A surface-resistant, high-flux reverse osmosis membrane and its preparation method

Abstract

This invention discloses a surface-resistant, high-flux reverse osmosis membrane and its preparation method, belonging to the field of polymer separation membrane materials science and engineering technology. The preparation method includes the following steps: First, an interfacial polymerization reaction is carried out on a porous support base membrane. The interfacial polymerization aqueous solution contains a main-chain amine monomer, an anchored amine monomer with active functional groups available for subsequent reactions, and surface-modified nanoporous fillers. This invention, by constructing a mass transfer channel enhanced by nanofillers in a polyamide layer, and combining the physical shielding and hydration layer effect formed by a surface-grafted superhydrophilic zwitterionic polymer brush layer, synergistically achieves a significant increase in membrane water flux and excellent, long-lasting antifouling performance against organic and biological pollutants, while maintaining an extremely high desalination rate and a stable functional layer structure. This solves the inherent technical problems of the permeation-selectivity trade-off effect and easy fouling inherent in traditional reverse osmosis membranes.

Description

Technical Field

[0001] This invention belongs to the field of polymer separation membrane technology, specifically, it relates to a surface-resistant, high-flux reverse osmosis membrane and its preparation method. Background Technology

[0002] Reverse osmosis (TOS) technology, as a highly efficient and reliable seawater desalination and water purification technology, has become one of the core technologies for ensuring clean water supply against the backdrop of increasingly severe global water scarcity. The core component of TOS technology is the semi-permeable membrane, among which the commercially dominant type is the polyamide thin-film composite membrane prepared by interfacial polymerization. This membrane typically consists of a polyester nonwoven fabric support layer, a porous polysulfone or polyethersulfone intermediate support layer, and an ultrathin polyamide active separation layer on the surface. The polyamide active layer is responsible for the selective separation of water molecules and solute ions, and its microstructure and physicochemical properties directly determine the overall performance of the reverse osmosis membrane. However, after decades of development, traditional TFC reverse osmosis membrane technology still faces several inherent contradictions and technical pain points in practical applications, severely restricting its operating efficiency, lifespan, and economic viability.

[0003] The bottleneck of the osmosis-selectivity trade-off: This is a fundamental limitation prevalent in the field of separation membranes. For traditional polyamide reverse osmosis membranes, to achieve higher water flux, the polyamide active layer typically needs to be made thinner. However, an excessively thin active layer is prone to structural defects such as pinholes, leading to leakage of solutes such as salt ions, thereby reducing the membrane's desalination rate. Conversely, increasing the thickness or cross-linking degree of the active layer to ensure a high desalination rate significantly increases the mass transfer resistance of water molecules through the membrane, resulting in a decrease in water flux. This "you can't have your cake and eat it too" dilemma has kept the water flux of traditional reverse osmosis membranes at a relatively low level (typically 30-40 L·m⁻²·h⁻¹, @2.0MPa), requiring reverse osmosis systems to operate at higher pressures or with larger membrane areas to achieve the target permeate volume, directly increasing the system's investment costs and energy consumption.

[0004] The unavoidable problem of membrane fouling: Membrane fouling is one of the most challenging and prevalent problems in the operation of reverse osmosis systems. The surface of the traditional polyamide active layer is not an ideally smooth plane; it exhibits a rough "ridge-valley" morphology at the nanoscale. This rough surface easily captures and accumulates pollutants such as colloids and suspended particles in the water. Furthermore, the polyamide molecular chain contains numerous amide groups and unreacted carboxyl groups, giving its surface a negative charge and a degree of hydrophobicity at typical operating pH. This results in a strong adsorption tendency for commonly found natural organic matter (such as humic acid), proteins, and polysaccharides in water, forming an organic fouling layer. Even more seriously, these adsorbed organic substances on the membrane surface provide abundant nutrients for microorganisms, inducing bacteria and other microorganisms to proliferate on the membrane surface and secrete extracellular polymeric substances (EPS), forming a difficult-to-remove biofilm, i.e., biofouling. Membrane fouling can rapidly lead to a sharp decline in permeate flux and a reduction in desalination rate, forcing the system to undergo frequent chemical cleaning (CIP) or shutdown for maintenance. This not only increases the consumption of chemical agents and the risk of secondary contamination, but also shortens the actual service life of membrane elements, significantly increasing the overall cost of reverse osmosis water treatment.

