Reverse osmosis membrane and preparation method thereof

Abstract

The invention relates to the technical field of water treatment membranes, in particular to a reverse osmosis membrane and a preparation method thereof. The invention provides a preparation method of a reverse osmosis membrane, which comprises the following steps: A) soaking a base membrane in a water phase solution, taking out the base membrane, drying the surface of the base membrane, coating the base membrane with an oil phase solution for interfacial polymerization reaction, and curing to obtain a nascent aromatic polyamide reverse osmosis membrane; b) rinsing the nascent state aromatic polyamide reverse osmosis membrane; and C) coating the surface of the polyamide layer obtained in the step B) with a post-treatment solution containing specific components, and drying to obtain the reverse osmosis membrane. In the prepared reverse osmosis membrane, a PVA-TA-Fe3O4 ternary synergistic system can be formed, the mechanical strength is greatly improved, the reverse osmosis membrane is resistant to pollution and scouring, the oxidation resistance is improved, and Fe3O4 nanoparticles are not prone to loss. Experimental results show that the reverse osmosis membrane prepared by the method has excellent water flux, salt rejection rate, pollution resistance and scouring resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment membranes, in particular to a reverse osmosis membrane and a preparation method thereof. Background Art

[0002] Reverse osmosis membranes have become a mainstream technology in membrane-based water treatment, but anti-fouling performance remains a significant constraint on their development. Membrane fouling can lead to a rapid decrease in water flux and retention rate. The development of nanomaterials has provided new avenues for the preparation and modification of reverse osmosis composite membranes. For example, graphene oxide, a carbon nanomaterial, is widely used in various fields due to its excellent chemical properties, high hydrophilicity, and good dispersibility. Silver nanomaterials are also widely used in antibacterial membranes due to their excellent antibacterial properties. Nanomaterials possess unique properties that differ from those of ordinary bulk materials due to their small size effects, surface effects, quantum size effects, and macroscopic quantum tunneling effects. However, due to their high surface free energy, they spontaneously aggregate, losing their inherent excellent properties. Furthermore, during the reverse osmosis membrane preparation process, nanomaterial agglomeration can seriously affect the integrity of the membrane product and reduce product quality.

[0003] Conventional reverse osmosis membranes generally consist of a polysulfone non-woven composite base membrane, a polyamide separation layer (PA layer), and a polyvinyl alcohol (PVA) anti-fouling layer. Some existing technologies dope inorganic nanomaterials into the polyamide separation layer of the reverse osmosis membrane. However, the high surface energy inorganic nanomaterials are not compatible with the organic polymers in the separation layer. Furthermore, the agglomeration effect of the nanomaterials leads to defects at the interface due to large gaps, significantly reducing the rejection rate of the reverse osmosis membrane. Some existing technologies dope inorganic nanomaterials into the PVA anti-fouling layer of the reverse osmosis membrane. Conventional anti-fouling layers have weak adhesion to the reverse osmosis membrane surface, low mechanical strength, and poor erosion resistance. As the reverse osmosis membrane operates, the anti-fouling layer gradually detaches, gradually degrading the anti-fouling properties of the reverse osmosis membrane. Consequently, the preparation process for nanomaterial-doped modified reverse osmosis membranes presents numerous challenges during scale-up, making it difficult to obtain a stable product.

[0004] Fe3O4 nanoparticles can produce local movement or thermal effects under the action of an external magnetic field, disturbing the water flow on the membrane surface, reducing the deposition of pollutants (such as organic molecules, bacteria, and colloids), and delaying membrane fouling; Fe3O4 can catalyze the production of reactive oxygen species (ROS) or directly destroy bacterial cell membranes, inhibiting biological fouling and extending membrane life; the Fe3O4 surface is rich in hydroxyl groups, which can enhance the hydrophilicity of the PVA coating and improve its anti-fouling properties; however, Fe3O4 has an oxidation risk and can only exist stably for a few months in a conventional PVA matrix.

[0005] The existing technology is to form Fe3O4@SiO2 through SiO2 coating to prevent it from oxidation. However, the SiO2 shell formed during the coating process is thicker, which will lead to a decrease in the magnetic properties of Fe3O4 and weak interface bonding between PVA and SiO2. At the same time, nanoparticle sedimentation is more likely to occur during the preparation process, all of which will affect the stability of the diaphragm performance. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a reverse osmosis membrane and a preparation method thereof, wherein the prepared reverse osmosis membrane has excellent water flux, desalination rate and anti-pollution and scouring resistance.

