High-flux anti-fouling composite reverse osmosis membrane, and preparation method and application thereof

Abstract

The application relates to the technical field of water treatment membranes, and provides a high-flux anti-pollution composite reverse osmosis membrane and a preparation method and application thereof, the method comprising the following steps: S1, anchoring a double-function group core-shell type MOF on a base film to form a modification layer; S2, covalently connecting different monomers on different types of function groups of the double-function group core-shell type MOF to perform an interface polymerization reaction and form a polyamide separation layer; S3, allowing an o-diphenol derivative to be oxidized and self-polymerized and to coat a pore-forming agent to obtain an initiation layer with hydrophilic channels; and S4, grafting an epoxy group-containing zwitterionic block copolymer on the initiation layer through an opening ring reaction to form a hydrophilic anti-pollution copolymer brush layer, thereby obtaining the high-flux anti-pollution composite reverse osmosis membrane. The application can solve the technical problems that the flux of the reverse osmosis membrane for treating brackish water is small in the prior art, the operation pressure needs to be maintained to be high when the reverse osmosis membrane is used for agricultural irrigation and other purposes, the anti-pollution capacity is insufficient, and it is difficult to process underground brackish water in a large quantity and at a high speed.

Description

Technical Field

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

[0002] Currently, membrane separation technology has become the mainstream process for conventional brackish water desalination due to its good desalination effect and stable effluent quality. In existing technologies, membrane separation units for brackish water desalination mainly employ either reverse osmosis membranes or nanofiltration membranes.

[0003] In existing technologies, reverse osmosis membranes for brackish water typically have high ion rejection rates, effectively removing most dissolved salts from the water. However, their membrane layers are dense, pore sizes are small, resistance to water molecule transport across the membrane is high, and water flux is relatively low. Under standard test conditions (using 2000 mg / L NaCl solution, 25℃, pH=8, recovery rate 15%), at an operating pressure of 225 psi (1.55 MPa), the permeate flux of conventional reverse osmosis membranes for brackish water is usually only 15-35 LMH. High operating pressure is required during operation to overcome osmotic pressure, resulting in problems such as low flux, high operating pressure, and high system energy consumption, leading to high operating costs and unsatisfactory permeate efficiency per unit energy consumption.

[0004] While nanofiltration membranes can operate at lower pressures and have relatively high flux, their rejection rate for monovalent ions is limited, resulting in higher TDS in the produced water, making it difficult to meet the basic salinity requirements for agricultural irrigation. Furthermore, the material costs and membrane module prices of nanofiltration membranes are typically higher than those of conventional reverse osmosis membranes, leading to higher initial investment costs. Therefore, although nanofiltration membranes offer certain advantages in flux and pressure, their effluent quality and cost control are insufficient to meet the demands of large-scale agricultural irrigation.

[0005] On the other hand, existing reverse osmosis membranes for brackish water are highly homogeneous in design with commonly used reverse osmosis membranes such as those for seawater desalination and water purification. Their design goals primarily focus on the removal of conventional pollutants such as suspended solids and colloids, as well as desalination rates. However, they lack specific design considerations for iron and manganese ions present in brackish water. Reverse osmosis membranes have extremely low tolerance thresholds for iron and manganese ions; the hydroxides or oxides formed by the oxidation of these ions easily adhere to the membrane surface or clog the pores, causing rapid flux decline. Even under strict requirements for feed water Fe < 0.05 ppm and Mn < 0.05 ppm, some existing reverse osmosis membranes may still experience severe fouling and clogging, necessitating frequent cleaning, shortening the membrane's effective lifespan, and increasing economic costs. Furthermore, the stringent feed water requirements often necessitate lengthy pretreatment processes in existing brackish water treatment systems, including sand filtration, microfiltration, ultrafiltration, and softening. These pretreatment units not only result in a large overall footprint, high investment costs, and low water recovery rates in the treatment system, but each stage of filtration also generates wastewater, further increasing the operational and maintenance burden and reducing the overall throughput of the treatment system.

[0006] In summary, there is an urgent need for a reverse osmosis membrane that can meet the water quality requirements for agricultural irrigation while possessing high flux, low operating pressure, and strong anti-fouling properties. This is of great significance for reducing energy consumption in brackish water desalination, simplifying pretreatment processes, reducing system investment and operating costs, and improving the utilization rate of brackish water resources. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a high-flux anti-fouling composite reverse osmosis membrane, its preparation method and application, which solves the technical problems of the prior art where the reverse osmosis membrane for brackish water treatment has a small flux, requires a high operating pressure when used for agricultural irrigation and other purposes, and has insufficient anti-fouling ability, making it difficult to treat ground brackish water in large quantities and at high speed.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0011] In a first aspect, the present invention provides a method for preparing a high-flux, anti-fouling composite reverse osmosis membrane, comprising the following steps:

[0012] S1: Substrate modification: A bifunctional core-shell MOF is anchored on the activated ultrafiltration support substrate to form a MOF modification layer;

[0013] S2: Separation layer construction: Interfacial polymerization reaction was carried out on the ultrafiltration support substrate after S1 treatment, followed by thermosetting to obtain a polyamide separation layer; the aqueous monomer and organic monomer in the interfacial polymerization reaction were covalently linked to different types of functional groups on the bifunctional core-shell MOF, respectively.

[0014] S3: Initiation layer construction: Catechol derivatives undergo oxidative self-polymerization under the action of an oxidant, depositing and coating a pore-forming agent on the surface of the polyamide separation layer to construct an initiation layer rich in primary / secondary amine groups; after removing the pore-forming agent, hydrophilic channels are formed in the initiation layer;

[0015] S4: Construction of the antifouling layer; through the ring-opening reaction of epoxy groups, zwitterionic copolymers containing epoxy groups are grafted onto the initiation layer to form a hydrophilic antifouling copolymer brush layer; thermal curing treatment is performed to obtain a high-flux antifouling composite reverse osmosis membrane.

[0016] According to a preferred embodiment of the present invention, in S1, the activation treatment includes: immersing the ultrafiltration support membrane in a Tris-HCl buffer solution of dopamine and reacting it at room temperature in the dark for 1-4 hours to obtain an activated membrane with a surface rich in hydroxyl and amino groups;

[0017] Subsequently, the activated substrate was immersed in an aqueous dispersion containing a bifunctional core-shell MOF for 0.5-2 hours to anchor the MOF to the substrate surface and form a MOF modified layer.

[0018] In the aqueous dispersion, the mass concentration of the bifunctional core-shell MOF was 0.02%-0.06%;

[0019] Bifunctional core-shell MOFs are bifunctional core-shell Zr-MOF materials, including a Zr-MOF core and a Zr-MOF bifunctional layer covering the outside of the core. The Zr-MOF bifunctional layer is a Zr-MOF constructed from organic ligands containing amino and sulfonic acid groups.

[0020] According to a preferred embodiment of the present invention, in S1, the preparation method of the bifunctional core-shell Zr-MOF material includes:

[0021] A1: A zirconium source, amino ligand, crystal form regulator and a first solvent are mixed and crystallized by hydrothermal reaction to obtain amino-containing zirconium-based MOF seed crystals; wherein, the molar ratio of zirconium source to amino ligand is 1:0.5-1:2, and the molar ratio of crystal form regulator to zirconium source is 80:1-150:1.

[0022] A2: The seed crystal is placed in a growth precursor solution containing zirconium source, amino ligand and sulfonic acid ligand, and a secondary growth reaction is carried out to obtain a bifunctional core-shell Zr-MOF material with both amino and sulfonic acid groups in the outer shell; wherein the ratio of the total molar amount of zirconium source to the total molar amount of amino ligand and sulfonic acid ligand is 1:0.8-1:1.5, and the molar ratio of amino ligand to sulfonic acid ligand is 1:0.5-1:5.

[0023] According to a preferred embodiment of the present invention, in S1, the zirconium source is at least one of zirconium tetrachloride, zirconium oxychloride, and zirconium acetate; the amino ligand is at least one of aminoterephthalic acid, diaminoterephthalic acid, aminoisophthalic acid, or aminobenzoic acid; the sulfonic acid ligand is at least one of sulfonic acid monosodium terephthalate, sulfonic acid monosodium terephthalate, sulfonic acid benzoic acid, and 2-sulfonic acid terephthalic acid; the first solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; and the crystal form regulator is at least one of glacial acetic acid, benzoic acid, formic acid, and trifluoroacetic acid.

[0024] According to a preferred embodiment of the present invention, in S2, the interfacial polymerization reaction includes: immersing the ultrafiltration support membrane treated in S1 into an aqueous monomer solution and an organic monomer solution successively and then removing it, followed by heat treatment and curing at 75-95°C for 5-15 minutes to allow the aqueous monomer and organic monomer to undergo interfacial polymerization and form a polyamide separation layer.

[0025] The aqueous phase monomer is a diamine or polyamine monomer, and the organic phase monomer is a polyacrylamide chloride monomer.

[0026] According to a preferred embodiment of the present invention, in S3, the ultrafiltration support membrane after S2 is immersed in a weakly alkaline buffer solution containing a catechol derivative and a pore-forming agent, and then an oxidant is added. The reaction is carried out at 25-40°C for 0.2-1 hours to deposit an initiation layer rich in primary / secondary amine groups on the membrane surface; the catechol derivative is a catechol derivative containing primary / secondary amine groups.

[0027] During the deposition of catechol derivatives, the porogen is encapsulated in the initiation layer; after deposition, the porogen is dissolved by rinsing with water, and nanoscale hydrophilic channels are formed in situ inside the initiation layer and at the interface with the polyamide separation layer.

