A novel high desalination rate anti-pollution reverse osmosis membrane material and a preparation method thereof

Abstract

The application belongs to the field of membrane separation technology, and particularly relates to a novel high desalination rate anti-pollution reverse osmosis membrane material and a preparation method thereof. The preparation method comprises the following steps: contacting a porous support membrane with an aqueous solution containing mixed polyamine monomers and amine-modified nano-silicon dioxide, and then interfacially polymerizing with an oil phase solution containing mixed polyacyl chloride monomers to form a polyamide separation layer; then coating a sulfonated polyether sulfone coating solution to form a first modified layer; and finally coating a reaction solution containing modified polyethyleneimine, carboxylated graphene oxide and a crosslinking agent to form a second modified layer. By compounding aromatic and alicyclic polyamines, and combining amine-modified nano-silicon dioxide anchored in the polyamide network to form a dense separation layer, high desalination rate is ensured; by chemical bonding between the sulfonated polyether sulfone layer and the modified polyethyleneimine / carboxylated graphene oxide / crosslinking agent layer, a stable double-layer modified structure is constructed, and excellent anti-pollution performance is given to the membrane surface. The obtained membrane material has high desalination rate, strong anti-pollution property and stable structure.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material and its preparation method. Background Technology

[0002] Reverse osmosis membrane separation technology, with its advantages of high selectivity, low energy consumption, and no phase change, has become a core technology in seawater desalination, industrial pure water production, and advanced wastewater treatment. With the increasing severity of water scarcity and continuously tightening environmental emission standards, the market is placing higher demands on the separation performance and service life of reverse osmosis membranes. The chemical structure and microstructure of membrane materials directly determine their permeability, desalination efficiency, and antifouling properties. Therefore, developing novel reverse osmosis membrane materials that combine high desalination rates with long-term stability has become a research hotspot in the field of membrane separation, and is crucial for expanding the application boundaries of membrane technology and reducing system operating costs.

[0003] Currently, the main technical approaches to improving the overall performance of reverse osmosis membranes focus on three main directions: optimization of interfacial polymerization processes, monomer molecular structure design, and membrane surface modification. While traditional aromatic polyamide composite membranes possess high desalination rates, residual carboxyl groups on their surface easily combine with calcium and magnesium ions and organic pollutants in the water, leading to severe membrane fouling and rapid flux decline. To address this issue, existing research attempts to improve membrane hydrophilicity by introducing hydrophilic polymer coatings or nanoparticle doping, such as using polyvinyl alcohol for surface coating. While this slows down the fouling process to some extent, the coating stability is poor, and it is prone to peeling off over long-term operation, often at the expense of water flux. Another technical approach focuses on developing novel aqueous or oil-phase monomers, attempting to construct thin and dense separation layers by controlling the cross-linking structure. However, overly dense cross-linking structures significantly reduce the water molecule transfer rate, while loose structures struggle to ensure efficient retention of monovalent ions. The inherent trade-off effect between desalination rate and permeability has yet to be fundamentally overcome. Furthermore, in existing preparation processes, the bonding between multiple modified layers largely relies on physical adsorption or simple ionic bonds, which easily leads to interlayer delamination under long-term high-pressure operation and frequent cleaning, resulting in membrane performance degradation. Therefore, it is particularly necessary to develop a novel reverse osmosis membrane material with high desalination rate, excellent antifouling performance, and strong interlayer bonding through molecular-level structural design. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to propose a novel high-desalination-rate, anti-fouling reverse osmosis membrane material and its preparation method, thereby solving the problems in the prior art where reverse osmosis membranes cannot simultaneously achieve high desalination rate and high water flux, where the surface modification layer and the base membrane have poor adhesion and are prone to detachment, and where multilayer structures are prone to interlayer delamination during long-term operation, leading to performance degradation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material includes the following steps: Step 1: Contact the porous support membrane with an aqueous solution to allow the aqueous solution to wet the porous support membrane. After wetting, remove the excess aqueous solution from the surface of the porous support membrane and then contact it with an oil solution to carry out an interfacial polymerization reaction. After the reaction is completed, wash and dry the membrane to form a polyamide separation membrane layer on the surface of the porous support membrane, thus obtaining a primary composite membrane. The aqueous solution comprises a mixture of polyamine monomers, amination-modified nanomaterials, an acid-binding agent, and a first surfactant. The oil phase solution comprises a mixed polyacryl chloride monomer, a second surfactant, and an oil phase solvent; Step 2: Apply the first modified layer coating liquid to the surface of the polyamide separation membrane layer of the primary composite membrane, and heat-treat the surface of the polyamide separation membrane layer to form the first modified layer, thereby obtaining the intermediate composite membrane; Step 3: Coat the surface of the first modified layer of the intermediate composite membrane with the reaction solution of the second modified layer, react, wash and dry after the reaction is completed, and form the second modified layer on the surface of the first modified layer to obtain the novel high desalination rate antifouling reverse osmosis membrane material.

[0006] Preferably, in step one, the porous support membrane comprises a porous polysulfone (PSF) nanofiber membrane; The aqueous solution is prepared by dispersing a mixture of polyamine monomers, amination-modified nanomaterials, an acid-binding agent, and a first surfactant in water. The mixed polyamine monomers include aromatic polyamines and alicyclic polyamines; The oil phase solution is prepared by dissolving a mixed polyacryl chloride monomer and a second surfactant in an oil phase solvent. The mixed polyacryl chloride monomers include aromatic triacryl chloride and aromatic diacryl chloride.

