A reverse osmosis membrane and its preparation method

Abstract

This invention relates to the field of water treatment membrane technology, and more particularly to a reverse osmosis membrane and its preparation method. The invention provides a method for preparing a reverse osmosis membrane, comprising the following steps: A) immersing a base membrane in an aqueous solution, removing it and allowing it to dry slightly, then coating the base membrane with an oil-phase solution for interfacial polymerization, followed by curing to obtain a nascent aromatic polyamide reverse osmosis membrane; B) rinsing the nascent aromatic polyamide reverse osmosis membrane; C) applying a post-treatment solution of specific components to the surface of the polyamide layer obtained in step B), and drying it to obtain the reverse osmosis membrane. The reverse osmosis membrane prepared by this invention can form a PVA-TA-Fe3O4 ternary synergistic system, significantly improving mechanical strength, enhancing antifouling and erosion resistance, improving oxidation resistance, and preventing the loss of Fe3O4 nanoparticles. Experimental results show that the reverse osmosis membrane prepared by this invention has excellent water flux, desalination rate, and excellent antifouling and erosion resistance.

Description

Technical Field

[0001] This invention relates to the field of water treatment membrane technology, and in particular to a reverse osmosis membrane and its preparation method. Background Technology

[0002] Reverse osmosis membranes have become the mainstream membrane-based water treatment technology, but antifouling performance remains a significant factor restricting the development of reverse osmosis technology. Membrane fouling leads to a rapid decline 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, as a carbon nanomaterial, is widely used in various fields due to its excellent chemical properties, high hydrophilicity, and good dispersibility; silver nanomaterials are widely used in antibacterial membranes due to their excellent antibacterial properties. Nanomaterials possess unique properties different from ordinary bulk materials due to their small size effect, surface effect, quantum size effect, and macroscopic quantum tunneling effect. Because of their high surface free energy, they spontaneously aggregate, losing their inherent superior nanomaterial properties. Furthermore, during the preparation of reverse osmosis membranes, the aggregation of nanomaterials can severely affect the integrity of the membrane product, reducing product quality.

[0003] Conventional reverse osmosis membranes typically consist of a polysulfone nonwoven composite base membrane, a polyamide separation layer (PA layer), and a polyvinyl alcohol (PVA) antifouling layer. Some existing technologies incorporate inorganic nanomaterials into the polyamide separation layer of the reverse osmosis membrane. However, the high surface energy of these inorganic nanomaterials leads to poor compatibility with the organic polymers in the separation layer. Furthermore, the aggregation effect of the nanomaterials results in large voids at the interface, creating defects and significantly reducing the membrane's rejection rate. Other existing technologies incorporate inorganic nanomaterials into the PVA antifouling layer. However, conventional antifouling layers exhibit weak adhesion to the reverse osmosis membrane surface, low mechanical strength, and poor erosion resistance. Consequently, the antifouling layer gradually detaches during operation, causing the membrane to gradually lose its antifouling properties. Therefore, the preparation process of nanomaterial-modified reverse osmosis membranes faces many challenges in scale-up production, making it difficult to obtain stable products.

[0004] Fe3O4 nanoparticles can generate localized 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 inhibit biofouling and extend membrane life by catalyzing the generation of reactive oxygen species (ROS) or directly destroying bacterial cell membranes. The surface of Fe3O4 is rich in hydroxyl groups, which can enhance the hydrophilicity of PVA coatings and improve antifouling properties. However, Fe3O4 has the risk of oxidation and can only exist stably for a few months in conventional PVA matrix.

[0005] Existing technology uses SiO2 to form Fe3O4@SiO2 to prevent its oxidation. However, the SiO2 shell formed during the coating process is thicker, which leads to a decrease in the magnetic properties of Fe3O4, a weaker interface between PVA and SiO2, and a greater likelihood of nanoparticle sedimentation during the preparation process. All of these factors affect the stability of the film 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 method for preparing the same, wherein the prepared reverse osmosis membrane has excellent water flux, desalination rate and antifouling and erosion resistance.

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

[0008] A) The base membrane is immersed in an aqueous solution, removed and dried, and then coated with an oil solution to carry out an interfacial polymerization reaction. After curing, a nascent aromatic polyamide reverse osmosis membrane is obtained.