[0028] According to a preferred embodiment of the present invention, in S3, the catechol derivative has a mass concentration of 0.5-2.0 mg / mL in a weakly alkaline buffer solution, the oxidant has a mass concentration of 1.0-10.0 mmol / L, the porogen has a mass concentration of 0.5-3.0 mg / mL, and the molecular weight is 400-2000 Da.

[0029] The pH of the weakly alkaline buffer solution is 7.5-9.0; the catechol derivative is dopamine hydrochloride, gelatin-dopamine conjugate, or chitosan-catechol coupling agent; the oxidant is at least one of sodium periodate or hydrogen peroxide; the porogen includes at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble polysaccharide, or hydrophilic ionic liquid.

[0030] According to a preferred embodiment of the present invention, in S4, the ultrafiltration support membrane after S3 is placed in a grafting reaction solution containing an epoxy-containing zwitterionic block copolymer, and the pH is adjusted to a weakly alkaline condition to carry out the grafting reaction.

[0031] The molecular structure of the epoxy-containing zwitterionic block copolymer is: hydrophobic segment - hydrophilic zwitterionic segment - epoxy functional end group, with a number average molecular weight of 2000-20000.

[0032] During the grafting reaction, the mass concentration of the epoxy-containing zwitterionic block copolymer in the reaction solution is 0.02%-0.5%, the pH of the system is adjusted to 8.5-9.5, and the reaction is carried out at 20-45℃ for 2-8 hours.

[0033] Secondly, the present invention also provides a high-flux, anti-fouling composite reverse osmosis membrane, comprising:

[0034] Ultrafiltration support membrane;

[0035] A bifunctional core-shell MOF is anchored on the surface of the ultrafiltration support membrane to form a MOF modification layer; the bifunctional core-shell MOF has a shell containing two different types of functional groups;

[0036] The polyamide separation layer is formed on the surface of the ultrafiltration support membrane. The polyamide separation layer is formed by interfacial polymerization reaction, and the aqueous monomer and organic monomer of the interfacial polymerization reaction are covalently connected to different types of functional groups in the shell of the bifunctional core-shell MOF.

[0037] An initiation layer is composited on the polyamide separation layer, and the initiation layer is an oxidized self-polymer of catechol derivative;

[0038] And a hydrophilic antifouling copolymer brush layer grafted and fixed to the surface of the dynamic adhesion initiation layer. This copolymer brush layer is obtained by covalently bonding an epoxy-containing zwitterionic block copolymer with the active sites on the surface of the initiation layer through the ring-opening reaction of the epoxy groups.

[0039] Thirdly, the present invention also provides an application of the high-flux antifouling composite reverse osmosis membrane as described in the second aspect in brackish water treatment, employing a treatment system comprising the following units:

[0040] The aeration pretreatment unit is used to oxidize brackish water with air, causing it to self-flocculate.

[0041] The inlet of the submersible ultrafiltration unit is connected to the outlet of the aeration pretreatment unit to reduce the turbidity of the product water.

[0042] A reverse osmosis unit, comprising at least one stage of a high-flux, fouling-resistant composite reverse osmosis membrane as described in the second aspect; the inlet of the reverse osmosis unit is connected to the outlet of the submerged ultrafiltration unit;

[0043] And a concentrate recovery unit, which is connected to the concentrate outlet of the reverse osmosis unit, for recovering and treating the reverse osmosis concentrate;

[0044] The permeate outlet of the reverse osmosis unit produces usable desalinated water.

[0045] (III) Beneficial Effects

[0046] The beneficial effects of this invention are as follows: the high-flux antifouling composite reverse osmosis membrane (hereinafter referred to as the composite membrane) and its preparation method of this invention adopt a scheme in which a bifunctional core-shell MOF is anchored on an activated ultrafiltration support membrane to form a MOF modified layer (hereinafter referred to as the MOF layer), and the aqueous phase monomer and the organic phase monomer are covalently linked to two different types of functional groups on the MOF, respectively, and a polyamide separation layer (hereinafter referred to as the separation layer) is constructed with the MOF as the three-dimensional connection base point. Compared with the prior art, this scheme enables the separation layer to grow in an orderly manner based on the anchored MOF molecules during formation, thereby forming a regular network structure based on MOF, rather than a randomly dispersed network structure. The regular channels of the MOF (Metal-Oxide-Foil) are interconnected with the polyamide network and further connected to the ultrafiltration support membrane, providing numerous interconnected and rapid transport paths for water molecules, significantly improving the membrane flux of the composite membrane of this invention. This regular network structure also ensures uniform stress on the separation layer, improving its compaction resistance and maintaining stable flux and desalination rate even under long-term operation or pressure fluctuations. This allows for efficient water production at lower operating pressures, reducing system energy consumption. Furthermore, the strong covalent bond between the MOF and both ends of the separation layer enhances the overall structural stability of the separation layer, reduces interface defects, and improves durability.

[0047] Meanwhile, this invention also employs a method of constructing an initiation layer on the surface of the polyamide separation layer through the oxidative self-polymerization of catechol derivatives, and then introducing a pore-forming agent therein followed by rinsing and dissolving to form nanoscale hydrophilic channels. Compared with existing technologies, this method can utilize the abundant primary / secondary amine groups in the initiation layer to provide high-density active sites for subsequent grafting, significantly improving the grafting density and adhesion of the antifouling brush, enhancing its antifouling effect, and making it less prone to detachment. The hydrophilic channels formed by the dissolution of the pore-forming agent penetrate the interior of the initiation layer and the interface with the separation layer, further reducing the transmembrane resistance of water molecules and increasing the flux of the composite membrane of this invention. The initiation layer itself also has certain hydrophilicity and antioxidant properties, which can inhibit the initial adhesion of pollutants to a certain extent. In addition, the size effect (nanoscale) of the channels makes it difficult for pollutants such as iron and manganese colloids to enter the channel interior for deposition. The combination of these two factors can effectively reduce the contact area of ​​pollutants and has a better antifouling effect.

[0048] Furthermore, this invention employs a method of grafting an epoxy-containing zwitterionic block copolymer onto the initiating layer via an epoxy ring-opening reaction to form a hydrophilic antifouling brush layer. Compared to existing technologies, this invention enables stable covalent bond connections through a ring-opening addition reaction between epoxy groups and primary / secondary amine groups on the initiating layer under alkaline conditions. The brush layer is less prone to detachment during hydraulic rinsing or chemical cleaning, exhibiting excellent long-term stability. Simultaneously, the zwitterionic block copolymer carries equal amounts of positive and negative charges on the same chain segment, enabling it to firmly bind water molecules through electrostatic interactions, forming a dense and stable hydration layer on the membrane surface. This effectively prevents the initial adhesion of iron-manganese hydroxide colloids, proteins, polysaccharides, microorganisms, and other substances through a dual mechanism of steric hindrance and hydration repulsion. This results in strong resistance to iron-manganese hydroxide, significantly reducing flux attenuation rates at high iron-manganese ion concentrations, greatly extending the chemical cleaning interval, and improving the service life of the composite membrane of this invention. Meanwhile, the hydrophilic channels in the initiation layer can work together with the hydration layer to further reduce the transport resistance of water molecules, ensuring that the present invention can achieve both high throughput and strong anti-fouling properties.

[0049] Based on the above effects, when the composite membrane of the present invention is used for the purification of agricultural irrigation water, only two-stage pretreatment of "aeration oxidation self-flocculation + submerged ultrafiltration" is required to meet the membrane feed water requirements. Moreover, the required water flux can be achieved under low pressure during reverse osmosis. Compared with the prior art, its treatment system has a smaller overall footprint, lower energy consumption costs, lower civil engineering investment and equipment costs, and a higher overall water recovery rate. It can significantly reduce the cost per ton of water treated, meet the needs of agricultural irrigation for low-cost, large-scale water use, and is more suitable for large-scale promotion and application in arid areas. Attached Figure Description

[0050] Figure 1This is a schematic diagram of the high-flux antifouling composite reverse osmosis membrane in various embodiments of the present invention.

[0051] [Explanation of Labels in the Attached Image]

[0052] 1: Ultrafiltration support membrane; 2: MOF modified layer; 3: Polyamide separation layer; 4: Initiation layer; 5: Hydrophilic antifouling copolymer brush layer. Detailed Implementation

[0053] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] In a first aspect, the present invention provides a method for preparing a high-flux, anti-fouling composite reverse osmosis membrane, comprising the following steps:

[0055] S1: Substrate Modification: The ultrafiltration support substrate 1 (referred to as the ultrafiltration substrate / substrate) is activated to enrich its surface with hydroxyl and amino groups. Subsequently, on the activated ultrafiltration support substrate 1, a bifunctional core-shell MOF (whose shell contains two different types of functional groups) is anchored through chemical bonds, or covalent bonds, to form the MOF modification layer 2.

[0056] In this scheme, MOFs are chemically bonded to the substrate membrane surface, forming a regular MOF-modified layer 2. This MOF layer subsequently serves as a base for the growth of the polyamide separation layer 3, guiding the separation layer to form a regular network structure with MOFs as the basic nodes, rather than random cross-linking. The regular channels of the MOFs themselves are interconnected with the polyamide network and further connected to the ultrafiltration support substrate membrane 1, providing additional fast transport paths for water molecules and significantly improving membrane flux. At the same time, the regular network structure ensures uniform stress on the separation layer, improving its compaction resistance and maintaining stable flux and desalination rate even under long-term operation or pressure fluctuations. This allows for high-efficiency water production at lower operating pressures, reducing system energy consumption. Furthermore, the covalent bonds between the MOFs and different monomers in the separation layer reduce interfacial defects in the subsequently formed separation layer, enhancing durability.