[0005] To this end, we provide a surface-resistant, high-flux reverse osmosis membrane and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to solve the problems in the prior art by proposing a surface-resistant, high-flux reverse osmosis membrane and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a surface-fouling-resistant high-flux reverse osmosis membrane includes the following steps: Step 1: Prepare a functionalized aqueous solution by dissolving or dispersing the main chain amine monomer, the anchored amine monomer, and the surface-hydrophilic modified nanoporous filler in an aqueous solution. The anchored amine monomer contains at least two active hydrogen atoms that can react with acyl chloride groups and at least one active functional group that does not participate in the interfacial polymerization reaction and can be used for subsequent chemical grafting. Step 2: Construct a composite polyamide active layer. Immerse the porous support base membrane in the functionalized aqueous solution obtained in Step 1. After removing the excess solution, contact it with a nonpolar organic phase solution containing polyfunctional acyl chloride monomers to undergo an interfacial polymerization reaction. A composite active layer is formed on the surface of the support base membrane, in which nanoporous fillers are embedded in the polyamide matrix and anchored amine monomer residues are covalently linked to the polymer chains. Step 3: Fix the polymerization initiator, and contact the film with the composite active layer obtained in Step 2 with a solution containing initiator precursor molecules, so that the initiator precursor molecules react chemically with the active functional groups on the anchored amine monomer residues, thereby covalently bonding the initiator residues of the controlled free radical polymerization to the surface of the composite active layer. Step 4: Grafting zwitterionic polymer brush layer. The membrane with the initiator fixed on the surface obtained in Step 3 is placed in a polymerization reaction solution containing zwitterionic monomers and a catalyst system. A dense, covalently linked zwitterionic polymer brush layer is grown in situ on the surface of the composite active layer by surface-initiated atom transfer radical polymerization (SI-ATRP), forming the final surface-antifouling high-flux reverse osmosis membrane.

[0008] Preferably, the main-chain amine monomer in step one is piperazine or its derivative; the anchored amine monomer is an amine compound containing a primary or secondary amine group and a hydroxyl group, specifically N-methyldiethanolamine, triethanolamine or 3-amino-1,2-propanediol; the molar ratio of the main-chain amine monomer to the anchored amine monomer is (5-20):1.

[0009] Preferably, the nanoporous filler in step one is a metal-organic framework (MOF) material or a zeolite imidazole ester framework (ZIF) material, with a native particle size of 50-200 nm; the surface hydrophilic modification is performed by coating the nanoporous filler with tannic acid or polydopamine.

[0010] Preferably, the porous supporting membrane in step two is an ultrafiltration membrane made of polysulfone, polyethersulfone, or polyvinylidene fluoride; the polyfunctional acyl chloride monomer is trimesoyl chloride (TMC); and the nonpolar organic phase solution is a solution of trimesoyl chloride dissolved in an alkane solvent with a concentration of 0.05-0.2% (w / v).

[0011] Preferably, when the anchored amine monomer is an amine compound containing hydroxyl groups, the reaction for fixing the polymerization initiator in step three is as follows: the hydroxyl groups on the surface of the composite active layer react with an α-haloacyl halide compound under the catalysis of an organic base to undergo an esterification reaction, thereby fixing the α-haloisobutyryl group as an initiator residue on the membrane surface; the α-haloacyl halide compound is 2-bromoisobutyryl bromide or 2-chloroisobutyryl chloride.

[0012] Preferably, the zwitterionic monomer in step four is sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), or (3-acrylamidopropyl)dimethylammonium propanesulfonic acid inner salt; the catalyst system is a combination of a monovalent copper halide and a nitrogen-containing ligand, specifically a combination of cuprous bromide (CuBr) and N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA).

[0013] Preferably, the conditions for the interfacial polymerization reaction in step two are: an aqueous phase contact time of 30-120 seconds, an organic phase contact time of 15-60 seconds, and a heat treatment at 60-95°C for 5-15 minutes after the reaction to promote the crosslinking of the polyamide network.

[0014] Preferably, the reaction conditions for surface-initiated atom transfer radical polymerization in step four are: under an inert atmosphere, the reaction is carried out at a temperature of 25-60°C for 0.5-5 hours; the dry film thickness of the formed zwitterionic polymer brush layer is measured to be 10-50 nm by atomic force microscopy (AFM) scratch method.

