High-flux anti-pollution composite reverse osmosis membrane and preparation method thereof

Abstract

The invention discloses a high-flux anti-pollution composite reverse osmosis membrane and a preparation method thereof, and relates to the technical field of water treatment membranes. The composite material comprises a porous support layer, an in-situ mineralized polyamide separation layer and a metal-polyphenol gradient functional layer. The in-situ mineralized polyamide separation layer is formed by carrying out interfacial polymerization reaction on a m-phenylenediamine aqueous phase solution and a trimesoyl chloride organic phase solution containing ammonium hexafluorosilicate, and fluosilicate nano-clusters are generated through in-situ hydrolysis; the metal-polyphenol gradient functional layer is formed by sequentially assembling and competitively coordinating a zirconium source solution and polyphenol solutions with different sodium citrate concentrations. According to the invention, the internal nano-clusters construct a water molecule transmission channel, the balance of anti-pollution performance and water mass transfer resistance is realized through the surface gradient functional layer, the obtained composite membrane has high flux and excellent anti-pollution performance, the preparation method is simple and controllable, and the composite membrane has a good industrial application prospect.

Description

A high-flux, fouling-resistant composite reverse osmosis membrane and its preparation method Technical Field

[0001] This invention relates to the field of water treatment membrane technology, specifically to a high-flux, fouling-resistant composite reverse osmosis membrane and its preparation method. Background Technology

[0002] Reverse osmosis membrane separation technology, with its advantages of high desalination performance, compact device structure, low operating energy consumption, and simple operation and maintenance, has been widely used in various water treatment fields such as seawater desalination, brackish water desalination, industrial wastewater treatment and reuse, and ultrapure water preparation. With the increasing severity of global water scarcity and continuously tightening emission standards, the market demand for reverse osmosis membrane technology continues to grow, placing higher demands on the separation performance, permeate flux, and long-term operational stability of membrane materials.

[0003] Polyamide composite reverse osmosis membranes are currently the most widely used type of reverse osmosis membrane, typically consisting of a polysulfone porous support layer and an aromatic polyamide separation layer formed through interfacial polymerization. This structural design gives the membrane both good mechanical strength and excellent desalination performance. However, polyamide composite reverse osmosis membranes still face two core constraints in practical applications: first, membrane fouling, where organic matter, colloids, microorganisms, and other contaminants in the feed solution are easily adsorbed and deposited on the membrane surface, leading to decreased membrane flux, increased operating pressure, and increased cleaning frequency, and in severe cases, irreversible degradation of membrane performance and shortened service life; second, the trade-off between permeability and selectivity, where increasing membrane flux often comes at the cost of sacrificing desalination rate, limiting further improvements in membrane performance and reductions in operating costs.

[0004] To address the aforementioned issues, one technical approach is to introduce nanomaterials into the polyamide separation layer to construct an organic-inorganic hybrid structure. Patent CN110026094B discloses a method for preparing an in-situ silica / polyamide reverse osmosis nanocomposite membrane. This method involves adding 3-aminopropyltriethoxysilane (APTES) to the organic phase, utilizing the acidic environment generated during the interfacial polymerization reaction to promote the hydrolysis of APTES and generate silica nanoparticles. However, the degree of APTES hydrolysis and the distribution of silica formation in this method are significantly affected by the local acid concentration. The size and dispersion uniformity of the nanoparticles are difficult to control, and the amino groups of APTES may participate in the polyamide crosslinking reaction, affecting the network structure of the separation layer.

[0005] Another technical approach is to construct a hydrophilic coating or graft layer on the polyamide membrane surface to improve the membrane's hydrophilicity and antifouling ability. Patent CN118767712A discloses a high-flux, antifouling polyamide composite reverse osmosis membrane, which uses small-molecule polyols grafted onto the polyamide membrane surface via esterification. However, ester bonds are prone to hydrolysis during long-term operation, leading to the gradual detachment of the functional layer, and the durability of the modification effect needs improvement. Patent CN107243262B uses terminal amino- and polyhydroxy small-molecule compounds to react with residual acyl chloride groups on the polyamide surface for graft modification. This method depends on the number and distribution of unreacted acyl chloride groups on the membrane surface, and since acyl chloride groups are easily hydrolyzed, the content of active groups on the surface of different batches of membranes varies significantly, affecting the reproducibility of the modification effect. Patent CN114618313B constructs a hydrophilic framework layer with a two-dimensional or three-dimensional pore structure between the reverse osmosis base membrane and the antifouling coating to reduce flux loss caused by the antifouling coating. However, the preparation cycle of hydrophilic framework materials (such as hydrophilic hydrogen-bonded organic frameworks) is long and the synthesis conditions are harsh, which is not conducive to large-scale production.

[0006] Furthermore, in existing surface modification technologies, whether physical coating or chemical grafting, the constructed functional layers are mostly homogeneous structures with a density and thickness that are essentially uniform across the entire membrane surface. While this homogeneous structure provides antifouling protection, it often increases the mass transfer resistance of water molecules through the membrane surface, making it difficult to simultaneously achieve high flux and excellent antifouling performance. Some studies have attempted to balance these two factors by controlling the thickness of the modified layer, but the fundamental nature of the homogeneous structure remains unchanged, limiting the potential for performance improvement.

[0007] In summary, existing reverse osmosis membrane modification technologies still have room for improvement in terms of the controllability of nanomaterial dispersion, the stability of functional layer bonding, and the synergistic achievement of antifouling and high throughput. There is an urgent need to develop a composite reverse osmosis membrane with a simple preparation process, controllable functional layer structure, and both high throughput and excellent antifouling performance, as well as its preparation method. Summary of the Invention

[0008] The purpose of this invention is to provide a high-flux, antifouling composite reverse osmosis membrane and its preparation method, aiming to improve the shortcomings of existing reverse osmosis membranes in terms of the balance between functional layer stability, permeation flux and antifouling performance.