[0057] S2: Separation Layer Construction: The ultrafiltration support membrane 1 treated in S1, or the MOF modified layer 2 obtained in S1, is sequentially brought into contact with the aqueous monomer and the organic monomer to undergo interfacial polymerization. First, one type of functional group on the bifunctional core-shell MOF is covalently linked to the aqueous monomer, and then another type of functional group on the bifunctional core-shell MOF is covalently linked to the organic monomer. After both monomers are linked, they are thermally cured together to crosslink the two different types of monomers, forming a polyamide separation layer 3 (referred to as the separation layer). This invention uses this method to covalently link the aqueous monomer and the organic monomer, one after the other, to different types of functional groups on the bifunctional core-shell MOF. This allows the polyamide separation layer 3 to grow in an orderly manner on the MOF layer, forming a regular network structure and optimizing the pore structure. This not only increases the number of interconnected channels in the polyamide separation layer 3, but also ensures that the channels in the MOF layer are interconnected with those in the polyamide network, providing more interconnected and rapid transport paths for water molecules, further enhancing flux and maintaining a high flux even at lower operating pressures. Furthermore, because the flux modification is achieved through optimized pore structure, it does not lead to a significant increase in pore diameter, thus avoiding a substantial decrease in desalination rate and other performance characteristics, preserving sufficient desalination efficiency and ensuring the desalination effect of this invention. The regular network structure also ensures uniform stress distribution on the separation layer, improving compaction resistance, reducing interface defects, and enhancing the durability of the separation layer. Depending on the specific preparation method chosen, the desalination rate of the reverse osmosis membrane obtained by this invention can be controlled within a suitable range of 93%-99% (usually not less than 95%), meeting the standards for agricultural irrigation water (product water TDS < 2000 mg / L), while avoiding the problems of low flux and high operating pressure caused by conventional reverse osmosis membranes that pursue excessively high desalination rates.

[0058] S3: Construction of Initiation Layer 4: The ultrafiltration membrane treated in S2 is immersed in a reaction solution containing catechol derivatives and porogens. On the surface of polyamide separation layer 3, the catechol derivatives are oxidized and self-polymerized under the action of an oxidant, depositing and encapsulating the porogens on the surface of polyamide separation layer 3, forming an initiation layer 4 rich in primary / secondary amine groups. Then, the porogens are removed by rinsing and other methods, forming hydrophilic channels, mainly nanoscale hydrophilic channels, in the initiation layer 4.

[0059] The initiation layer 4, through its abundant primary / secondary amine groups, provides a high-density active site for subsequent ring-opening grafting, significantly improving the grafting density and adhesion of the antifouling brush and making it less prone to detachment. Furthermore, the initiation layer 4 itself possesses certain hydrophilicity and antioxidant properties, which can inhibit the initial adhesion of pollutants to a certain extent. The nanoscale hydrophilic channels (typically 2-20 nm in diameter) formed by the pore-forming agent can further penetrate the interior of the initiation layer 4 and the interface with the separation layer, reducing the transmembrane resistance of water molecules and increasing membrane flux. Simultaneously, the size effect of the channels makes it difficult for pollutants such as iron and manganese colloids to enter and deposit inside the channels, and also reduces the effective fouling area on the membrane surface, playing a passive antifouling role.

[0060] S4: Construction of the antifouling layer. Through the ring-opening reaction of epoxy groups, zwitterionic copolymers containing epoxy groups are grafted onto the initiating layer 4 to form a hydrophilic antifouling copolymer brush layer 5. Then, the brush layer is cleaned and thermally cured to obtain a high-flux antifouling composite reverse osmosis membrane.

[0061] The invention utilizes the epoxy groups in an epoxy-containing zwitterionic block copolymer to undergo ring-opening addition reactions with primary / secondary amine groups under alkaline conditions, forming stable covalent bonds. This makes the antifouling brush layer less prone to detachment during hydraulic rinsing or chemical cleaning, exhibiting excellent long-term stability. Simultaneously, the zwitterionic block copolymer used in this invention carries equal amounts of positive and negative charges on the same chain segment, firmly binding water molecules through electrostatic interactions to form a dense and stable hydration layer on the membrane surface. This hydration layer effectively prevents the initial adhesion of iron-manganese hydroxide colloids, as well as contaminants such as proteins, polysaccharides, and microorganisms, through a dual mechanism of steric hindrance and hydration repulsion. This gives the membrane strong resistance to iron-manganese ions, significantly reducing flux attenuation rates at high iron-manganese contents, greatly extending the chemical cleaning interval, and improving membrane lifespan. Furthermore, the hydrophilic channels in the initiation layer 4 work synergistically with the hydration layer to further reduce water molecule transport resistance, ensuring that this invention balances high flux and strong antifouling properties.

[0062] The composite reverse osmosis membrane prepared according to the above steps of this invention, when used in brackish water treatment, first contacts the outermost hydrophilic antifouling copolymer brush layer 5 on the membrane surface. This hydration layer inhibits the initial adhesion of iron-manganese colloids, proteins, and microorganisms. Water molecules then enter the initiation layer 4, where nanoscale hydrophilic channels effectively reduce the transport resistance of water molecules, allowing them to quickly enter the polyamide separation layer 3. As water molecules pass through the polyamide separation layer 3, the numerous interconnected pores allow for rapid water permeation and effective retention of salt ions, achieving desalination. After passing through the separation layer, water molecules enter the MOF-modified layer 2. The anchored MOF channels are interconnected with the polyamide network, providing a rapid transport path for water molecules. Finally, water molecules flow into the permeate collection side through the ultrafiltration support membrane 1.

[0063] Preferably, in step S1, the ultrafiltration support membrane 1 is immersed in a Tris-HCl buffer solution of dopamine (pH around 8.5) and reacted at room temperature in the dark for 1-4 hours to obtain an activated membrane with a surface rich in hydroxyl and amino groups, thus completing the activation process. Specifically, the self-polymerization reaction of dopamine under weakly alkaline conditions forms a polydopamine layer rich in phenolic hydroxyl and amino groups on the membrane surface, providing sufficient chemical binding sites for subsequent MOF anchoring and improving the wettability of the membrane surface.

[0064] Preferably, in S1, after activation, the activated substrate is immersed in an aqueous dispersion containing a bifunctional core-shell MOF for a certain period of time, so that the MOF can chemically bond with the hydroxyl and amino groups on the surface of the activated substrate through its shell functional groups, and anchor itself to the substrate surface to form MOF modification layer 2.

[0065] More preferably, in S1, the mass concentration of the bifunctional core-shell MOF in the aqueous dispersion is 0.02%-0.06%, and the impregnation time is 0.5-2 hours. Controlling the impregnation time of the MOF ensures sufficient diffusion and reaction with the substrate, avoiding multilayer accumulation. Controlling the concentration range avoids incomplete anchoring and partial exposure of the substrate surface due to excessively low concentration. Excessively high concentration can easily lead to MOF particle aggregation or the formation of multilayer structures, affecting the orderly growth of the subsequent separation layer. More preferably, the thickness of the MOF-modified layer 2 is controlled to be 30-80 nanometers.

[0066] Preferably, in S1, the bifunctional core-shell MOF is a bifunctional core-shell Zr-MOF material, comprising a Zr-MOF core and a Zr-MOF bifunctional layer covering the core. The bifunctional groups are amino and sulfonic acid groups. The shell contains both amino and sulfonic acid groups. This allows the MOF to achieve bidirectional ordered growth of the polyamide layer on the MOF layer through the reaction of amino groups with organic monomers (such as trimesoyl chloride) and the electrostatic adsorption or covalent bonding of sulfonic acid groups with aqueous monomers (such as m-phenylenediamine), forming a well-organized cross-linked network based on the MOF. Specifically, the core and shell can adopt structures such as UiO-66-NH2 as the basic architecture of the MOF, ensuring the introduction of bifunctional groups.

[0067] Preferably, in S1, the preparation method of the bifunctional core-shell Zr-MOF material includes:

[0068] A1: A zirconium-based MOF seed crystal containing amino groups was obtained by mixing zirconium source, amino ligand, crystal form regulator and first solvent, followed by hydrothermal reaction and crystallization.

[0069] A2: The seed crystal is placed in a growth precursor solution containing zirconium source, amino ligand and sulfonic acid ligand, and a secondary growth reaction is carried out to obtain a bifunctional core-shell Zr-MOF material with an amino core and an outer shell containing both amino and sulfonic acid groups.

[0070] Among them, the seed-secondary growth method is adopted. First, a seed crystal is prepared and then a shell is grown on the seed crystal. This method can effectively control the relative content of the two functional groups in the shell and make its core-shell structure have a clear interface and adjustable shell thickness. This is beneficial to forming a uniform anchoring layer on the film surface, while avoiding the problems of MOF particle agglomeration and uneven distribution of functional groups in the physical mixing method.

[0071] Preferably, in A1, the molar ratio of zirconium source to amino ligand is 1:0.5-1:2, and the molar ratio of crystal form regulator to zirconium source is 80:1-150:1, ensuring the acquisition of seed crystals with high crystallinity. In A2, the ratio of the total molar amount of zirconium source to the total molar amount of amino ligand and sulfonic acid ligand is 1:0.8-1:1.5, ensuring charge balance. The molar ratio of amino ligand to sulfonic acid ligand is 1:0.5-1:5, and this ratio is adjustable. By adjusting this ratio, the proportion of functional groups on the shell surface can be changed, thereby adjusting the binding strength and number of MOFs of the present invention with different monomers, and thus adjusting the regular structure of the separation layer, its strength, and flux.