[0007] Preferably, the mass percentage of the mixed polyamine monomer in the aqueous solution is 1%-6%, the molar ratio of the aromatic polyamine to the alicyclic polyamine is (1-2):(1-3), the aromatic polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine, and the alicyclic polyamine is selected from at least one of N-aminoethylpiperazine, isophorone diamine, and 1,3-cyclohexanedimethylamine; The amination-modified nanomaterial has a mass percentage content of 0.05%-0.3% in the aqueous solution, and the amination-modified nanomaterial includes amination-modified nano-silica. The acid-binding agent has a mass percentage content of 0.02%-0.5% in the aqueous solution, and the acid-binding agent is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine, and N,N-dimethylpiperazine. The first surfactant has a mass percentage content of 0.01%-0.2% in the aqueous solution, and the first surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfonate.

[0008] Preferably, the amination-modified nano-silica is prepared by the following steps: S1. Place the nano-silica in a vacuum drying oven to dry and remove the surface adsorbed moisture. Take 5-10g of the dried nano-silica and add it to 200-500mL of anhydrous toluene. Disperse it by ultrasonication for 30-60min to make the nano-silica uniformly dispersed and obtain a nano-silica suspension. S2. Dissolve N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (silane coupling agent KH-792) in anhydrous ethanol to prepare a solution with a mass fraction of 10%-20%; add deionized water, the amount of deionized water being 1-3 times the mass of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane; adjust the pH to 4-5 with glacial acetic acid; stir and hydrolyze at room temperature for 30-60 minutes to obtain the hydrolyzed silane coupling agent solution. The nano-silica suspension was stirred and heated to 80-110℃ under nitrogen protection, and the hydrolyzed silane coupling agent solution was added dropwise at a rate of 1-3 mL / min. After the addition was complete, the reaction was stirred for 8-24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried to obtain amination-modified nano-silica. The mass ratio of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane to nano-silica is (0.1-0.5):1.

[0009] Preferably, the mass percentage of the mixed polyacryl chloride monomer in the oil phase solution is 0.05%-0.5%, and the mixed polyacryl chloride monomer is composed of an aromatic triacryl chloride and an aromatic diacryl chloride in a molar ratio of (2-5):1, wherein the aromatic triacryl chloride is selected from trimesoyl pyromellitic chloride, and the aromatic diacryl chloride is selected from at least one of isophthaloyl chloride, terephthaloyl chloride, and phthaloyl chloride; The second surfactant has a mass percentage content of 0.05%-0.1% in the oil phase solution, and the second surfactant is selected from at least one of sorbitan monooleate, sorbitan monolaurate, and polyoxyethylene sorbitan monooleate. The oil phase solvent is selected from at least one of n-hexane, cyclohexane, and heptane.

[0010] Preferably, in step one, the wetting temperature is 10-40℃ and the wetting time is 2-8 min; the interfacial polymerization reaction temperature is 30-80℃ and the interfacial polymerization reaction time is 4-12 min.

[0011] Preferably, in step two, the coating amount of the first modified layer coating liquid is 60-80 g / m². 2 The heat treatment temperature is 80-120℃, and the heat treatment time is 60-90 min; The first modified layer coating solution is prepared by dissolving sulfonated polyethersulfone in an organic solvent; The sulfonated polyethersulfone has a mass percentage content of 0.5%-3% in the first modified layer coating solution; The organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran.

[0012] Preferably, in step three, the coating amount of the second modified layer reaction solution is 50-100 g / m, the environment is controlled at 0-10℃ during the coating process, and the coating is immediately placed in a temperature environment of 40-70℃ for 30-120 min after coating. The reaction solution for the second modified layer includes modified polyethyleneimine, carboxylated graphene oxide, and a crosslinking agent.

[0013] Preferably, the preparation method of the second modified layer reaction solution includes: dispersing modified polyethyleneimine, carboxylated graphene oxide and crosslinking agent in deionized water in proportion, and adjusting the pH value of the reaction solution to 8.5-11 with an alkaline pH adjuster to obtain the second modified layer reaction solution; After the second modified layer reaction solution is prepared, it is stored in an ice-water bath for later use. The alkaline pH adjuster is selected from at least one of sodium hydroxide solution, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, borax-sodium hydroxide buffer, or sodium carbonate-sodium bicarbonate buffer; the modified polyethyleneimine has a mass percentage content of 0.1%-2% in the second modified layer coating solution, the carboxylated graphene oxide has a mass percentage content of 0.01%-0.2% in the second modified layer coating solution, and the crosslinking agent has a mass percentage content of 0.05%-0.5% in the second modified layer coating solution.

[0014] Preferably, the modified polyethyleneimine is prepared by reacting polyethyleneimine with glycidyltrimethylammonium chloride, and the specific preparation method is as follows: Branched polyethyleneimine was dissolved in deionized water to prepare a 10wt%-20wt% solution. The pH of the solution was adjusted to 9-10 with hydrochloric acid. Under stirring, glycidyltrimethylammonium chloride aqueous solution was added dropwise, controlling the dropping rate to keep the reaction temperature below 40℃. The molar ratio of glycidyltrimethylammonium chloride to amino groups in polyethyleneimine was (0.2-0.5):1. After the addition was complete, the reaction was carried out at 40-60℃ for 2-6 hours. After the reaction was completed, the pH was adjusted to 6.5-7.5 with hydrochloric acid, and the product was purified to obtain the modified polyethyleneimine product. The carboxylated graphene oxide is prepared by the following steps: Nano-graphene oxide was prepared using nano-graphene as a raw material. Nano-graphene oxide was dispersed in deionized water, mixed acid was added, and the reaction was carried out at 60-80℃ for 4-8 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain carboxylated graphene oxide. The crosslinking agent includes polyethylene glycol diglycidyl ether.

