Reverse osmosis membrane and method for producing the same

Abstract

This invention relates to the field of reverse osmosis membrane technology, specifically providing a reverse osmosis membrane and its preparation method, aiming to solve the technical problems of silver ion leakage risk and poor performance stability in existing antibacterial reverse osmosis membranes. To this end, the preparation method of the reverse osmosis membrane of this invention includes: step S1, preparing a base membrane; step S2, applying a coating liquid, the coating liquid containing a zwitterionic functional monomer and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; step S3, placing the membrane obtained in step S2 under crosslinking agent vapor for crosslinking and curing treatment. The reverse osmosis membrane prepared by this method does not rely on the release of bactericidal substances, eliminates the risk of silver ion leakage into drinking water, and has a long service life and performance stability.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, and specifically provides a reverse osmosis membrane and its preparation method. Background Technology

[0002] Reverse osmosis membranes are a core component of water treatment technology, widely used in seawater desalination and pure water production. However, during long-term operation or stagnant periods, the surface of reverse osmosis membranes is highly susceptible to biofouling. Microorganisms and residual organic matter in the water accumulate on the membrane surface, forming a biofilm. This not only leads to a membrane flux decline rate of over 40% and an increase in operating pressure requirements of 30%-50%, thus shortening the lifespan of the filter cartridge, but more seriously, the formation of biofilms can breed pathogenic microorganisms such as Legionella and Escherichia coli, posing a direct threat to drinking water safety.

[0003] To address the problem of biofouling, existing technologies have proposed reverse osmosis membranes with antibacterial properties. For example, Chinese patent application CN112516811A discloses a silver-containing antibacterial thin-layer composite membrane and its preparation method, which achieves the antibacterial effect by loading a silver-containing compound into a polyamide separation layer. However, this method has significant drawbacks: firstly, silver ions pose a migration risk, and under long-term water flow, the released silver ions may exceed drinking water safety standards, causing secondary pollution; secondly, silver compounds may dissociate under specific pH conditions, damaging the network structure of the polyamide separation layer and leading to a decrease in the membrane's desalination performance.

[0004] Therefore, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the technical problems of silver ion leakage risk and poor performance stability of antibacterial reverse osmosis membranes in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing a reverse osmosis membrane, the method comprising: step S1, preparing a base membrane; step S2, applying a coating liquid, the coating liquid comprising a zwitterionic functional monomer and comprising at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; and step S3, placing the membrane obtained in step S2 under crosslinking agent vapor for crosslinking and curing treatment.

[0007] In the preferred embodiment of the above-mentioned method for preparing a reverse osmosis membrane, before step S2, the preparation method further includes the following step: performing plasma activation treatment on the surface of the base membrane.

[0008] In the preferred embodiment of the above-mentioned method for preparing reverse osmosis membrane, the crosslinking agent includes glutaraldehyde, succinaldehyde, genipin, polycarbodiimide, or epoxy crosslinking agent.

[0009] When using the above technical solution, the method for preparing a reverse osmosis membrane includes: step S1, preparing a base membrane; step S2, applying a coating liquid, wherein the coating liquid contains a zwitterionic functional monomer and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; and step S3, placing the membrane obtained in step S2 into a crosslinking agent vapor for crosslinking and curing treatment.

[0010] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The physical repulsion generated by the strong hydration layer on its surface resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum anti-fouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety.

[0011] Preferably, before step S2, the preparation method further includes the following step: performing plasma activation treatment on the surface of the base film.

[0012] Plasma activation introduces active groups on the surface of the base membrane, enhancing the adhesion of subsequent coatings and better preventing the antifouling coating from peeling off during long-term high-pressure scouring or chemical cleaning, thus ensuring the long service life and performance stability of the reverse osmosis membrane.

[0013] In a second aspect, the present invention provides a method for preparing a reverse osmosis membrane, the method comprising: step S1, preparing a base membrane; step S2, forming a biomimetic adhesion layer composed of a tannic acid-ferric ion complex on the surface of the base membrane; step S3, applying a coating liquid to the surface of the biomimetic adhesion layer, the coating liquid comprising a zwitterionic functional monomer and comprising at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; and step S4, placing the membrane obtained in step S3 under crosslinking agent vapor for crosslinking curing treatment.