[0072] The raw materials for the MOF in this invention can be flexibly selected based on actual raw material costs and supply conditions, as long as they can form a MOF with a bifunctional core-shell structure. Preferably, in S1, the zirconium source is at least one of zirconium tetrachloride, zirconium oxychloride, or zirconium acetate. The amino ligand is at least one of aminoterephthalic acid, diaminoterephthalic acid, aminoisophthalic acid, or aminobenzoic acid. The sulfonic acid ligand is at least one of monosodium sulfonate terephthalate, monosodium sulfonate isophthalate, sulfonate benzoic acid, or 2-sulfonate terephthalic acid. The first solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. The crystal form regulator is at least one of glacial acetic acid, benzoic acid, formic acid, or trifluoroacetic acid. All of these substances can form MOFs with relatively regular topological structures, such as the UiO-66 structure, through similar hydrothermal reaction pathways, and can achieve functionalization of the amino and sulfonic acid groups. All options can yield core-shell MOF materials with regular channels and bifunctional surfaces, and the actual materials can be industrialized according to cost and actual conditions.

[0073] Preferably, in S2, the ultrafiltration support membrane 1 treated in S1 is immersed in the aqueous monomer solution and the organic monomer solution in turn, reacted for a predetermined time, and then taken out. It is then heat-treated and cured at 75-95℃ for 5-15 minutes to allow the aqueous monomer and the organic monomer to undergo interfacial polymerization, cross-linking and curing, forming a polyamide separation layer 3.

[0074] The aqueous phase monomer is a diamine or polyamine monomer, and the organic phase monomer is a polyacrylamide monomer. The solvent in the aqueous phase monomer solution is water, and the organic phase monomer solution can use a conventional organic solvent, such as the same as the first solvent, which will not be elaborated in this invention.

[0075] More preferably, the aqueous phase monomer comprises m-phenylenediamine, and the organic phase monomer comprises pyromellitic acid chloride.

[0076] By controlling the aqueous phase immersion time and organic phase contact time, the adsorption amount of m-phenylenediamine on the MOF layer surface and its diffusion into the MOF channels can be adjusted, thereby affecting the crosslinking density and thickness of the polyamide layer. The selection of heat treatment temperature and time must ensure that the amidation reaction proceeds fully to form a complete crosslinked network. If the reaction time is too short or the temperature is too low, the crosslinking will be incomplete, resulting in insufficient desalination. If the time is too long or the temperature is too high, the crosslinking will be excessive, leading to an overly dense separation layer and a decrease in throughput.

[0077] More preferably, in this invention, the contact time of the aqueous solution is 1-5 minutes, preferably 2-3 minutes. The contact time of the organic phase is 10-60 seconds, preferably 15-30 seconds. By controlling the aqueous phase wetting time, the adsorption amount of m-phenylenediamine on the MOF layer surface and the degree of diffusion into the MOF channels can be adjusted. If the wetting time is too short (e.g., less than 1 minute), the adsorption of m-phenylenediamine is insufficient, which may lead to insufficient subsequent crosslinking points, defects in the separation layer, and problems such as excessive decrease in desalination rate. If the wetting time is too long (e.g., more than 5 minutes), excessive adsorption may lead to an excessively thick separation layer and excessive crosslinking, increased resistance to water molecule transport, and reduced flux. The organic phase contact time of 10-60 seconds ensures sufficient reaction between trimesoyl chloride and m-phenylenediamine and the functional groups of the MOF. If the contact time is too short, the interfacial polymerization is incomplete, and the separation layer is incomplete. If the contact time is too long, an excessively thick and dense crosslinked layer may be formed, which is not conducive to improving flux.

[0078] Preferably, in step S3, the ultrafiltration support membrane 1, after treatment in step S2, is immersed in a weakly alkaline buffer solution containing a catechol derivative and a porogen. An oxidant is then added, and the reaction is carried out at 25-40°C for 0.2-1 hours, depositing an initiation layer 4 rich in primary / secondary amine groups on the membrane surface. The porogen is encapsulated within the initiation layer 4 during the deposition of the catechol derivative. After deposition, the membrane is rinsed or soaked in water to dissolve the porogen, forming nanoscale hydrophilic channels within the initiation layer 4 and at its interface with the polyamide separation layer 3, providing additional low-resistance pathways for water molecules.

[0079] Among these, the oxidant accelerates the oxidative self-polymerization reaction of catechol derivatives, enabling the deposition process to be completed quickly and resulting in a more uniform coating. More importantly, while catalyzing self-polymerization, the oxidant also oxidatively modifies the surface of the polyamide separation layer 3, altering and regulating its crosslinking state and surface chemical properties. This adjusts the desalination rate of the separation layer from the conventional 99.5% or higher to a more suitable range of 93%-99%, and also achieves better resistance to oxidative contamination.

[0080] This invention employs an oxidative self-polymerization method that can efficiently construct an initiation layer 4 rich in active sites and achieve hydrophilic channel pore formation while simultaneously regulating the desalination performance of the separation layer. No additional processing steps are required, resulting in a more compact process flow.

[0081] Of course, if the operation speed is fast enough, the catechol derivative, pore-forming agent and oxidant can be directly mixed to form a mixed solution, and then the S2-treated substrate can be immediately immersed in the mixed solution to ensure that the catechol derivative can be oxidized and self-polymerized on the substrate.

[0082] Preferably, in S3, the mass concentration of the catechol derivative in the weakly alkaline buffer solution is 0.5-2.0 mg / mL, and the mass concentration of the oxidant is 1.0-10.0 mmol / L, ensuring sufficient oxidation effect while avoiding excessive oxidation effect that would lead to a significant decrease in desalination rate.

[0083] Preferably, the oxidant is at least one of sodium periodate or hydrogen peroxide. The selection of the oxidant must balance catalytic efficiency and safety. This invention preferably uses sodium periodate or hydrogen peroxide, both of which are relatively mild strong oxidants, capable of effectively catalyzing self-polymerization while controlling oxidative damage to the polyamide layer. Furthermore, strong oxidants such as potassium permanganate should be avoided, as their excessive oxidizing power can easily lead to over-oxidation of the separation layer, causing irreversible decreases in desalination rate and other problems.

[0084] More preferably, in S3, the pH value of the weakly alkaline buffer solution is 7.5-9.0 to ensure a moderate reaction rate and a uniform and dense coating. The weakly alkaline buffer solution can be any conventional weakly alkaline buffer solution, such as a conventional carbonate buffer solution (with water as the solvent), which can be selected according to the actual situation.

[0085] Preferably, the catechol derivative is a catechol derivative containing primary / secondary amine groups. The primary / secondary amine groups enrich the interface formation of the primary / secondary amine groups, providing a better foundation for subsequent grafting of epoxy zwitterions. Simultaneously, the primary / secondary amine groups can accelerate the self-polymerization process of the adhesion layer and avoid problems such as excessive oxidation.

[0086] Preferably, the catechol derivative is at least one of dopamine hydrochloride, chitosan-catechol coupling compound, and gelatin-dopamine conjugate, all of which contain a large number of amine groups to ensure the effects of grafting and oxidative self-polymerization.

[0087] Furthermore, it should be noted that this invention does not necessarily require the selection of catechol derivatives containing primary / secondary amine groups as raw materials. Since the activation treatment in S1 negatively introduces amino groups onto the substrate, and the bifunctional core-shell Zr-MOF material used in this application may also contain a large number of amino groups (primary amine groups), when using catechol derivatives containing unsaturated carbonyl compounds, they may also undergo conjugated addition reactions through these residual, exposed amino groups, converting the primary amine into a secondary amine to form the basic initiation layer 4 structure. However, the resulting hierarchical structure may be relatively incomplete, and the number of secondary amine sites provided may be limited; therefore, it is generally not used as the primary initiation layer 4 construction material. If necessary, other types of catechol derivatives can also be added as supplements to the raw materials used in this application, and used in combination with catechol derivatives containing primary / secondary amine groups to improve the utilization rate of amine groups and further enhance the desalination effect.

[0088] Preferably, the catechol derivative containing an unsaturated carbonyl compound can be selected from 4-butylbenzaldehyde and 3,4-dihydroxybenzaldehyde, etc.

[0089] Preferably, in step S3, the porogen concentration is 0.5-3.0 mg / mL to ensure the formation of a sufficient number of interconnected channels in the initiation layer 4. The molecular weight is 400-2000 Da to ensure the pore size formed by the porogen is moderate (within the range of 2-20 nanometers), allowing for rapid water molecule passage while preventing contaminants from entering. Excessively large molecular weight may hinder porogen dissolution or reduce desalination rate, while excessively small molecular weight results in overly small and easily collapsed channels. By controlling the concentration and molecular chain of the porogen, the pore size and distribution of the nanoscale hydrophilic channels are ensured to be controllable, maintaining a balance between water molecule transport resistance and desalination rate.

[0090] Preferably, in S3, the pore-forming agent includes at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble polysaccharide, or hydrophilic ionic liquid, ensuring that it can be effectively dissolved by water washing.

[0091] More preferably, in S4, after the initiation layer 4 is formed, it is cleaned, and after the pore-forming agent is removed, it is immersed in an aqueous solution containing a reducing agent to avoid problems such as oxidant residue.

[0092] Preferably, in step S4, the ultrafiltration support membrane 1 treated in step S3 is placed in a grafting reaction solution containing an epoxy-containing zwitterionic block copolymer, the pH is adjusted to a weakly alkaline condition, and the grafting reaction is carried out under stirring or standing conditions.

[0093] Preferably, when adjusting the pH, water can be used as a solvent, and conventional inorganic bases such as sodium hydroxide and ammonia can be used for adjustment. Alternatively, buffer solutions such as carbonate buffer or Tris-HCl buffer solution can be directly prepared and used as solvents to maintain pH stability.