[0007] The present invention provides a method for preparing a reverse osmosis membrane, which is characterized by comprising the following steps:

[0008] A) soaking the base membrane in an aqueous solution, taking it out and allowing it to dry, coating the base membrane with an oil solution for interfacial polymerization, and curing it to obtain a nascent aromatic polyamide reverse osmosis membrane;

[0009] B) rinsing the nascent aromatic polyamide reverse osmosis membrane;

[0010] C) applying the post-treatment solution to the surface of the polyamide layer obtained in step B), and drying the polyamide layer to obtain a reverse osmosis membrane;

[0011] The post-treatment solution is prepared from raw materials; the raw materials include 1 wt% to 4 wt% of polyvinyl alcohol, 0.1 wt% to 5 wt% of a cross-linking agent, 0.5 wt% to 2 wt% of glycerol, 0.02 wt% to 0.2 wt% of a pH regulator, 1 wt% to 5 wt% of Fe3O4@LAD particles, 0.08 wt% to 0.12 wt% of FeCl3, and the balance of water;

[0012] The Fe3O4@LAD particles include an Fe3O4 core and a lauramidopropyl betaine coating layer formed on the outer surface of the Fe3O4 core.

[0013] Preferably, the preparation method of the post-treatment solution comprises the following steps:

[0014] a) dissolving polyvinyl alcohol powder in an aqueous solution of a crosslinking agent, adjusting the pH to 7-8 with a pH adjuster, and then stirring and mixing with glycerol to obtain a premixed solution;

[0015] b) mixing the premixed solution, Fe3O4@LAD particles and FeCl3, and performing a cross-linking reaction under ultrasonic conditions to obtain a post-treatment solution.

[0016] Preferably, the cross-linking agent is tannic acid.

[0017] Preferably, the preparation method of the Fe3O4@LAD particles comprises the following steps:

[0018] An aqueous solution of lauramidopropyl betaine was mixed with the Fe3O4 cores, ultrasonically mixed, and placed in a magnetic field. After the particles were adsorbed to the container wall, the supernatant was poured out, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. Ultrasonic dispersion was performed, and the adsorption and washing steps under the magnetic field were repeated until the pH value of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

[0019] Preferably, the preparation method of the Fe3O4 core comprises the following steps:

[0020] FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water. Under nitrogen protection, ammonia water was added dropwise until the pH value was 9-11, and then reacted to obtain Fe3O4 core.

[0021] The molar ratio of FeCl3·6H2O to FeSO4·7H2O is 1.8-2.2:0.8-1.2;

[0022] The reaction temperature is 55-65°C and the reaction time is 0.5-1.5 h.

[0023] Preferably, the aqueous phase solution is obtained by adjusting the pH value of the aqueous phase base liquid to 7-9;

[0024] The aqueous base liquid includes 0.5 wt% to 5 wt% of a multifunctional amine, 0.05 wt% to 2 wt% of a surfactant, 3 wt% to 10 wt% of a polar solvent, and the balance is water;

[0025] The polyfunctional amine includes at least one of an aromatic amine, an aliphatic amine and an alicyclic amine;

[0026] The surfactant includes sodium dodecyl sulfate or sodium lauryl sulfate;

[0027] The polar solvent includes dimethyl sulfoxide and / or N-methylpyrrolidone.

[0028] Preferably, the oil phase solution comprises an acyl halide and an oil phase solvent;

[0029] In the oil phase solution, the mass content of the acyl halide is 0.05% to 0.3%;

[0030] The acyl halide includes trimesoyl chloride;

[0031] The oil phase solvent includes at least one of n-hexane, Isopar G and Isopar L.

[0032] Preferably, the rinsing comprises: rinsing the nascent aromatic polyamide reverse osmosis membrane sequentially with deionized water, citric acid aqueous solution, deionized water, isopropyl alcohol aqueous solution, deionized water, and glycerol aqueous solution.

[0033] Preferably, the deionized water rinsing temperature is 15-30°C and the rinsing time is 1-5 min;

[0034] The mass concentration of the citric acid aqueous solution is 1% to 5%; the rinsing temperature of the citric acid aqueous solution is 40 to 80°C, and the rinsing time is 1 to 5 minutes;

[0035] The mass concentration of the isopropyl alcohol aqueous solution is 1% to 10%; the rinsing temperature of the isopropyl alcohol aqueous solution is 40 to 80°C, and the rinsing time is 1 to 5 minutes;

[0036] The mass concentration of the glycerol aqueous solution is 2% to 6%; the rinsing temperature of the glycerol aqueous solution is 15 to 30° C., and the rinsing time is 1 to 5 minutes.

[0037] The present invention also provides a reverse osmosis membrane prepared by the above preparation method.

[0038] The reverse osmosis membrane prepared by this invention forms a ternary synergistic system of PVA, TA, and Fe₃O₄, significantly enhancing mechanical strength, improving pollution resistance and erosion resistance, and enhancing antioxidant properties, while also preventing Fe₃O₄ nanoparticle loss. This synergistic system combines the chemical switching of LAD with the physical drive of Fe₃O₄, and in conjunction with TA, achieves dynamic anti-pollution, static protection, intelligently triggered release, and in-situ cleaning of reverse osmosis membrane contaminants, significantly improving the membrane's anti-pollution capabilities, self-cleaning efficiency, and lifespan.