[0009] In a first aspect, the present invention provides a high-flux, antifouling composite reverse osmosis membrane, comprising a porous support layer, an in-situ mineralized polyamide separation layer, and a metal-polyphenol gradient functional layer arranged sequentially. The in-situ mineralized polyamide separation layer is formed by contacting the porous support layer with an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate, followed by interfacial polymerization. The metal-polyphenol gradient functional layer is formed by sequentially assembling and competitively coordinating the porous support layer loaded with the in-situ mineralized polyamide separation layer with a zirconium source solution and polyphenol solutions of different sodium citrate concentrations.

[0010] As a preferred embodiment of the present invention, the porous support layer is one of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, or a polyacrylonitrile ultrafiltration membrane, with a molecular weight cutoff of 50-150 kDa.

[0011] As a preferred embodiment of the present invention, in the aqueous solution of m-phenylenediamine, the mass concentration of m-phenylenediamine is 2-4%, the mass concentration of camphor sulfonic acid is 2.5-4.5%, the mass concentration of triethylamine is 1-2.5%, and the solvent is deionized water.

[0012] As a preferred embodiment of the present invention, in the aqueous solution of m-phenylenediamine, the mass ratio of m-phenylenediamine to camphor sulfonic acid is 1:(0.8-1.5), and camphor sulfonic acid is used as an aqueous additive to adjust the adsorption uniformity of m-phenylenediamine on the surface of the support layer.

[0013] As a preferred embodiment of the present invention, in the aqueous solution of m-phenylenediamine, the mass ratio of m-phenylenediamine to triethylamine is (2-3):1, and the triethylamine is used to neutralize the hydrogen chloride generated during the interfacial polymerization reaction.

[0014] As a preferred embodiment of the present invention, the aqueous solution of m-phenylenediamine further contains sodium dodecyl sulfate with a mass concentration of 0.05-0.2%, which is used to reduce the surface tension of the aqueous solution and promote the uniform spreading of m-phenylenediamine on the surface of the support layer.

[0015] As a preferred embodiment of the present invention, the aqueous solution of m-phenylenediamine further contains N-methylpyrrolidone with a mass concentration of 0.5-2%, which is used to adjust the solubility and diffusion rate of m-phenylenediamine in the aqueous phase.

[0016] As a preferred embodiment of the present invention, the pH value of the m-phenylenediamine aqueous solution is 9-10.5, which is controlled by adjusting the amount of triethylamine added.

[0017] As a preferred technical solution of the present invention, the preparation method of the m-phenylenediamine aqueous solution is as follows: camphor sulfonic acid is dissolved in deionized water, triethylamine is added to adjust the pH value, then m-phenylenediamine is added and stirred to dissolve, and finally dimethyl sulfoxide is added. The mixture is stirred at 20-30°C for 10-30 minutes, and then allowed to stand to remove bubbles before use.

[0018] As a preferred embodiment of the present invention, the aqueous solution of m-phenylenediamine further contains polyethylene glycol 400 with a mass concentration of 0.1-0.5%, which is used to regulate the interfacial polymerization reaction rate and the microstructure of the polyamide layer.

[0019] As a preferred embodiment of the present invention, the m-phenylenediamine aqueous solution needs to be kept at a constant temperature of 25℃±2℃ for more than 30 minutes before it comes into contact with the support layer, so as to ensure that the solution temperature is uniform.

[0020] As a preferred embodiment of the present invention, the molar ratio of camphor sulfonic acid to triethylamine in the m-phenylenediamine aqueous solution is 1:(1.1-1.5), so that the camphor sulfonic acid exists in the form of salt, thereby enhancing its adsorption capacity on the surface of the support layer.

[0021] As a preferred embodiment of the present invention, the mass concentration of dimethyl sulfoxide in the aqueous solution of m-phenylenediamine is 0.2-0.8%, which is used to improve the solubility of m-phenylenediamine in the aqueous phase and improve the crosslinking structure of the polyamide layer.

[0022] As a preferred technical solution of the present invention, the aqueous solution of m-phenylenediamine should be used within 4 hours after preparation to avoid the m-phenylenediamine being oxidized by air, which would cause the solution color to darken.

[0023] As a preferred embodiment of the present invention, in the pyromellitic tricarboxylate organic phase solution, the mass concentration of pyromellitic tricarboxylate is 0.1-0.25%, the mass concentration of ammonium hexafluorosilicate is 0.05-0.3%, and the solvent is one of the isoparaffin solvents Isopar G, n-heptane, or n-hexane.

[0024] As a preferred embodiment of the present invention, in the pyromellitic trimethylol chloride organic phase solution, the mass ratio of pyromellitic trimethylol chloride to ammonium hexafluorosilicate is 1:(0.5-1.5).

[0025] As a preferred embodiment of the present invention, the pyromellitic methyl chloride organic phase solution further contains tributyl phosphate with a mass concentration of 0.01-0.1%, which is used to suppress the aggregation of ammonium hexafluorosilicate in the organic phase and promote its uniform dispersion during the interfacial polymerization process.

[0026] As a preferred embodiment of the present invention, the pyromellitic trimethylol chloride organic phase solution further contains polyethylene glycol dimethylsiloxane copolymer with a mass concentration of 0.005-0.05%, which acts as a surfactant to adjust the interfacial tension between the organic phase and the surface of the support layer.

[0027] As a preferred embodiment of the present invention, the ammonium hexafluorosilicate is ground before use to make its average particle size less than 5 μm, or is subjected to solvent displacement treatment to make it dispersed in the organic phase at the nanoscale.

[0028] As a preferred technical solution of the present invention, the preparation method of the pyromellitic tricarboxylate organic phase solution is as follows: dissolve pyromellitic tricarboxylate in a solvent, stir until completely dissolved, then add ammonium hexafluorosilicate and camphor sulfonyl chloride, and ultrasonically disperse at 15℃-25℃ for 5-20 minutes under inert gas protection to obtain a uniformly dispersed organic phase solution.

[0029] As a preferred embodiment of the present invention, the pyromellitic trimethylol chloride organic phase solution contains camphor sulfonyl chloride with a mass concentration of 0.01-0.10%, which is used to adjust the interfacial polymerization reaction rate and the crosslinking structure of the polyamide layer.

[0030] As a preferred embodiment of the present invention, the moisture content of the pyromellitic trimethylol chloride organic phase solution is less than 0.02%, which is controlled by adding molecular sieves to the solvent and drying for more than 24 hours.