[0015] Preferably, the structure of the membrane, from the inside out, comprises: a porous support base membrane; a composite active layer covalently bonded thereto with a thickness of 80-200 nm, the composite active layer being composed of a cross-linked polyamide network with embedded surface-hydrophilized modified nanoporous fillers; and a polymer brush layer covalently bonded to the surface of the composite active layer, composed of zwitterionic polymer chains with a thickness of 10-50 nm.

[0016] Preferably, the membrane has a water flux greater than 60 L·m⁻²·h⁻¹ and a sodium chloride rejection rate greater than 99.5% under the test conditions of 2.0 MPa operating pressure, 2000 ppm sodium chloride solution, and 25 °C; and a flux recovery rate (FRR) greater than 95% after a static fouling experiment with bovine serum albumin (BSA) solution that has been running continuously for 24 hours.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this invention, by introducing surface-modified hydrophilic nanoporous fillers (such as MOFs) into the aqueous phase of interfacial polymerization, and utilizing their regular nanopore structure and the interfacial voids formed with the polymer matrix, a large number of rapid mass transfer channels for preferential water molecules are constructed in the dense polyamide selective layer. This achieves a water flux of more than 50% compared with traditional reverse osmosis membranes without sacrificing or even slightly increasing the salt rejection rate, thereby significantly alleviating or even breaking through the osmosis-selectivity trade-off.

[0018] 2. In this invention, anchored amine monomers are introduced as "chemical anchors" during the formation of the polyamide network. Based on this, a dense, uniform zwitterionic polymer brush layer is grown in situ on the membrane surface using controlled surface-initiated atom transfer radical polymerization (SI-ATRP). This achieves precise control over the hydrophilicity, electroneutrality, and microstructure of the membrane surface, thereby endowing the membrane surface with excellent and long-lasting resistance to organic and biofouling, significantly extending the membrane's service life and cleaning cycle.

[0019] 3. In this invention, the two key steps of constructing a nanocomposite structure to improve flux and surface grafting functionalization to enhance antifouling properties are organically integrated into a single, well-structured, and mild preparation process. The initiator fixation and subsequent graft polymerization reactions are carried out without disrupting the precisely separated structure of the underlying polyamide, ensuring the intrinsic high desalination performance of the membrane. Furthermore, the formed covalently bonded functional layer exhibits extremely high chemical and mechanical stability, thus achieving a comprehensive effect of good reproducibility of the preparation method, excellent overall product performance, and stable reliability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow for preparing a surface-fouling-resistant high-flux reverse osmosis membrane according to the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment provides a method for preparing a surface-resistant, high-flux reverse osmosis membrane using ZIF-8 as a nanoporous packing material, N-methyldiethanolamine as an anchoring monomer, and sulfobetaine methacrylate (SBMA) as a grafting monomer.

[0024] Step 1: Preparation of functionalized aqueous solution Surface modification of nanoporous fillers: 1.0 g of zeolite imidazole ester framework-8 (ZIF-8) nanocrystals (purchased from Jilin Yixi Technology Co., Ltd., average particle size approximately 80 nm) were dispersed in 200 mL of deionized water and sonicated for 30 minutes to ensure uniform dispersion. 2.0 g of tannic acid (TA) was dissolved in 50 mL of deionized water and slowly added dropwise to the ZIF-8 dispersion under magnetic stirring. The reaction was continued at room temperature for 12 hours. After the reaction, the product was collected by centrifugation (8000 rpm, 10 min) and washed three times with deionized water to remove unreacted tannic acid. Finally, the obtained tannic acid-modified ZIF-8 (denoted as TA@ZIF-8) was freeze-dried for later use. The phenolic hydroxyl groups of tannic acid can be stably coated on the surface of ZIF-8 through coordination and hydrogen bonding, giving it excellent hydrophilicity.

[0025] Preparation of the aqueous solution: Accurately weigh 2.0 g of piperazine (PIP) as the main-chain amine monomer, 0.2 g of N-methyldiethanolamine (MDEA) as the anchoring amine monomer (PIP to MDEA molar ratio approximately 14:1), and 0.1 g of the TA@ZIF-8 nanofiller prepared above, and dissolve / disperse them together in 97.7 g of deionized water. To ensure uniform dispersion, the solution was ultrasonically treated for 30 minutes before use.