[0014] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The strong hydration layer on its surface creates a physical repulsion that resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum antifouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety. Furthermore, after preparing the base membrane, a biomimetic adhesion layer composed of tannic acid-ferric ion complex is first formed on the surface of the base membrane. Then, a coating liquid is applied to the surface of the biomimetic adhesion layer and cross-linked and cured. This improves the adhesion strength between the covalently cross-linked zwitterionic polymer coating and the base membrane, better preventing the antifouling coating from peeling off during long-term high-pressure scouring or chemical cleaning, ensuring the long service life and performance stability of the reverse osmosis membrane.

[0015] In a third aspect, the present invention provides a method for preparing a reverse osmosis membrane, the method comprising: step S1, preparing a base membrane; step S2, subjecting the surface of the base membrane to plasma activation treatment; step S3, forming a biomimetic adhesion layer composed of a tannic acid-ferric ion complex on the surface of the membrane obtained in step S2; step S4, applying a coating liquid to the surface of the biomimetic adhesion layer, the coating liquid comprising a zwitterionic functional monomer and comprising at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; and step S5, subjecting the membrane obtained in step S4 to crosslinking curing treatment in a crosslinking agent vapor.

[0016] In the preferred embodiment of the above-mentioned method for preparing reverse osmosis membrane, the plasma activation treatment is atmospheric pressure plasma jet treatment, and the treatment gas is a mixture of helium and oxygen, wherein the oxygen volume percentage is 4%-6%.

[0017] In the preferred embodiment of the above-mentioned method for preparing reverse osmosis membrane, step S3 specifically includes: preparing tannic acid solution and ferric chloride solution respectively, wherein the solvent is a mixed solution of ethanol and water; mixing the tannic acid solution and the ferric chloride solution to form a tannic acid-ferric ion complexation reaction solution; applying the complexation reaction solution to the surface of the membrane treated in step S2, and then drying and curing it to form the biomimetic adhesion layer.

[0018] In the preferred embodiment of the above-mentioned method for preparing reverse osmosis membrane, the coating liquid comprises polyethylene glycol and sulfobetaine methacrylate as the zwitterionic functional monomer.

[0019] In the preferred embodiment of the above-mentioned method for preparing reverse osmosis membrane, the crosslinking agent vapor contains glutaraldehyde at a concentration of 6 vol%-10 vol% and an inert gas as a carrier gas.

[0020] When using the above technical solution, the method for preparing a reverse osmosis membrane includes: step S1, preparing a base membrane; step S2, performing plasma activation treatment on the surface of the base membrane; step S3, forming a biomimetic adhesion layer composed of tannic acid-ferric ion complex on the surface of the membrane obtained in step S2; step S4, applying a coating liquid to the surface of the biomimetic adhesion layer, the coating liquid containing zwitterionic functional monomers and containing at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; and step S5, placing the membrane obtained in step S4 under crosslinking agent vapor for crosslinking and curing treatment.

[0021] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The strong hydration layer on this surface creates a physical repulsion that resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum antifouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety. Plasma activation introduces active groups onto the base membrane surface, enhancing the adhesion of subsequent coatings. A tannic acid-ferric ion biomimetic adhesion layer, serving as an intermediate layer, significantly strengthens the bond between the antifouling coating and the base membrane, effectively preventing the antifouling coating from peeling off during long-term high-pressure rinsing or chemical cleaning, ensuring the long-term service life and performance stability of the reverse osmosis membrane.

[0022] Preferably, the plasma activation treatment is atmospheric pressure plasma jet treatment, and the treatment gas is a mixture of helium and oxygen, wherein the oxygen volume percentage is 4%-6%.