[0039] Experimental results show that the reverse osmosis membrane prepared by the present invention has excellent water flux, desalination rate and excellent anti-pollution and scouring resistance. In addition, the present invention is consistent with the existing conventional reverse osmosis membrane production line process, with minimal equipment changes, which is conducive to industrial production. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The present invention provides a method for preparing a reverse osmosis membrane, comprising the following steps:

[0042] A) soaking the base membrane in an aqueous solution, taking it out and allowing it to dry, coating the base membrane with an oil solution for interfacial polymerization, and curing it to obtain a nascent aromatic polyamide reverse osmosis membrane;

[0043] B) rinsing the nascent aromatic polyamide reverse osmosis membrane;

[0044] C) applying the post-treatment solution to the surface of the polyamide layer obtained in step B), and drying the polyamide layer to obtain a reverse osmosis membrane;

[0045] The post-treatment solution is prepared from raw materials; the raw materials include 1 wt% to 4 wt% of polyvinyl alcohol, 0.1 wt% to 5 wt% of a cross-linking agent, 0.5 wt% to 2 wt% of glycerol, 0.02 wt% to 0.2 wt% of a pH regulator, 1 wt% to 5 wt% of Fe3O4@LAD particles, 0.08 wt% to 0.12 wt% of FeCl3, and the balance of water;

[0046] The Fe3O4@LAD particles include a Fe3O4 core and a lauramidopropyl betaine (LAD) coating layer formed on the outer surface of the Fe3O4 core.

[0047] Regarding step A):

[0048] The base membrane is immersed in an aqueous solution, taken out and dried, and then an oil phase solution is coated on the base membrane to perform an interfacial polymerization reaction. After curing, a primary aromatic polyamide reverse osmosis membrane is obtained.

[0049] In some embodiments of the present invention, the method for preparing the basement membrane comprises the following steps:

[0050] The casting solution is coated on a non-woven fabric and solidified into a film through phase inversion to obtain a base film;

[0051] The casting solution is a polysulfone solution. The solvent of the polysulfone solution is N,N-dimethylformamide (DMF). The mass concentration of the casting solution is 12% to 18%, for example, 16%. The casting solution is obtained by dissolving polysulfone in N,N-dimethylformamide (DMF) and allowing it to stand for degassing. The dissolution temperature is 70°C to 90°C, for example, 75°C. The degassing time is 8 to 24 hours, for example, 12 hours.

[0052] The coating amount of the casting solution is 20~60 g / m 2 , for example 30 g / m 2 .

[0053] The phase inversion method may be soaking in deionized water.

[0054] After the film is solidified, the process further includes: rinsing, annealing, and removing excess water from the surface using a water absorbing plate.

[0055] The rinsing adopts RO water.

[0056] The annealing temperature is 40-60° C., such as 50° C., and the annealing time is 1-5 min, such as 3 min.

[0057] In some embodiments of the present invention, the aqueous solution is obtained by adjusting the pH value of the aqueous base liquid to 7 to 9, specifically, the pH value is 7.8. The aqueous base liquid includes 0.5 wt% to 5 wt% of a multifunctional amine, 0.05 wt% to 2 wt% of a surfactant, 3 wt% to 10 wt% of a polar solvent, and the remainder is water. Specifically, in the aqueous base liquid, the mass content of the multifunctional amine is 2.5%, the mass content of the surfactant is 0.1%, and the mass content of the aqueous solvent is 7%. The reagent used for adjusting the pH value is an alkaline reagent, such as sodium hydroxide. The present invention has no special restrictions on the preparation method of the aqueous base liquid. In certain embodiments of the present invention, the preparation method of the aqueous base liquid includes the following steps: mixing the multifunctional amine, the surfactant, the aqueous solvent and water to obtain the aqueous base liquid. The mixing is carried out at room temperature.

[0058] The polyfunctional amine is selected from at least one of aromatic amines, aliphatic amines and alicyclic amines; for example, at least one of m-phenylenediamine, ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, N-(2-hydroxyethyl)ethylenediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, diethylenetriamine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, piperazine and 4-aminomethylpiperazine.

[0059] The surfactant is selected from sodium lauryl sulfate or sodium lauryl sulfate.

[0060] The polar solvent is selected from dimethyl sulfoxide and / or N-methylpyrrolidone.

[0061] The water is deionized water.

[0062] The present invention controls the pH value of the aqueous solution under the above conditions, which is conducive to the absorption of by-product hydrochloric acid molecules in the interfacial polymerization process and the formation of polyamide with a high degree of cross-linking. If the pH value is too low or too high, the amide bond is easily hydrolyzed, affecting the separation performance of the polyamide separation layer.

[0063] The invention soaks the base film in an aqueous solution, takes it out and allows it to dry on the surface, then coats the base film with an oil solution to carry out an interfacial polymerization reaction, and solidifies it to obtain a nascent aromatic polyamide reverse osmosis membrane.

[0064] In some embodiments of the present invention, the base film is immersed in the aqueous solution for 3 to 8 seconds, such as 5 seconds.

[0065] The present invention has no particular limitation on the surface drying method, and any surface drying method well known to those skilled in the art may be used.

[0066] In some embodiments of the present invention, the oil phase solution comprises an acyl halide and an oil phase solvent, wherein the mass content of the acyl halide in the oil phase solution is 0.05% to 0.3%, such as 0.25%.