[0094] Preferably, in S4, the block structure of the zwitterionic block copolymer containing epoxy groups is hydrophobic segment-hydrophilic zwitterionic segment-epoxy functional end group (hydrophobic segment-block-hydrophilic zwitterionic segment-block-epoxy functional end group), with a number average molecular weight of 2000-20000, ensuring that the segments have sufficient anti-fouling properties and avoiding steric hindrance caused by excessively large molecular weight affecting grafting density.

[0095] Preferably, in step S4, the mass concentration of the zwitterionic copolymer containing epoxy groups in the grafting reaction solution is 0.02%-0.5%. The grafting reaction is carried out under alkaline conditions with a pH of 8.5-9.5, for a reaction time of 2-8 hours, and at a reaction temperature of 20-45°C. The goal is to ensure the formation of a uniform and dense brush layer.

[0096] Preferably, the epoxy-containing zwitterionic block copolymer is selected from at least one of glycidyl ether-b-polysulfonyl betaine methacrylate block copolymer and polystyrene-b-polycarboxybetaine methacrylate block copolymer, and the molecular chain of the block copolymer is bonded to epoxy-based active functional groups.

[0097] More preferably, the epoxy-based active functional group is polypropylene oxide or cyclohexane ethyl ether, and more preferably, the epoxy-containing zwitterionic block copolymer is at least one of polypropylene oxide-block-polysulfobetaine methyl methacrylate-block-glycidyl ether, or polystyrene-block-polycarboxybetaine methyl methacrylate-block-cyclohexane ethyl ether. Both polymers have good resistance to protein and inorganic colloidal contamination, and the linkages formed after the epoxy ring-opening reaction have high chemical stability, making the brush layer less prone to peeling off.

[0098] Preferably, in step S4, the thermosetting process is performed in a vacuum environment at a thermosetting temperature of 50-85°C for 20-40 minutes. This ensures effective removal of the solvent and complete curing.

[0099] In a second aspect, the present invention also provides a high-flux, anti-fouling composite reverse osmosis membrane prepared by the preparation method as described in any one of the first aspects, comprising:

[0100] Ultrafiltration support membrane 1;

[0101] A bifunctional core-shell MOF is anchored on the surface of the ultrafiltration support membrane 1 to form an MOF modification layer 2; the bifunctional core-shell MOF has a shell containing two different types of functional groups;

[0102] A polyamide separation layer 3 is formed on the surface of the ultrafiltration support membrane 1. The polyamide separation layer 3 is formed by interfacial polymerization reaction, and the aqueous monomer and organic monomer of the interfacial polymerization reaction are covalently connected to different types of functional groups in the shell of the bifunctional core-shell MOF.

[0103] An initiation layer 4 is composited on the polyamide separation layer 3, and the initiation layer 4 is an oxidative self-polymer of catechol derivative;

[0104] And a hydrophilic antifouling copolymer brush layer grafted and fixed to the surface of the dynamic adhesion initiation layer 4. This copolymer brush layer is obtained by covalently bonding a zwitterionic block copolymer containing epoxy groups to the primary / secondary amine active sites on the surface of the initiation layer 4 through the ring-opening reaction of epoxy groups.

[0105] In the reverse osmosis membrane prepared by this invention, the ultrafiltration support substrate 1 provides basic mechanical strength, and the MOF modified layer 2 serves as an ordered growth base, guiding the separation layer to form a regular network. The polyamide separation layer 3 ensures good ion retention even at high flux. The nanochannels in the initiation layer 4 reduce water transport resistance and provide active grafting sites. The brush layer forms a hydration layer and further resists contaminant adhesion. The synergistic effect of these layers enables the reverse osmosis membrane of this invention to possess characteristics such as high flux, low operating pressure, strong antifouling performance, and suitable desalination rate, making it suitable for treating agricultural irrigation water.

[0106] Preferably, the thickness of the ultrafiltration support membrane 1 is 50-150 micrometers, providing sufficient mechanical strength without excessively increasing water resistance. The pure water flux of the ultrafiltration support membrane 1 is not less than 200 L / (m²). 2 (·h·bar), to prevent it from limiting the flux of the reverse osmosis membrane.

[0107] The ultrafiltration support membrane 1 is made of at least one of polysulfone, polyethersulfone, polyacrylonitrile, or polyvinylidene fluoride, and the average pore size of the ultrafiltration support membrane 1 does not exceed 100 nm. Those skilled in the art can confirm the actual material and its average pore size based on the specific circumstances, ensuring the proper preparation of the reverse osmosis membrane.

[0108] Preferably, the particle size of the bifunctional core-shell Zr-MOF is 30-200 nanometers, more preferably 30-80 nanometers, ensuring that it is uniformly anchored on the surface of the substrate membrane without clogging the pores of the ultrafiltration substrate membrane. The thickness of the MOF modification layer 2 is 30-200 nanometers, more preferably 30-80 nanometers. More preferably, the MOF modification layer 2 is a layered structure formed by the stacking of single-layer or double-layer particles of bifunctional core-shell Zr-MOF. It is important to avoid the MOF modification layer 2 causing multiple layers of bifunctional core-shell MOF to accumulate, thus preventing damage to its guiding effect and the inability to construct regular pores.

[0109] Preferably, the thickness of the polyamide separation layer 3 is 50-300 nanometers to ensure sufficient desalination performance without excessively reducing the throughput due to excessive thickness.

[0110] Preferably, the thickness of the initiating layer 4 is 20-100 nanometers, avoiding problems such as insufficient grafting sites due to excessive thinness and increased water resistance due to excessive thickness. In the initiating layer 4, the average pore size of the nanoscale hydrophilic channels is 2-20 nanometers, and the porosity is 30%-50%, ensuring that it can effectively reduce water resistance and prevent contaminants from entering. The thickness of the hydrophilic antifouling copolymer brush layer 5 is 10-80 nanometers, while avoiding excessive thickness that would reduce flux.

[0111] Thirdly, the present invention also provides an application of the high-flux antifouling composite reverse osmosis membrane as described in the second aspect in brackish water treatment, employing a treatment system comprising the following units:

[0112] The aeration pretreatment unit is used to oxidize brackish water with air, converting dissolved ferrous ions into ferric ions, which then form ferric hydroxide colloids and self-flocculate and precipitate. At the same time, some manganese ions can also be oxidized to form manganese dioxide particles or form colloids after the pH increases.

[0113] The submersible ultrafiltration unit has its inlet connected to the outlet of the aeration pretreatment unit, and is used to further remove residual suspended solids, colloidal particles and some microorganisms in the water, thereby reducing the turbidity of the produced water.

[0114] The reverse osmosis unit comprises at least one high-flux, fouling-resistant composite reverse osmosis membrane as described in the second aspect. The inlet of the reverse osmosis unit is connected to the outlet of the submerged ultrafiltration unit for further removal of residual iron, manganese, and other ions, thereby desalinizing the effluent to meet agricultural irrigation water standards.

[0115] The system also includes a concentrate recovery unit, which is connected to the concentrate outlet of the reverse osmosis unit. This unit is used to recover and treat the reverse osmosis concentrate, such as by evaporation and crystallization to recover salts, or by further concentration for use as industrial raw materials, thus avoiding environmental problems caused by direct discharge of concentrate.

[0116] The reverse osmosis unit produces usable desalinated water at its product outlet, which can be connected to an agricultural water system for use as desalinated irrigation water for agricultural purposes. Of course, it can also be connected to other systems when necessary for use as farmland reclaimed water, domestic miscellaneous water, greywater, non-drinking reclaimed water, or water-saving alternative water sources for other purposes.

[0117] It should be noted that, due to the use of the high-flux, fouling-resistant composite reverse osmosis membrane of this invention, its tolerance to iron, manganese colloids, and organic matter is significantly superior to that of conventional reverse osmosis membranes. Even when the iron content in the reverse osmosis feed water reaches 0.1-0.2 mg / L and the manganese content reaches 0.05-0.10 mg / L (approximately 2-4 times the recommended feed water limit for conventional reverse osmosis membranes), the membrane of this invention can still maintain stable flux and desalination rate, with a low flux decline rate over long-term operation. Therefore, the system of this invention does not require the multi-stage pretreatment units such as sand filtration, multi-media filtration, manganese sand filtration, and softening necessary in conventional brackish water treatment processes. Only two stages of treatment, aeration oxidation + submerged ultrafiltration, are needed to meet the basic feed water requirements of the reverse osmosis unit. Compared with conventional multi-stage pretreatment processes (usually containing 5-7 units), the pretreatment process of this system is significantly shortened, the floor space is reduced, and the civil engineering and equipment investment costs are greatly reduced. At the same time, each reduction in a filtration unit reduces the corresponding backwash water and sewage losses, and the overall water recovery rate of the system is improved. The entire system has a short process for treating brackish water into qualified irrigation water, is highly integrated, and is easy to operate. The cost per ton of water treated is significantly lower than that of conventional processes, making it suitable for large-scale agricultural irrigation in arid regions.

[0118] Preferably, the aeration pretreatment unit can be a conventional microporous aeration disc or aeration pipe aeration system.

[0119] In a cotton-growing region, the common water quality parameters of brackish groundwater are: TDS 8-20 g / L, Fe content <10 ppm, SO4 2- Content > 2000 ppm, turbidity < 10 NTU. Under these conditions, during aeration, the air-to-water volume ratio can be controlled between 2:1 and 5:1, and the residence time can be 20-40 minutes. This can basically reduce the iron content from a few milligrams per liter to below 0.2 milligrams per liter, and the manganese content to below 0.1 milligrams per liter, while also reducing some of the turbidity.