[0023] Atmospheric pressure plasma jet treatment eliminates the need for a vacuum environment, resulting in a simple process suitable for continuous production and high efficiency. A specific ratio of oxygen efficiently generates oxygen-containing active groups (such as carboxyl and hydroxyl groups) on the membrane surface, providing ample anchoring points for the subsequent construction of the biomimetic adhesion layer. Simultaneously, it avoids damage to the membrane structure from excessive etching, thereby further improving the stability and lifespan of the permeate membrane structure.

[0024] Preferably, step S3 specifically includes: preparing tannic acid solution and ferric chloride solution respectively, wherein the solvent is a mixture of ethanol and water; mixing the tannic acid solution and the ferric chloride solution to form a tannic acid-ferric ion complexation reaction solution; applying the complexation reaction solution to the surface of the membrane treated in step S2, and then drying and curing to form the biomimetic adhesion layer, wherein the concentration of the tannic acid solution is 1.0wt%-2.0wt%, the concentration of the ferric chloride solution is 0.3wt%-0.7wt%, and the mass ratio of ethanol to water in the solvent is 0.8:1 to 1.2:1.

[0025] Through in-situ complexation reaction, an adhesion layer can be uniformly formed on the membrane surface, which is simple to operate and has good controllability.

[0026] Preferably, the crosslinking agent vapor contains glutaraldehyde at a concentration of 6 vol%-10 vol% and an inert gas as a carrier gas.

[0027] The steam crosslinking method results in a mild, rapid, and uniform reaction, allowing the crosslinking reaction to occur primarily on the surface and within the coating, forming a stable three-dimensional network structure without damaging the underlying reverse osmosis membrane substrate. Using an inert gas as a carrier gas helps prevent side reactions.

[0028] In a fourth aspect, the present invention also provides a reverse osmosis membrane, wherein the reverse osmosis membrane is prepared by the reverse osmosis membrane preparation method described in any of the above technical solutions.

[0029] It should be noted that this reverse osmosis membrane has all the technical effects of the reverse osmosis membrane preparation method described in any of the above technical solutions, and will not be repeated here. Attached Figure Description

[0030] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which: Figure 1 This is a diagram showing the main steps of the preparation method of the first reverse osmosis membrane of the present invention; Figure 2 This is a diagram showing the main steps of the preparation method of the second reverse osmosis membrane of the present invention; Figure 3 This is a diagram showing the main steps of the preparation method of the third reverse osmosis membrane of the present invention. Detailed Implementation

[0031] First, those skilled in the art should understand that the embodiments described below are merely for explaining the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0032] The existing antibacterial reverse osmosis membranes mentioned in the background technology suffer from the technical problems of silver ion leakage risk and poor performance stability. The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The physical repulsion generated by the strong hydration layer formed on its surface resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum antifouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety.

[0033] The following reference Figures 1 to 3 The preparation method of the reverse osmosis membrane of the present invention is described in detail. Among other things, Figure 1 This is a diagram showing the main steps of the preparation method of the first reverse osmosis membrane of the present invention; Figure 2 This is a diagram showing the main steps of the preparation method of the second reverse osmosis membrane of the present invention; Figure 3 This is a diagram showing the main steps of the preparation method of the third reverse osmosis membrane of the present invention.

[0034] In a first embodiment of the present invention, as Figure 1 As shown, the method for preparing a reverse osmosis membrane includes the following steps.

[0035] Step S1: Prepare the base film.

[0036] Specifically, polysulfone is dissolved in N,N-dimethylformamide to prepare a polysulfone casting solution. The casting solution is then coated onto a polyester nonwoven fabric and cured in water to obtain a polysulfone support layer. m-phenylenediamine is dissolved in pure water to prepare an aqueous solution, and pyromellitic methyl chloride is dissolved in an organic solvent to prepare an oil solution. The polysulfone support layer is immersed in the aqueous solution, removed, and excess aqueous solution is removed from the surface. Then, an oil solution is applied to the surface of the support layer to carry out an interfacial polymerization reaction. After the reaction, excess oil solution is removed, and the layer is washed and dried to obtain a base film.