[0026] Step 2: Constructing the composite polyamide active layer Base membrane preparation: Cut a commercial polyethersulfone (PES) ultrafiltration membrane (molecular weight cutoff 20,000 Da) the size of an A4 sheet of paper as a porous support base membrane, immerse it in deionized water for more than 2 hours to wet the pores and wash away the protective agent.

[0027] Interfacial polymerization: Remove the wetted PES substrate film and gently wipe away excess moisture with a lint-free paper. Fix it onto a glass plate and pour the functionalized aqueous solution prepared in step one onto it, immersing for 2 minutes. Then, gently roll the film surface with a rubber spatula to remove excess aqueous solution.

[0028] Immediately immerse the substrate membrane with the aqueous solution attached into a pre-prepared organic phase solution. This organic phase solution is a 0.15% (w / v) hexane solution of trimesoyl chloride (TMC). After immersion for 45 seconds, remove the membrane and blow away any remaining organic phase solution from the surface using an air gun.

[0029] The initial composite membrane was heat-treated in a 60°C oven for 10 minutes to promote the cross-linking and curing of the polyamide and enhance its adhesion to the supporting substrate membrane. The resulting membrane is designated PA-MDEA@TA@ZIF-8 / PES.

[0030] Step 3: Fixing the polymerization initiator The above PA-MDEA@TA@ZIF-8 / PES membrane was immersed in 100 mL of anhydrous toluene, and 2 mL of triethylamine was added as an acid-binding agent.

[0031] 2 mL of 2-bromoisobutyryl bromide was slowly added dropwise to the solution under ice-water bath and magnetic stirring.

[0032] Remove the ice-water bath and react at room temperature for 24 hours. During this process, the hydroxyl groups provided by MDEA residues on the membrane surface undergo esterification with 2-bromoisobutyryl bromide, covalently bonding the ATRP initiator (α-bromoisobutyryl group) to the surface of the polyamide layer.

[0033] After the reaction was complete, the membrane was removed and thoroughly rinsed sequentially with toluene, ethanol, and deionized water to remove all unreacted chemicals. The resulting membrane was labeled PA-Br@TA@ZIF-8 / PES.

[0034] Step 4: Grafting zwitterionic polymer brush layer In a three-necked flask that has been thoroughly dried and purged with nitrogen, add 2.79 g of sulfobetaine methacrylate (SBMA) monomer and 50 mL of a methanol / water mixture (4:1 by volume). Purge with nitrogen and bubble for 30 minutes to completely remove oxygen.

[0035] Weigh 14.3 mg of cuprous bromide (CuBr) and 34.6 mg of N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) as the catalyst system, and rapidly add them to the above solution under nitrogen protection. Stir until the catalyst system is completely dissolved to form a homogeneous polymerization reaction solution.

[0036] The PA-Br@TA@ZIF-8 / PES membrane prepared above was quickly immersed in the polymerization reaction solution to ensure that the membrane was completely submerged.

[0037] The reaction was carried out in a constant temperature water bath at 30°C under a nitrogen atmosphere for 3 hours.

[0038] After the reaction is complete, the membrane is removed and immediately rinsed with plenty of deionized water. It is then soaked and shaken in 500 mL of deionized water for 24 hours to thoroughly remove physically adsorbed polymers and residual catalyst. The resulting membrane is the finished product, designated PSBMA-PA@TA@ZIF-8 / PES, and stored in deionized water for later use.

[0039] Example 2

[0040] This embodiment provides a method for preparing a surface-resistant, high-flux reverse osmosis membrane using ZIF-8 as the nanoporous packing material, 3-amino-1,2-propanediol as the anchoring monomer, and carboxybetaine methacrylate (CBMA) as the grafting monomer. Most of the steps are the same as in Example 1, with the main difference being the types of anchoring amine monomer and the zwitterionic monomer grafted onto the surface.

[0041] Step 1: Preparation of functionalized aqueous solution Surface modification of nanoporous fillers: This step is exactly the same as in Example 1. 1.0 g of zeolite imidazole ester framework-8 (ZIF-8) nanocrystals (average particle size approximately 80 nm) were weighed and dispersed in 200 mL of deionized water, and sonicated for 30 minutes. 2.0 g of tannic acid (TA) was weighed and dissolved in 50 mL of deionized water. Under magnetic stirring, the tannic acid solution was slowly added dropwise to the ZIF-8 dispersion, and the reaction was continued at room temperature for 12 hours. After the reaction was complete, the product was collected by centrifugation and washed three times with deionized water. The resulting tannic acid-modified ZIF-8 (denoted as TA@ZIF-8) was freeze-dried for later use.