[0120] Preferably, the submerged ultrafiltration unit can be a conventional hollow tubular ultrafiltration membrane with a pore size of 20-50 nanometers and a length of 1-2 meters. This membrane can effectively intercept the iron and manganese hydroxide flocs generated after aeration, reducing the turbidity of the product water to below 0.2 NTU and almost completely removing suspended solids. At the same time, the iron and manganese content is further reduced to the acceptable range of the reverse osmosis unit of this invention (e.g., iron ≤ 0.1-0.2 mg / L, manganese ≤ 0.05-0.10 mg / L).

[0121] Preferably, the reverse osmosis unit is also equipped with a scale inhibitor addition port, allowing for the addition of an appropriate amount of scale inhibitor as needed. The scale inhibitor includes at least one of organophosphonates, polycarboxylate salts, or sulfonates. The dosage can be determined based on the specific circumstances, such as 1-5 mg / L.

[0122] It should be noted that the reverse osmosis membrane of this invention, due to its zwitterionic brush layer and nano-hydrophilic channels, exhibits excellent adaptability to scale inhibitors and can work synergistically with conventional scale inhibitors. Compared to conventional reverse osmosis membranes, which often require higher scale inhibitor dosages (typically 3-8 mg / L) in the treatment of high-hardness, high-sulfate brackish water, the membrane of this invention, due to its strong antifouling properties, can achieve the same or even better scale inhibition effects with lower scale inhibitor dosages (e.g., 1-3 mg / L), helping to reduce reagent costs and chemical discharge risks. Furthermore, even if slight scaling occurs due to operational fluctuations or insufficient reagent dosage, the membrane of this invention, due to its regular MOF guided network structure and stable antifouling brush layer, shows less flux decline and desalination rate reduction than conventional membranes. Therefore, the membrane of this invention can be flexibly adapted to conventional scale inhibitors or other auxiliary methods to extend membrane life (such as periodic low-pressure flushing, online chemical enhanced backwashing, etc.), allowing users to choose the most economical and effective combination scheme based on specific water quality conditions and operation and maintenance levels.

[0123] Furthermore, it should be noted that in order to maximize the service life of the membrane module, reduce the frequency of chemical cleaning, and maintain a higher stable flux, the pretreatment parameters can still be appropriately enhanced. For example, the aeration residence time can be extended to 40-60 minutes, or the filtration accuracy of the ultrafiltration membrane can be improved (pore size below 20 nanometers), further reducing the iron and manganese content in the reverse osmosis feed water to below 0.05 mg / L. This can further delay the accumulation of contaminants on the membrane surface, thus extending the membrane's service life. However, it should be pointed out that even with a conventional two-stage pretreatment without enhancement, the membrane of this invention can still operate stably for a long time with a low flux decline rate. During use, the degree of pretreatment can be flexibly selected according to cost and quality requirements, without being forced to adopt a long-process, high-cost pretreatment process simply to meet the membrane's stringent feed water requirements.

[0124] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0125] It should be noted in advance that the general structure of the high-flux antifouling composite reverse osmosis membrane prepared in the following embodiments can be referred to as [reference needed]. Figure 1 The structure includes an ultrafiltration support membrane 1, an MOF modification layer 2, a polyamide separation layer 3, an initiation layer 4, and a hydrophilic antifouling copolymer brush layer 5. The corresponding layer structure may vary in thickness, porosity, etc., depending on the process of each embodiment, but the overall structure can remain basically stable and meet the relevant indicators in the specification.

[0126] Example 1:

[0127] This invention provides a method for preparing a high-flux, anti-fouling composite reverse osmosis membrane, comprising the following steps:

[0128] Raw material preparation: Select several polysulfone ultrafiltration support membranes 1 (molecular weight cutoff 30,000, thickness 120 micrometers), soak them in deionized water for 24 hours, changing the deionized water 3 times during the period to complete the pretreatment of the membranes, and set them aside for use.

[0129] Preparation of bifunctional core-shell MOFs:

[0130] A1: Preparation of seed crystals:

[0131] Zirconium tetrachloride and 2-aminoterephthalic acid were added to N,N-dimethylformamide in a molar ratio of 1:1, controlling the concentration of zirconium tetrachloride at 0.0156 mol / L. The solution was sonicated for 30 minutes until completely dissolved, yielding a homogeneous and transparent solution. Glacial acetic acid was added to the solution at a molar ratio of 150:1 to zirconium tetrachloride, and the mixture was stirred for 10 minutes. The mixture was then transferred to a hydrothermal reactor, sealed, and reacted at a constant temperature of 120°C for 12 hours. After natural cooling to room temperature, a UiO-66-NH2 seed suspension was obtained, which was directly used in the next step.

[0132] A2: Preparation of bifunctional core-shell Zr-MOFs:

[0133] Zirconium tetrachloride, 2-aminoterephthalic acid, and monosodium 2-sulfonic acid terephthalate were added to N,N-dimethylformamide at a total molar ratio of 1:0.3:0.7, with the concentration of zirconium tetrachloride controlled at 0.0075 mol / L. The solution was sonicated for 20 minutes until completely dissolved, yielding a growth precursor solution. The precursor solution was added dropwise at a rate of 0.5 mL / min to the seed suspension obtained in A1 (the volume ratio of seed suspension to precursor solution was 2:1), with stirring throughout the process. After the addition was complete, stirring was continued for 30 minutes. The solution was then transferred to a hydrothermal reactor and reacted at a constant temperature of 120°C for 12 hours, followed by natural cooling to room temperature. The resulting suspension was centrifuged, and the supernatant was discarded. The obtained solid was washed three times by centrifugation with N,N-dimethylformamide and three times by centrifugation with anhydrous methanol, with each wash being sonicated for 15 minutes. The washed product was placed in a vacuum drying oven at 60°C for 12 hours to activate it under vacuum, thus obtaining bifunctional core-shell Zr-MOF nanopowder.

[0134] Preparation of epoxy-based zwitterionic block copolymers:

[0135] Hydroxyl-terminated polypropylene oxide (number average molecular weight 2000) was dissolved in anhydrous dichloromethane to prepare a 50 g / L solution. Triethylamine (mass ratio of triethylamine to polypropylene oxide 1:10) was added, and after cooling in an ice bath, epichlorohydrin (molar ratio of epichlorohydrin to polypropylene oxide 3:1) was added dropwise. The reaction was carried out at room temperature for 24 hours to obtain an epoxy-terminated polypropylene oxide macromolecular initiator. Dimethylaminoethyl methacrylate and 1,3-propanesulfonate lactone were mixed in an equimolar ratio and reacted at room temperature for 24 hours to obtain sulfobetaine ethyl methacrylate monomer. An epoxy-terminated polypropylene oxide macromolecular initiator, sulfobetaine ethyl methacrylate monomer, cuprous bromide, and pentamethyldiethylenetriamine were added to dimethyl sulfoxide in a molar ratio of 1:50:1:1.2, controlling the total monomer concentration to 0.2 mol / L. After deoxygenation by purging with nitrogen, the reaction was carried out at 60°C for 12 hours. After dialyzing and freeze-drying, a polypropylene oxide-block-polysulfobetaine ethyl methacrylate block copolymer was obtained. This block copolymer was dissolved in N,N-dimethylformamide to prepare a solution with a concentration of 20 g / L. Potassium carbonate (potassium carbonate to copolymer mass ratio of 1:5) and glycidyl ether (glycidyl ether to copolymer molar ratio of 2:1) were added, and the reaction was carried out at 80°C for 8 hours. After precipitation and drying, an epoxy-based zwitterionic block copolymer (polypropylene oxide-block-polysulfobetaine ethyl methacrylate-block-glycidyl ether, number average molecular weight 5000) was obtained.

[0136] Membrane preparation:

[0137] S1: The pretreated (cleaned) polysulfone ultrafiltration support membrane 1 was immersed in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH=8.5) containing 2 parts by weight of dopamine (mass concentration of dopamine 2 mg / mL) for 30 minutes at room temperature in the dark. After removal, it was rinsed three times with deionized water to obtain an activated membrane with a surface rich in hydroxyl and amino groups. An aqueous dispersion of bifunctional core-shell Zr-MOF was prepared with a MOF mass concentration of 0.05 mg / mL (solvent is deionized water), and sonicated for 30 minutes. The activated membrane was immersed in the dispersion and immersed at room temperature for 30 minutes to form MOF modified layer 2. After removal, the membrane surface was gently rinsed twice with deionized water and dried with nitrogen to obtain a membrane anchored with MOF modified layer 2.

[0138] S2: Construction of polyamide separation layer 3:

[0139] Prepare an aqueous solution containing 2 mg / mL m-phenylenediamine and 0.15 mg / mL triethylamine (deionized water) and stir until completely dissolved. Pour the aqueous solution evenly onto the surface of the substrate membrane anchored with MOF-modified layer 2 and allow it to soak at room temperature for 2 minutes. After discarding the excess aqueous phase, prepare an organic phase solution containing 0.12 mg / mL trimesoyl chloride (hexane) and pour it evenly onto the membrane surface, allowing it to contact for 20 seconds. Discard the excess organic phase and allow it to evaporate naturally for 1 minute. Place the nascent membrane in a 75°C forced-air drying oven for 7 minutes, then remove it and immerse it in deionized water for storage at 4°C.

[0140] S3: Initiates the deposition of layer 4:

[0141] A mixed solution was prepared using a pH 8.5 tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution as the solvent. The chitosan-catechol coupling agent had a mass concentration of 1.5 mg / mL, polyethylene glycol (molecular weight 600) had a mass concentration of 0.5 mg / mL, and sodium periodate had a mass concentration of 0.6 mg / mL. The solution was stirred until completely dissolved. The membrane obtained in S2 was immersed in the above mixed solution and reacted at 25°C for 15 minutes to complete the deposition. After the reaction, the membrane was removed and rinsed three times with deionized water to remove the polyethylene glycol, forming an initiation layer 4 with nanoscale hydrophilic channels.