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

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

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

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

[0013] Preferably, the method for preparing the post-treatment solution includes the following steps:

[0014] a) Dissolve polyvinyl alcohol powder in an aqueous solution of a crosslinking agent, adjust the pH to 7-8 using a pH adjuster, and then mix with glycerin to obtain a premixed solution;

[0015] b) The premixed solution, Fe3O4@LAD particles and FeCl3 are mixed and subjected to a cross-linking reaction under ultrasonic conditions to obtain a post-treatment solution.

[0016] Preferably, the crosslinking agent is tannic acid.

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

[0018] The lauramidopropyl betaine aqueous solution was mixed with the Fe3O4 core and ultrasonically mixed. Then, the mixture was placed under a magnetic field. After the particles were adsorbed onto the container wall, the supernatant was poured off, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. The particles were then ultrasonically dispersed. The adsorption and washing steps under the aforementioned magnetic field were repeated until the pH of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

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

[0020] FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water, and ammonia was added dropwise under nitrogen protection until the pH value was 9-11, and then the reaction was carried out 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 is carried out at a temperature of 55-65°C for a time of 0.5-1.5 h.

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

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

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

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

[0027] The polar solvents include dimethyl sulfoxide and / or N-methylpyrrolidone.

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

[0029] The oil phase solution contains 0.05% to 0.3% by mass.

[0030] The acyl halide includes pyromellitic acid chloride;

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

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

[0033] Preferably, the temperature of the deionized water rinsing is 15~30℃ and the time is 1~5 min.

[0034] The citric acid aqueous solution has a mass concentration of 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 isopropanol aqueous solution is 1%~10%; the rinsing temperature of the isopropanol aqueous solution is 40~80℃, and the time is 1~5 min;

[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 preparation method described above.

[0038] The reverse osmosis membrane prepared by this invention can form a PVA-TA-Fe3O4 ternary synergistic system, which significantly improves mechanical strength, enhances antifouling and erosion resistance, improves antioxidant performance, and prevents the loss of Fe3O4 nanoparticles. This synergistic system combines the chemical switching of LAD with the physical driving force of Fe3O4, and works in conjunction with TA to achieve dynamic antifouling, static protection, intelligent triggered release, and in-situ cleaning of contaminants in the reverse osmosis membrane, significantly improving the membrane's antifouling ability, self-cleaning efficiency, and lifespan.

[0039] Experimental results show that the reverse osmosis membrane prepared by this invention has excellent water flux, desalination rate and excellent antifouling and erosion resistance. Moreover, the process of this invention is consistent with that of existing conventional reverse osmosis membrane production lines, with minimal equipment modification, which is conducive to industrial production. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

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

[0042] A) The base membrane is immersed in an aqueous solution, removed and dried, and then coated with an oil solution to carry out an interfacial polymerization reaction. After curing, a nascent aromatic polyamide reverse osmosis membrane is obtained.

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

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

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

[0046] The Fe3O4@LAD particles comprise 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, removed and dried, and then coated with an oil solution for interfacial polymerization. After curing, a nascent aromatic polyamide reverse osmosis membrane is obtained.

[0049] In some embodiments of the present invention, the method for preparing the base film includes the following steps:

[0050] The casting solution is coated onto a nonwoven fabric, and then cured into a film through phase inversion to obtain the base film;

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

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

[0053] The phase transformation method can be soaking in deionized water.

[0054] After the film is cured, the process also includes rinsing, annealing, and removing excess moisture from the surface using an absorbent plate.

[0055] The rinsing process uses RO water.

[0056] The annealing temperature is 40~60℃, for example 50℃; the time is 1~5 min, for example 3 min.

[0057] In some embodiments of the present invention, the aqueous solution is obtained by adjusting the pH of the aqueous base solution to 7-9, specifically, the pH is 7.8. The aqueous base solution comprises 0.5 wt%-5 wt% of a polyfunctional amine, 0.05 wt%-2 wt% of a surfactant, 3 wt%-10 wt% of a polar solvent, and the balance being water. Specifically, in the aqueous base solution, the mass content of the polyfunctional 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 pH adjustment is an alkaline reagent, such as sodium hydroxide. The present invention does not impose any special limitations on the preparation method of the aqueous base solution. In some embodiments of the present invention, the preparation method of the aqueous base solution includes the following steps: mixing the polyfunctional amine, surfactant, aqueous solvent, and water to obtain the aqueous base solution. 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, mesonemine, piperazine, and 4-aminomethylpiperazine.