[0015] The present invention also discloses a novel high desalination rate antifouling reverse osmosis membrane material prepared by the preparation method of the novel high desalination rate antifouling reverse osmosis membrane material as described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a mixed polyamine monomer composed of aromatic and alicyclic polyamines in the interfacial polymerization step, reacting it with a mixed polyacrylamide chloride monomer composed of aromatic triacrylamide chlorides and aromatic diacrylamide chlorides. Simultaneously, surface-modified amination-modified nano-silica is introduced into the aqueous phase. This allows the amination-modified nano-silica to chemically bond with the polyacrylamide chloride monomers through its surface amino groups, uniformly and stably anchoring it within the cross-linked network structure of the polyamide separation layer. On one hand, the rigid alicyclic structure of the alicyclic polyamine increases the packing density of the polyamide molecular chains; on the other hand, the introduction of amination-modified nano-silica fills the nanopores in the polyamide network. The synergistic effect of these two factors forms a denser and defect-free separation layer structure, significantly improving the rejection rate of monovalent ions. Furthermore, the amino hydrophilic groups on the surface of the amination-modified nano-silica provide additional channels for water molecule transport, maintaining a high water flux while ensuring a high desalination rate, effectively overcoming the trade-off limitation between desalination rate and water flux in traditional polyamide membranes. This invention sequentially constructs a first modified layer formed by sulfonated polyethersulfone and a second modified layer formed by the reaction of modified polyethyleneimine, carboxylated graphene oxide, and a crosslinking agent (polyethylene glycol diglycidyl ether) on the surface of a polyamide separation layer. The sulfonic acid groups in the first modified layer react with the retained amine groups of the modified polyethyleneimine and the epoxy groups of the crosslinking agent in the second modified layer under alkaline conditions to form chemical bonds through a ring-opening reaction. Simultaneously, the carboxyl groups on the surface of the carboxylated graphene oxide interact with the amine groups in the modified polyethyleneimine through amide bonds or ionic bonds, resulting in the second modified layer being firmly grafted onto the surface of the first modified layer through multiple chemical bonds. This avoids the problem of easy peeling during long-term operation caused by traditional coatings that rely on physical adsorption or single ionic bond bonding. The quaternary ammonium salt cation introduced by the modified polyethyleneimine in the second modified layer after modification with glycidyltrimethylammonium chloride forms a zwitterion pair with the sulfonic acid anion in the first modified layer at the interface. Through electrostatic interaction, a large number of water molecules are combined to form a dense hydration layer, which can effectively block the adsorption of pollutants such as proteins and oil droplets on the membrane surface. The nano-size effect and rich functional groups of carboxylated graphene oxide further enhance the hydrophilicity and smoothness of the membrane surface, giving the membrane material long-term stable antifouling performance. This invention constructs a multilayer composite membrane system with a gradient structure through the synergistic cooperation of a polyamide separation layer, a first modified layer, and a second modified layer. The polyamide separation layer provides the core separation function with a high desalination rate. The first modified layer, as a transition layer, not only enhances the surface hydrophilicity through its sulfonic acid groups but also provides sufficient chemical bonding sites for the second modified layer. The second modified layer endows the membrane surface with excellent antifouling properties. The three-layer structure is firmly bonded by multiple chemical bonds, avoiding interlayer delamination and ensuring the structural stability of the membrane material under long-term high-pressure operation and frequent chemical cleaning conditions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the novel high desalination rate and antifouling reverse osmosis membrane material of the present invention; Figure 2 The graph shows the results of the desalination rate and water flux measurement of the reverse osmosis membrane materials prepared in Examples 4-6 and Comparative Examples 1-4 of the present invention. Figure 3 The graph shows the surface hydrophilicity measurement results of the reverse osmosis membrane materials prepared in Examples 4-6 and Comparative Examples 1-4 of the present invention; Figure 4 The graph shows the results of the antifouling performance test of the reverse osmosis membrane materials prepared in Examples 4-6 and Comparative Examples 1-4 of the present invention; Figure 5 The graph shows the stability test results of the reverse osmosis membrane materials prepared in Examples 4-6 and Comparative Examples 1-4 of the present invention; In the figure, 1 is the porous support membrane; 2 is the polyamide separation membrane layer; 3 is the first modified layer; and 4 is the second modified layer. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to 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.

[0019] Example 1 This embodiment provides a method for preparing amination-modified nano-silica, including the following steps: S1. Place nano-silica (average particle size 50nm) in a vacuum drying oven and dry at 100-120℃ for 6-12h to remove surface adsorbed moisture. Take 8g of dried nano-silica and add it to 350mL of anhydrous toluene. Disperse it by ultrasonication for 45min to make the nano-silica uniformly dispersed and obtain nano-silica suspension. N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane was dissolved in anhydrous ethanol to prepare a 15% (w / w) solution. Deionized water was added in an amount twice the mass of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane. The pH was adjusted to 4.5 with glacial acetic acid. The solution was stirred and hydrolyzed for 50 min at room temperature to obtain the hydrolyzed silane coupling agent solution. The mass ratio of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane to nano-silica is 0.4:1. S2. Under nitrogen protection, the nano-silica suspension was stirred and heated to 95°C. The hydrolyzed silane coupling agent solution was added dropwise at a rate of 2 mL / min. After the addition was complete, the reaction was stirred for 20 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged (8000 r / min, 15 min). The precipitate was collected and washed three times with anhydrous ethanol and deionized water, respectively. The precipitate was then dried in a vacuum drying oven at 50°C to constant weight to obtain amination-modified nano-silica.

[0020] Example 2 This embodiment provides a method for preparing modified polyethyleneimine, including the following steps: Branched polyethyleneimine (number average molecular weight 10,000) was dissolved in deionized water to prepare a 10 wt% solution. The pH of the solution was adjusted to 9 with 1 mol / L hydrochloric acid. Under stirring, 30 wt% glycidyltrimethylammonium chloride aqueous solution was added dropwise, controlling the dropping rate to keep the reaction temperature below 40°C. The molar ratio of glycidyltrimethylammonium chloride to amino groups in polyethyleneimine was 0.35:1. After the addition was complete, the reaction was carried out at 50°C for 4 h. After the reaction was completed, the pH of the reaction solution was adjusted to 6.5 with 1 mol / L hydrochloric acid. The reaction solution was then placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in deionized water for 24 h to remove unreacted small molecules. The solution was then freeze-dried to obtain the modified polyethyleneimine product.

