A reverse osmosis membrane, its preparation method and application

Abstract

This invention discloses a reverse osmosis membrane, its preparation method, and its application, belonging to the field of reverse osmosis membrane technology. The reverse osmosis membrane of this invention is prepared by the following method: a support layer is prepared using a casting solution containing polysulfone and polyethersulfone; a transition buffer layer is formed using an aqueous solution containing polyvinyl ammonium phosphate and phosphate; a separation layer is formed using an aqueous solution containing graphene oxide quantum dots and an oil solution containing polyacrylamide chlorides; then, the membrane is treated with an alkaline solution and an antifouling layer is formed on its surface using divalent metal salts and polymers. The reverse osmosis membrane of this invention possesses characteristics such as high flux, moderate desalination, medium-pressure stability, high salt tolerance, and antifouling properties. It is compatible with two-stage and three-stage reverse osmosis units in countercurrent reverse osmosis processes, which helps reduce the overall operating cost of the unit and promotes the development of high-salt wastewater resource utilization technology.

Description

Technical Field

[0001] This invention relates to the field of permeation membrane technology, and also to the field of high-salt wastewater resource treatment technology, particularly to a reverse osmosis process, specifically a reverse osmosis membrane, its preparation method, and its application. Background Technology

[0002] In the field of high-salinity wastewater resource treatment, the countercurrent reverse osmosis process, with its innovative design of "multiple reverse osmosis units in series + purified water recirculation," achieves efficient concentration and low-energy operation of high-salinity wastewater. Its core process is as follows: after the high-salinity wastewater is initially concentrated by a first-stage reverse osmosis unit, the concentrated water enters the second and third-stage reverse osmosis units for further concentration. At the same time, the purified water produced by the second and third-stage reverse osmosis units is recirculated back to the first stage to dilute the salt concentration of the feed water and reduce the osmotic pressure difference across the membrane. This not only extends the membrane life and reduces energy consumption, but also achieves a significant increase in salt content under normal temperature and medium pressure, combining technological advancement with economic feasibility. In this process system, the second and third stage reverse osmosis units together constitute the core of the deep concentration process, undertaking the crucial task of continuously concentrating high-salt wastewater and directly determining the concentration efficiency of the entire process and the energy consumption of the subsequent evaporation system. The second stage reverse osmosis unit treats the high-salt concentrate (salt content typically greater than 70,000 mg / L) after the first stage concentration. Its core task is to perform preliminary deep concentration of this concentrate, creating better feed conditions for the third stage reverse osmosis unit, and simultaneously reducing the operating pressure of the first stage by recirculating purified water. The third stage reverse osmosis unit treats the ultra-high-salt concentrate (salt content typically greater than 90,000 mg / L) after the second stage concentration. Its core task is to perform final deep concentration of this concentrate, minimizing the amount of water entering the subsequent evaporation system, and serving as the key link between membrane concentration and evaporation crystallization. This step-by-step concentration setup places stringent performance requirements on the reverse osmosis membranes used in the second and third stage reverse osmosis units.

[0003] High flux is the primary indicator. The core objective of both the two-stage and three-stage reverse osmosis units is "rapid concentration": to separate more water from high-salt concentrate per unit time, significantly increasing the salt content of the remaining concentrate. For the two-stage unit, high flux improves overall concentration efficiency; for the three-stage unit, high flux directly reduces the amount of water entering the evaporation system, lowering evaporation energy consumption. Maintaining a high water flux in high osmotic pressure environments with salt concentrations above 70,000 mg / L is a core challenge faced by existing reverse osmosis membranes.

[0004] There's no need to pursue an extreme desalination rate. The purified water from the second and third stages of the reverse osmosis unit is returned to the first stage, and its salt content needs to be lower than that of the feed water from the first stage to achieve dilution. Therefore, neither needs to pursue an extreme desalination rate of over 99.5%. Moderate salt permeation is acceptable and can actually reduce the difficulty of membrane fabrication, creating conditions for increasing water flux.

[0005] High salt stability. Reverse osmosis membranes need to operate in high-salt environments, resisting the chemical erosion of membrane materials by high concentrations of salt, while maintaining a stable physical structure under high osmotic pressure to avoid problems such as membrane shrinkage and decreased porosity.