[0067] The acyl halide is selected from trimesoyl chloride.

[0068] The oil phase solvent is selected from at least one of n-hexane, Isopar G and Isopar L.

[0069] The present invention has no particular limitation on the method for preparing the oil phase solution. In certain embodiments of the present invention, the method for preparing the oil phase solution comprises the following steps: mixing an acyl halide and an oil phase solvent to obtain an oil phase solution. The mixing is performed at room temperature.

[0070] The present invention has no particular limitation on the coating amount of the oil phase solution, which is generally applied in excess. In some embodiments of the present invention, the coating amount of the oil phase solution is 50-200 mg / m 2 , for example 100 mg / m 2 .

[0071] In some embodiments of the present invention, the drying temperature is 55-65° C., such as 60° C., and the drying time is 2-4 min, such as 3 min.

[0072] Regarding step B):

[0073] The nascent aromatic polyamide reverse osmosis membrane is rinsed.

[0074] In some embodiments of the present invention, the rinsing comprises: rinsing the nascent aromatic polyamide reverse osmosis membrane sequentially with deionized water, citric acid aqueous solution, deionized water, isopropyl alcohol aqueous solution, deionized water, and glycerol aqueous solution.

[0075] The deionized water rinsing temperature is 15-30° C., such as 20° C., and the rinsing time is 1-5 min, such as 2 min.

[0076] The mass concentration of the citric acid aqueous solution is 1% to 5%, such as 3%. The rinsing temperature of the citric acid aqueous solution is 40 to 80° C., such as 60° C., and the rinsing time is 1 to 5 minutes, such as 5 minutes.

[0077] The mass concentration of the isopropyl alcohol aqueous solution is 1% to 10%, such as 3%. The rinsing temperature of the isopropyl alcohol aqueous solution is 40 to 80° C., such as 60° C., and the rinsing time is 1 to 5 minutes.

[0078] The mass concentration of the glycerol aqueous solution is 2% to 6%. The rinsing temperature of the glycerol aqueous solution is 15 to 30° C., such as 25° C., and the rinsing time is 1 to 5 minutes, such as 5 minutes.

[0079] Regarding step C):

[0080] Applying the post-treatment solution to the surface of the polyamide layer obtained in step B), and drying it to obtain a reverse osmosis membrane;

[0081] The post-treatment solution is prepared from raw materials; the raw materials include 1 wt% to 4 wt% of polyvinyl alcohol, 0.1 wt% to 5 wt% of a cross-linking agent, 0.5 wt% to 2 wt% of glycerol, 0.02 wt% to 0.2 wt% of a pH regulator, 1 wt% to 5 wt% of Fe3O4@LAD particles, 0.08 wt% to 0.12 wt% of FeCl3, and the balance of water;

[0082] The Fe3O4@LAD particles include a Fe3O4 core and a lauramidopropyl betaine (LAD) coating layer formed on the outer surface of the Fe3O4 core.

[0083] In some embodiments of the present invention, the Fe3O4 core is prepared by coprecipitation. The preparation method of the Fe3O4 core comprises the following steps:

[0084] FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water. Under nitrogen protection, ammonia water was added dropwise until the pH value was 9-11, and then the reaction was carried out to obtain the Fe3O4 core.

[0085] The molar ratio of FeCl3·6H2O to FeSO4·7H2O is 1.8~2.2:0.8~1.2, for example 2:1.

[0086] The mass concentration of the ammonia water is 25% to 28%, such as 26%.

[0087] Specifically, aqueous ammonia was added dropwise until the pH value reached 10.

[0088] The reaction temperature is 55-65°C, such as 60°C; and the reaction time is 0.5-1.5 h, such as 1 h.

[0089] In some embodiments of the present invention, the method for preparing the Fe3O4@LAD particles comprises the following steps:

[0090] An aqueous solution of lauramidopropyl betaine (LAD) was mixed with the Fe3O4 core, ultrasonically mixed, and placed in a magnetic field. The particles were adsorbed to the container wall within seconds, the supernatant was poured out, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. Ultrasonic dispersion was performed, and the adsorption and washing steps under the magnetic field were repeated until the pH value of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

[0091] The LAD is a zwitterionic surfactant. By coating Fe3O4 with LAD, stable dispersion of nanoparticles and functional coupling are achieved.

[0092] The mass ratio of the LAD aqueous solution to the Fe3O4 core is 1-2:1-5, for example, 1:3. The mass concentration of the LAD aqueous solution is 0.5%-2%, for example, 1%.

[0093] The ultrasonic mixing time is 0.5-1.5 h, for example 1 h.

[0094] The magnetic field condition is: 0.3 T ≤ magnetic field strength ≤ 1 T. If it is too low < 0.1 T, it will lead to incomplete separation, and if it is too high > 1 T, it may cause magnetic agglomeration of particles.

[0095] The decanted supernatant contains unreacted Fe 2+ / Fe 3+ , ammonia water, etc.

[0096] The ultrasonic dispersion time is 5 to 10 minutes, for example, 7 minutes.