[0142] The resulting base film with initiation layer 4 was then preserved by immersing it in a sodium bisulfite solution with a mass concentration of 0.5 mg / mL.

[0143] S4: Grafting of hydrophilic antifouling copolymer brush layer 5:

[0144] Using the epoxy-based zwitterionic block copolymer prepared above, a grafting reaction solution was prepared using a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution at pH 9.5 as the solvent. The copolymer concentration was 0.8 mg / mL, and the mixture was sonicated for 15 minutes. The bottom membrane with initiation layer 4 obtained in S3 was removed, its surface moisture was dried with nitrogen, and it was immersed in the above grafting reaction solution. The reaction was carried out at a constant temperature of 30°C for 2.5 hours to form a hydrophilic antifouling copolymer brush layer 5. After the reaction, the membrane was removed, its surface was rinsed four times with deionized water, then rinsed once with anhydrous ethanol, and then the membrane was placed in a vacuum drying oven at 50°C for 30 minutes (thermo-curing treatment). After cooling to room temperature, the high-flux antifouling composite reverse osmosis membrane of this embodiment was obtained.

[0145] Example 2:

[0146] This embodiment provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 is that, in step S2, the mass concentration of intermediate-phenylenediamine in the aqueous phase solution is adjusted to 2.5 mg / mL, and the wetting time is extended to 4 minutes; the mass concentration of trimesoyl chloride in the organic phase solution is adjusted to 0.15 mg / mL, and the contact time is extended to 30 seconds; the heat treatment temperature is increased to 85°C, and the time is extended to 10 minutes. The remaining steps are the same as in Example 1.

[0147] Example 3:

[0148] This embodiment provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 is that in step S3, the concentration of the oxidant sodium periodate is adjusted to 1.4 mg / mL. The remaining steps are the same as in Example 1.

[0149] Example 4:

[0150] This embodiment provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 lies in the ligand replacement of the bifunctional core-shell MOF: 2-aminoterephthalic acid in A1 and A2 is replaced with 2,5-diaminoterephthalic acid, while the remaining molar ratios and solvent volumes remain unchanged. The resulting MOF core is UiO-66-(NH2)2, and the shell contains both amino and sulfonic acid groups. The remaining steps are the same as in Example 1.

[0151] Example 5:

[0152] This embodiment provides a method for preparing a high-flux, anti-fouling composite reverse osmosis membrane. The difference from Example 1 is that polyethylene glycol (a pore-forming agent) is not added to the mixed solution in S5, while the remaining components and reaction conditions remain unchanged. The remaining steps are the same as in Example 1.

[0153] Comparative Example 1

[0154] This comparative example provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 is that in S1, the MOF modification layer 2 is not anchored; in S2, bifunctional core-shell Zr-MOF nanopowder is directly mixed with an aqueous monomer to prepare an aqueous solution containing 0.05 mg / mL MOF and 2 mg / mL m-phenylenediamine, and then the interfacial polymerization step in S2 is performed. The remaining steps are the same as in Example 1.

[0155] In this comparative example, there is no obvious MOF modification layer 2; the MOF is randomly dispersed within the polyamide layer.

[0156] Comparative Example 2:

[0157] This comparative example provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 is that the MOF is a monofunctional (amino-only) structure, and UiO-66-NH2 nanoparticles in A1 are directly synthesized hydrothermally using zirconium tetrachloride and 2-aminoterephthalic acid in a molar ratio of 1:1, without core-shell growth in A2. The remaining steps are the same as in Example 1.

[0158] Comparative Example 3:

[0159] This comparative example provides a method for preparing a high-flux, anti-fouling composite reverse osmosis membrane. The difference from Example 1 is that step S3 is omitted; that is, step S4 is performed directly after step S2. The remaining steps are the same as in Example 1.

[0160] The reverse osmosis membrane obtained in this comparative example has no initiation layer 4, and the brush layer is directly grafted onto the surface of the polyamide separation layer 3, without nanoscale hydrophilic channels.

[0161] Comparative Example 4:

[0162] This comparative example provides a method for preparing a high-flux, antifouling composite reverse osmosis membrane. The difference from Example 1 is that, in step S4, instead of an epoxy ring-opening reaction, a physical coating is used: epoxy-free polysulfonated betaine methacrylate (PSBMA, number average molecular weight 5000) is dissolved in deionized water to prepare a coating solution with a mass concentration of 0.8 mg / mL. The membrane obtained in step S3 is immersed in the coating solution and allowed to stand at 30°C for 2.5 hours. After removal, it is rinsed with deionized water and vacuum dried at 50°C for 30 minutes. The remaining steps are the same as in Example 1.

[0163] The processing system of the present invention was used to conduct experiments with reverse osmosis membranes of several embodiments and comparative examples. The processing system includes an aeration pretreatment unit, a submerged ultrafiltration unit, a reverse osmosis unit, and a concentrate recovery unit connected in sequence.

[0164] The aeration pretreatment unit uses commercially available microporous aeration discs (0.2mm aperture), arranged at the bottom of the aeration tank, supplied with air by a blower, with an air-to-water volume ratio of 3:1 and a residence time of 30 minutes, allowing Fe... 2+ Oxidized to Fe 3+ And it condenses itself.

[0165] The submersible ultrafiltration unit uses a commercially available polyvinylidene fluoride hollow fiber ultrafiltration membrane module with a membrane pore size of 30nm, a porosity of 65%, an operating pressure of 0.05MPa, and a product water turbidity of <0.2NTU.

[0166] The reverse osmosis unit is constructed by assembling the reverse osmosis membranes prepared in Examples 1-5 and Comparative Examples 1-4 into standard spiral wound membrane modules (effective membrane area 2.5 m²). 2 Each component was tested individually. Operating conditions: inlet water pressure 1.5 MPa, temperature 25°C, recovery rate 50%.

[0167] The concentrate recovery unit is an evaporation device. By collecting reverse osmosis concentrate, the water quality indicators of the brackish water treated with salts are shown in Table 1 after evaporation and crystallization.

[0168] Table 1: Raw water indicators for brackish water

[0169]

[0170] Note: Fe and Mn ions may exist in multiple valence states, and their specific valence states are not indicated in the table.

[0171] The water quality parameters after aeration pretreatment and submerged ultrafiltration are shown in Table 2.

[0172] Table 2: Pretreated effluent parameters

[0173]

[0174] The pretreated effluent was then passed into reverse osmosis membrane modules prepared using the membrane modules of Examples 1-5 and Comparative Examples 1-4, respectively, and the following tests were conducted:

[0175] Initial performance test: After stabilizing at 1.5 MPa and 25℃ for 30 minutes, the permeate flux (L / (m³)) was measured. 2 The desalination rate (%) and the desalination rate (%) are recorded in Table 3.

[0176] Long-term operation test: Continuous operation for 200 hours (physical flushing for 10 minutes every 24 hours, without chemical cleaning), then the permeate flux and desalination rate were measured again, and the flux decay rate (initial flux - 200h flux) / initial flux × 100% was calculated. The iron and manganese content in the permeate was also measured. Recorded in Table 4.

[0177] Table 3: Initial Performance Test Results

[0178]

[0179] Table 4: Results of Long-Term Operation Tests

[0180]

[0181] Based on the above, we can find that:

[0182] Example 1, employing the complete technical solution of this invention, exhibits a high initial flux, excellent product water quality, and a high degree of matching between the desalination rate (96.2%) and the iron and manganese removal rates (Fe 95.8%, Mn 96.7%), making it suitable for agricultural irrigation requirements. After long-term operation, the flux decreases by only 10%, while the desalination rate and iron and manganese removal rates remain stable, demonstrating excellent overall performance and pollution resistance.

[0183] Compared to Example 1, Example 2 has a higher initial flux due to the increased concentration of interfacial polymer monomers, extended reaction and heat treatment time, thicker polyamide separation layer 3, and higher crosslinking density. However, the desalination rate and iron and manganese removal rate are further improved, the long-term flux decay is smaller (8%), and the compaction resistance and anti-fouling performance are better.

[0184] Compared to Example 1, Example 3 increased the initial flux due to the increased concentration of oxidant, which led to more nanoscale hydrophilic channels and larger pore sizes in the initiation layer 4. However, the desalination rate (95.0%) and iron and manganese removal rate decreased slightly (but still met the requirements for agricultural irrigation). The flux decay was slightly higher in the long term, indicating that excessive pore formation would slightly reduce the anti-pollution ability while increasing the flux.

[0185] Compared to Example 1, Example 4 replaced the amino ligand with 2,5-diaminoterephthalic acid, which increased the amino density of the MOF shell. Its various properties were basically the same as those of Example 1, indicating that the technical solution of the present invention has a certain degree of universality for MOF ligands.

[0186] Compared to Example 1, Example 5 did not add a pore-forming agent, so there were no nanoscale hydrophilic channels in the initiation layer 4. The resistance of water molecules across the membrane increased, resulting in a decrease in initial flux and a slight increase in desalination rate. However, the lack of hydrophilic channels hindered the maintenance of high flux and the auxiliary antifouling effect, and the flux decay rate during long-term operation was higher than that of Example 1.

[0187] Compared to Example 1, Comparative Example 1 directly physically mixes MOF into the aqueous monomer. The MOF is randomly dispersed in the polyamide layer and cannot form an ordered anchoring and bidirectional connection network. Therefore, the initial flux and desalination rate are significantly reduced, the iron and manganese removal rate is significantly deteriorated, and the MOF is easy to fall off after long-term operation, the flux decays severely, and the desalination rate drops to 90%.