[0037] First, the polysulfone support layer is fully immersed in an aqueous solution, allowing the aqueous monomers to adsorb into its pores and on its surface. After removal, excess liquid is removed from the surface, and then an oil-phase solution is applied to or brought into contact with it. Because water and organic solvents are immiscible, the polymerization reaction occurs instantaneously only at the water-oil interface, forming a dense polyamide thin layer. By precisely controlling the reaction conditions, a separation layer with high desalination rate and good water flux can be obtained.

[0038] Step S2: Apply a coating liquid containing zwitterionic functional monomers and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan.

[0039] Step S3: Place the membrane obtained in step S2 into crosslinking agent vapor for crosslinking and curing treatment.

[0040] Specifically, crosslinking agents include glutaraldehyde, succinaldehyde, genipin, polycarbodiimide, or epoxy crosslinking agents. It is understood that other suitable crosslinking agents can also be used.

[0041] A zwitterionic functional monomer and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan are cross-linked and cured by a cross-linking agent to form a covalently cross-linked zwitterionic polymer coating on the surface of a base membrane, thereby forming a reverse osmosis membrane with a covalently cross-linked zwitterionic polymer coating on the surface.

[0042] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The physical repulsion generated by the strong hydration layer on its surface resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum anti-fouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety.

[0043] Preferably, before step S2, the preparation method further includes the following step: performing plasma activation treatment on the surface of the base film.

[0044] Specifically, the plasma activation treatment is atmospheric pressure plasma jet treatment, and the treatment gas is a mixture of helium and oxygen, with oxygen accounting for 4%-6% of the volume.

[0045] Atmospheric pressure plasma jet treatment, compared to traditional vacuum plasma treatment, eliminates the need for a vacuum chamber, enabling online and continuous processing, significantly improving production efficiency and reducing equipment costs. Helium, as the primary carrier gas, generates a stable and uniform plasma jet. Introducing an appropriate amount of oxygen allows for the generation of reactive oxygen species within the plasma. These species interact with the membrane surface, efficiently generating active sites such as carboxyl groups. Too low an oxygen content results in ineffective activation; too high a content may lead to over-etching and damage to the polyamide layer structure. Setting the oxygen content to 4%-6% achieves a balance between efficient activation and protection of the membrane structure.

[0046] Preferably, the concentration of intermediate-phenylenediamine in the aqueous solution is 1.5wt%-2.5wt%; and the concentration of pyromellitic acid chloride in the oil solution is 0.1wt%-0.2wt%.

[0047] By adjusting the concentration ratio of the two monomers, the rate and extent of the interfacial polymerization reaction can be effectively controlled, thereby affecting the degree of crosslinking, thickness, and surface morphology of the polyamide separation layer. Higher monomer concentrations typically result in a denser separation layer with a higher degree of crosslinking, thus improving the desalination rate, but may sacrifice some water flux. By setting the concentrations as described above, a balance is achieved between desalination rate and water flux, enabling the preparation of a base membrane with excellent overall performance.

[0048] In a second embodiment of the invention, such as Figure 2 As shown, the method for preparing a reverse osmosis membrane includes the following steps.

[0049] Step S1: Prepare the base film.

[0050] Specifically, polysulfone is dissolved in N,N-dimethylformamide to prepare a polysulfone casting solution. The casting solution is then coated onto a polyester nonwoven fabric and cured in water to obtain a polysulfone support layer. m-phenylenediamine is dissolved in pure water to prepare an aqueous solution, and pyromellitic methyl chloride is dissolved in an organic solvent to prepare an oil solution. The polysulfone support layer is immersed in the aqueous solution, removed, and excess aqueous solution is removed from the surface. Then, an oil solution is applied to the surface of the support layer to carry out an interfacial polymerization reaction. After the reaction, excess oil solution is removed, and the layer is washed and dried to obtain a base film.

[0051] Step S2: A biomimetic adhesion layer composed of tannic acid-ferric ion complex is formed on the surface of the base film.