[0097] The drying is vacuum drying; the drying temperature is 55-65°C, such as 60°C.

[0098] In some embodiments of the present invention, the alcoholysis degree of the polyvinyl alcohol is ≥99%.

[0099] In some embodiments of the present invention, the cross-linking agent is tannic acid (TA).

[0100] In some embodiments of the present invention, the pH adjuster is hydrochloric acid.

[0101] In the present invention, FeCl3 is an oxidative cross-linking catalyst.

[0102] In some embodiments of the present invention, the water is deionized water.

[0103] In some embodiments of the present invention, in the raw materials, the content of PVA is 2 wt%, 3 wt%, and 4 wt%; the content of the cross-linking agent is 1 wt%, 2 wt%, and 4 wt%; the content of glycerol is 1 wt%, 2 wt%; the content of the pH regulator is 0.08 wt%, 0.06 wt%, and 0.1 wt%; the content of Fe3O4@LAD particles is 3 wt%, 1 wt%, and 5 wt%; and the content of FeCl3 is 0.1 wt%.

[0104] In some embodiments of the present invention, the method for preparing the post-treatment solution comprises the following steps:

[0105] a) dissolving polyvinyl alcohol (PVA) powder in an aqueous solution of a cross-linking agent, adjusting the pH to 7-8 with a pH adjuster, and then stirring and mixing with glycerin to obtain a premixed solution;

[0106] b) mixing the premixed solution, Fe3O4@LAD particles and FeCl3, and performing a cross-linking reaction under ultrasonic conditions to obtain a post-treatment solution.

[0107] Regarding step a):

[0108] The aqueous solution of the crosslinking agent is obtained by dissolving the crosslinking agent in water at 55-65° C. Specifically, the temperature of the water is 60° C.

[0109] The PVA powder is dissolved in the crosslinking agent aqueous solution at a temperature of 85-95° C., such as 90° C. The dissolution is performed by stirring and the dissolution time is 1.5-2.5 h, such as 2 h.

[0110] In the present invention, the pH value is adjusted to 7-8, such as 7.5, by using a pH adjuster to avoid excessive oxidation of the cross-linking agent.

[0111] The time for stirring and mixing with glycerol is 25 to 35 minutes, for example, 30 minutes.

[0112] In the present invention, glycerol is added after TA cross-linking to avoid interfering with TA-PVA bonding. The small molecular structure of glycerol (containing 3 hydroxyl groups) can be inserted into the PVA-TA cross-linking network to improve flexibility; the hydrophilic hydroxyl groups of glycerol can compensate for the hydrophobicity of the TA benzene ring.

[0113] Regarding step b):

[0114] The FeCl3 in the post-treatment solution is a catalyst that catalyzes the oxidative cross-linking of TA-PVA.

[0115] The frequency of the ultrasound is 20-40 kHz, for example, 30 kHz.

[0116] The cross-linking reaction temperature is 50-70° C., such as 60° C., and the reaction time is 1.5-2.5 h, such as 2 h.

[0117] The baking time is 2 to 9 minutes, for example, 5 minutes.

[0118] After obtaining the post-treatment solution, the post-treatment solution is applied to the surface of the polyamide layer obtained in step B), and dried to obtain a reverse osmosis membrane.

[0119] In some embodiments of the present invention, the coating amount of the post-treatment solution is 50-200 mg / m 2 , such as 120 mg / m 2 The contact time between the post-treatment solution and the surface of the polyamide layer is 2 to 4 seconds, for example, 3 seconds.

[0120] After the coating is completed, the method further includes: removing excess solution.

[0121] The drying temperature is 75-85° C., such as 80° C., and the drying time is 1.5-2.5 min, such as 2 min.

[0122] The present invention also provides a reverse osmosis membrane prepared by the above-mentioned preparation method. The reverse osmosis membrane provided by the present invention fixes the Fe3O4@LAD nanocomposite material through a tannic acid (TA)-polyvinyl alcohol (PVA) cross-linked network.

[0123] The reverse osmosis membrane provided by the present invention has Fe3O4 nanoparticles doped in the PVA layer, and has a better rejection rate than the prior art in which Fe3O4 nanoparticles are doped in the polyamide (PA) separation layer.

[0124] In the reverse osmosis membrane provided by the present invention, a PVA-TA-Fe3O4 three-dimensional network can be formed, the mechanical strength is greatly improved, and the membrane is more resistant to erosion, and the Fe3O4 nanoparticles are not easily lost.

[0125] The amphiphilic structure of LAD (hydrophobic tail chain + hydrophilic betaine group) can adsorb onto the Fe3O4 surface, forming a monolayer, reducing the van der Waals forces between particles and preventing agglomeration. Under neutral or alkaline conditions, LAD is negatively charged (the betaine group is ionized), generating electrostatic repulsion with the Fe3O4 surface charge (pH-dependent), further improving dispersibility. The TA chelating layer prevents Fe3O4 from agglomerating, promoting uniform distribution within the PVA matrix. Furthermore, organic matter (such as humic acid) adsorbed on the membrane surface can be slowly oxidized by TA.