[0006] Medium-pressure tolerance and antifouling resistance. The "medium-pressure operation" characteristic of the process requires both to have matched mechanical strength to avoid membrane rupture and interlayer delamination; at the same time, as pollutants in the wastewater gradually accumulate in the second and third stages of the concentration process, strong antifouling ability is required to reduce adsorption and delay flux decline.

[0007] Currently, existing commercial reverse osmosis membranes are insufficient to fully meet the aforementioned requirements of second- and third-stage reverse osmosis units, exhibiting significant performance compatibility defects. For example, traditional seawater desalination membranes, while possessing high desalination rates (≥99.5%), suffer from high osmotic pressure suppression in environments with salt concentrations >70,000 mg / L, resulting in a sharp drop in water flux (typically below 15 L / m²·h), failing to meet the high-efficiency concentration requirements of second- and third-stage reverse osmosis units. Another example is conventional ultra-high pressure concentration membranes, whose active layers are typically designed to be overly dense to withstand high-salt environments. While maintaining a certain level of salt tolerance, this results in generally low water flux and excessively high desalination rates (≥99.7%), leading to unnecessary energy waste. Furthermore, ordinary antifouling membranes, while possessing some antifouling capabilities, lack tolerance to high-salt environments; prolonged contact with high-salt wastewater leads to material degradation and a decrease in structural stability.

[0008] Therefore, developing a special reverse osmosis membrane with "high flux, moderate desalination, high salt tolerance, fouling resistance, and medium pressure stability" for the special operating conditions of the second and third stage reverse osmosis units in the countercurrent reverse osmosis process is the key to breaking through the bottleneck of concentration efficiency in the existing process and reducing the overall operating cost. It is of great significance to promoting the upgrading of high-salt wastewater resource treatment technology. Summary of the Invention

[0009] To address the aforementioned problems, one objective of this invention is to provide a reverse osmosis membrane and its preparation method. The reverse osmosis membrane of this invention comprises a support layer, a transition buffer layer, a separation layer, and an antifouling layer stacked sequentially. The layers work synergistically to achieve high flux, moderate desalination, medium pressure stability, high salt tolerance, and antifouling properties.

[0010] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0011] A method for preparing a reverse osmosis membrane includes the following steps:

[0012] S1. Preparation of the support layer: A polar solvent is used to prepare a casting solution with a solid content of 15.1wt%~18wt%, a polysulfone to polyethersulfone mass ratio of 1.85~3, a total polysulfone and polyethersulfone content of 15%~17wt%, and a pore-forming agent content of 0.1wt%~1wt%. The casting solution is coated onto a polyester nonwoven fabric substrate, immersed in a deionized water coagulation bath, and then removed and dried to obtain the support layer.

[0013] S2. Coating a transition buffer layer: Prepare an aqueous solution with a polyvinyl alcohol ammonium phosphate content of 0.8wt%~1.2wt% and a phosphate content of 2.0wt%~3.0wt%. Apply the aqueous solution uniformly to the surface of the support layer by dip coating. Then heat-treat at 80℃~120℃ for 1min~5min to allow the hydroxyl groups of polyvinyl alcohol ammonium phosphate to cross-link with the phosphate groups of phosphate to form a transition buffer layer.

[0014] S3. Preparation of the separation layer: Prepare an aqueous solution with a polyamine monomer content of 2.5wt%~3.5wt%, an alkaline acid binder content of 0.8wt%~1.2wt%, a cationic surfactant content of 0.08wt%~0.12wt%, an aminosulfonate content of 4.5wt%~5.5wt%, and a graphene oxide quantum dot content of 0.02wt%~0.07wt%. Coat the solution uniformly onto the surface of the transition buffer layer by roller coating. After standing, remove excess solution by tilting method to obtain the aqueous phase surface. Prepare an oil phase solution with a polyacrylamide chloride content of 0.18wt%~0.22wt%. Coat the oil phase solution uniformly onto the aqueous phase surface by spraying to form the separation layer.

[0015] S4. Alkaline activation treatment: Spray an alkaline solution with a pH of 12.5~13.5 onto the surface of the separation layer to decompose the ammonium phosphate groups of polyvinyl alcohol ammonium phosphate in the transition buffer layer into phosphate groups, forming hydrophilic sites on the surface of the separation layer. Then rinse with deionized water until the filtrate is neutral.