[0031] As a preferred embodiment of the present invention, the pyromellitic methyl chloride organic phase solution further contains N,N-dimethylformamide with a mass concentration of 0.05-0.3%, which is used to adjust the interfacial tension between the organic phase and the aqueous phase and promote the uniformity of the interfacial polymerization reaction.

[0032] As a preferred embodiment of the present invention, the pyromellitic trimethylol chloride organic phase solution further contains terephthaloyl chloride with a mass concentration of 0.02-0.1%, which is used to adjust the crosslinking degree and network structure of the polyamide separation layer.

[0033] As a preferred technical solution of the present invention, the pyromellitic tricarboxylic acid organic phase solution needs to be kept at a constant temperature of 15℃-20℃ before use to avoid temperature fluctuations causing the precipitation of ammonium hexafluorosilicate or the hydrolysis of pyromellitic tricarboxylic acid.

[0034] As a preferred embodiment of the present invention, the zirconium source solution is a water-ethanol solution of zirconium oxychloride octahydrate, wherein the mass concentration of zirconium oxychloride octahydrate is 0.1-0.6%, the volume ratio of water to ethanol is (6-8):(2-4), and the pH value of the solution is 3.5-4.5.

[0035] As a preferred embodiment of the present invention, the zirconium source solution also contains hydrochloric acid at a concentration of 0.5-2 mmol / L, which is used to precisely adjust the pH of the solution to 3.6-4 and inhibit the early hydrolysis and polymerization of zirconium ions.

[0036] As a preferred embodiment of the present invention, the zirconium source solution also contains citric acid, the mass concentration of which is 0.01-0.05%, which serves as an auxiliary coordinating agent to regulate the coordination activity between zirconium ions and the subsequent polyphenol layer.

[0037] As a preferred embodiment of the present invention, the zirconium source solution further contains polyethylene glycol 200 with a mass concentration of 0.05-0.20%, which is used to improve the wetting and spreading properties of the zirconium source solution on the film surface.

[0038] As a preferred technical solution of the present invention, the method for preparing the zirconium source solution is as follows: dissolve zirconium oxychloride octahydrate in deionized water, stir until completely dissolved, then slowly add anhydrous ethanol while stirring, finally adjust the pH value to 3.5-4.5 with dilute hydrochloric acid, and use after standing and aging at 20℃-25℃ for 1-4 hours.

[0039] As a preferred embodiment of the present invention, the zirconium ions in the zirconium source solution are in the form of Zr. 4+ Zr(OH) 3+ Zr(OH)2 2+ Multiple hydrolysis forms coexist, including Zr. 4+ The molar proportion is 30%-60%, and the proportion of different hydrolysis forms can be achieved by adjusting the pH value and the water-to-alcohol ratio.

[0040] As a preferred embodiment of the present invention, the zirconium source solution also contains sodium chloride, with a mass concentration of 0.05%-0.15%, which is used to adjust the ionic strength and promote the uniform adsorption of zirconium ions on the membrane surface.

[0041] As a preferred technical solution of the present invention, the zirconium source solution needs to be kept at a constant temperature of 25℃±2℃ before contacting the composite membrane, and the temperature fluctuation of the solution during the contact process shall not exceed ±1℃.

[0042] As a preferred embodiment of the present invention, the mass ratio of zirconium oxychloride octahydrate to citric acid in the zirconium source solution is (10-20):1, and the amount of citric acid added is limited to not causing significant precipitation of zirconium ions.

[0043] As a preferred technical solution of the present invention, the zirconium source solution should be used within 8 hours after preparation to avoid prolonged storage leading to increased degree of zirconium ion hydrolysis and polymerization and the appearance of nano-sized colloidal particles in the solution.

[0044] As a preferred embodiment of the present invention, the volume ratio of water to ethanol in the zirconium source solution is 7:3. Under this ratio, zirconium ions maintain appropriate coordination activity and have a suitable wetting and spreading coefficient on the membrane surface.

[0045] As a preferred embodiment of the present invention, the zirconium source solution also contains acetylacetone, with a mass concentration of 0.005-0.02%, which serves as an auxiliary ligand to temporarily stabilize zirconium ions and delay their reaction with carbon dioxide in the air.

[0046] As a preferred technical solution of the present invention, the surface tension of the zirconium source solution is 30mN / m-40mN / m, which is achieved by adjusting the ethanol content. This surface tension range is beneficial to the uniform spreading and penetration of the solution on the surface of the polyamide film.

[0047] As a preferred embodiment of the present invention, the mass ratio of zirconium oxychloride octahydrate to polyethylene glycol 200 in the zirconium source solution is (3-6):1. In addition to improving wettability, polyethylene glycol 200 can also be used as a soft template to regulate the microstructure of the subsequent metal-polyphenol coordination layer.

[0048] As a preferred embodiment of the present invention, the zirconium source solution can be filtered through a 0.22μm or 0.45μm filter membrane before processing the composite membrane to remove any trace amounts of insoluble matter or hydrolyzed aggregates that may be present.

[0049] As a preferred embodiment of the present invention, the zeta potential of zirconium ions in the zirconium source solution is +15mV to +30mV. This potential range is favorable for the electrostatic attraction and adsorption of zirconium ions with negative potential points on the membrane surface by adjusting the pH value and the water-to-alcohol ratio.

[0050] As a preferred embodiment of the present invention, the polyphenol solution comprises gallic acid, tris(hydroxymethyl)aminomethane, and sodium citrate, wherein the mass concentration of gallic acid is 0.3-1.2%, the mass concentration of tris(hydroxymethyl)aminomethane is 0.5-1.5%, the mass concentration of sodium citrate is 0-0.1%, the solvent is deionized water, and the pH value of the solution is adjusted to 7.5-8.5 by tris(hydroxymethyl)aminomethane.

[0051] As a preferred technical solution of the present invention, the polyphenol solution includes three formulations with different sodium citrate concentrations during the layer-by-layer assembly process: the first polyphenol solution contains no sodium citrate; the second polyphenol solution contains 0.01-0.02% sodium citrate by mass; and the third polyphenol solution contains 0.03-0.08% sodium citrate by mass.