[0126] LAD forms dynamic micelles, effectively solubilizing hydrophobic pollutants through a hydrophobic wrapping-hydrophilic shielding mechanism, creating "pseudo-water-soluble" complexes that are flushed away from the membrane surface by the water flow. Both LAD and Fe₃O₄ increase the hydrophilicity of PVA, enhancing its anti-pollution capabilities. LAD can also provide antioxidant protection for Fe₃O₄ particles.

[0127] The Fe3O4 particles used in the present invention can also resist oxidation and enhance antibacterial effects.

[0128] The reverse osmosis membrane provided by the present invention has magnetic response dynamic anti-pollution ability, pH response self-cleaning function and long-term synergistic antibacterial properties.

[0129] The present invention uses a LAD coating process, which is simpler than the SiO2 coating process and is compatible with existing reverse osmosis membrane production lines (coating-crosslinking-film formation). Material costs are manageable (LAD and Fe3O4 are both commercial products), reducing costs by approximately 20%, making it suitable for industrial production. Furthermore, the TA and PVA in the present invention provide synergistic antioxidant properties, significantly extending stability.

[0130] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0131] In order to further illustrate the present invention, a reverse osmosis membrane and a preparation method thereof provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0132] In the Examples and Comparative Examples:

[0133] The preparation method of the basement membrane is as follows:

[0134] 1) Preparation of casting solution: 84 parts by mass of N,N-dimethylformamide and 16 parts by mass of polysulfone were mixed, stirred at 75°C until dissolved, and allowed to stand for 12 hours to degas to obtain a uniform and transparent casting solution.

[0135] 2) Apply the casting solution on the non-woven fabric with a coating amount of 30 g / m 2 After soaking in deionized water, the film was solidified by phase conversion, rinsed with RO water, annealed at 50℃ for 3 min, and the excess water on the surface was removed by a water absorption plate to obtain a base film.

[0136] The Fe3O4 core was prepared by co-precipitation method:

[0137] FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water at a molar ratio of 2:1. Under nitrogen protection, ammonia water (mass concentration of 26%) was added dropwise to a pH of 10. The mixture was reacted at 60°C for 1 h to obtain the Fe3O4 core.

[0138] Preparation of Fe3O4@LAD particles:

[0139] A 1% LAD aqueous solution was mixed with Fe₃O₄ cores in a 1:3 mass ratio. After ultrasonic mixing for 1 hour, the particles were placed in a magnetic field (0.3T ≤ ≤ 1T). The particles were adsorbed to the container wall within seconds. The supernatant was then decanted, the magnetic field removed, and the particles were washed with deionized water. Ultrasonic dispersion was performed for 7 minutes. The adsorption and washing steps under magnetic field conditions were repeated until the pH of the supernatant was neutral. After vacuum drying at 60°C, pure Fe₃O₄@LAD particles were obtained. The Fe₃O₄@LAD particles consisted of an Fe₃O₄ core and a LAD coating formed on the outer surface of the Fe₃O₄ core.

[0140] Example 1

[0141] 1) Apply aqueous solution on the base film (coating amount is 100 mg / m 2 ), and then apply the oil phase solution (the coating amount is 100mg / m 2 ), and then dried at 60°C for 3 min to obtain the primary aromatic polyamide reverse osmosis membrane;

[0142] Preparation of aqueous solution:

[0143] A polyfunctional amine (m-phenylenediamine), a surfactant (sodium dodecylbenzenesulfonate), a polar solvent (dimethyl sulfoxide) and deionized water are mixed at room temperature to obtain an aqueous base liquid; the aqueous base liquid contains 2.5% by mass of the polyfunctional amine, 0.1% by mass of the surfactant and 7% by mass of the aqueous solvent.

[0144] The pH value of the aqueous base liquid was adjusted to 7.8 using sodium hydroxide to obtain an aqueous solution.

[0145] Preparation of oil phase solution:

[0146] The acyl halide (trimesoyl chloride) and the oil phase solvent (n-hexane) are mixed at room temperature to obtain an oil phase solution; the mass content of the acyl halide in the oil phase solution is 0.25%.

[0147] 2) rinsing the nascent aromatic polyamide reverse osmosis membrane, comprising: first rinsing with 20°C deionized water for 2 min, then rinsing with a 60°C citric acid aqueous solution (mass concentration of 3%) for 5 min, then rinsing with 20°C deionized water for 2 min, then rinsing with a 60°C isopropanol aqueous solution (mass concentration of 3%) for 5 min, then rinsing with 20°C deionized water for 2 min, and finally rinsing with a 25°C glycerol aqueous solution (concentration of 3 wt%) for 5 min.

[0148] 3) Preparation of post-treatment solution:

[0149] The post-treatment solution is prepared from raw materials; the raw materials include 2 wt% of PVA (alcoholysis degree ≥99%), 1 wt% of cross-linking agent TA, 1 wt% of glycerol, 0.08 wt% of pH adjuster (hydrochloric acid), 3 wt% of Fe3O4@LAD particles, 0.1 wt% of FeCl3, and the balance of water;

[0150] 3-1) Dissolve the crosslinker TA in 60°C deionized water, add PVA powder, and stir at 90°C for 2 h until completely dissolved. Adjust the pH to 7.5 with a pH adjuster, then add glycerol and stir for 30 min to obtain a premix.

