration (flow rate 1.5 m / s), the inhibition rate against Staphylococcus aureus is still >99% (according to GB / T31402-2015). Antifouling performance: After circulating filtration with 1 g / L BSA solution for 2 hours, the flux decrease rate was only 1 / 6 of that of the pure PSf membrane (from 40% to 6.7%), and the flux recovery rate (FRR) reached 92% (68% for the pure PSf membrane), indicating that the bacteria on its surface were killed in time and biofilm formation was effectively inhibited. Anchoring stability: After continuous ultrasonic rinsing (power 200W) for 24 hours, no significant decrease in antibacterial activity was observed, proving that there is a strong physical entanglement and anchoring between the C22 segment and the PSf matrix.

[0047] Example 3: Conventional hydrophobic modified PVDF antibacterial ultrafiltration membrane (DDSA modified tea saponin) In this embodiment, tea saponin was modified with dodecyl succinic anhydride, which has a shorter carbon chain (C12), and then blended with PVDF to form a film, in order to verify the wide applicability of the present invention.

[0048] 1. Preparation of modified tea saponin (DDSA-TS): Following the method in Example 2, 100g of tea saponin and 20g of dodecyl succinic anhydride (DDSA) were reacted at 80°C for 6 hours to obtain moderately hydrophobic modified tea saponin DDSA-TS. Figure 2 The typical structure of tea saponin modified with DDSA is shown, in which the introduction of long-chain alkyl groups alters the hydrophilic-hydrophobic balance of the molecule.

[0049] 2. Preparation of casting solution and film formation: Take 18 parts by weight of polyvinylidene fluoride (PVDF), 1.5 parts of DDSA-TS, 10 parts of PVP, and 70.5 parts of NMP. Dissolve by stirring at 60°C, allow to stand to remove bubbles, scrape the film with a 200μm doctor blade, pre-evaporate in air for 10 seconds, and immerse in a 30°C deionized water coagulation bath to form a film.

[0050] 3. Performance Characterization: Antifouling properties: When filtered with BSA solution, the flux recovery rate (FRR) of the membrane is 35% higher than that of pure PVDF membrane.

[0051] Antibacterial rate: Plate count test for Escherichia coli showed an inhibition rate of >99%.

[0052] As can be seen from the above three embodiments, regardless of whether a copolymerization path or a blending path is used, or a modifier with different carbon chain lengths is used, the present invention can successfully prepare a green separation membrane with excellent long-lasting antibacterial and anti-fouling properties, proving the universality and robustness of the technical solution of the present invention.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A modified tea saponin-based green antibacterial separation membrane, characterized in that, It is prepared from raw materials containing the following parts by weight of component A or component B. Component A: 10-25 parts of polymer membrane matrix resin; Modified tea saponin 0.5-5 parts; 0-10 parts of pore-forming agent; Solvent 60-80 parts; In component A, the polymeric membrane matrix resin is selected from one or more of polysulfone, polyethersulfone, polyvinylidene fluoride, and polyacrylonitrile; the modified tea saponin is an esterification or etherification product generated by the reaction of natural tea saponin with a long-chain aliphatic compound; and the long-chain aliphatic compound is selected from one of dodecyl succinic anhydride, octadecenyl succinic anhydride, stearoyl chloride, lauroyl chloride, and erucic acid chloride. The components of component A are mixed to prepare a casting solution, which is then used to form a film by a non-solvent-induced phase inversion method. Component B: 10-25 parts of matrix monomer; Modified tea saponin 0.5-5 parts; Initiator 0.1-1 part; 60-100 parts solvent; In component B, the modified tea saponin is a copolymeric functional monomer generated by the reaction of natural tea saponin with a monomer containing unsaturated double bonds, wherein the monomer containing unsaturated double bonds is selected from maleic anhydride and glycidyl methacrylate. Furthermore, component B involves solution copolymerization of modified tea saponin containing unsaturated double bonds and matrix monomers under the action of an initiator. After copolymerization, an intrinsic antibacterial copolymer is formed, which is then film-formed using a non-solvent-induced phase inversion method.

2. The modified tea saponin-based green antibacterial separation membrane according to claim 1, characterized in that, The matrix monomer in component B is at least one of acrylonitrile and methyl methacrylate.

3. The modified tea saponin-based green antibacterial separation membrane according to claim 1, characterized in that, The modified tea saponin is fixed to the membrane substrate by covalent bonding or intermolecular entanglement of long chains, and can migrate directionally to the membrane surface during the non-solvent-induced phase inversion film formation process, where it accumulates on the membrane surface and forms an antibacterial functional layer.

4. The method for preparing the modified tea saponin-based green antibacterial separation membrane according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Preparation of modified tea saponin: Natural tea saponin is reacted with long-chain aliphatic compounds or monomers containing unsaturated double bonds in an organic solvent to obtain functional monomers with a degree of substitution of 0.3-1.5, which are then obtained as modified tea saponin. S2: Casting solution preparation: prepared by one of the following methods: Method 1: If the modified tea saponin in step S1 is obtained by reacting natural tea saponin with long-chain aliphatic compounds, the casting solution preparation steps are as follows: Dissolve the modified tea saponin, polymer membrane matrix resin, and pore-forming agent obtained in step S1 in a solvent, stir at 50-80℃ until uniform, let stand to remove bubbles, and prepare the casting solution. Method 2: If the modified tea saponin in step S1 is obtained by reacting natural tea saponin with a monomer containing unsaturated double bonds, the casting solution preparation steps are as follows: The modified tea saponin containing unsaturated double bonds and the matrix monomer are copolymerized in solution under the action of an initiator to obtain the intrinsic antibacterial copolymer of modified tea saponin. Then, the copolymer is dissolved in a solvent to prepare the casting solution. S3: Using a non-solvent-induced phase inversion method, the casting liquid from step S2 is scraped into a liquid film, and then immersed in a coagulation bath for phase exchange and solidification to obtain the green antibacterial separation membrane.

5. The method for preparing the modified tea saponin-based green antibacterial separation membrane according to claim 4, characterized in that, In step S2, the porogen is polyvinylpyrrolidone, polyvinyl alcohol, or polyethylene glycol; the solvent is THF, DMF, or NMP; and the initiator is ammonium persulfate, azobisisobutyronitrile, or benzoyl peroxide.

6. The method for preparing the modified tea saponin-based green antibacterial separation membrane according to claim 5, characterized in that, In step S2, the modified tea saponin is mixed with the polymer membrane matrix resin only through physical blending, and the carbon chain length of the long-chain aliphatic compound is C18-C22.

7. The method for preparing the modified tea saponin-based green antibacterial separation membrane according to claim 5, characterized in that, In step S3, the coagulation bath temperature is 20-40℃, the phase transformation time is 5-30 min, and the film thickness is 100-300 μm.

8. The application of the modified tea saponin-based green antibacterial separation membrane according to any one of claims 1-3 or the separation membrane prepared by the preparation method according to any one of claims 4-7 in the field of deep water treatment purification or wastewater reuse.

9. The application according to claim 8, characterized in that, The green antibacterial separation membrane has an inhibition rate of >99% against Escherichia coli or Staphylococcus aureus; after 500 hours of continuous operation, the peak intensity retention rate of tea saponin characteristic elements or groups on the membrane surface is greater than 90%.

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