[0059] The surfactant is selected from sodium dodecyl sulfonate 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 hydrochloric acid molecules, a byproduct of the interfacial polymerization process, and to the formation of highly cross-linked polyamides. If the pH value is too low or too high, the amide bonds are prone to hydrolysis, which affects the separation performance of the polyamide separation layer.

[0063] In this invention, the base membrane is immersed in an aqueous solution, and after being removed and dried, an oil solution is coated on the base membrane to carry out an interfacial polymerization reaction. After curing, a nascent aromatic polyamide reverse osmosis membrane is obtained.

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

[0065] The present invention does not impose any special limitations on the surface drying method; any surface drying method well known to those skilled in the art can be used.

[0066] In some embodiments of the present invention, the oil phase solution comprises an acyl halide and an oil phase solvent. The mass content of the acyl halide in the oil phase solution is 0.05% to 0.3%, for example, 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] This invention does not impose any particular limitations on the preparation method of the oil phase solution. In some embodiments of this invention, the preparation method of the oil phase solution includes the following steps: mixing an acyl halide and an oil phase solvent to obtain an oil phase solution. The mixing is carried out at room temperature.

[0070] This invention does not impose any particular limitation on the coating amount of the oil phase solution; generally, over-coating is permitted. In some embodiments of this invention, the coating amount of the oil phase solution is 50~200 mg / m³. 2 For example, 100 mg / m 2 .

[0071] In some embodiments of the present invention, the drying temperature is 55~65°C, for example 60°C; and the drying time is 2~4 min, for example 3 min.

[0072] Regarding step B):

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

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

[0075] The temperature of the deionized water rinsing is 15~30℃, for example 20℃; the time is 1~5 min, for example 2 min.

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

[0077] The mass concentration of the isopropanol aqueous solution is 1% to 10%, for example, 3%. The rinsing temperature of the isopropanol aqueous solution is 40 to 80°C, for example, 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, for example, 25°C; and the rinsing time is 1 to 5 minutes, for example, 5 minutes.

[0079] Regarding step C):

[0080] The post-treatment solution is applied to the surface of the polyamide layer obtained in step B), and after drying, a reverse osmosis membrane is obtained.

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

[0082] The Fe3O4@LAD particles comprise 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 a co-precipitation method. The preparation method of the Fe3O4 core includes the following steps:

[0084] FeCl3·6H2O and FeSO4·7H2O were dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise until the pH value was 9-11, and the reaction was carried out to obtain 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%, for example, 26%.

[0087] Specifically, add ammonia water until the pH value reaches 10.

[0088] The reaction is carried out at a temperature of 55-65°C, for example, 60°C, for a time of 0.5-1.5 h, for example, 1 h.

[0089] In some embodiments of the present invention, the preparation method of the Fe3O4@LAD particles includes the following steps:

[0090] A lauramidopropyl betaine (LAD) aqueous solution was mixed with Fe3O4 cores and ultrasonically mixed. Then, the mixture was placed under a magnetic field. The particles were adsorbed onto the container wall within a few seconds. The supernatant was then poured off, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. The particles were then ultrasonically dispersed. The adsorption and washing steps under the aforementioned magnetic field conditions were repeated until the pH of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

[0091] The LAD is an amphoteric surfactant. By coating Fe3O4 with LAD, stable dispersion and functional coupling of nanoparticles 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 conditions are: 0.3T ≤ magnetic field strength ≤ 1T. Too low a value (<0.1T) will lead to incomplete separation, while too high a value (>1T) may cause particle magnetization and agglomeration.

[0095] The poured supernatant contained unreacted Fe. 2+ / Fe 3+ Ammonia, etc.

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

[0097] The drying process is vacuum drying; the drying temperature is 55~65℃, for example, 60℃.

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

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

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

[0101] In this invention, FeCl3 is used as an oxidative crosslinking catalyst.