[0052] Specifically, tannic acid solution and ferric chloride solution are prepared separately, with the solvent being a mixture of ethanol and water; the tannic acid solution and ferric chloride solution are mixed to form a tannic acid-ferric ion complexation reaction solution; the complexation reaction solution is applied to the surface of the base film, and then dried and cured to form a biomimetic adhesion layer.

[0053] Step S3: Apply a coating liquid to the surface of the biomimetic adhesion layer. The coating liquid contains zwitterionic functional monomers and includes at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan.

[0054] Step S4: Place the membrane obtained in step S3 into crosslinking agent vapor for crosslinking and curing treatment.

[0055] Specifically, crosslinking agents include glutaraldehyde, succinaldehyde, genipin, polycarbodiimide, or epoxy crosslinking agents. It is understood that other suitable crosslinking agents can also be used.

[0056] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The physical repulsion generated by the strong hydration layer on its surface resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum anti-fouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety.

[0057] After preparing the base membrane, a biomimetic adhesion layer composed of tannic acid-ferric ion complex is first formed on the surface of the base membrane. Then, a coating liquid is applied to the surface of the biomimetic adhesion layer and cross-linked and cured. This improves the adhesion strength between the covalently cross-linked zwitterionic polymer coating and the base membrane, and can better prevent the antifouling coating from peeling off during long-term high-pressure scouring or chemical cleaning, thus ensuring the long service life and performance stability of the reverse osmosis membrane.

[0058] In a third embodiment of the invention, such as Figure 3 As shown, the method for preparing a reverse osmosis membrane includes the following steps.

[0059] Step S1: Prepare the base film.

[0060] Specifically, polysulfone is dissolved in N,N-dimethylformamide to prepare a polysulfone casting solution. The casting solution is then coated onto a polyester nonwoven fabric and cured in water to obtain a polysulfone support layer. m-phenylenediamine is dissolved in pure water to prepare an aqueous solution, and pyromellitic methyl chloride is dissolved in an organic solvent to prepare an oil solution. The polysulfone support layer is immersed in the aqueous solution, removed, and excess aqueous solution is removed from the surface. Then, an oil solution is applied to the surface of the support layer to carry out an interfacial polymerization reaction. After the reaction, excess oil solution is removed, and the layer is washed and dried to obtain a base film.

[0061] Step S2: Perform plasma activation treatment on the surface of the base film.

[0062] Specifically, the plasma activation treatment is atmospheric pressure plasma jet treatment, and the treatment gas is a mixture of helium and oxygen, with oxygen accounting for 4%-6% of the volume.

[0063] Atmospheric pressure plasma jet treatment, compared to traditional vacuum plasma treatment, eliminates the need for a vacuum chamber, enabling online and continuous processing, significantly improving production efficiency and reducing equipment costs. Helium, as the primary carrier gas, generates a stable and uniform plasma jet. Introducing an appropriate amount of oxygen allows for the generation of reactive oxygen species within the plasma. These species interact with the membrane surface, efficiently generating active sites such as carboxyl groups. Too low an oxygen content results in ineffective activation; too high a content may lead to over-etching and damage to the polyamide layer structure. Setting the oxygen content to 4%-6% achieves a balance between efficient activation and protection of the membrane structure.

[0064] Step S3: A biomimetic adhesion layer composed of tannic acid-ferric ion complex is formed on the surface of the base film.

[0065] Specifically, tannic acid solution and ferric chloride solution are prepared separately, with the solvent being a mixture of ethanol and water; the tannic acid solution and ferric chloride solution are mixed to form a tannic acid-ferric ion complexation reaction solution; the complexation reaction solution is applied to the surface of the base film, and then dried and cured to form a biomimetic adhesion layer.

[0066] Step S4: Apply a coating liquid to the surface of the biomimetic adhesion layer. The coating liquid contains zwitterionic functional monomers and includes at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan.

[0067] Step S5: Place the membrane obtained in step S4 into crosslinking agent vapor for crosslinking and curing treatment.

[0068] Specifically, crosslinking agents include glutaraldehyde, succinaldehyde, genipin, polycarbodiimide, or epoxy crosslinking agents. It is understood that other suitable crosslinking agents can also be used.