[0021] Example 3 This embodiment provides a method for preparing carboxylated graphene oxide, including the following steps: Take 2g of nano-graphene (2-10nm) and mix it evenly with 1g of sodium nitrate. Under ice-water bath conditions, add 80mL of concentrated sulfuric acid (98% mass concentration) dropwise and stir for 30min. Under vigorous stirring, slowly add 10g of potassium permanganate in batches, controlling the reaction temperature below 10℃ and the addition time to 1h. After the potassium permanganate is completely added, remove the ice-water bath, raise the temperature of the reaction system to 35℃, and continue stirring for 2h. After the reaction is completed, under ice-water bath and stirring conditions, add 150mL of deionized water dropwise for dilution, controlling the temperature below 50℃. Then raise the temperature of the reaction system to 90℃ and continue stirring for 15min. Finally, 10 mL of 30 wt% hydrogen peroxide was added, and the mixture changed from brownish-yellow to bright yellow. The mixture was then centrifuged while hot (8000 r / min, 10 min), and the supernatant was discarded. The precipitate was washed twice with 5% dilute hydrochloric acid and then with deionized water until the pH was close to neutral. The washed product was redispersed in deionized water and sonicated for 30 min to obtain a dispersion. The dispersion was placed in a dialysis bag (molecular weight cutoff 12000 Da) and dialyzed in deionized water for 3 days, changing the water twice daily. The dialyzed product was freeze-dried (-50℃, vacuum <10 Pa, 48 h) to obtain graphene oxide. Graphene oxide was dispersed in deionized water to prepare a dispersion with a mass concentration of 0.5 mg / mL. The dispersion was ultrasonicated for 30 min to ensure uniform dispersion. Solid chloroacetic acid was added, with a mass ratio of chloroacetic acid to graphene oxide of 5:1. Simultaneously, 2 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 10. The mixture was heated to 70℃ and reacted under stirring for 2 h. After the reaction was completed, the product was cooled to room temperature, and the pH was adjusted to neutral with 1 mol / L hydrochloric acid. The reaction solution was placed in a dialysis bag (molecular weight cutoff of 12000 Da) and dialyzed in deionized water for 2 days, with the water changed twice a day. The dialyzed product was freeze-dried (-50℃, vacuum degree <10 Pa, 24 h) to obtain carboxylated graphene oxide.

[0022] Example 4 This embodiment provides a method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material, including the following steps: Step 1: Disperse the mixed polyamine monomer, the amination-modified nano silica prepared in Example 1, the acid-binding agent and the first surfactant in water to prepare an aqueous solution; The mixture comprises 1% by mass of polyamine monomers in the aqueous solution, which are composed of m-phenylenediamine and N-aminoethylpiperazine mixed in a molar ratio of 1:3; 0.05% by mass of amination-modified nano-silica in the aqueous solution; 0.02% by mass of sodium hydroxide as the acid binder; and 0.01% by mass of sodium dodecyl sulfate as the first surfactant. A mixed polyacryl chloride monomer and a second surfactant were dissolved in an oil phase solvent to prepare an oil phase solution; The mixed polyacrylamide chloride monomer has a mass percentage of 0.05% in the oil phase solution and is composed of a mixture of trimesoyl chloride and isophthaloyl chloride in a molar ratio of 2:1; the second surfactant is sorbitan monooleate (Span 80), which has a mass percentage of 0.05% in the oil phase solution; the oil phase solvent is n-hexane. A porous polysulfone nanofiber membrane (average pore size of 30 nm) was selected as the porous support membrane. The porous support membrane was contacted and immersed in an aqueous solution at 10 °C for 8 min to allow the aqueous solution to wet the porous support membrane. After wetting, excess aqueous solution was removed from the surface of the porous support membrane by blowing with an air knife. Then, it was contacted with an oil solution at 10 °C for 8 min to carry out an interfacial polymerization reaction. The reaction was carried out at 30 °C for 12 min. After the reaction, it was washed with deionized water for 2 min and dried at 30 °C for 12 h to form a polyamide separation membrane layer on the surface of the porous support membrane, thus obtaining the primary composite membrane. Step 2: Dissolve sulfonated polyethersulfone (sulfonation degree 1.2, number average molecular weight 20000) in N,N-dimethylformamide to obtain the first modified layer coating solution. The mass percentage of sulfonated polyethersulfone in the first modified layer coating solution is 0.5%. The first modified layer coating liquid was coated on the surface of the polyamide separation membrane layer of the primary composite membrane at a coating amount of 60 g / m, and heat-treated at 80°C for 90 min to form the first modified layer on the surface of the polyamide separation membrane layer, thus obtaining the intermediate composite membrane. Step 3: Disperse the modified polyethyleneimine obtained in Example 2, the carboxylated graphene oxide obtained in Example 3, and polyethylene glycol diglycidyl ether (number average molecular weight of 400) in deionized water, and adjust the pH value to 8.5 with 1 mol / L sodium hydroxide solution to obtain the second modified layer reaction solution. After the second modified layer reaction solution is prepared, it is stored in an ice-water bath (0-5℃) for later use. The modified polyethyleneimine has a mass percentage of 0.1% in the reaction solution of the second modified layer, the carboxylated graphene oxide has a mass percentage of 0.01% in the reaction solution of the second modified layer, and the polyethylene glycol diglycidyl ether has a mass percentage of 0.05% in the reaction solution of the second modified layer. Under 0-10℃ environmental conditions, the above-mentioned second modified layer reaction solution is coated on the surface of the first modified layer of the intermediate composite membrane obtained in step (II) at a coating amount of 50g / m. After coating, it is immediately placed in a 40℃ environment for 120min reaction. After the reaction, it is washed with deionized water for 2min and dried at 30℃ for 12h to form a second modified layer on the surface of the first modified layer, thus obtaining the novel high desalination rate antifouling reverse osmosis membrane material.