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

[0103] In some embodiments of the present invention, the raw materials contain PVA at 2 wt%, 3 wt%, and 4 wt%; crosslinking agent at 1 wt%, 2 wt%, and 4 wt%; glycerol at 1 wt% and 2 wt%; pH adjuster at 0.08 wt%, 0.06 wt%, and 0.1 wt%; Fe3O4@LAD particles at 3 wt%, 1 wt%, and 5 wt%; and FeCl3 at 0.1 wt%.

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

[0105] a) Dissolve polyvinyl alcohol (PVA) powder in an aqueous solution of a crosslinking agent, adjust the pH to 7-8 using a pH adjuster, and then mix with glycerin to obtain a premixed solution;

[0106] b) The premixed solution, Fe3O4@LAD particles and FeCl3 are mixed and subjected to 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 aqueous solution of the crosslinking agent at a temperature of 85~95℃, for example, 90℃. The dissolution is performed by stirring. The dissolution time is 1.5~2.5 h, for example, 2 h.

[0110] In this invention, a pH adjuster is used to adjust the pH value to 7-8, such as 7.5, which can prevent the crosslinking agent from being over-oxidized.

[0111] The mixing time with glycerin is 25-35 minutes, for example, 30 minutes.

[0112] In this invention, glycerol is added after TA crosslinking, which can avoid interfering with TA-PVA bonding. The small molecular structure of glycerol (containing 3 hydroxyl groups) can be inserted into the PVA-TA crosslinking network, which can 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 crosslinking of TA-PVA.

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

[0116] The cross-linking reaction is carried out at a temperature of 50~70℃, for example 60℃, and for a time of 1.5~2.5 h, for example 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 after drying, a reverse osmosis membrane is obtained.

[0119] In some embodiments of the present invention, the application rate of the post-treatment solution is 50~200 mg / m³. 2 For example, 120mg / m 2 The contact time between the post-treatment solution and the surface of the polyamide layer is 2-4 seconds, for example, 3 seconds.

[0120] After the application is completed, the process also includes removing excess solution.

[0121] The drying temperature is 75~85℃, for example 80℃; the drying time is 1.5~2.5 min, for example 2 min.

[0122] This invention also provides a reverse osmosis membrane prepared by the method described above. The reverse osmosis membrane provided by this invention immobilizes Fe3O4@LAD nanocomposite material through a tannic acid (TA)-polyvinyl alcohol (PVA) crosslinking network.

[0123] The reverse osmosis membrane provided by this invention has Fe3O4 nanoparticles doped in the PVA layer, which has a better retention rate than the prior art that does not dop in the polyamide (PA) separation layer.

[0124] The reverse osmosis membrane provided by this invention can form a three-dimensional PVA-TA-Fe3O4 network, which greatly improves mechanical strength and makes it 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 interparticle van der Waals forces and preventing aggregation. Under neutral or alkaline conditions, LAD carries a negative charge (ionization of the betaine group), generating electrostatic repulsion with the Fe3O4 surface charge (pH-dependent), further improving dispersibility. The TA chelating layer prevents Fe3O4 aggregation, enhancing uniform distribution within the PVA matrix. Furthermore, organic matter adsorbed on the membrane surface (such as humic acid) can be slowly oxidized by TA.

[0126] LAD (Liquid Acid) forms dynamic micelles, achieving efficient solubilization of hydrophobic pollutants through a hydrophobic encapsulation-hydrophilic shielding mechanism, creating "pseudo-water-soluble" complexes that are then washed away from the membrane surface by water flow. Both LAD and Fe3O4 can enhance the hydrophilicity of PVA and improve its antifouling ability. LAD can also be used for the antioxidant protection of Fe3O4 particles.

[0127] The Fe3O4 particles used in this invention also have antioxidant and antibacterial effects.

[0128] The reverse osmosis membrane provided by this invention has magnetically responsive dynamic antifouling capability, pH-responsive self-cleaning function, and long-lasting synergistic antibacterial properties.

[0129] This invention utilizes a LAD coating process, which is simpler than the SiO2 coating process, compatible with existing reverse osmosis membrane production lines (coating-crosslinking-film formation), and offers controllable material costs (both LAD and Fe3O4 are commercially available products), reducing costs by approximately 20% and making it suitable for industrial production. Furthermore, the synergistic antioxidant properties of TA and PVA in this invention significantly extend stability.