[0069] The reverse osmosis membrane prepared by this method has a covalently cross-linked zwitterionic polymer coating on its surface. The physical repulsion generated by the strong hydration layer on its surface resists the adsorption of microorganisms and organic matter, achieving a highly efficient and broad-spectrum anti-fouling effect. This reverse osmosis membrane does not rely on the release of bactericidal substances, thus eliminating the risk of silver ion leakage into drinking water and ensuring drinking water safety.

[0070] Plasma activation introduces active groups on the surface of the base membrane, enhancing the adhesion of subsequent coatings. The tannic acid-ferric ion biomimetic adhesion layer, as an intermediate layer, greatly enhances the bonding force between the antifouling coating and the base membrane, effectively preventing the antifouling coating from peeling off during long-term high-pressure scouring or chemical cleaning, thus ensuring the long service life and performance stability of the reverse osmosis membrane.

[0071] Preferably, the concentration of intermediate-phenylenediamine in the aqueous solution is 1.5wt%-2.5wt%; and the concentration of pyromellitic acid chloride in the oil solution is 0.1wt%-0.2wt%.

[0072] By adjusting the concentration ratio of the two monomers, the rate and extent of the interfacial polymerization reaction can be effectively controlled, thereby affecting the degree of crosslinking, thickness, and surface morphology of the polyamide separation layer. Higher monomer concentrations typically result in a denser separation layer with a higher degree of crosslinking, thus improving the desalination rate, but may sacrifice some water flux. By setting the concentrations as described above, a balance is achieved between desalination rate and water flux, enabling the preparation of a base membrane with excellent overall performance.

[0073] Preferably, the concentration of the tannic acid solution is 1.0wt%-2.0wt%, the concentration of the ferric chloride solution is 0.3wt%-0.7wt%, and the mass ratio of ethanol to water in the solvent is 0.8:1 to 1.2:1.

[0074] The concentration ratio of tannic acid to ferric chloride directly affects the stoichiometry of the complex and the structure and properties of the final adhesive layer. A tannic acid solution concentration of 1.0wt%-2.0wt% and a ferric chloride solution concentration of 0.3wt%-0.7wt% can form a stable complex network with good adhesion. The mass ratio of ethanol to water in the solvent can be controlled between 0.8:1 and 1.2:1, preferably 1:1. This ensures the surface tension, viscosity, and volatility of the solution, thereby optimizing the uniformity of coating spread on the film surface, avoiding defects such as droplets or streaks, and ensuring the quality of the adhesive layer.

[0075] Preferably, the coating liquid contains polyethylene glycol and sulfobetaine methacrylate as the zwitterionic functional monomer, wherein the concentration of sulfobetaine methacrylate is 8wt%-12wt% and the concentration of polyvinyl alcohol is 3wt%-5wt%.

[0076] This setup ensures that the coating contains a sufficient amount of sulfobetaine methacrylate to provide strong resistance to biofouling, while the polyvinyl alcohol content is sufficient to form a complete film and provide enough hydroxyl functional groups for subsequent crosslinking reactions, making the final coating both functional and stable.

[0077] Preferably, the coating liquid also contains 0.3wt%-0.7wt% sodium citrate.

[0078] Sodium citrate can act as a pH buffer and stabilizer, maintaining the pH value of the coating solution and preventing denaturation or flocculation of sulfobetaine methacrylate and polyvinyl alcohol during storage or coating. In addition, it can also have a weak electrostatic interaction with the zwitterionic groups of sulfobetaine methacrylate, which helps the sulfobetaine methacrylate monomer to be more uniformly dispersed in the polyvinyl alcohol matrix, thereby forming a more uniform anti-fouling functional surface after cross-linking and curing.

[0079] Preferably, the crosslinking agent vapor contains glutaraldehyde at a concentration of 6 vol%-10 vol% and an inert gas as a carrier gas. Further, the crosslinking curing treatment lasts for 30-60 seconds.