[0052] As a preferred embodiment of the present invention, the mass ratio of gallic acid to tris(hydroxymethyl)aminomethane in the first polyphenol solution is 1:(1.2-1.8); the mass ratio of gallic acid to sodium citrate in the second polyphenol solution is (15-30):1; and the mass ratio of gallic acid to sodium citrate in the third polyphenol solution is (8-15):1.

[0053] As a preferred embodiment of the present invention, the polyphenol solution further contains sodium chloride, the mass concentration of which is 0.05-0.2%, which is used to adjust the ionic strength to promote the dispersion stability of polyphenol molecules in the solution.

[0054] As a preferred technical solution of the present invention, the preparation method of the polyphenol solution is as follows: gallic acid, tris(hydroxymethyl)aminomethane and sodium citrate are added sequentially to deionized water, stirred and dissolved at 20-30°C for 10-30 minutes, and then the pH is adjusted to 7.5-8.5 with dilute hydrochloric acid or dilute sodium hydroxide solution.

[0055] As a preferred embodiment of the present invention, the polyphenol solution needs to be aged at 4-10°C for 1-4 hours before use to promote partial pre-assembly of polyphenol molecules and form an oligomer structure that is beneficial to subsequent coordination reactions.

[0056] As a preferred embodiment of the present invention, the molar ratio of gallic acid to tris(hydroxymethyl)aminomethane in the polyphenol solution is 1:(2-4). In addition to serving as a pH buffer, the amino group of tris(hydroxymethyl)aminomethane can undergo an amidation reaction with the carboxyl group of gallic acid during heat treatment, thereby enhancing the crosslinking density within the functional layer.

[0057] As a preferred embodiment of the present invention, the concentration gradient design of sodium citrate in the polyphenol solution is such that in the constructed metal-polyphenol gradient functional layer, the coordination molar ratio of gallic acid to zirconium ions on the side near the polyamide separation layer is (2.5-3.5):1, and the coordination molar ratio of gallic acid to zirconium ions on the side away from the polyamide separation layer is (1.2-1.8):1.

[0058] A second aspect of the present invention provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane, comprising the following steps: S1, preparing an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate; contacting the surface of a porous support layer with the aqueous solution for 0.5-2 min; removing excess aqueous solution; then contacting it with the organic solution for 0.5-2 min; performing an interfacial polymerization reaction at room temperature; and subsequently heat-treating at 80-100°C for 3-8 min to obtain an in-situ mineralized polyamide composite membrane; S2, preparing an aqueous-ethanol solution containing zirconium oxychloride octahydrate as a zirconium source solution; and applying the membrane obtained in step S1... S2. The composite membrane is contacted with the zirconium source solution for 2-6 minutes, then removed and rinsed with deionized water to obtain a zirconium ion-anchored composite membrane; S3. Three polyphenol solutions are prepared sequentially, and the composite membrane obtained in step S2 is contacted with each of the three polyphenol solutions for 2-4 minutes at a contact temperature of 20-30℃. The contact process is accompanied by slight oscillation at a speed of 30-60 r / min. After each contact, it is rinsed with deionized water to obtain a gradient-assembled composite membrane; S4. The composite membrane obtained in step S3 is heat-treated at 50-70℃ and relative humidity greater than 60% for 3-8 minutes to obtain a high-flux antifouling composite reverse osmosis membrane.

[0059] In step S1, during the interfacial polymerization reaction between m-phenylenediamine and trimesoyl chloride on the porous support layer surface to form the polyamide separation layer, hydrogen chloride is released. This hydrogen chloride creates a locally acidic microenvironment within the nanoscale confinement space formed by the polyamide layer, potentially promoting the in-situ hydrolysis of ammonium hexafluorosilicate in the organic phase, generating fluorosilicate nanoclusters. The formation of these nanoclusters occurs synchronously with the formation of the polyamide network, and therefore they may be in-situ encapsulated within the polyamide separation layer, forming an organic-inorganic interpenetrating network structure. This structure can help increase the transport channels for water molecules within the membrane without compromising the integrity of the polyamide layer. Furthermore, the introduction of fluoride ions enhances the weak negative charge on the membrane surface, potentially positively impacting water flux and the repulsion of negatively charged pollutants. In step S2, zirconium ions combine with residual fluoride ions on the membrane surface and amide groups in the polyamide layer through coordination, forming stable anchoring sites. In step S3, a metal-polyphenol functional layer is constructed using a layer-by-layer assembly method. The polyphenolic structure of gallic acid can form stable coordination bonds with zirconium ions. Tris(hydroxymethyl)aminomethane acts as a buffer to regulate the assembly environment and introduces additional hydroxyl groups to enhance hydrophilicity. Sodium citrate acts as a competitive coordinating agent, regulating the binding density of gallic acid and zirconium ions through the coordination competition between its carboxyl groups and zirconium ions, thereby forming a gradient structure with gradually decreasing coordination density from the membrane surface outwards. In this gradient structure, the relatively dense coordination network in the inner layer may help block pollutants from contacting the membrane surface, while the relatively loose coordination network in the outer layer helps reduce the mass transfer resistance of water molecules through the functional layer. The heat treatment process in step S4 promotes further optimization of the coordination bonds and may endow the functional layer with a certain degree of self-healing ability.

[0060] It should be further explained that when the high-flux, antifouling composite reverse osmosis membrane prepared by this invention is applied to seawater desalination or wastewater treatment, its internal nanocluster structure and surface gradient functional layer work synergistically to achieve high-flux operation while maintaining a high desalination rate, and to reduce the adsorption and accumulation of pollutants on the membrane surface, thus extending the membrane's service life. This technical solution avoids the cumbersome process of pre-synthesizing nanomaterials through an in-situ mineralization strategy, achieves controllable construction and structural gradient of the functional layer through metal-polyphenol coordination assembly, and optimizes the spatial distribution of functional layer density through competitive coordination regulation, providing a new technical path for improving the overall performance of reverse osmosis membranes.

[0061] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite reverse osmosis membrane provided by the present invention is composed of a porous support layer, an in-situ mineralized polyamide separation layer and a metal-polyphenol gradient functional layer. This structural design enables the membrane to have both high flux and good antifouling performance.