[0023] Example 5 This embodiment provides a method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material, including the following steps: The mixed polyamine monomer, the amination-modified nano silica prepared in Example 1, the acid-binding agent and the first surfactant were dispersed in water to prepare an aqueous solution.

[0024] The mixture comprises 6% by mass of polyamine monomers in the aqueous solution, consisting of p-phenylenediamine and isophorone diamine mixed in a molar ratio of 2:1; 0.3% by mass of amination-modified nano-silica in the aqueous solution; 0.5% by mass of a mixture of sodium bicarbonate and triethylamine (mass ratio 1:1); and 0.2% by mass of a mixture of sodium dodecylbenzenesulfonate and sodium dodecyl sulfonate (mass ratio 1:1). A mixed polyacryl chloride monomer and a second surfactant were dissolved in an oil phase solvent to prepare an oil phase solution. The mixed polyacrylamide chloride monomer has a mass percentage of 0.5% in the oil phase solution and is composed of pyromellitic trimethylol chloride and terephthaloyl chloride in a molar ratio of 5:1; the second surfactant is a mixture of sorbitan monolaurate (Span 20) and polyoxyethylene sorbitan monooleate (Tween 80) (mass ratio 1:1), with a total mass percentage of 0.1% in the oil phase solution; the oil phase solvent is a mixture of cyclohexane and heptane (volume ratio 1:1). A porous polysulfone nanofiber membrane (average pore size of 30 nm) was selected as the porous support membrane. The porous support membrane was contacted and immersed in an aqueous solution at 40 °C for 2 min to allow the aqueous solution to wet the porous support membrane. After wetting, excess aqueous solution on the surface of the porous support membrane was removed by rolling with a rubber roller. Then, it was contacted with an oil solution at 40 °C for 2 min to carry out an interfacial polymerization reaction. The reaction was carried out at 80 °C for 4 min. After the reaction, it was washed with deionized water for 2 min and dried at 30 °C for 12 h to form a polyamide separation membrane layer on the surface of the porous support membrane, thus obtaining the primary composite membrane. Step 2: Dissolve sulfonated polyethersulfone (sulfonation degree 1.2, number average molecular weight 20000) in a mixed solvent of N-methylpyrrolidone and dimethyl sulfoxide (volume ratio 1:1) to obtain the first modified layer coating solution. The mass percentage of sulfonated polyethersulfone in the first modified layer coating solution is 3%. The first modified layer coating liquid was coated on the surface of the polyamide separation membrane layer of the primary composite membrane at a coating amount of 80 g / m, and heat-treated at 120°C for 60 min to form the first modified layer on the surface of the polyamide separation membrane layer, thus obtaining the intermediate composite membrane. Step 3: Disperse the modified polyethyleneimine obtained in Example 2, the carboxylated graphene oxide obtained in Example 3, and polyethylene glycol diglycidyl ether (number average molecular weight of 800) in deionized water, and adjust the pH value to 11 with borax-sodium hydroxide buffer to obtain the second modified layer reaction solution. After the second modified layer reaction solution is prepared, it is stored in an ice-water bath for later use. The modified polyethyleneimine has a mass percentage of 2% in the reaction solution of the second modified layer, the carboxylated graphene oxide has a mass percentage of 0.2% in the reaction solution of the second modified layer, and the polyethylene glycol diglycidyl ether has a mass percentage of 0.5% in the reaction solution of the second modified layer. Under 0-10℃ environmental conditions, the above-mentioned second modified layer reaction solution is coated onto the surface of the first modified layer of the intermediate composite membrane obtained in step two at a coating amount of 100g / m. After coating, it is immediately placed in a 70℃ environment for 30min reaction. After the reaction, it is washed with deionized water for 2min and dried at 30℃ for 12h to form a second modified layer on the surface of the first modified layer, thus obtaining the novel high desalination rate antifouling reverse osmosis membrane material.

[0025] Example 6 This embodiment provides a method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material, including the following steps: Step 1: Disperse the mixed polyamine monomer, the amination-modified nano silica prepared in Example 1, the acid-binding agent and the first surfactant in water to prepare an aqueous solution; The mixture comprises 3.5% by mass of polyamine monomers in the aqueous solution, consisting of m-phenylenediamine and 1,3-cyclohexanedimethylamine in a molar ratio of 1.5:2; 0.17% by mass of amination-modified nano-silica in the aqueous solution; 0.26% by mass of a mixture of sodium carbonate and N,N-dimethylpiperazine (mass ratio 1:1); and 0.1% by mass of the first surfactant, sodium dodecyl sulfate. A mixed polyacryl chloride monomer and a second surfactant were dissolved in an oil phase solvent to prepare an oil phase solution. The mixed polyacrylamide chloride monomer has a mass percentage of 0.27% in the oil phase solution and is composed of pyromellitic trimethylol chloride and phthaloyl chloride in a molar ratio of 3.5:1; the second surfactant is sorbitan monooleate, which has a mass percentage of 0.075% in the oil phase solution; and the oil phase solvent is n-hexane. A porous polysulfone nanofiber membrane (average pore size of 30 nm) was selected as the porous support membrane. The porous support membrane was contacted and immersed in an aqueous solution at 25 °C for 5 min to allow the aqueous solution to wet the porous support membrane. After wetting, the excess aqueous solution on the surface of the porous support membrane was drained off. Then, it was contacted with an oil solution at 25 °C for 5 min to carry out an interfacial polymerization reaction. The reaction was carried out at 55 °C for 8 min. After the reaction, it was washed with deionized water for 2 min and dried at 30 °C for 12 h to form a polyamide separation membrane layer on the surface of the porous support membrane, thus obtaining the primary composite membrane. Step 2: Dissolve sulfonated polyethersulfone (sulfonation degree of 1.2, number average molecular weight of 20000) in N,N-dimethylacetamide to obtain the first modified layer coating solution. The mass percentage of sulfonated polyethersulfone in the first modified layer coating solution is 1.7%.