[0016] S5. Constructing an antifouling layer: Prepare an aqueous solution with a divalent metal salt content of 1.0wt%~1.5wt% and a polymer content of 0.3wt%~0.4wt%. Coat the solution onto the surface of the alkaline-activated separation layer using a slit coating method. Then, heat-treat the solution at 50℃~70℃ for 5min~15min to obtain a reverse osmosis membrane containing an antifouling layer.

[0017] In step S1, the polar solvent can be N,N-dimethylacetamide, N,N-dimethylformamide, etc., and the pore-forming agent can be polyvinylpyrrolidone, polyethylene glycol, etc.; in step S3, the organic solvent in the oil phase solution can be isoparaffin, n-hexane, cyclohexane, etc.; in step S4, the alkaline solution can be sodium hydroxide solution, potassium hydroxide solution, etc.

[0018] As a specific embodiment of the present invention, the reverse osmosis membrane prepared in step S5 is further cooled to room temperature and then immersed in deionized water to fully remove unreacted monomers and impurities remaining on the surface of the reverse osmosis membrane. After immersion, the reverse osmosis membrane is taken out and dried to obtain the final reverse osmosis membrane.

[0019] In one specific embodiment of the present invention, in step S2, the phosphate is sodium hexametaphosphate, sodium tripolyphosphate, or sodium dipolyphosphate.

[0020] In one specific embodiment of the present invention, in step S3, the polyamine monomer is m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, or 4,4'-diaminodiphenylmethane; the alkaline acid-binding agent is triethylamine (TEA), sodium hydroxide (NaOH), sodium hydrogen phosphate, or N,N-dimethylpiperazine; the cationic surfactant is dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, or hexadecyltrimethylammonium bromide; and the aminosulfonate is sodium cyclohexylaminosulfonate, ammonium aminosulfonate, sodium p-toluenesulfonate, or sodium laurylsulfonate.

[0021] In one specific embodiment of the present invention, in step S3, the polyacryl chloride is pyromellitic trichloroisocyanurate, terephthalic acid chloride, isophthalic acid chloride, orthophthalic acid chloride or biphenyl chloride.

[0022] In one specific embodiment of the present invention, in step S5, the divalent metal salt is magnesium chloride, calcium chloride, or magnesium sulfate, and the polymer is anionic polyacrylamide, cationic polyacrylamide, or quaternary ammonium salt chitosan.

[0023] A reverse osmosis membrane is prepared using the method described above.

[0024] Another object of the present invention is to provide an application of the above-mentioned reverse osmosis membrane as a reverse osmosis membrane in the second and third stage reverse osmosis devices in a countercurrent reverse osmosis process.

[0025] Beneficial effects

[0026] The reverse osmosis membrane of this invention comprises a support layer, a transition buffer layer, a separation layer, and an antifouling layer stacked sequentially. These layers work synergistically to achieve high flux, moderate desalination, medium-pressure stability, high salt tolerance, and antifouling properties. Specifically, the support layer of the reverse osmosis membrane uses a polysulfone and polyethersulfone composite system combined with a polyester nonwoven fabric substrate, enhancing the membrane's medium-pressure tolerance and high-salt corrosion resistance. This allows it to maintain structural stability in high-salt environments for extended periods, preventing mechanical damage and salting-out degradation. In the transition buffer layer, the cross-linked structure formed by the hydroxyl groups of the aqueous polymer and the phosphate groups of the phosphate strengthens the interlayer bonding, reducing the risk of interlayer delamination and buffering osmotic pressure shocks to ensure overall membrane stability. The separation layer incorporates graphene oxide quantum dots, whose nanoscale size allows for the construction of additional water transport channels, optimizing the membrane's pore structure and distribution, enabling it to maintain a high water flux even in high-salt environments. Alkaline treatment creates hydrophilic sites, which, combined with the flocculation barrier of divalent metal salts and polymers, significantly improves the membrane's antifouling performance, reducing cleaning frequency and extending membrane lifespan.