[0062] (2) This invention generates a nanocluster structure inside the polyamide layer by in-situ hydrolysis and mineralization of ammonium hexafluorosilicate during the interfacial polymerization process, thereby constructing an internal water molecule transport channel, which helps to improve the permeation flux of the membrane without sacrificing the desalination performance.

[0063] (3) The present invention constructs a metal-polyphenol functional layer with a gradient structure on the membrane surface by layer-by-layer coordination assembly of zirconium ions and polyphenols. The functional layer is firmly bonded to the membrane substrate, and its gradient structure design may achieve a balance between antifouling performance and water mass transfer resistance.

[0064] (4) The present invention adopts a competitive coordination strategy to regulate the density distribution of the functional layer, so that the functional layer presents a gradient structure with gradually decreasing coordination density from the membrane surface outward. The relatively dense network of the inner layer helps to block pollutants, while the relatively loose network of the outer layer helps to reduce the mass transfer resistance of water molecules.

[0065] (5) The preparation method of the present invention is simple and mild. It avoids the pre-synthesis and additional addition of nanomaterials through in-situ reaction and realizes the controllable construction of functional layers through coordination assembly, which has good prospects for industrial application. Detailed Implementation

[0066] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] The preparation steps of the m-phenylenediamine aqueous solution in Example 1 are as follows: Camphor sulfonic acid was added to deionized water and stirred at 25°C until completely dissolved; triethylamine was added to the above solution to adjust the pH to 10 and stirred evenly; m-phenylenediamine was then added and stirred until completely dissolved; sodium dodecyl sulfate was added and stirred for another 10 min; the above solution was transferred to a 100 mL volumetric flask and diluted to the mark with deionized water to obtain an m-phenylenediamine aqueous solution with a mass concentration of 3% m-phenylenediamine, 3% camphor sulfonic acid, 1.8% triethylamine, and 0.1% sodium dodecyl sulfate; the prepared solution was allowed to stand at 25°C for 30 min to remove bubbles before use.

[0068] Preparation Example 2: The preparation steps of the pyromellitic trimethylolpropionate (PTP) organic phase solution containing ammonium hexafluorosilicate are as follows: PTP was weighed and added to the isoparaffin solvent Isopar G, and stirred at 20°C until completely dissolved; ammonium hexafluorosilicate was weighed and ground into a fine powder in a mortar, and added to the above solution; tributyl phosphate was added; the mixed solution was placed in an ultrasonic cleaner and ultrasonically dispersed at 20°C for 15 min with an ultrasonic power of 200 W; the dispersed solution was filtered through a 0.45 μm organic filter membrane to remove undispersed particles; the filtrate was transferred to a brown reagent bottle, sealed, and kept at 18°C ​​for later use, resulting in a pyromellitic trimethylolpropionate (PTP) organic phase solution with a PTP mass concentration of 0.15%, an ammonium hexafluorosilicate mass concentration of 0.15%, and a tributyl phosphate mass concentration of 0.02%.

[0069] Preparation of Example 3: The preparation steps of the water-ethanol solution containing zirconium oxychloride octahydrate are as follows: Weigh zirconium oxychloride octahydrate and add it to deionized water. Stir at 25°C until completely dissolved. Slowly add anhydrous ethanol while stirring and continue stirring for 5 min. Adjust the pH of the solution to 3.8 with 0.1 mol / L dilute hydrochloric acid. Add polyethylene glycol 200 and stir for 10 min. Transfer the above solution to a 100 mL volumetric flask and dilute to 100 mL with a mixed solvent of deionized water and ethanol in a volume ratio of 6:4 to obtain a zirconium source solution with a zirconium oxychloride octahydrate mass concentration of 0.3% and a polyethylene glycol 200 mass concentration of 0.05%. Let the prepared solution stand at 25°C for 2 h before use.

[0070] The preparation steps of the polyphenol solution in Example 4 are as follows: Three polyphenol solutions with different sodium citrate concentrations were prepared respectively: First polyphenol solution: Gallic acid and tris(hydroxymethyl)aminomethane were weighed and added to deionized water and stirred to dissolve at 25°C; the pH value was adjusted to 8 with 0.1 mol / L dilute hydrochloric acid; the solution was transferred to a 100 mL volumetric flask and diluted to the mark with deionized water to obtain a polyphenol solution with a gallic acid mass concentration of 0.6%, a tris(hydroxymethyl)aminomethane mass concentration of 1.0%, and a sodium citrate mass concentration of 0%.

[0071] Second polyphenol solution: Weigh gallic acid, tris(hydroxymethyl)aminomethane and sodium citrate, and prepare them according to the same steps as above to obtain a polyphenol solution with a gallic acid mass concentration of 0.6%, a tris(hydroxymethyl)aminomethane mass concentration of 1.0%, and a sodium citrate mass concentration of 0.015%.

[0072] Third polyphenol solution: Weigh gallic acid, tris(hydroxymethyl)aminomethane and sodium citrate, and prepare them according to the same steps as above to obtain a polyphenol solution with a gallic acid mass concentration of 0.6%, a tris(hydroxymethyl)aminomethane mass concentration of 1.0% and a sodium citrate mass concentration of 0.5%.

[0073] The three solutions were allowed to stand at 4°C for 2 hours before use. Example

[0074] S1. Prepare an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate. Contact the surface of the porous support layer with the aqueous solution for 1 min, remove excess aqueous solution, and then contact it with the organic solution for 1 min. Perform interfacial polymerization at room temperature, followed by heat treatment at 90°C for 5 min to obtain an in-situ mineralized polyamide composite membrane. S2. Prepare an aqueous-ethanol solution containing zirconium oxychloride octahydrate as a zirconium source solution. Contact the composite membrane obtained in step S1 with the zirconium source solution for 4 min, then remove it and use a deionizer. S2. Rinse with water to obtain a zirconium ion-anchored composite membrane; S3. Prepare three polyphenol solutions in sequence, and contact the composite membrane obtained in step S2 with the first, second and third polyphenol solutions for 3 minutes each. The contact temperature is 25°C, and slight oscillation is accompanied during the contact process at a speed of 45 r / min. After each contact, rinse with deionized water to obtain a gradient-assembled composite membrane; S4. Heat treat the composite membrane obtained in step S3 at 60°C and 60% relative humidity for 5 minutes to obtain a high-flux antifouling composite reverse osmosis membrane.