[0026] The first modified layer coating liquid was coated on the surface of the polyamide separation membrane layer of the primary composite membrane at a coating amount of 70 g / m, and then heat-treated at 100°C for 75 min to form the first modified layer on the surface of the polyamide separation membrane layer, thus obtaining the intermediate composite membrane. Step 3: Disperse the modified polyethyleneimine obtained in Example 2, the carboxylated graphene oxide obtained in Example 3, and polyethylene glycol diglycidyl ether (number average molecular weight of 600) in deionized water, and adjust the pH value to 10 with sodium carbonate-sodium bicarbonate buffer solution to obtain the second modified layer reaction solution. After the second modified layer reaction solution is prepared, it is stored in an ice-water bath (0-5℃) for later use. The modified polyethyleneimine has a mass percentage of 1.05% in the reaction solution of the second modified layer, the carboxylated graphene oxide has a mass percentage of 0.1% in the reaction solution of the second modified layer, and the polyethylene glycol diglycidyl ether has a mass percentage of 0.27% in the reaction solution of the second modified layer. Under 0-10℃ environmental conditions, the above-mentioned second modified layer reaction solution is coated onto the surface of the first modified layer of the intermediate composite membrane obtained in step two at a coating amount of 75g / m. After coating, it is immediately placed in a 55℃ environment for 75min reaction. After the reaction, it is washed with deionized water for 2min and dried at 30℃ for 12h to form a second modified layer on the surface of the first modified layer, thus obtaining the novel high desalination rate antifouling reverse osmosis membrane material.

[0027] Comparative Example 1 This comparative example provides a method for preparing a novel high-desalination-rate, anti-fouling reverse osmosis membrane material. The difference between this example and Example 4 is that no amination-modified nano-silica is added in step one, while the remaining steps and parameters are the same as in Example 4.

[0028] Comparative Example 2 This comparative example provides a method for preparing a novel high-desalination-rate, anti-fouling reverse osmosis membrane material. The difference between this example and Example 4 is that carboxylated graphene oxide is not added in step three, while the remaining steps and parameters are the same as in Example 4.

[0029] Comparative Example 3 This comparative example provides a method for preparing a novel high-desalination-rate, anti-fouling reverse osmosis membrane material. The difference between this example and Example 4 is that the first modified layer is not coated, i.e., the construction of the first modified layer is omitted. The remaining steps and parameters are the same as in Example 4.

[0030] Comparative Example 4 This comparative example provides a method for preparing a novel high-desalination-rate, anti-fouling reverse osmosis membrane material. The difference from Example 4 is that the second modified layer is not coated, i.e., the construction of the second modified layer is omitted. The remaining steps and parameters are the same as in Example 4.

[0031] In the above embodiments and comparative examples, the average pore size of the porous polysulfone nanofiber membrane is 30 nm, and the morphology is as follows: Figure 1 As shown.

[0032] Test case The performance of the reverse osmosis membrane materials prepared in Examples 4-6 and Comparative Examples 1-4 was determined: (1) Desalination rate and water flux determination: Take a membrane sample and use a cross-flow filtration device to filter a 2000 mg / L NaCl aqueous solution under the conditions of operating pressure of 1.55 MPa, temperature of 25℃ and flow rate of 1 L / min. After the system has been running stably for 30 minutes, record the data and calculate the water flux and desalination rate. The formula for calculating water flux is as follows: ×Δt); In the formula: J is the water flux (L·m -2 ·h -1 V is the permeate volume (L), and A is the effective membrane area (m²). 2 ), where Δt is the collection time (h); The formula for calculating the desalination rate is: -C p / C f )×100%; In the formula: C p The osmotic salt concentration (mg / L) is C. f The feed solution salt concentration is (mg / L); the salt concentration was calculated by measuring the solution conductivity using a conductivity meter; the results of water flux and desalination rate measurements are shown in Table 1. Table 1

[0033] As shown in Table 1, the reverse osmosis membrane material prepared by this invention has good separation performance, with high water flux and desalination rate. Compared with Example 4: In Comparative Example 1, without the addition of amination-modified nano-silica, both the desalination rate and water flux decreased, indicating that the amination-modified nano-silica, through its surface amine groups chemically bonded to polyacrylamide monomers, anchors in the polyamide network to form a dense separation layer, which plays a key role in improving the desalination rate and maintaining the water flux; In Comparative Example 2, without the addition of carboxylated graphene oxide, the desalination rate did not change significantly, but the water flux decreased slightly, indicating that carboxylated graphene oxide has little effect on the desalination performance of the separation layer, but its hydrophilic functional groups contribute to the water flux; In Comparative Example 3, without the first modification layer, neither the desalination rate nor the water flux changed significantly, indicating that the main function of the first modification layer is not to directly improve the separation performance; In Comparative Example 4, without the second modification layer, the desalination rate and water flux also remained at a high level, indicating that the main function of the second modification layer is not to improve the separation performance.