[0027] The reverse osmosis membrane of the present invention has the characteristics of high flux, moderate desalination, medium pressure stability, high salt resistance and antifouling. It is compatible with the second and third stage reverse osmosis devices in the countercurrent reverse osmosis process, which helps to reduce the overall operating cost of the device and promotes the development of high-salt wastewater resource treatment technology. Detailed Implementation

[0028] To more clearly illustrate the present invention, specific embodiments are described below. Those skilled in the art should understand that the following description is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0029] In the following examples and comparative examples, the polysulfone was from McLean, model number MKL-P875323; the polyethersulfone was from Xinfuda, model number Tepla® T6000; and the graphene oxide quantum dots were from Meryer, model number E62806.

[0030] Example 1

[0031] A reverse osmosis membrane for use in a countercurrent reverse osmosis process is prepared by a method comprising the following steps:

[0032] S1. Preparation of the support layer: Polysulfone and polyethersulfone are dissolved in N,N-dimethylacetamide at a mass ratio of 7:3, with the sum of the mass fractions of polysulfone and polyethersulfone being 16wt%. Then, 0.5wt% (based on the total mass of the casting solution) of porogen polyvinylpyrrolidone is added, and the mixture is stirred at 70°C for 4 hours until completely dissolved to form a casting solution. The casting solution is then coated onto a polyester nonwoven fabric substrate using a coating machine (wet film thickness 200μm). The substrate is then immediately immersed in a 25°C deionized water coagulation bath for phase separation. After removal, the substrate is dried in an 80°C vacuum drying oven for 2 hours to obtain the reinforced support layer.

[0033] S2. Coating the transition buffer layer: Prepare an aqueous solution containing 1.0 wt% polyvinyl ammonium phosphate and 2.5 wt% sodium hexametaphosphate. Coat the solution evenly on the surface of the support layer by dip coating (speed 0.5 m / min). Remove excess solution by air knife. Then heat treat in a 100℃ hot air drying oven for 3 minutes to form a 20 nm thick transition buffer layer.

[0034] S3. Preparation of the separation layer:

[0035] Aqueous phase coating: Using deionized water as solvent, an aqueous phase solution containing 3.0 wt% m-phenylenediamine, 1.0 wt% triethylamine, 0.10 wt% dodecyltrimethylammonium bromide, 5.0 wt% sodium cyclohexylaminosulfonate, and 0.05 wt% graphene oxide quantum dots (200 nm in diameter) was prepared. The aqueous phase solution was coated onto the surface of the transition buffer layer by roller coating. After standing for 60 seconds, the excess solution was removed by tilting, leaving an aqueous phase film of about 20 μm thickness.

[0036] Oil phase polymerization: Using isoparaffin solvent (Isopar-L) as solvent, an oil phase solution containing 0.20 wt% trimesoyl chloride is prepared. The oil phase solution is sprayed onto the surface of the aqueous phase liquid film. The reaction temperature is controlled at 45℃ and the reaction time is 40 seconds to form a polyamide separation layer.

[0037] S4. Alkaline activation treatment: Treat the surface of the separation layer with a sodium hydroxide solution of pH=13.0 (temperature 25℃) by spraying for 30 seconds, and then rinse with deionized water until the filtrate is neutral.

[0038] S5. Constructing an antifouling layer: Prepare an aqueous solution with 1.2 wt% magnesium chloride and 0.35 wt% anionic polyacrylamide. Coat the surface of the separation layer with the aqueous solution by slit coating. Let it stand for 30 seconds to form a flocculated structure. Then place the membrane in a 60°C oven for 10 minutes for heat treatment to obtain a reverse osmosis membrane with an antifouling layer.

[0039] S6. Post-processing step: Take the reverse osmosis membrane prepared in step S5 out of the oven, let it cool naturally to room temperature, soak it in deionized water for 2 hours, take it out and gently absorb the surface moisture with clean filter paper, put it in a vacuum drying oven and dry it at 40°C for 4 hours to obtain a reverse osmosis membrane suitable for the countercurrent reverse osmosis process.

[0040] Example 2

[0041] Example 2 was carried out in accordance with Example 1, except that when the transition buffer layer was coated, the mass fraction of polyvinyl alcohol ammonium phosphate was 0.8% and the mass fraction of sodium hexametaphosphate was 2.0%.