[0075] In this embodiment, some of the raw materials used are the same as those obtained in Preparation Examples 1-4; the other examples are the same. Examples

[0076] S1. Prepare an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate. Contact the surface of the porous support layer with the aqueous solution for 0.5 min, remove excess aqueous solution, and then contact it with the organic solution for another 0.5 min. Perform interfacial polymerization at room temperature, followed by heat treatment at 80℃ for 3 min to obtain an in-situ mineralized polyamide composite membrane. S2. Prepare a water-ethanol solution containing zirconium oxychloride octahydrate as a zirconium source solution. Contact the composite membrane obtained in step S1 with the zirconium source solution for 2 min, then remove and use... S2. Rinse with deionized water to obtain a zirconium ion-anchored composite membrane; S3. Prepare three polyphenol solutions sequentially, and contact the composite membrane obtained in step S2 with the first, second, and third polyphenol solutions sequentially for 2 minutes each. The contact temperature is 20°C, and slight oscillation is performed during the contact process at a speed of 30 r / min. After each contact, rinse with deionized water to obtain a gradient-assembled composite membrane; S4. Heat-treat the composite membrane obtained in step S3 at 50°C and a relative humidity greater than 60% for 3 minutes to obtain a high-flux, anti-fouling composite reverse osmosis membrane. Example

[0077] S1. Prepare an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate. Contact the surface of the porous support layer with the aqueous solution for 2 minutes. After removing excess aqueous solution, contact it with the organic solution for another 2 minutes. Perform interfacial polymerization at room temperature, followed by heat treatment at 100°C for 8 minutes to obtain an in-situ mineralized polyamide composite membrane. S2. Prepare a water-ethanol solution containing zirconium oxychloride octahydrate as a zirconium source solution. Contact the composite membrane obtained in step S1 with the zirconium source solution for 6 minutes. After removal, rinse with deionized water. S2. Rinse to obtain a zirconium ion-anchored composite membrane; S3. Prepare three polyphenol solutions in sequence, and contact the composite membrane obtained in step S2 with the first, second and third polyphenol solutions for 4 min each. The contact temperature is 30℃, and slight oscillation is accompanied during the contact process at a speed of 60 r / min. After each contact, rinse with deionized water to obtain a gradient-assembled composite membrane; S4. Heat treat the composite membrane obtained in step S3 at 70℃ and relative humidity greater than 60% for 3-8 min to obtain a high-flux antifouling composite reverse osmosis membrane.

[0078] Comparative Example 1 differs from Example 1 in that ammonium hexafluorosilicate is not added to the organic phase solution in step S1. The remaining steps are the same as in Example 1: S1, preparing an aqueous solution of m-phenylenediamine and an organic phase solution of trimesoyl chloride, wherein the trimesoyl chloride organic phase solution is prepared by dissolving 0.15 g of trimesoyl chloride in 100 mL of isoparaffin solvent Isopar. In step G, ammonium hexafluorosilicate is not added; the surface of the porous support layer is contacted with an aqueous solution for 1 min, and after removing excess aqueous solution, it is contacted with an organic solution for 1 min. Interfacial polymerization is carried out at room temperature, followed by heat treatment at 90°C for 5 min to obtain a polyamide composite membrane; S2, a water-ethanol solution containing zirconium oxychloride octahydrate is prepared as a zirconium source solution. The composite membrane obtained in step S1 is contacted with the zirconium source solution for 4 min, and then rinsed with deionized water to obtain a zirconium ion-anchored composite membrane; S3, three polyphenol solutions are prepared sequentially, and the composite membrane obtained in step S2 is contacted with each of the three polyphenol solutions for 3 min sequentially. The contact temperature is 25°C, and slight oscillation is accompanied during the contact process at a speed of 45 r / min. After each contact, it is rinsed with deionized water to obtain a gradient-assembled composite membrane; S4, the composite membrane obtained in step S3 is heat-treated at 60°C and relative humidity greater than 60% for 5 min to obtain a composite reverse osmosis membrane.

[0079] Comparative Example 2 differs from Example 1 in that the zirconium source solution treatment in step S2 is omitted, while the remaining steps are the same as in Example 1: S1, Prepare an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate. Contact the surface of the porous support layer with the aqueous solution for 1 min, remove excess aqueous solution, and then contact it with the organic solution for 1 min. Perform interfacial polymerization at room temperature, followed by heat treatment at 90°C for 5 min to obtain an in-situ mineralized polyamide composite membrane; S2, omitted; S3, Prepare three polyphenol solutions sequentially, and contact the composite membrane obtained in step S1 with each of the three polyphenol solutions for 3 min. The contact temperature is 25°C, and slight oscillation is accompanied during the contact process at a speed of 45 r / min. After each contact, rinse with deionized water to obtain the assembled composite membrane; S4, Heat treat the composite membrane obtained in step S3 at 60°C and relative humidity greater than 60% for 5 min to obtain a composite reverse osmosis membrane.

[0080] Comparative Example 3 differs from Example 1 in that step S3 uses only the first polyphenol solution for a single treatment without gradient assembly; the remaining steps are the same as in Example 1: S1, prepare an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate. The porous support layer surface is contacted with the aqueous solution for 1 min, excess aqueous solution is removed, and then it is contacted with the organic solution for 1 min. Interfacial polymerization is carried out at room temperature, followed by heat treatment at 90°C for 5 min to obtain an in-situ mineralized polyamide composite membrane; S2, prepare a water-ethanol solution containing zirconium oxychloride octahydrate. As a zirconium source solution, the composite membrane obtained in step S1 is contacted with the zirconium source solution for 4 minutes, then removed and rinsed with deionized water to obtain a zirconium ion-anchored composite membrane; S3, a first polyphenol solution (excluding sodium citrate) is prepared, and the composite membrane obtained in step S2 is contacted with the first polyphenol solution for 9 minutes at a contact temperature of 25°C, accompanied by slight oscillation at a speed of 45 r / min. After contact, it is rinsed with deionized water to obtain an assembled composite membrane; S4, the composite membrane obtained in step S3 is heat-treated at 60°C and relative humidity greater than 60% for 5 minutes to obtain a composite reverse osmosis membrane.