[0130] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0131] To further illustrate the present invention, the following detailed description of a reverse osmosis membrane and its preparation method provided by the present invention is provided in conjunction with embodiments, but it 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 base film is as follows:

[0134] 1) Preparation of casting solution: 84 parts by weight of N,N-dimethylformamide and 16 parts by weight of polysulfone were mixed and stirred at 75°C until dissolved. After standing for 12 hours to remove bubbles, a uniform and transparent casting solution was obtained.

[0135] 2) Coat the casting solution onto the nonwoven fabric at a coating amount of 30 g / m². 2 The film is solidified by phase conversion after being soaked in deionized water, rinsed with RO water, annealed at 50℃ for 3 min, and excess water is removed from the surface by a water-absorbing plate to obtain the base film.

[0136] 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 until the pH value was 10. The reaction was carried out at 60°C for 1 h to obtain Fe3O4 core.

[0138] Preparation of Fe3O4@LAD particles:

[0139] A 1% LAD aqueous solution was mixed with a Fe3O4 core at a mass ratio of 1:3. After ultrasonic mixing for 1 h, the mixture was placed under a magnetic field (0.3T ≤ magnetic field strength ≤ 1T). The particles were adsorbed onto the container wall within seconds. The supernatant was then poured off, the magnetic field was removed, and deionized water was added to wash the particles. The particles were then ultrasonically dispersed for 7 min. The adsorption and washing steps under the aforementioned 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 comprise a Fe3O4 core and an LAD coating layer formed on the outer surface of the Fe3O4 core.

[0140] Example 1

[0141] 1) Coat the base membrane with an aqueous solution (coating amount: 100 mg / m²). 2 Then coat with an oil phase solution (coating amount 100 mg / m³). 2 After drying at 60℃ for 3 min, a nascent aromatic polyamide reverse osmosis membrane was obtained.

[0142] Preparation of aqueous solutions:

[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; in the aqueous base liquid, the mass content of the polyfunctional amine is 2.5%, the mass content of the surfactant is 0.1%, and the mass content of the aqueous solvent is 7%.

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

[0145] Preparation of oil phase solution:

[0146] An acyl halide (pyromellitic trimethylolpropionate chloride) and an 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) The nascent aromatic polyamide reverse osmosis membrane is rinsed, including: first rinsing with 20℃ deionized water for 2 min, then rinsing with 60℃ citric acid aqueous solution (mass concentration of 3%) for 5 min, then rinsing with 20℃ deionized water for 2 min, then rinsing with 60℃ isopropanol aqueous solution (mass concentration of 3%) for 5 min, then rinsing with 20℃ deionized water for 2 min, and finally rinsing with 25℃ glycerol aqueous solution (concentration of 3wt%) for 5 min.

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

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

[0150] 3-1) Dissolve the crosslinking agent TA in deionized water at 60℃, add PVA powder, stir at 90℃ for 2 h until completely dissolved, adjust the pH to 7.5 with a pH adjuster, add glycerol, stir and mix for 30 min to obtain a premixed solution;

[0151] 3-2) Add Fe3O4@LAD particles to the premixed solution, then add FeCl3, and after crosslinking reaction at 60℃ for 2 h under ultrasonic conditions (ultrasonic frequency of 30kHz), the post-treatment solution is obtained.

[0152] 3-3) Apply the post-treatment solution (application amount: 120 mg / m²). 2 The polyamide layer obtained in step 2) is dried at 80°C for 2 min to obtain a reverse osmosis membrane.

[0153] Example 2

[0154] The difference from Example 1 is as follows:

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

[0156] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[0157] Example 3

[0158] The difference from Example 1 is as follows:

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

[0160] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

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

[0164] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[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 in step 3) is prepared from the raw materials; the raw materials include 2 wt% PVA (degree of alcoholysis ≥99%), 1 wt% crosslinking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 0.1 wt% FeCl3, and the balance being water;

[0168] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[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 in step 3) is prepared from the raw materials; the raw materials include 2 wt% PVA (degree of alcoholysis ≥99%), 1 wt% crosslinking agent TA, 1 wt% glycerol, 0.08 wt% pH adjuster (hydrochloric acid), 3 wt% Fe3O4 core, 0.1 wt% FeCl3, and the balance being water;

[0172] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[0173] Comparative Example 4

[0174] The difference from Example 1 is that the crosslinking agent TA is replaced with the crosslinking agent glutaraldehyde, specifically:

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

[0176] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[0177] Comparative Example 5

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

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

[0180] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[0181] Comparative Example 6

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

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

[0184] The remaining steps are the same as in Example 1, and a reverse osmosis membrane is obtained.