[0080] Using steam crosslinking instead of liquid immersion effectively avoids the swelling or dissolution of the underlying sulfobetaine methacrylate-polyvinyl alcohol coating and subsequent layers by solvents, thus better maintaining the integrity of the membrane's multilayer structure. If the crosslinking curing time is too short, the crosslinking will be insufficient, resulting in poor coating durability; if the time is too long, it may lead to over-crosslinking, making the coating brittle, or excessive reaction that clogs the membrane pores. Controlling the crosslinking curing time to 30-60 seconds ensures sufficient crosslinking while preventing coating brittleness and membrane pore blockage.

[0081] To illustrate the technical solution of the present invention in more detail, a detailed preparation method is described below.

[0082] Polysulfone was dissolved in N,N-dimethylformamide to prepare a 16.8 wt% polysulfone casting solution. This casting solution was uniformly coated onto a polyester nonwoven fabric, and then the nonwoven fabric with the casting solution was immersed in deionized water for phase inversion. After curing, a polysulfone support layer was obtained. m-phenylenediamine was dissolved in pure water to prepare a 2 wt% aqueous solution, and trimesoyl chloride was dissolved in n-decane to prepare a 0.15 wt% oil solution. The polysulfone support layer was immersed in the aqueous solution for 1 min, removed and drained, and then coated with the oil solution. Interfacial polymerization was carried out for 1 min. After the reaction, excess oil solution was removed, and the membrane surface was rinsed with deionized water for 1 min. Then, it was immersed in 90°C hot water for 2 min to promote complete reaction. Finally, the membrane was immersed in a 3.5 wt% glycerol aqueous solution for 30 s, removed and drained, and then placed in a 90°C oven for heat treatment for 2 min. After drying, the modified reverse osmosis membrane base membrane was obtained.

[0083] Next, the surface of the base film is modified.

[0084] First, the prepared reverse osmosis membrane substrate is passed through an atmospheric pressure plasma jet (APPJ) device at a linear velocity of 5 m / min. The device uses a mixture of helium and oxygen (volume ratio 95:5) as the working gas, and the discharge power is set to 100 W.

[0085] Next, a biomimetic adhesion layer was constructed. A 1.5 wt% tannic acid solution and a 0.5 wt% ferric chloride solution were prepared, both using a 1:1 mixture of ethanol and water as solvents. Equal volumes of these two solutions were mixed to immediately form a TA-Fe³⁺ complexation reaction solution. This complexation solution was then uniformly sprayed onto the activated reverse osmosis membrane surface using an atomizing nozzle, with droplet size controlled to approximately 50 μm. After spraying, the membrane was placed in a 60°C oven for 1 minute to cure, forming a robust TA-Fe³⁺ nano-biomimetic adhesion layer.

[0086] Finally, an antifouling layer was coated and cross-linked for curing. A coating solution containing 10 wt% sulfobetaine methacrylate, 4 wt% polyvinyl alcohol, and 0.5 wt% sodium citrate was prepared and uniformly applied to the surface of the membrane with the nano-biomimetic adhesion layer, controlling the wet film thickness of the coating to be between 5 μm and 10 μm. The membrane was then placed in a reaction chamber filled with glutaraldehyde vapor. The concentration of glutaraldehyde vapor in the reaction chamber was 8 vol%, using nitrogen as the carrier gas. The membrane was treated in the vapor for 45 s, during which polyvinyl alcohol and glutaraldehyde underwent an acetal cross-linking reaction. In this step, a stable three-dimensional cross-linked network structure was formed through the acetal reaction between the aldehyde groups of glutaraldehyde and the hydroxyl groups on the polyvinyl alcohol molecular chain. Through this cross-linking, sulfobetaine methacrylate was firmly fixed within the polyvinyl alcohol network, forming the final antifouling coating. The prepared modified reverse osmosis membrane was stored in a cool, dry place away from light for later use.