[0042] Example 3

[0043] Example 3 was carried out in accordance with Example 1, except that the mass fraction of m-phenylenediamine in the aqueous coating for preparing the separation layer was 2.5%.

[0044] Example 4

[0045] Example 4 was carried out in accordance with Example 1, except that when constructing the antifouling layer, the mass fraction of magnesium chloride was 1.0% and the mass fraction of anionic polyacrylamide was 0.3%.

[0046] Example 5

[0047] Example 5 was carried out in accordance with Example 1, except that the mass fraction of pyromellitic trimethylol chloride in the oil phase polymerization for preparing the separation layer was 0.18%.

[0048] Comparative Example 1

[0049] Comparative Example 1 was carried out in accordance with Example 1, except that the step of coating the transition buffer layer was omitted, that is, the transition buffer layer was not prepared, and the raw materials for preparing the transition buffer layer (ammonium polyvinyl phosphate and sodium hexametaphosphate) were directly added to the aqueous solution for preparing the separation layer.

[0050] Comparative Example 2

[0051] Comparative Example 2 was carried out in accordance with Example 1, except that polyvinyl alcohol ammonium phosphate was replaced with polyvinyl alcohol when preparing the transition buffer layer.

[0052] Test Example 1

[0053] The water flux, desalination rate, membrane flux decay rate, and membrane flux recovery rate of the reverse osmosis membranes in Examples 1-5 and Comparative Examples 1-2 were tested respectively. For each type of reverse osmosis membrane, the following steps were included:

[0054] A1. Take the prepared reverse osmosis membrane and measure its water flux and desalination rate;

[0055] Test conditions: Test pressure was 1200 psi, NaCl original aqueous solution concentration was 70 g / L, solution temperature was 25°C, pH value was 7.0, and test time was 1 h;

[0056] Water flux calculation formula:

[0057] in: J Indicates water flux. ; V This represents the actual volume of water that passes through the membrane. L ; A The membrane area is represented by m. 2 ; t Indicates the test time, in hours (h).

[0058] Desalination rate calculation formula:

[0059] in: R The percentage of salt removal is expressed as %; C p Indicates the conductivity of the permeate; C f Indicates the conductivity of the original solution;

[0060] A2. Take the reverse osmosis membrane after the test in step A1 and conduct a continuous operation test on it using simulated wastewater containing pollutants. Test the water flux of the reverse osmosis membrane after 180 minutes of operation.

[0061] The composition of pollutants in the wastewater is: bovine serum albumin (BSA, 1.0 g / L) + sodium alginate (0.5 g / L) + NaCl (70 g / L).

[0062] Test conditions: operating pressure 1200 psi, solution temperature 25℃, solution pH 7.0;

[0063] A3. Take the reverse osmosis membrane after the test in step A2, and rinse the membrane surface with pure water at a flow rate of 3 m / s in the normal operating direction under a low pressure of 0.2 MPa. After rinsing for 30 minutes, test the water flux of the membrane again.

[0064] Test conditions: Test pressure was 1200 psi, NaCl original aqueous solution concentration was 70 g / L, solution temperature was 25°C, and pH value was 7.0.

[0065] The flux decay rate and recovery rate are calculated using the following formulas:

[0066] Membrane flux decay rate = (Initial water flux - Water flux after 180 min of wastewater treatment) / Initial water flux × 100%

[0067] Membrane flux recovery rate = (Water flux after cleaning / Initial water flux) × 100%

[0068] Table 1 Performance of Reverse Osmosis Membranes in Each Example and Comparative Example

[0069]

[0070] As shown in Table 1, the reverse osmosis membranes of Examples 1-5 are superior to those of Comparative Examples 1-2 in four key indicators: water flux (initial water flux), desalination rate, antifouling (membrane flux decay rate), and cleaning recovery ability (membrane flux recovery rate) under high salt conditions, demonstrating excellent high salt resistance and antifouling stability.

