High-flux high-pollution-resistance nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-flux high-pollution-resistance nanofiltration membrane as well as a preparation method and application thereof. The scheme is realized by constructing a gradient separation layer compounded by modified MOF and polyamide on a porous support layer; the preparation method comprises the following steps: preparing a water phase from modified MOF grafted with carboxylate radical and sulfonate ion recognition groups on the surface, a polyamine monomer and an ion channel regulator, carrying out interfacial polymerization on the water phase and an oil phase containing a fluorine-containing acyl chloride monomer on the surface of a porous support membrane, and carrying out heat treatment and metal ion post-treatment, the modified MOF in gradient distribution in the nanofiltration membrane can specifically adsorb Ca < 2 + >, Mg < 2 + > and other scaling ions, and scale formation is inhibited from the source; the composite structure simultaneously realizes high flux and high selectivity; the retention rate of the membrane to Na2SO4 under 0.6 MPa is greater than or equal to 99.2%, the retention rate of the membrane to NaCl is less than or equal to 15%, the flux of pure water is greater than or equal to 20 L.m <-2 >. H <-1 >. Bar <-1 >, and the flux attenuation rate is less than or equal to 16.7% after the membrane runs in high-hardness, high-COD and high-salinity wastewater for 120 hours; the scheme is particularly suitable for zero-discharge pretreatment of high-salinity wastewater such as solid waste percolate with the TDS of 5-30% and chemical engineering.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology and water treatment, specifically relating to a composite nanofiltration membrane with gradient structure and scale-causing ion differentiation function constructed by regulating the interfacial polymerization process through functionalized MOF materials. Background Technology

[0002] High-salinity wastewater refers to wastewater with a total salt content of at least 3.5 wt%, mainly containing Cl. - SO4 2- Na + Ca 2+ High-salinity wastewater, containing inorganic salt ions, heavy metals, and organic pollutants, originates from industries such as chemical, pharmaceutical, and dyeing. Its high salinity easily leads to ecological problems such as soil compaction and eutrophication of water bodies. In my country, high-salinity wastewater accounts for 5% of total wastewater volume, with an annual growth rate of 2%. The challenges in its treatment lie in crystallization and scaling, secondary pollution, and inhibition of microbial activity. Zero-discharge (ZLD) technology for high-salinity wastewater has become a necessity for environmental protection in industries such as solid waste, chemicals, and power. Besides the aforementioned inorganic salt ions, the types of inorganic salts contained in industrial wastewater vary greatly across different industries. Some high-salinity wastewater contains heavy metals. Due to the large volume of industrial wastewater discharge in my country and the bioaccumulation effect of heavy metals and other inorganic salts, long-term discharge of industrial wastewater poses a serious threat to the environment and organisms. Taking solid wastewater as an example, its main characteristics are high salinity, with TDS reaching 5%-30%, primarily composed of inorganic salts such as NaCl, and some containing combined COD and heavy metal pollution, requiring multi-stage synergistic removal. The water quality and salinity fluctuate significantly due to the influence of solid waste sources, with TDS ranging from 5% to 30%, requiring dynamic adjustment of reagent dosage. It also exhibits high hardness and high calcium content in the water. 2+ Mg 2+ Coexisting with silicates, traditional softening methods easily generate CaSiO3 colloids that clog filter membranes. High organic content is also a concern, as leachate from solid waste incineration fly ash and landfills may contain recalcitrant organic compounds such as dioxins and polycyclic aromatic hydrocarbons. The current treatment processes face three core challenges: high treatment costs, low salt resource utilization rates, and poor system stability. These challenges are also pressing issues for businesses.