[0151] 3-2) adding Fe3O4@LAD particles to the premixed solution, and then adding FeCl3, and performing a cross-linking reaction at 60°C for 2 h under ultrasonic conditions (ultrasonic frequency of 30 kHz) to obtain a post-treatment solution;

[0152] 3-3) Apply the post-treatment solution (the coating amount is 120 mg / m 2 ) on the surface of the polyamide layer obtained in step 2), and drying at 80° C. for 2 min to obtain a reverse osmosis membrane.

[0153] Example 2

[0154] The difference from Example 1 is:

[0155] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 3 wt% of PVA (alcoholysis degree ≥99%), 2 wt% of cross-linking agent TA, 2 wt% of glycerol, 0.06 wt% of pH adjuster (hydrochloric acid), 1 wt% of Fe3O4@LAD particles, 0.1 wt% of FeCl3, and the balance of water.

[0156] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0157] Example 3

[0158] The difference from Example 1 is:

[0159] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 4 wt% PVA (alcoholysis degree ≥99%), 4 wt% cross-linking agent TA, 2 wt% glycerol, 0.1 wt% pH adjuster (hydrochloric acid), 5 wt% Fe3O4@LAD particles, 0.1 wt% FeCl3, and the balance water.

[0160] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0161] Comparative Example 1

[0162] The difference from Example 1 is that the post-treatment solution does not contain the cross-linking agent TA, specifically:

[0163] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% Fe3O4@LAD particles, 0.1 wt% FeCl3, and the balance water.

[0164] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0165] Comparative Example 2

[0166] The difference from Example 1 is that the post-treatment solution does not contain Fe3O4@LAD particles, specifically:

[0167] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% cross-linking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 0.1 wt% FeCl3, and the balance water;

[0168] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0169] Comparative Example 3

[0170] The difference from Example 1 is that the post-treatment solution does not contain LAD, specifically:

[0171] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% cross-linking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% Fe3O4 core, 0.1 wt% FeCl3, and the balance water;

[0172] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0173] Comparative Example 4

[0174] The difference from Example 1 is that the cross-linking agent TA is replaced by the cross-linking agent glutaraldehyde, specifically:

[0175] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% cross-linking agent glutaraldehyde, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% Fe3O4@LAD particles, 0.1 wt% FeCl3, and the balance water;

[0176] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0177] Comparative Example 5

[0178] The difference from Example 1 is that the Fe3O4@LAD particles are replaced by a mixture obtained by directly mixing Fe3O4 and LAD, specifically:

[0179] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% cross-linking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% of a mixture obtained by directly mixing Fe3O4 and LAD, 0.1 wt% FeCl3, and the balance water;

[0180] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0181] Comparative Example 6

[0182] The difference from Example 1 is that LAD is replaced by surfactant cocamidopropyl betaine (CAB), specifically:

[0183] The post-treatment solution of step 3) is prepared from raw materials; the raw materials include 2 wt% PVA (alcoholysis degree ≥99%), 1 wt% cross-linking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% Fe3O4@CAB particles, 0.1 wt% FeCl3, and the balance water;

[0184] The remaining steps were the same as in Example 1 to obtain a reverse osmosis membrane.

[0185] Performance testing:

[0186] The reverse osmosis membranes prepared in the above embodiments and comparative examples were respectively loaded into membrane tanks, and the raw aqueous solution containing Escherichia coli was run at a pressure of 1.03 MPa, a temperature of 25°C, and a membrane surface flow rate of 1.1 GPM / min for 0 h, 3 h, 12 h, and 24 h; then, deionized water was run for 15 min at a pressure of 1.03 MPa, a temperature of 25°C, and a membrane surface flow rate of 1.1 GPM / min; then, a 1500 ppm sodium chloride aqueous solution was filtered at a pressure of 1.03 MPa, a temperature of 25°C, and a membrane surface flow rate of 1.1 GPM / min, and the volume of the permeate and the concentration of sodium chloride therein were measured.

[0187] The water permeation of the reverse osmosis membrane is calculated according to formula (1):

[0188] J = Q / (A·t) (1);

[0189] In formula (1), J is the water flux, gfd; Q is the water permeation, L; A is the effective membrane area of the composite reverse osmosis membrane, m 2 ; t is time, h;

[0190] The salt rejection rate of the reverse osmosis membrane is calculated according to formula (2):

[0191] R = (Cp - Cf) / Cp × 100% Formula (2);

[0192] In formula (2), R is the desalination rate, %; Cp is the concentration of sodium chloride in the raw solution, ppm; Cf is the concentration of sodium chloride in the permeate, ppm.

[0193] The test results are shown in Table 1.