[0042] Preparation of the aqueous solution: Accurately weigh 2.0 g of piperazine (PIP) as the main-chain amine monomer, 0.153 g of 3-amino-1,2-propanediol (APD) as the anchoring amine monomer (its molar amount is equivalent to MDEA in Example 1), and 0.1 g of the TA@ZIF-8 nanofiller prepared above, and dissolve / disperse them together in 97.747 g of deionized water. To ensure uniform dispersion, the solution was ultrasonically treated for 30 minutes before use.

[0043] Step 2: Constructing the composite polyamide active layer Base membrane preparation: Cut a piece of commercial polyethersulfone (PES) ultrafiltration membrane (molecular weight cutoff 20,000 Da) the size of an A4 sheet of paper as a porous support base membrane, and immerse it in deionized water for more than 2 hours.

[0044] Interfacial polymerization: Remove the wetted PES substrate film and gently wipe away excess moisture with a lint-free paper. Fix it onto a glass plate and pour the functionalized aqueous solution prepared in step one onto it, immersing for 2 minutes. Then, gently roll the film surface with a rubber spatula to remove excess aqueous solution.

[0045] Immediately immerse the substrate membrane with the aqueous solution attached into a 0.15% (w / v) hexane solution of trimesoyl chloride (TMC). After immersion contact for 45 seconds, remove the membrane and blow away any remaining organic phase solution on the surface with an air gun.

[0046] The initial composite membrane was heat-treated in an oven at 60°C for 10 minutes. The resulting membrane was designated PA-APD@TA@ZIF-8 / PES. Since the 3-amino-1,2-propanediol molecule contains one primary amine group and two hydroxyl groups, the primary amine group participates in interfacial polymerization, covalently incorporating structural units with two hydroxyl groups into the polyamide network.

[0047] Step 3: Fixing the polymerization initiator The above PA-APD@TA@ZIF-8 / PES membrane was immersed in 100 mL of anhydrous toluene, and 2 mL of triethylamine was added as an acid-binding agent.

[0048] 2 mL of 2-bromoisobutyryl bromide was slowly added dropwise to the solution under ice-water bath and magnetic stirring.

[0049] Remove the ice-water bath and react at room temperature for 24 hours. During this process, the two ortho-hydroxyl groups provided by the APD residues on the membrane surface undergo esterification with 2-bromoisobutyryl bromide, covalently bonding the ATRP initiator (α-bromoisobutyryl group) to the surface of the polyamide layer.

[0050] After the reaction was complete, the membrane was removed and thoroughly rinsed with toluene, ethanol, and deionized water in sequence. The resulting membrane was labeled PA-Br@TA@ZIF-8 / PES.

[0051] Step 4: Grafting zwitterionic polymer brush layer In a three-necked flask that has been thoroughly dried and purged with nitrogen, 2.15 g of carboxy betaine methacrylate (CBMA) monomer (the molar amount of which is equivalent to SBMA in Example 1) and 50 mL of methanol / water (volume ratio 4:1) mixed solvent are added, and nitrogen is bubbled through for 30 minutes to completely remove oxygen.

[0052] Weigh 14.3 mg of cuprous bromide (CuBr) and 34.6 mg of N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) as the catalyst system, and rapidly add them to the above solution under nitrogen protection, stirring until the catalyst system is completely dissolved.

[0053] The PA-Br@TA@ZIF-8 / PES membrane prepared above was quickly immersed in the polymerization reaction solution.

[0054] The reaction was carried out in a constant temperature water bath at 30°C under a nitrogen atmosphere for 3 hours.

[0055] After the reaction is complete, the membrane is removed and immediately rinsed with plenty of deionized water. It is then soaked and shaken in 500 mL of deionized water for 24 hours to thoroughly remove physically adsorbed polymers and residual catalyst. The resulting membrane is the finished product, designated PCBMA-PA@TA@ZIF-8 / PES, and stored in deionized water for later use.