[0071] Water flux analysis: The initial water flux of each embodiment was 17.7~18.9 LHM (L / m²·h), significantly higher than the 14.7~15.2 LHM of the comparative examples. In each embodiment, a transition buffer layer was prepared using polyvinyl ammonium phosphate and sodium hexametaphosphate. Through a "dip-coating-pre-fixing" process, the two components were uniformly distributed on the surface of the support layer, avoiding the problem of "uneven raw material diffusion" in the interfacial polymerization reaction. In each embodiment, polyvinyl ammonium phosphate (containing hydroxyl and phosphate groups) and sodium hexametaphosphate could form a stable bond, constructing a highly interconnected "transition bridge," reducing the resistance to water molecule transfer, thereby increasing the water flux. In Comparative Example 1 (without a transition layer, the components were directly added to the aqueous phase), the interfacial polymerization reaction was completed instantaneously, and the aqueous polymer (polyvinyl alcohol ammonium phosphate) needed to diffuse in a very short time, which easily led to uneven dispersion. This resulted in a large gap between the separation layer and the support layer, poor structural connectivity, and reduced water molecule transfer efficiency, with a water flux of only 14.7 LHM. In Comparative Example 2 (the transition layer was replaced with polyvinyl alcohol instead of polyvinyl alcohol ammonium phosphate), polyvinyl alcohol did not have phosphate groups and could not form a strong interaction with the subsequent polyamide separation layer through phosphate groups like polyvinyl alcohol ammonium phosphate. This resulted in a decrease in membrane structure density and connectivity, with a water flux of only 15.2 LHM.

[0072] Desalination rate analysis: The desalination rates of the comparative examples and embodiments are concentrated in the range of 76.4% to 80.8%, all of which meet the requirement of "no extreme desalination (<99.5%) but lower than the salt content of the first influent". This indicates that the present invention has successfully balanced the relationship between desalination rate and water flux through formulation design (such as not pursuing an excessively dense active layer). Comparative Example 1 has no transition layer, and the separation layer and support layer are not tightly bonded, which easily forms tiny gaps, resulting in the penetration of some salt ions. The polyvinyl alcohol transition layer of Comparative Example 2 lacks the "charge repulsion effect" of phosphate ions, and its ability to retain salt ions is weaker than that of the polyvinyl alcohol ammonium phosphate transition layer. Therefore, the desalination rates of the comparative examples are lower than those of the embodiments.

[0073] Membrane flux decay rate analysis: The membrane flux decay rates of each embodiment were all between 22.4% and 23.5%, far lower than the 33.9%-35.6% of the comparative examples, indicating that their antifouling ability was superior. The transition layer of the embodiments used "polyvinyl alcohol ammonium phosphate + sodium hexametaphosphate". Both components contain hydrophilic groups such as hydroxyl groups and phosphate groups, which can enhance the hydrophilicity of the membrane surface through intermolecular hydrogen bonds. At the same time, the negative charge of phosphate groups can reduce pollutant adsorption through electrostatic repulsion, reducing the risk of membrane pore blockage. Comparative example 1 had no transition layer, and the antifouling layer and separation layer were not firmly bonded. Pollutants easily damaged the interlayer structure and accelerated membrane pore blockage. The polyvinyl alcohol transition layer of comparative example 2 had few hydrophilic sites (no phosphate groups) and could not form a stable "hydrophilic surface layer". Pollutants could more easily penetrate to the surface of the separation layer, resulting in rapid flux decay.

[0074] Membrane flux recovery rate analysis: The membrane flux recovery rates of each embodiment were all between 91.2% and 92.3%, and most of the initial flux could be recovered after cleaning, indicating that the membrane efficiency can be maintained through simple cleaning during long-term operation. The recovery rate of 92.3% in Example 1 reflects the synergistic effect of the antifouling layer and the hydrophilic surface formed by alkaline activation treatment (reducing pollutant adhesion). In Comparative Example 1, there was no transition layer, and the transition layer components were directly added to the aqueous solution. Without the "interface regulation" of the transition layer, the separation layer and the support layer were loosely bonded, and even small gaps appeared. Pollutants could easily penetrate into the gaps and deposit, forming "deep fouling" that pure water rinsing could not reach, resulting in a decrease in membrane flux recovery rate. In Comparative Example 2, polyvinyl alcohol was used instead of polyvinyl ammonium phosphate in the transition layer. Polyvinyl alcohol does not have phosphate groups and cannot form a strong interaction with the separation layer. The surface of the separation layer is prone to uneven defects. Pollutants can embed into the membrane through the defects, and the defects may expand during cleaning, further reducing the membrane flux recovery rate.