[0081] Testing: I. Membrane separation performance testing was conducted according to GB / T 32373-2015 "Reverse Osmosis Membrane Test Methods," using a cross-flow membrane performance evaluation device to test the membrane's water flux and desalination rate. Test conditions were: sodium chloride aqueous solution concentration 32000 mg / L, operating pressure 5.52 MPa, temperature 25℃, and effective membrane area 14.6 cm². 2 After pre-pressurization for 30 minutes, the permeate volume and conductivity were measured. Water flux was calculated using the formula J = V / (A × t), and desalination rate was calculated using the formula R = (1 - C) / (A × t). p / C f Calculated as 100%, where V is the permeate volume (L) and A is the effective membrane area (m²). 2 ), where t is the test time (h), Cp is the concentration corresponding to the conductivity of the permeate (mg / L), and Cf is the concentration of the feed solution (mg / L).

[0082] II. Antifouling Performance Test: Bovine serum albumin (BSA) was used as a model pollutant to test the membrane's antifouling performance. Test Procedure: First, the membrane was pre-pressurized at 5.52 MPa and 25°C with 32000 mg / L NaCl solution for 30 min, and the initial water flux J0 was measured and the membrane was stabilized for 150 min. Then, BSA was added to the feed solution to a concentration of 500 mg / L, and the membrane was run under the same conditions for 450 min. The flux J after fouling was recorded. p Finally, the membrane surface was rinsed with deionized water at 0.1 MPa for 30 min, and the water flux J after cleaning was measured again. w Calculate the flux decay rate FDR = (J0 - J p) / J0×100% and flux recovery rate FRR=J w / J0×100%.

[0083] III. Functional Layer Integration Stability Test: The membrane sample was placed in deionized water and treated in a 40kHz, 200W ultrasonic cleaner for 30 minutes. After removal, the water flux and desalination rate of the membrane were measured again, and the performance change rate before and after ultrasonic treatment was calculated. Simultaneously, the change in contact angle after ultrasonic treatment was tested to evaluate the erosion resistance of the functional layer.

[0084] IV. Surface hydrophilicity test: The static water contact angle of the membrane surface was measured using the seated drop method on a contact angle meter. Test conditions: room temperature 25℃, deionized water droplet volume 2μL, 5 different locations were randomly selected for measurement for each sample, and the average value was taken.

[0085] V. Zeta potential measurement of membrane surface: The Zeta potential of the membrane surface was measured using a solid surface Zeta potential analyzer. Test conditions: background electrolyte was 1 mmol / L KCl solution, pH was 7, and temperature was 25℃.

[0086] VI. Summary of Results

[0087] VII. Results and Discussion As shown in Table 1, the high-flux antifouling composite reverse osmosis membranes prepared in Examples 1-3 of this invention maintained a high desalination rate while exhibiting significantly higher water flux than Comparative Example 1 (without ammonium hexafluorosilicate). This indicates that the fluorosilicate nanoclusters generated in situ within the polyamide layer effectively constructed water molecule transport channels, enhancing the membrane's permeability. The contact angles of Examples 1-3 were significantly lower than those of the Comparative Example, indicating that the metal-polyphenol gradient functional layer imparts excellent hydrophilicity to the membrane surface, facilitating the formation of a hydration layer to resist pollutant adsorption. In the antifouling test, the flux decay rate (FDR) of Examples 1-3 was lower than that of the Comparative Example, while the flux recovery rate (FRR) was higher, confirming the effective blocking and easy-to-clean characteristics of the gradient functional layer against organic pollutants. After ultrasonic treatment, the flux retention rates of all examples were above 98%, while that of Comparative Example 2 (without zirconium source treatment) decreased significantly, indicating that the chemical bonding formed by zirconium ion anchoring and polyphenol coordination significantly enhanced the bonding strength between the functional layer and the base membrane. The absolute values ​​of the Zeta potentials in Examples 1-3 are higher than those in Comparative Example 1, attributed to the enhanced surface charge resulting from the introduction of fluoride ions, which helps to electrostatically repel negatively charged contaminants. The performance of Comparative Example 3 (without gradient assembly) falls between that of Examples 1-2 and Comparative Example 1, demonstrating the advantage of gradient structure design in balancing antifouling and flux. In summary, this invention achieves a balance between high flux and excellent antifouling performance in reverse osmosis membranes through in-situ mineralization and synergistic modification via metal-polyphenol gradient coordination, while maintaining good stability of the functional layer.

[0088] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0089] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the scope defined by the invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A high-flux, anti-fouling composite reverse osmosis membrane, characterized in that: It comprises a porous support layer, an in-situ mineralized polyamide separation layer, and a metal-polyphenol gradient functional layer arranged sequentially. The in-situ mineralized polyamide separation layer is formed by interfacial polymerization of an aqueous solution of m-phenylenediamine and an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate on the surface of the porous support layer. The metal-polyphenol gradient functional layer is formed by sequential assembly and competitive coordination regulation of a zirconium source solution and a polyphenol solution.

2. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 1, characterized in that: The porous support layer is one of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, or a polyacrylonitrile ultrafiltration membrane, with a molecular weight cutoff of 50-150 kDa.

3. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 1, characterized in that: In the aqueous phase solution of m-phenylenediamine, the mass concentration of m-phenylenediamine is 2-4%, the mass concentration of camphor sulfonic acid is 2.5-4.5%, the mass concentration of triethylamine is 1-2.5%, the mass concentration of sodium dodecyl sulfate is 0-0.2%, the mass concentration of N-methylpyrrolidone is 0-2%, the mass concentration of polyethylene glycol 400 is 0-0.5%, the mass concentration of dimethyl sulfoxide is 0-0.8%, and the balance is deionized water; the pH value of the aqueous phase solution of m-phenylenediamine is 9-10.5, and the molar ratio of camphor sulfonic acid to triethylamine is 1:(1.1-1.5).

4. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 1, characterized in that: In the organic phase solution containing ammonium hexafluorosilicate and trimesoyl chloride, the mass concentration of trimesoyl chloride is 0.1-0.25%, the mass concentration of ammonium hexafluorosilicate is 0.05-0.3%, the mass concentration of tributyl phosphate is 0.01-0.1%, the mass concentration of polyethylene glycol dimethylsiloxane copolymer is 0-0.05%, the mass concentration of camphor sulfonyl chloride is 0-0.1%, the mass concentration of N,N-dimethylformamide is 0-0.3%, the mass concentration of terephthaloyl chloride is 0-0.1%, and the balance is one of isoparaffin solvent, n-heptane, or n-hexane; the mass ratio of trimesoyl chloride to ammonium hexafluorosilicate is 1:(0.5-1.5), and the water content of the organic phase solution is less than 0.02%.

5. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 1, characterized in that: The zirconium source solution is a water-ethanol solution of zirconium oxychloride octahydrate, wherein the mass concentration of zirconium oxychloride octahydrate is 0.1-0.6%, the mass concentration of polyethylene glycol 200 is 0-0.2%, the mass concentration of citric acid is 0-0.05%, the mass concentration of sodium chloride is 0-0.15%, the mass concentration of acetylacetone is 0-0.02%, and the balance is a mixed solvent of water and ethanol, with a volume ratio of water to ethanol of (6-8):(2-4); the pH value of the zirconium source solution is 3.5-4.5, the surface tension is 30-40 mN / m, the zeta potential of zirconium ions is +15 to +30 mV, the mass ratio of zirconium oxychloride octahydrate to citric acid is (10-20):1, and the mass ratio of zirconium oxychloride octahydrate to polyethylene glycol 200 is (3-6):

1.

6. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 1, characterized in that: The polyphenol solution comprises three formulations with different sodium citrate concentrations: In the first polyphenol solution, the mass concentration of gallic acid is 0.3-1.2%, the mass concentration of tris(hydroxymethyl)aminomethane is 0.5-1.5%, the mass concentration of sodium chloride is 0.05-0.2%, and the remainder is deionized water; the pH value of the solution is 7.5-8.5, and the mass ratio of gallic acid to tris(hydroxymethyl)aminomethane is 1:(1.2-1.8); In the second polyphenol solution, in addition to the first polyphenol solution, sodium citrate is added, with a mass concentration of 0.01-0.02%, and the mass ratio of gallic acid to sodium citrate is (15-30):1; In the third polyphenol solution, in addition to the first polyphenol solution, sodium citrate is added, with a mass concentration of 0.03-0.08%, and the mass ratio of gallic acid to sodium citrate is (8-15):

1.

7. The high-flux, anti-fouling composite reverse osmosis membrane according to claim 6, characterized in that: In the metal-polyphenol gradient functional layer, the coordination molar ratio of gallic acid to zirconium ions on the side closer to the in-situ mineralized polyamide separation layer is (2.5-3.5):1, and the coordination molar ratio of gallic acid to zirconium ions on the side farther from the in-situ mineralized polyamide separation layer is (1.2-1.8):

1.

8. A method for preparing a high-flux, anti-fouling composite reverse osmosis membrane as described in any one of claims 1-7, characterized in that: Includes the following steps: S1. The surface of the porous support layer is contacted with an aqueous solution of m-phenylenediamine for 0.5-2 min. After removing excess aqueous solution, it is then contacted with an organic solution of trimesoyl chloride containing ammonium hexafluorosilicate for 0.5-2 min. Interfacial polymerization is carried out at room temperature, followed by heat treatment at 80-100℃ for 3-8 min to obtain an in-situ mineralized polyamide composite membrane. S2. The composite membrane obtained in step S1 is contacted with a zirconium source solution for 2-6 min. After removal, it is rinsed with deionized water to obtain a zirconium ion-anchored composite membrane. S3. The composite membrane obtained in step S2 is sequentially contacted with a first polyphenol solution, a second polyphenol solution, and a third polyphenol solution for 2-4 min each. The contact temperature is 20-30℃. After each contact, it is rinsed with deionized water to obtain a gradient-assembled composite membrane. S4. The composite membrane obtained in step S3 is heat-treated at 50-70℃ and a relative humidity greater than 60% for 3-8 min to obtain the high-flux antifouling composite reverse osmosis membrane.

9. The preparation method according to claim 8, characterized in that: The aqueous phase solution of m-phenylenediamine in step S1 is prepared as follows: camphor sulfonic acid is dissolved in deionized water, triethylamine is added to adjust the pH value, then m-phenylenediamine is added and stirred to dissolve, and finally additive 1 is added. The mixture is stirred at 20-30℃ for 10-30 min, allowed to stand to remove bubbles, and then used. The organic phase solution of pyromellitic trimethylbenzene chloride containing ammonium hexafluorosilicate in step S1 is prepared as follows: pyromellitic trimethylbenzene chloride is dissolved in a solvent and stirred until completely dissolved. Then ammonium hexafluorosilicate and tributyl phosphate are added, and additive 2 is added. The mixture is ultrasonically dispersed at 15-25℃ for 5-20 min under inert gas protection, and then filtered through a 0.22-0.45μm filter membrane before use. Additive 1 is one of sodium dodecyl sulfate, N-methylpyrrolidone, polyethylene glycol 400, and dimethyl sulfoxide. Additive 2 is one of polyethylene glycol dimethylsiloxane copolymer, camphor sulfonyl chloride, N,N-dimethylformamide, and terephthaloyl chloride.

10. The preparation method according to claim 8, characterized in that: The zirconium source solution in step S2 is prepared as follows: Zirconium oxychloride octahydrate is dissolved in deionized water and stirred until completely dissolved. Then, anhydrous ethanol is added while stirring, additive 3 is added, and finally the pH value is adjusted to 3.5-4.5 with dilute hydrochloric acid. After standing and aging at 20-25℃ for 1-4 hours, it is used. The additive 3 is one of polyethylene glycol 200, citric acid, sodium chloride and acetylacetone.

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