[0056] Example 3

[0057] This embodiment provides a method for preparing a surface-resistant, high-flux reverse osmosis membrane using polydopamine-modified UiO-66-NH2 as a nanoporous packing material, N-methyldiethanolamine as an anchoring monomer, and sulfobetaine methacrylate (SBMA) as a grafting monomer. Most of the steps are the same as in Example 1; the main difference lies in the type of nanoporous packing material and its surface modification method.

[0058] Step 1: Preparation of functionalized aqueous solution Surface modification of nanoporous fillers: 1.0 g of amino-functionalized metal-organic framework material UiO-66-NH2 (purchased from Strem Chemicals, Inc., average particle size approximately 150 nm) was dispersed in 200 mL of 10 mM Tris-HCl buffer solution (pH 8.5) and sonicated for 30 min to ensure uniform dispersion. 0.2 g of dopamine hydrochloride was dissolved in 10 mL of the above Tris-HCl buffer solution. Under vigorous magnetic stirring, the dopamine hydrochloride solution was added to the UiO-66-NH2 dispersion. The reaction was continued for 24 hours at room temperature under open conditions with stirring, utilizing oxygen in the air to initiate the self-polymerization of dopamine, forming a dense polydopamine (PDA) coating layer on its surface. After the reaction was completed, the product was collected by centrifugation (8000 rpm, 10 min) and washed repeatedly with deionized water several times until the supernatant was clear and colorless. Finally, the obtained PDA-modified UiO-66-NH2 (denoted as PDA@UiO-66-NH2) was freeze-dried for later use.

[0059] Preparation of the aqueous solution: Accurately weigh 2.0 g of piperazine (PIP) as the main-chain amine monomer, 0.2 g of N-methyldiethanolamine (MDEA) as the anchoring amine monomer, and 0.1 g of the prepared PDA@UiO-66-NH2 nanofiller, and dissolve / disperse them together in 97.7 g of deionized water. To ensure uniform dispersion, the solution was ultrasonically treated for 30 minutes before use.

[0060] Step 2: Constructing the composite polyamide active layer This step is exactly the same as in Example 1. A commercial PES ultrafiltration membrane was sequentially immersed in the functionalized aqueous solution prepared in step one (2 minutes) and then in a 0.15% (w / v) TMC n-hexane solution (45 seconds) to carry out interfacial polymerization, followed by heat treatment at 60°C for 10 minutes. The resulting membrane is designated PA-MDEA@PDA@UiO-66-NH2 / PES.

[0061] Step 3: Fixing the polymerization initiator This step is exactly the same as in Example 1. The membrane obtained in the previous step is reacted with 2-bromoisobutyryl bromide in anhydrous toluene in the presence of triethylamine for 24 hours, covalently bonding the ATRP initiator to the hydroxyl group of the MDEA residue. The resulting membrane is designated PA-Br@PDA@UiO-66-NH2 / PES.

[0062] Step 4: Grafting zwitterionic polymer brush layer This step is exactly the same as in Example 1. The membrane with the initiator fixed is immersed in a methanol / water mixed solvent containing 2.79 g of SBMA monomer and CuBr / PMDETA catalyst system, and a surface-initiated atom transfer radical polymerization reaction is carried out at 30°C under nitrogen protection for 3 hours. After the reaction, the membrane is thoroughly washed to obtain the final product membrane, denoted as PSBMA-PA@PDA@UiO-66-NH2 / PES, which is stored in deionized water for later use.

[0063] In summary, three comparative examples are also provided: Comparative Example 1 (Traditional TFC Membrane) The preparation method is similar to that in Example 1, but in the aqueous solution of step one, no anchored amine monomer (MDEA) or nanoporous filler (TA@ZIF-8) is added; only 2.2 g of piperazine is dissolved in 97.8 g of deionized water. Subsequent steps three and four are not performed. The final product is a conventional polyamide reverse osmosis membrane.

[0064] Comparative Example 2 (Membrane with enhanced flux only) The preparation method was similar to that of Example 1, except that the anchored amine monomer (MDEA) was not added to the aqueous solution in step one; that is, the aqueous phase composition was 2.2 g piperazine and 0.1 g TA@ZIF-8 dissolved in 97.7 g deionized water. Subsequent steps three and four were not performed. This comparative example aims to verify the effect of introducing only nanofillers on performance.