[0087] By precisely controlling the monomer concentration during interfacial polymerization and subsequent heat treatment processes, the base membrane itself was ensured to possess high desalination rates and good initial water flux. Atmospheric pressure plasma activation provided a solid bonding foundation for subsequent coatings in a highly efficient yet gentle manner. The TA-Fe³⁺ biomimetic adhesion layer acted as a strong adhesive interlayer, effectively solving the interfacial compatibility problem between the polyamide substrate and the hydrophilic antifouling coating, ensuring the coating's superior adhesion and enabling it to withstand long-term water flow erosion and chemical cleaning. Finally, through a sulfobetaine methacrylate-polyvinyl alcohol coating formulation and a steam crosslinking process, a stable, dense, and highly efficient antifouling layer was constructed on the membrane surface. This coating not only endowed the membrane with excellent antifouling properties but also greatly enhanced its physicochemical stability due to the presence of the crosslinked network.

[0088] Furthermore, the present invention also provides a reverse osmosis membrane, which is a reverse osmosis membrane prepared by the method of preparing the reverse osmosis membrane of any of the above embodiments.

[0089] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, The preparation method includes: Step S1: Prepare the base film; Step S2: Apply a coating liquid, wherein the coating liquid contains a zwitterionic functional monomer and contains at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan; Step S3: Place the membrane obtained in step S2 into crosslinking agent vapor for crosslinking and curing treatment.

2. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, Prior to step S2, the preparation method further includes the following steps: The surface of the base film is subjected to plasma activation treatment.

3. The method for preparing a reverse osmosis membrane according to claim 1 or 2, characterized in that, The crosslinking agent includes glutaraldehyde, succinaldehyde, genipin, polycarbodiimide, or epoxy crosslinking agents.

4. A method for preparing a reverse osmosis membrane, characterized in that, The preparation method includes: Step S1: Prepare the base film; Step S2: A biomimetic adhesion layer composed of tannic acid-ferric ion complex is formed on the surface of the base film; Step S3: Apply a coating liquid to the surface of the biomimetic adhesion layer. The coating liquid contains a zwitterionic functional monomer and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan. Step S4: Place the membrane obtained in step S3 into crosslinking agent vapor for crosslinking and curing treatment.

5. A method for preparing a reverse osmosis membrane, characterized in that, The preparation method includes: Step S1: Prepare the base film; Step S2: Perform plasma activation treatment on the surface of the base film; Step S3: A biomimetic adhesion layer composed of tannic acid-ferric ion complex is formed on the surface of the membrane obtained in step S2; Step S4: Apply a coating liquid to the surface of the biomimetic adhesion layer. The coating liquid contains a zwitterionic functional monomer and at least one of polyethylene glycol, polyvinylpyrrolidone, and chitosan. Step S5: Place the membrane obtained in step S4 into crosslinking agent vapor for crosslinking and curing treatment.

6. The method for preparing a reverse osmosis membrane according to claim 5, characterized in that, The plasma activation treatment is an atmospheric pressure plasma jet treatment, and the treatment gas is a mixture of helium and oxygen, wherein the oxygen volume percentage is 4%-6%.

7. The method for preparing a reverse osmosis membrane according to claim 5, characterized in that, Step S3 specifically includes: Prepare tannic acid solution and ferric chloride solution separately, using a mixture of ethanol and water as the solvent; The tannic acid solution is mixed with the ferric chloride solution to form a tannic acid-ferric ion complexation reaction solution. The complexing reaction solution is applied to the surface of the membrane treated in step S2, and then dried and cured to form the biomimetic adhesion layer.

8. The method for preparing a reverse osmosis membrane according to claim 5, characterized in that, The coating liquid contains polyethylene glycol and sulfobetaine methacrylate, which is the zwitterionic functional monomer.

9. The method for preparing a reverse osmosis membrane according to claim 5, characterized in that, The crosslinking agent vapor contains glutaraldehyde at a concentration of 6 vol%-10 vol% and an inert gas as a carrier gas.

10. A reverse osmosis membrane, characterized in that, The reverse osmosis membrane is a reverse osmosis membrane prepared by the method described in any one of claims 1 to 9.

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