[0185] Performance testing:

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

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

[0188] J = Q / (A·t) Equation (1);

[0189] In equation (1), J is the water flux (gfd); Q is the water permeation rate (L); and A is the effective membrane area of ​​the composite reverse osmosis membrane (m²). 2 t represents time, h;

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

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

[0192] In equation (2), R is the desalination rate (%), Cp is the concentration of sodium chloride in the original solution (ppm), and 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 the reverse osmosis membranes prepared in the 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 antifouling and erosion resistance and long-lasting synergistic antibacterial properties. Moreover, the process of the present invention is consistent with that of existing conventional reverse osmosis membrane production lines, with minimal equipment modification, which is conducive to industrial production.

[0197] The descriptions of the above embodiments are merely illustrative of the methods and core ideas 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 invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, Includes the following steps: A) The base membrane is immersed in an aqueous solution, removed and dried, and then coated with an oil solution to carry out an interfacial polymerization reaction. After curing, a nascent aromatic polyamide reverse osmosis membrane is obtained. B) Rinse the nascent aromatic polyamide reverse osmosis membrane; C) Apply the post-treatment solution to the surface of the polyamide layer obtained in step B), and after drying, obtain a reverse osmosis membrane; The post-treatment solution is prepared from the raw materials; the raw materials include 1 wt%~4 wt% polyvinyl alcohol, 0.1 wt%~5 wt% crosslinking agent, 0.5 wt%~2 wt% glycerol, 0.02 wt%~0.2 wt% pH adjuster, 1 wt%~5 wt% Fe3O4@LAD particles, 0.08 wt%~0.12 wt% FeCl3, and the balance being water; The crosslinking agent is tannic acid; The Fe3O4@LAD particles comprise a 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 method for preparing the post-treatment solution includes the following steps: a) Dissolve polyvinyl alcohol powder in an aqueous solution of a crosslinking agent, adjust the pH to 7-8 using a pH adjuster, and then mix with glycerin to obtain a premixed solution; b) The premixed solution, Fe3O4@LAD particles and FeCl3 are mixed and subjected to a cross-linking reaction under ultrasonic conditions to obtain a post-treatment solution.

3. The preparation method according to claim 1, characterized in that, The preparation method of the Fe3O4@LAD particles includes the following steps: The lauramidopropyl betaine aqueous solution was mixed with the Fe3O4 core and ultrasonically mixed. Then, the mixture was placed under a magnetic field. After the particles were adsorbed onto the container wall, the supernatant was poured off, the magnetic field was removed, and deionized water and / or ethanol were added to the particles for washing. The particles were then ultrasonically dispersed. The adsorption and washing steps under the aforementioned magnetic field were repeated until the pH of the supernatant was neutral. After drying, pure Fe3O4@LAD particles were obtained.

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

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

6. The preparation method according to claim 1, characterized in that, The oil phase solution comprises an acyl halide and an oil phase solvent; The oil phase solution contains 0.05% to 0.3% by mass. The acyl halide includes pyromellitic acid chloride; The oil phase solvent includes at least one of n-hexane, Isopar G, and Isopar L.

7. The preparation method according to claim 1, characterized in that, The rinsing process includes rinsing the nascent aromatic polyamide reverse osmosis membrane sequentially with deionized water, citric acid aqueous solution, deionized water, isopropanol aqueous solution, deionized water, and glycerol aqueous solution.

8. The preparation method according to claim 7, characterized in that, The temperature of the deionized water rinsing is 15~30℃ and the time is 1~5 min. The citric acid aqueous solution has a mass concentration of 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 isopropanol aqueous solution is 1%~10%; the rinsing temperature of the isopropanol aqueous solution is 40~80℃, and the time is 1~5 min; 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.

9. The reverse osmosis membrane prepared by the preparation method according to any one of claims 1 to 8.

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