[0194] Table 1 Performance test results of reverse osmosis membranes prepared in Examples and Comparative Examples

[0195]

[0196] As can be seen from Table 1, the reverse osmosis membrane provided by the present invention has excellent water flux and desalination rate; as well as excellent anti-pollution and scour resistance and long-term synergistic antibacterial properties. In addition, the process of the present invention is consistent with that of the existing conventional reverse osmosis membrane production line, and the equipment modification is small, which is conducive to industrial production.

[0197] The above embodiments are intended only to facilitate understanding of the methods and core concepts of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that: The following steps are involved: A) soaking the base membrane in an aqueous solution, taking it out and allowing it to dry, coating the base membrane with an oil solution for interfacial polymerization, and curing it to obtain a nascent aromatic polyamide reverse osmosis membrane; B) rinsing the nascent aromatic polyamide reverse osmosis membrane; C) applying the post-treatment solution to the surface of the polyamide layer obtained in step B), and drying the polyamide layer to obtain a reverse osmosis membrane; The post-treatment solution is prepared from raw materials; the raw materials include 1 wt% to 4 wt% of polyvinyl alcohol, 0.1 wt% to 5 wt% of a cross-linking agent, 0.5 wt% to 2 wt% of glycerol, 0.02 wt% to 0.2 wt% of a pH regulator, 1 wt% to 5 wt% of Fe3O4@LAD particles, 0.08 wt% to 0.12 wt% of FeCl3, and the balance of water; The Fe3O4@LAD particles include an Fe3O4 core and a lauramidopropyl betaine coating layer formed on the outer surface of the Fe3O4 core.

2. The preparation method according to claim 1, characterized in that The preparation method of the post-treatment solution comprises the following steps: a) dissolving polyvinyl alcohol powder in an aqueous solution of a crosslinking agent, adjusting the pH to 7-8 with a pH adjuster, and then stirring and mixing with glycerol to obtain a premixed solution; b) mixing the premixed solution, Fe3O4@LAD particles and FeCl3, and performing a cross-linking reaction under ultrasonic conditions to obtain a post-treatment solution.

3. The preparation method according to claim 2, characterized in that The cross-linking agent is tannic acid.

4. The preparation method according to claim 1, characterized in that The preparation method of the Fe3O4@LAD particles comprises the following steps: An aqueous solution of lauramidopropyl betaine was mixed with the Fe3O4 cores, ultrasonically mixed, and placed in a magnetic field. After the particles were adsorbed to the container wall, the supernatant was poured out, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. Ultrasonic dispersion was performed, and the adsorption and washing steps under the magnetic field were repeated until the pH value of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

5. The preparation method according to claim 1, characterized in that The preparation method of the Fe3O4 core comprises the following steps: FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water. Under nitrogen protection, ammonia water was added dropwise until the pH value was 9-11, and then reacted to obtain Fe3O4 core. The molar ratio of FeCl3·6H2O to FeSO4·7H2O is 1.8-2.2:0.8-1.2; The reaction temperature is 55-65°C and the reaction time is 0.5-1.5 h.

6. The preparation method according to claim 1, characterized in that The aqueous phase solution is obtained by adjusting the pH value of the aqueous phase base liquid to 7-9; The aqueous base liquid includes 0.5 wt% to 5 wt% of a multifunctional amine, 0.05 wt% to 2 wt% of a surfactant, 3 wt% to 10 wt% of a polar solvent, and the balance is water; The polyfunctional amine includes at least one of an aromatic amine, an aliphatic amine and an alicyclic amine; The surfactant includes sodium dodecyl sulfate or sodium lauryl sulfate; The polar solvent includes dimethyl sulfoxide and / or N-methylpyrrolidone.

7. The preparation method according to claim 1, characterized in that The oil phase solution comprises an acyl halide and an oil phase solvent; In the oil phase solution, the mass content of the acyl halide is 0.05% to 0.3%; The acyl halide includes trimesoyl chloride; The oil phase solvent includes at least one of n-hexane, Isopar G and Isopar L.

8. The preparation method according to claim 1, characterized in that The rinsing comprises: rinsing the nascent aromatic polyamide reverse osmosis membrane sequentially with deionized water, citric acid aqueous solution, deionized water, isopropyl alcohol aqueous solution, deionized water, and glycerol aqueous solution.

9. The preparation method according to claim 8, characterized in that The deionized water rinsing temperature is 15-30°C and the time is 1-5 minutes; The mass concentration of the citric acid aqueous solution is 1% to 5%; the rinsing temperature of the citric acid aqueous solution is 40 to 80°C, and the rinsing time is 1 to 5 minutes; The mass concentration of the isopropyl alcohol aqueous solution is 1% to 10%; the rinsing temperature of the isopropyl alcohol aqueous solution is 40 to 80°C, and the rinsing time is 1 to 5 minutes; The mass concentration of the glycerol aqueous solution is 2% to 6%; the rinsing temperature of the glycerol aqueous solution is 15 to 30° C., and the rinsing time is 1 to 5 minutes.

10. The reverse osmosis membrane obtained by the preparation method according to any one of claims 1 to 9.

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