[0065] Comparative Example 3 (film with surface antifouling modification only) The preparation method was similar to that of Example 1, except that no nanoporous filler (TA@ZIF-8) was added to the aqueous solution in step one; that is, the aqueous phase composition was 2.0 g piperazine and 0.2 g MDEA dissolved in 97.8 g deionized water. Subsequent steps two, three, and four were exactly the same as in Example 1. This comparative example aims to verify the effect of surface grafting modification alone on performance.

[0066] Performance Testing and Results Analysis The membrane samples prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to standard performance tests, and the results are summarized in the table below.

[0067] Test conditions: Separation performance: Water flux and desalination rate were tested using a cross-flow test device under the conditions of 2.0 MPa operating pressure, 25°C, and 2000 ppm NaCl solution as feed liquid.

[0068] Antifouling performance: After completing the separation performance test, the feed solution was replaced with a phosphate buffer solution (pH=7.4) containing 1.0 g / L bovine serum albumin (BSA), and accelerated fouling was carried out continuously for 5 hours at 0.5 MPa pressure. The initial flux J0 and the flux after fouling were recorded. p Then, the membrane surface was rinsed with deionized water under low pressure for 30 minutes, and its flux Jᵣ under pure water conditions was measured. The flux recovery rate (FRR) was calculated as FRR(%) = (Jᵣ / J0) × 100%.

[0069] Surface hydrophilicity: characterized by static water contact angle (WCA).

[0070] Performance test results

[0071] Results analysis: Verification of the synergistic effect: The samples of Examples 1-3 showed overwhelming advantages in all performance indicators compared with all comparative examples. Taking Example 1 as an example, its water flux (72.5 L·m⁻²·h⁻¹) was almost twice that of Comparative Example 1 (conventional membrane, 38.2 L·m⁻²·h⁻¹), while maintaining an extremely high salt rejection rate (99.6%). This strongly demonstrates that by introducing TA@ZIF-8 nanofiller into the polyamide layer, a fast water molecule channel was successfully constructed, breaking through the traditional "trade-off" effect.

[0072] Improved antifouling performance: The water contact angle of Example 1 (25.8°) is significantly lower than that of Comparative Example 1 (75.3°) and Comparative Example 2 (72.8°), indicating that its surface has superior hydrophilicity. This is attributed to the PSBMA brush layer grafted onto the surface, which is rich in hydrophilic groups. In the antifouling test, Example 1 achieved a flux recovery rate (FRR) of 97.2%, while the FRR of Comparative Examples 1 and 2 without surface modification was only 45.6% and 52.3%, respectively. This demonstrates that pollutants are difficult to adhere firmly to the membrane surface of Example 1 and are easily removed by water flow. Although Comparative Example 3 also grafted a PSBMA brush layer and achieved an FRR of 95.8%, its water flux (40.5 L·m⁻²·h⁻¹) was no different from that of conventional membranes. This again highlights the synergistic advantage of combining flux enhancement with antifouling modification in this invention.

[0073] Feasibility and universality of the method: Examples 2 and 3 changed the types of anchoring monomers / grafting monomers and nanofillers, respectively. The performance of the final products was at the same excellent level as that of Example 1, which proves that the integrated preparation strategy of "nanocomposite-anchor pre-embedding-surface grafting" proposed in this invention has good universality and is not limited to a few specific chemical substances, providing a broad platform for the customized design of high-performance reverse osmosis membranes.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a surface-fouling-resistant high-flux reverse osmosis membrane, characterized in that, Includes the following steps: Step 1: Prepare a functionalized aqueous solution by dissolving or dispersing the main chain amine monomer, the anchored amine monomer, and the surface-hydrophilic modified nanoporous filler in an aqueous solution. The anchored amine monomer contains at least two active hydrogen atoms that can react with acyl chloride groups and at least one active functional group that does not participate in the interfacial polymerization reaction and can be used for subsequent chemical grafting. Step 2: Construct a composite polyamide active layer. Immerse the porous support base membrane in the functionalized aqueous solution obtained in Step 1. After removing the excess solution, contact it with a nonpolar organic phase solution containing polyfunctional acyl chloride monomers to undergo an interfacial polymerization reaction. A composite active layer is formed on the surface of the support base membrane, in which nanoporous fillers are embedded in the polyamide matrix and anchored amine monomer residues are covalently linked to the polymer chains. Step 3: Fix the polymerization initiator, and contact the film with the composite active layer obtained in Step 2 with a solution containing initiator precursor molecules, so that the initiator precursor molecules react chemically with the active functional groups on the anchored amine monomer residues, thereby covalently bonding the initiator residues of the controlled free radical polymerization to the surface of the composite active layer. Step 4: Grafting zwitterionic polymer brush layer. The membrane with the initiator fixed on the surface obtained in Step 3 is placed in a polymerization reaction solution containing zwitterionic monomers and a catalyst system. A dense, covalently linked zwitterionic polymer brush layer is grown in situ on the surface of the composite active layer by surface-initiated atom transfer radical polymerization (SI-ATRP), forming the final surface-antifouling high-flux reverse osmosis membrane.