[0034] (2) Surface hydrophilicity determination: The static water contact angle of the membrane sample surface was measured using a contact angle meter. The membrane sample was cut into strips of 1cm × 3cm and flattened on a glass slide. At room temperature, 2μL of deionized water was dropped onto the upper surface of the membrane sample (i.e., the surface of the second modified layer in Examples 4-6 and Comparative Examples 1-3, and the surface of the first modified layer in Comparative Example 4). Five different locations were randomly selected for measurement for each sample, and the average value was taken as the contact angle value of the sample. The smaller the contact angle, the stronger the hydrophilicity of the membrane surface. The measurement results are shown in Table 2: Table 2

[0035] As shown in Table 2, the reverse osmosis membrane material prepared by this invention has good surface hydrophilicity. Compared with Example 4: In Comparative Example 1, without the addition of amination-modified nano-silica, the contact angle increased significantly, indicating that the amino hydrophilic groups on the surface of the amination-modified nano-silica play an important role in improving the surface hydrophilicity of the membrane; in Comparative Example 2, without the addition of carboxylated graphene oxide, the contact angle increased, indicating that the abundant carboxyl groups and other hydrophilic functional groups on the surface of carboxylated graphene oxide significantly enhanced the surface hydrophilicity of the membrane; in Comparative Example 3, without the first modification layer, the contact angle increased, indicating that the sulfonic acid groups in the first modification layer contribute to the surface hydrophilicity; in Comparative Example 4, without the second modification layer, the contact angle increased sharply, indicating that the hydrophilic layer formed by the synergistic effect of the quaternary ammonium salt cations introduced by the modified polyethyleneimine and the carboxylated graphene oxide in the second modification layer is the core factor endowing the membrane surface with excellent hydrophilicity.

[0036] (3) Determination of antifouling performance: First, the initial flux J0 of the membrane sample in deionized water was measured. Then, the feed solution was switched to a BSA solution containing 500 mg / L bovine serum albumin (prepared with phosphate buffer, pH=7.4). The membrane was filtered for 1 h at a pressure of 0.5 MPa, and the stable flux J was recorded. p Then rinse the membrane surface with deionized water for 20 minutes, and re-measure the recovery flux J1 of the membrane sample in deionized water. Calculate the flux attenuation rate and flux recovery rate of the membrane sample. The formula for calculating the flux decay rate is as follows: -J p / J0)×100%; The formula for calculating flux recovery rate is: J1 / J0×100%; The results of flux decay rate and flux recovery rate measurements are shown in Table 3: Table 3

[0037] As shown in Table 3, the reverse osmosis membrane material prepared by this invention exhibits excellent antifouling performance. Compared with Example 4: In Comparative Example 1, without the addition of amination-modified nano-silica, the flux decay rate increased and the flux recovery rate decreased, indicating that the introduction of amination-modified nano-silica enhanced the density of the separation layer and reduced the irreversible adsorption of pollutants inside the membrane; In Comparative Example 2, without the addition of carboxylated graphene oxide, the flux decay rate increased and the flux recovery rate decreased, indicating that the dense hydration layer formed by the interaction between the carboxyl groups on the surface of carboxylated graphene oxide and the amino groups of modified polyethyleneimine is a key component in resisting protein adsorption and improving antifouling performance. In Comparative Example 3, the absence of the first modified layer significantly reduced the antifouling performance, indicating that the chemical bonding between the sulfonic acid groups contained in the first modified layer and the second modified layer is crucial for the formation of a stable antifouling layer. In Comparative Example 4, the absence of the second modified layer drastically reduced the antifouling performance, demonstrating that the zwitterionic pair formed by the quaternary ammonium salt cations introduced by the modified polyethyleneimine in the second modified layer and the sulfonic acid anions in the first modified layer, which combine with a large number of water molecules through electrostatic interaction to form a dense hydrated layer, is the core mechanism that endows the membrane surface with excellent antifouling performance.

[0038] (4) Stability test: The membrane sample was continuously operated at a pressure of 1.55 MPa for 30 days. The feed solution was a 2000 mg / L NaCl aqueous solution. The desalination rate and water flux were measured every 5 days. The desalination rate retention rate (the ratio of the desalination rate on day 30 to the initial desalination rate) was calculated. The test results are shown in Table 4. Table 4

[0039] As shown in Table 4, the reverse osmosis membrane material prepared by this invention has good stability. Compared with Example 4: In Comparative Example 1, without the addition of amination-modified nano-silica, the desalination rate retention rate decreased, indicating that the amination-modified nano-silica is anchored in the polyamide network through chemical bonding between its surface amine groups and polyacrylamide monomers, enhancing the structural stability of the separation layer and reducing network relaxation and defects caused by water molecule impact during long-term operation; In Comparative Example 2, without the addition of carboxylated graphene oxide, the desalination rate retention rate decreased slightly, indicating that the crosslinking effect of carboxylated graphene oxide and modified polyethyleneimine contributes to the structural stability of the second modified layer; In Comparative Example 3, the first modified layer was missing, and the desalination rate retention rate decreased slightly. The significant decrease in salt retention rate indicates that the multiple chemical bonds formed between the sulfonic acid groups of the first modified layer and the second modified layer, as a transition layer, are crucial for maintaining the overall stability of the multilayer structure. The absence of the first modified layer leads to insufficient bonding between the second modified layer and the polyamide separation layer, resulting in interlayer delamination or interface defects during long-term operation and a severe decline in desalination performance. In Comparative Example 4, the absence of the second modified layer also resulted in a significant decrease in the desalination retention rate, demonstrating that the second modified layer not only imparts antifouling properties to the membrane surface, but its chemical bonds with the first modified layer are also an important factor in ensuring the stability of the multilayer structure and preventing damage to the separation layer.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material, characterized in that, Includes the following steps: Step 1: Contact the porous support membrane with an aqueous solution to allow the aqueous solution to wet the porous support membrane. After wetting, remove the excess aqueous solution from the surface of the porous support membrane and then contact it with an oil solution to carry out an interfacial polymerization reaction. After the reaction is completed, wash and dry the membrane to form a polyamide separation membrane layer on the surface of the porous support membrane, thus obtaining a primary composite membrane. The aqueous solution comprises a mixture of polyamine monomers, amination-modified nanomaterials, an acid-binding agent, and a first surfactant. The oil phase solution comprises a mixed polyacryl chloride monomer, a second surfactant, and an oil phase solvent; Step 2: Apply the first modified layer coating liquid to the surface of the polyamide separation membrane layer of the primary composite membrane, and heat-treat the surface of the polyamide separation membrane layer to form the first modified layer, thereby obtaining the intermediate composite membrane; Step 3: Coat the surface of the first modified layer of the intermediate composite membrane with the reaction solution of the second modified layer, react, wash and dry after the reaction is completed, and form the second modified layer on the surface of the first modified layer to obtain the novel high desalination rate antifouling reverse osmosis membrane material.

2. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 1, characterized in that, In step one, the porous support membrane includes a porous polysulfone nanofiber membrane; The aqueous solution is prepared by dispersing a mixture of polyamine monomers, amination-modified nanomaterials, an acid-binding agent, and a first surfactant in water. The mixed polyamine monomers include aromatic polyamines and alicyclic polyamines; The oil phase solution is prepared by dissolving a mixed polyacryl chloride monomer and a second surfactant in an oil phase solvent. The mixed polyacryl chloride monomers include aromatic triacryl chloride and aromatic diacryl chloride.

3. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 2, characterized in that, The mass percentage of the mixed polyamine monomer in the aqueous solution is 1%-6%, the molar ratio of the aromatic polyamine to the alicyclic polyamine is (1-2):(1-3), the aromatic polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine, and the alicyclic polyamine is selected from at least one of N-aminoethylpiperazine, isophorone diamine, and 1,3-cyclohexanedimethylamine; The amination-modified nanomaterial has a mass percentage content of 0.05%-0.3% in the aqueous solution, and the amination-modified nanomaterial includes amination-modified nano-silica. The acid-binding agent has a mass percentage content of 0.02%-0.5% in the aqueous solution, and the acid-binding agent is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine, and N,N-dimethylpiperazine. The first surfactant has a mass percentage content of 0.01%-0.2% in the aqueous solution, and the first surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfonate.

4. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 2, characterized in that, The mass percentage of the mixed polyacryl chloride monomer in the oil phase solution is 0.05%-0.5%, and the mixed polyacryl chloride monomer is composed of aromatic triacryl chloride and aromatic diacryl chloride in a molar ratio of (2-5):

1. The aromatic triacryl chloride is selected from pyromellitic triacryl chloride, and the aromatic diacryl chloride is selected from at least one of isophthaloyl chloride, terephthaloyl chloride, and phthaloyl chloride. The second surfactant has a mass percentage content of 0.05%-0.1% in the oil phase solution, and the second surfactant is selected from at least one of sorbitan monooleate, sorbitan monolaurate, and polyoxyethylene sorbitan monooleate. The oil phase solvent is selected from at least one of n-hexane, cyclohexane, and heptane.

5. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 1, characterized in that, In step one, the wetting temperature is 10-40℃ and the wetting time is 2-8 min; the interfacial polymerization reaction temperature is 30-80℃ and the interfacial polymerization reaction time is 4-12 min.

6. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 1, characterized in that, In step two, the coating amount of the first modified layer coating liquid is 60-80 g / m². 2 The heat treatment temperature is 80-120℃, and the heat treatment time is 60-90 min; The first modified layer coating solution is prepared by dissolving sulfonated polyethersulfone in an organic solvent; The sulfonated polyethersulfone has a mass percentage content of 0.5%-3% in the first modified layer coating solution; The organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran.

7. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 1, characterized in that, Preferably, in step three, the coating amount of the second modified layer reaction solution is 50-100 g / m², the environment is controlled at 0-10℃ during the coating process, and the coating is immediately placed in a temperature environment of 40-70℃ for 30-120 min after coating. The reaction solution for the second modified layer includes modified polyethyleneimine, carboxylated graphene oxide, and a crosslinking agent.

8. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 7, characterized in that, The preparation method of the second modified layer reaction solution includes: dispersing modified polyethyleneimine, carboxylated graphene oxide and crosslinking agent in deionized water in proportion, and adjusting the pH value of the reaction solution to 8.5-11 with an alkaline pH adjuster to obtain the second modified layer reaction solution; After the second modified layer reaction solution is prepared, it is stored in an ice-water bath for later use. The alkaline pH adjuster is selected from at least one of sodium hydroxide solution, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, borax-sodium hydroxide buffer, or sodium carbonate-sodium bicarbonate buffer; the modified polyethyleneimine has a mass percentage content of 0.1%-2% in the second modified layer coating solution, the carboxylated graphene oxide has a mass percentage content of 0.01%-0.2% in the second modified layer coating solution, and the crosslinking agent has a mass percentage content of 0.05%-0.5% in the second modified layer coating solution.

9. The method for preparing a novel high-desalination-rate, fouling-resistant reverse osmosis membrane material according to claim 7, characterized in that, The modified polyethyleneimine is prepared by reacting polyethyleneimine with glycidyltrimethylammonium chloride, and the specific preparation method is as follows: Branched polyethyleneimine was dissolved in deionized water to prepare a 10wt%-20wt% solution. The pH of the solution was adjusted to 9-10 with hydrochloric acid. Under stirring, glycidyltrimethylammonium chloride aqueous solution was added dropwise, controlling the dropping rate to keep the reaction temperature below 40℃. The molar ratio of glycidyltrimethylammonium chloride to amino groups in polyethyleneimine was (0.2-0.5):

1. After the addition was complete, the reaction was carried out at 40-60℃ for 2-6 hours. After the reaction was completed, the pH was adjusted to 6.5-7.5 with hydrochloric acid, and the product was purified to obtain the modified polyethyleneimine product. The carboxylated graphene oxide is prepared by the following steps: Nano-graphene oxide was prepared using nano-graphene as a raw material. Nano-graphene oxide was dispersed in deionized water, mixed acid was added, and the reaction was carried out at 60-80℃ for 4-8 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain carboxylated graphene oxide. The crosslinking agent includes polyethylene glycol diglycidyl ether.

10. A novel high-desalination-rate anti-fouling reverse osmosis membrane material prepared by the preparation method of the novel high-desalination-rate anti-fouling reverse osmosis membrane material as described in claims 1-9.

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