[0188] Compared to Example 1, Comparative Example 2 uses a monofunctional MOF containing only amino groups, lacking the covalent connection between sulfonic acid groups and monomers. The polyamide layer is not firmly bonded to the MOF, and the ordered network is incomplete. Therefore, the initial flux and desalination rate are lower than those of Example 1, the iron and manganese removal rate is poor, and the performance degrades rapidly after long-term operation.

[0189] Compared to Example 1, Comparative Example 3 omitted the initiation layer 4 and directly grafted zwitterionic copolymer onto the polyamide layer. Due to the small number of active sites and low grafting density, the brush layer thickness was only 20-30 nm and the adhesion was poor. The initial performance was acceptable, but after long-term operation, the brush layer was easy to fall off, the flux was severely reduced, the desalination rate dropped to 92%, and the iron and manganese removal rate also decreased significantly.

[0190] Compared to Example 1, Comparative Example 4 uses a zwitterionic polymer with physical coating instead of epoxy ring-opening covalent grafting. There is no covalent bond between the brush layer and the substrate. The initial performance is similar to that of Example 1, but after long-term operation, the coating layer gradually peels off, the flux decay is the most severe, the desalination rate drops to 90%, and the iron and manganese removal rate is the worst.

[0191] In summary, the present invention can solve the technical problems existing in the prior art, such as the low flux of reverse osmosis membranes used for brackish water treatment, the need to maintain high operating pressure when used for industrial irrigation and other purposes, insufficient anti-fouling ability, and difficulty in large-scale and high-speed treatment of underground brackish water.

[0192] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-flux, fouling-resistant composite reverse osmosis membrane, characterized in that, Includes the following steps: S1: Substrate modification: A bifunctional core-shell MOF is anchored on the activated ultrafiltration support substrate (1) to form a MOF modification layer (2). In S1, the activation treatment includes: immersing the ultrafiltration support membrane (1) in a Tris-HCl buffer solution of dopamine and reacting it at room temperature in the dark to obtain an activated membrane with a surface rich in hydroxyl and amino groups; Subsequently, the activated substrate was immersed in an aqueous dispersion containing a bifunctional core-shell MOF to anchor the MOF to the substrate surface, forming a MOF modification layer (2); the mass concentration of the bifunctional core-shell MOF in the aqueous dispersion was 0.02%-0.06%; the bifunctional core-shell MOF was a bifunctional core-shell Zr-MOF material, including a Zr-MOF core and a Zr-MOF bifunctional layer covering the core, wherein the Zr-MOF bifunctional layer was a Zr-MOF constructed from organic ligands containing amino and sulfonic acid groups; S2: Separation layer construction: an interfacial polymerization reaction is carried out on the ultrafiltration support membrane (1) after S1 treatment, followed by thermal curing to obtain a polyamide separation layer (3); the aqueous monomer and organic monomer in the interfacial polymerization reaction are covalently linked to different types of functional groups on the bifunctional core-shell MOF respectively; S3: Construction of the initiation layer (4): Catechol derivatives undergo oxidative self-polymerization under the action of an oxidant, and a pore-forming agent is deposited and coated on the surface of the polyamide separation layer (3) to construct an initiation layer (4) rich in primary / secondary amine groups; after removing the pore-forming agent, a hydrophilic channel is formed in the initiation layer (4); S4: Construction of antifouling layer; through epoxy ring-opening reaction, zwitterionic copolymer containing epoxy groups is grafted onto the initiation layer (4) to form hydrophilic antifouling copolymer brush layer (5); heat curing treatment is performed to obtain high-flux antifouling composite reverse osmosis membrane.

2. The preparation method according to claim 1, characterized in that, In S1, the preparation method of the bifunctional core-shell Zr-MOF material includes: A1: A zirconium source, amino ligand, crystal form regulator and a first solvent are mixed and crystallized by hydrothermal reaction to obtain amino-containing zirconium-based MOF seed crystals; wherein, the molar ratio of zirconium source to amino ligand is 1:0.5-1:2, and the molar ratio of crystal form regulator to zirconium source is 80:1-150:

1. A2: The seed crystal is placed in a growth precursor solution containing a zirconium source, an amino ligand, and a sulfonic acid ligand to carry out a secondary growth reaction, thereby obtaining a bifunctional core-shell Zr-MOF material with both amino and sulfonic acid groups in its outer shell; wherein the ratio of the total molar amount of the zirconium source to the total molar amount of the amino and sulfonic acid ligands is 1:0.8-1:1.5, and the molar ratio of the amino ligand to the sulfonic acid ligand is 1:0.5-1:

5.

3. The preparation method according to claim 2, characterized in that, In S1, the zirconium source is at least one of zirconium tetrachloride, zirconium oxychloride, and zirconium acetate; the amino ligand is at least one of aminoterephthalic acid, diaminoterephthalic acid, aminoisophthalic acid, or aminobenzoic acid; the sulfonic acid ligand is at least one of sulfonic acid monosodium terephthalate, sulfonic acid monosodium terephthalate, sulfonic acid benzoic acid, and 2-sulfonic acid terephthalic acid; the first solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; and the crystal form regulator is at least one of glacial acetic acid, benzoic acid, formic acid, and trifluoroacetic acid.

4. The preparation method according to claim 1, characterized in that, In S2, the interfacial polymerization reaction includes: immersing the ultrafiltration support membrane (1) after S1 treatment into the aqueous monomer solution and the organic monomer solution and taking it out, and then heat-treating and curing it at 75-95℃ for 5-15 minutes to allow the aqueous monomer and the organic monomer to undergo interfacial polymerization to form a polyamide separation layer (3). The aqueous phase monomer is a diamine or polyamine monomer, and the organic phase monomer is a polyacrylamide monomer.

5. The preparation method according to claim 1, characterized in that, In S3, the ultrafiltration support membrane (1) after S2 treatment is immersed in a weakly alkaline buffer solution containing catechol derivatives and pore-forming agents, and then an oxidant is added. The reaction is carried out at 25-40°C for 0.2-1 hours to deposit an initiation layer (4) rich in primary / secondary amine groups on the membrane surface; the catechol derivative is a catechol derivative containing primary / secondary amine groups. During the deposition of catechol derivatives, the pore-forming agent is encapsulated in the initiation layer (4); After deposition, the pore-forming agent is dissolved by rinsing with water, and nanoscale hydrophilic channels are formed in situ inside the initiation layer (4) and at its interface with the polyamide separation layer (3).

6. The preparation method according to claim 5, characterized in that, In S3, the catechol derivative has a mass concentration of 0.5-2.0 mg / mL in a weakly alkaline buffer solution, the oxidant has a mass concentration of 1.0-10.0 mmol / L, the porogen has a mass concentration of 0.5-3.0 mg / mL, and the molecular weight is 400-2000 Da. The pH of the weakly alkaline buffer solution is 7.5-9.0; the catechol derivative is dopamine hydrochloride, gelatin-dopamine conjugate, and chitosan-catechol coupling agent; the oxidant is at least one of sodium periodate or hydrogen peroxide; the porogen includes at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble polysaccharide, or hydrophilic ionic liquid.

7. The preparation method according to claim 1, characterized in that, In S4, the ultrafiltration support membrane (1) after S3 treatment is placed in a grafting reaction solution containing an epoxy-containing zwitterionic block copolymer, and the pH is adjusted to a weakly alkaline condition to carry out the grafting reaction. The molecular structure of the epoxy-containing zwitterionic block copolymer is: hydrophobic segment - hydrophilic zwitterionic segment - epoxy functional end group, with a number average molecular weight of 2000-20000. During the grafting reaction, the mass concentration of the zwitterionic block copolymer containing epoxy groups in the reaction solution is 0.02%-0.5%, the pH value of the system is adjusted to 8.5-9.5, and the reaction is carried out at 20-45℃ for 2-8 hours.

8. A high-flux, antifouling composite reverse osmosis membrane prepared by the preparation method according to any one of claims 1-7, characterized in that, include: Ultrafiltration support membrane (1); A bifunctional core-shell MOF is anchored on the surface of the ultrafiltration support membrane (1) to form a MOF modification layer (2); the bifunctional core-shell MOF has a shell containing two different types of functional groups; A polyamide separation layer (3) is formed on the surface of the ultrafiltration support membrane (1). The polyamide separation layer (3) is formed by interfacial polymerization reaction, and the aqueous monomer and organic monomer of the interfacial polymerization reaction are covalently connected to different types of functional groups in the shell of the bifunctional core-shell MOF. An initiation layer (4) is composited on the polyamide separation layer (3), wherein the initiation layer (4) is an oxidative self-polymer of catechol derivative; And a hydrophilic antifouling copolymer brush layer grafted onto the surface of the initiation layer (4), which is obtained by covalently bonding the zwitterionic block copolymer containing epoxy groups to the active sites on the surface of the initiation layer (4) through the ring-opening reaction of epoxy groups.

9. The application of the high-flux antifouling composite reverse osmosis membrane according to claim 8 in brackish water treatment, characterized in that, The processing system employs the following units: The aeration pretreatment unit is used to oxidize brackish water with air, causing it to self-flocculate. The inlet of the submerged ultrafiltration unit is connected to the outlet of the aeration pretreatment unit to reduce the turbidity of the product water. A reverse osmosis unit, comprising at least one high-flux antifouling composite reverse osmosis membrane as described in claim 8; the inlet of the reverse osmosis unit is connected to the outlet of the submerged ultrafiltration unit; And a concentrate recovery unit, which is connected to the concentrate outlet of the reverse osmosis unit, for recovering and treating the reverse osmosis concentrate; The reverse osmosis unit produces usable desalinated water at its permeate outlet.

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