[0075] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, Includes the following steps: S1. Preparation of the support layer: A casting solution is prepared using a polar solvent. The casting solution contains 15.1 wt% to 18 wt% solids, a polysulfone to polyethersulfone mass ratio of 1.85 to 3, a total polysulfone to polyethersulfone content of 15% to 17 wt%, and a pore-forming agent content of 0.1 wt% to 1 wt%. The casting solution is coated onto a polyester nonwoven fabric substrate, immersed in a deionized water coagulation bath, and then removed and dried to obtain the support layer. S2. Coating a transition buffer layer: Prepare an aqueous solution with a polyvinyl alcohol ammonium phosphate content of 0.8wt%~1.2wt% and a phosphate content of 2.0wt%~3.0wt%. The aqueous solution is uniformly coated onto the surface of the support layer by dip coating. Then, it is heat-treated at 80℃~120℃ for 1min~5min to allow the hydroxyl groups of polyvinyl alcohol ammonium phosphate to cross-link with the phosphate groups of phosphate to form a transition buffer layer. S3. Preparation of the separation layer: Prepare an aqueous solution containing 2.5wt%~3.5wt% polyamine monomer, 0.8wt%~1.2wt% alkaline acid binder, 0.08wt%~0.12wt% cationic surfactant, 4.5wt%~5.5wt% aminosulfonate, and 0.02wt%~0.07wt% graphene oxide quantum dots. Coat the solution uniformly onto the surface of the transition buffer layer using a roller coating method. After standing, remove excess solution using an inclined method to obtain the aqueous phase surface. Prepare an oil phase solution containing 0.18wt%~0.22wt% polyacrylamide chloride. Spray the solution uniformly onto the aqueous phase surface to form the separation layer. S4. Alkaline activation treatment: Spray an alkaline solution with a pH of 12.5~13.5 onto the surface of the separation layer to decompose the ammonium phosphate groups of polyvinyl alcohol ammonium phosphate in the transition buffer layer into phosphate groups, forming hydrophilic sites on the surface of the separation layer. Then rinse with deionized water until the filtrate is neutral. S5. Constructing an antifouling layer: Prepare an aqueous solution with a divalent metal salt content of 1.0wt%~1.5wt% and a polymer content of 0.3wt%~0.4wt%, and coat it onto the surface of the separation layer after alkaline activation treatment by slit coating. Then, heat treat it at 50℃~70℃ for 5min~15min to obtain a reverse osmosis membrane with an antifouling layer.

2. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, The reverse osmosis membrane prepared in step S5 is cooled to room temperature and then immersed in deionized water to fully remove unreacted monomers and impurities remaining on the surface of the reverse osmosis membrane. After immersion, the reverse osmosis membrane is removed and dried to obtain the final reverse osmosis membrane.

3. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, In step S2, the phosphate is sodium hexametaphosphate, sodium tripolyphosphate, or sodium dipolyphosphate.

4. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, In step S3, the polyamine monomer is m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, or 4,4'-diaminodiphenylmethane; the alkaline acid-binding agent is triethylamine (TEA), sodium hydroxide (NaOH), sodium hydrogen phosphate, or N,N-dimethylpiperazine; the cationic surfactant is dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, or hexadecyltrimethylammonium bromide; and the aminosulfonate is sodium cyclohexylaminosulfonate, ammonium aminosulfonate, sodium p-toluenesulfonate, or sodium laurylsulfonate.

5. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, In step S3, the polyacrylamide chloride is pyromellitic methyl methacrylate chloride, terephthaloyl chloride, isophthaloyl chloride, orthophthaloyl chloride or biphenyl chloride.

6. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, In step S5, the divalent metal salt is magnesium chloride, calcium chloride, or magnesium sulfate, and the polymer is anionic polyacrylamide, cationic polyacrylamide, or quaternary ammonium salt chitosan.

7. A reverse osmosis membrane, characterized in that, It is prepared by the reverse osmosis membrane preparation method according to any one of claims 1 to 6.

8. An application of a reverse osmosis membrane, characterized in that, The reverse osmosis membrane described in claim 7 is used as the reverse osmosis membrane in the second and third stage reverse osmosis devices in the countercurrent reverse osmosis process.

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