2. The preparation method according to claim 1, characterized in that, The main-chain amine monomer in step one is piperazine or its derivative; the anchored amine monomer is an amine compound containing a primary or secondary amine group and a hydroxyl group, specifically N-methyldiethanolamine, triethanolamine or 3-amino-1,2-propanediol; the molar ratio of the main-chain amine monomer to the anchored amine monomer is (5-20):

1.

3. The preparation method according to claim 1, characterized in that, The nanoporous filler in step one is a metal-organic framework (MOF) material or a zeolite imidazole ester framework (ZIF) material, with a native particle size of 50-200 nm; the surface hydrophilic modification is to use tannic acid or polydopamine to coat the surface of the nanoporous filler.

4. The preparation method according to claim 1, characterized in that, The porous supporting membrane in step two is an ultrafiltration membrane made of polysulfone, polyethersulfone, or polyvinylidene fluoride; the polyfunctional acyl chloride monomer is trimesoyl chloride (TMC); the nonpolar organic phase solution is a solution of trimesoyl chloride dissolved in an alkane solvent, with a concentration of 0.05-0.2% (w / v).

5. The preparation method according to claim 2, characterized in that, When the anchored amine monomer is an amine compound containing hydroxyl groups, the reaction for fixing the polymerization initiator in step three is as follows: the hydroxyl groups on the surface of the composite active layer react with an α-haloacyl halide compound under the catalysis of an organic base to undergo an esterification reaction, thereby fixing the α-haloisobutyryl group as an initiator residue on the membrane surface; the α-haloacyl halide compound is 2-bromoisobutyryl bromide or 2-chloroisobutyryl chloride.

6. The preparation method according to claim 1, characterized in that, The zwitterionic monomer in step four is sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), or (3-acrylamidopropyl)dimethylammonium propanesulfonic acid inner salt; the catalyst system is a combination of a monovalent copper halide and a nitrogen-containing ligand, specifically a combination of cuprous bromide (CuBr) and N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA).

7. The preparation method according to claim 4, characterized in that, The conditions for the interfacial polymerization reaction in step two are as follows: the contact time between the aqueous phase and the organic phase is 30-120 seconds, the contact time between the organic phase and the reaction is 15-60 seconds, and after the reaction, the reaction is subjected to heat treatment at a temperature of 60-95°C for 5-15 minutes to promote the crosslinking of the polyamide network.

8. The preparation method according to claim 6, characterized in that, The reaction conditions for surface-initiated atom transfer radical polymerization in step four are as follows: under an inert atmosphere, the reaction is carried out at a temperature of 25-60°C for 0.5-5 hours; the dry film thickness of the formed zwitterionic polymer brush layer is 10-50 nm as determined by atomic force microscopy (AFM) scratch method.

9. A surface-resistant, high-flux reverse osmosis membrane prepared by the method according to any one of claims 1 to 8, characterized in that, The structure of the membrane, from the inside out, consists of: a porous support base membrane; a composite active layer covalently bonded thereto with a thickness of 80-200 nm, which is composed of a cross-linked polyamide network with embedded surface-hydrophilized modified nanoporous fillers; and a polymer brush layer covalently bonded to the surface of the composite active layer, composed of zwitterionic polymer chains with a thickness of 10-50 nm.

10. The reverse osmosis membrane according to claim 9, characterized in that, The membrane exhibits a water flux greater than 60 L·m⁻²·h⁻¹ and a sodium chloride rejection rate greater than 99.5% under operating conditions of 2.0 MPa, 2000 ppm sodium chloride solution, and 25 °C. After a static fouling experiment with bovine serum albumin (BSA) solution for 24 hours of continuous operation, its flux recovery rate (FRR) is greater than 95%.

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