[0003] Nanofiltration membranes play an irreplaceable role in drinking water softening, advanced wastewater treatment, and material separation and concentration due to their high rejection rate for divalent ions and small organic molecules, while retaining relatively low levels of monovalent ions. Currently, interfacial polymerization is the most successful technology for preparing commercial thin-layer composite nanofiltration membranes. It involves the irreversible polycondensation reaction of aqueous amine monomers and oil-phase acyl chloride monomers on the surface of a porous supported membrane to form an ultrathin polyamide separation layer. CN118477494A discloses a method for preparing a high-flux, anti-wetting, anti-fouling, and anti-scaling dense Janus membrane, which involves interfacial polymerization of a hydrophilic modified membrane with an active monomer, followed by drying to obtain the target dense Janus distillation membrane. CN120094423A uses a styrene-maleic anhydride copolymer and a fluoropolymer as substrates, employing thermally induced phase separation technology to prepare a "fluoropolymer / styrene-maleic anhydride" porous membrane. Then, the chemical reaction between the anhydride on the membrane surface and a small number of amine groups in the chitosan chains is utilized to load chitosan onto the porous membrane surface. The pH-responsive chitosan molecular chains not only enhance the hydrophilicity of the membrane, thus slowing down the deposition of inorganic scale on the membrane surface, but also undergo a reversible conformational change from "curling" to "unfurling" during the membrane's acid-alkali washing process. This loosens the hardened inorganic scale deposited on the membrane surface and weakens its binding force, facilitating effective removal of the inorganic scale through subsequent surface water rinsing. CN115400612A utilizes bulk doping to incorporate nanomaterials montmorillonite / modified montmorillonite into the polyamide membrane separation layer based on existing interfacial polymerization. The process is simple and highly operable. CN113244780B addresses the stability and yellowing issues of reverse osmosis membrane coatings by modifying the coating through active polymerization. It utilizes the amphoteric monomers 2-(methacryloyloxy)ethyldimethyl-(3-sulfopropyl)ammonium hydroxide (MEDSAH), ethylene glycol methacrylate (EGMA), and anti-yellowing particles isobutoxymethacrylamide (IBMA) to graft onto the reverse osmosis membrane surface, forming a three-network high-performance PMEDSAH / PEGMA / PIBMA polymeric coating. Through the three-system regulation of the PA layer's activity, PMEDSAH exhibits high compatibility, PEGMA provides stability, high hydrophilicity, and resistance to protein fouling, and finally, PIBMA coating the membrane surface achieves anti-yellowing. CN117225194A utilizes zwitterionic monomers as gel layer precursors and employs simple coating and thermal crosslinking techniques to prepare high-flux anti-fouling / wetting composite distillation membranes. The preparation method is simple, low-cost, and suitable for industrial production. However, the polyamide layer structure formed by traditional interfacial polymerization has inherent limitations. To achieve high selectivity, a dense and thick cross-linked network is often formed, resulting in high water mass transfer resistance and low flux (the "flux-selectivity trade-off" effect). At the same time, the inherent wrinkles and negative charge on its surface easily lead to the adsorption and deposition of hydrophobic pollutants, organic macromolecules and microorganisms, causing serious membrane fouling problems, resulting in increased operating energy consumption, shortened membrane life and high cleaning costs.

[0004] In particular, scale-forming ions (Ca) in high-salinity wastewater 2+ Mg 2+ ) and SiO3 2- When these substances coexist, dense CaSiO3 colloidal scale easily forms on the membrane surface. Traditional anti-scaling strategies (such as adding scale inhibitors) are prone to secondary pollution and have limited effectiveness. Therefore, there is an urgent need to develop a novel nanofiltration membrane that can regulate the membrane structure at the molecular level to achieve in-situ differentiation of scale-causing ions and reduce local supersaturation. Summary of the Invention

[0005] This invention provides a high-performance nanofiltration membrane for high-salinity wastewater treatment and its preparation method, particularly relating to a composite nanofiltration membrane with a gradient structure and scale-causing ion separation function constructed by controlling the interfacial polymerization process using functionalized MOF materials. This invention achieves a breakthrough in membrane performance by constructing a MOF / polyamide composite separation layer with gradient functions and ion recognition capabilities.

[0006] This invention aims to solve three major technical challenges of existing nanofiltration membranes in treating high-salinity wastewater: 1) difficulty in simultaneously achieving high flux and selectivity; 2) insufficient anti-scaling performance, especially for Ca2+. 2+ -SiO3 2- 3) Poor inhibition effect of complex scale; 4) Low long-term operational stability under complex water conditions.

[0007] One objective of this invention is to provide a high-flux, highly fouling-resistant nanofiltration membrane, comprising a porous support layer and a composite separation layer loaded thereon; the composite separation layer is a MOF / polyamide composite layer with a three-dimensional gradient structure, wherein modified MOF nanoparticles are anchored in the polyamide network by chemical bonds and are distributed in a gradient direction in the thickness direction of the separation layer.

[0008] Preferably, the thickness of the composite separation layer is 80~180 nm.

[0009] A second objective of this invention is to provide a method for preparing a high-flux, highly fouling-resistant nanofiltration membrane, comprising the following steps: S1, Preparation of modified MOF nanoparticles: Select a matrix MOF containing amino groups on its surface, and graft at least two different ion recognition groups onto its surface by ligand modification to obtain modified MOF nanoparticles. S2, Preparation of functionalized aqueous solution: Dissolve the polyamine monomer, the modified MOF nanoparticles described in S1 and the ion channel modifier in deionized water and disperse them evenly to obtain the functionalized aqueous solution; S3, interfacial polymerization reaction: The porous support membrane is immersed in the functionalized aqueous solution prepared in S2, so that the aqueous components are adsorbed on its surface, and then it is contacted with an oil solution containing polyacrylamide chloride monomer to carry out an interfacial polymerization reaction. S4, Post-treatment: After removing the oil phase, the membrane after the reaction is heat-treated, then immersed in an aqueous solution containing metal ions for functional enhancement treatment, and after cleaning, the high-flux, high-fouling-resistant nanofiltration membrane is obtained.

[0010] Preferably, in S1, the matrix MOF is selected from at least one of UiO-66-NH2, MIL-101-NH2 or ZIF-8; the ion recognition group is selected from at least two of carboxylate, sulfonate and phosphate groups.

[0011] Preferably, in S1, the ligand modification method is as follows: the matrix MOF is dispersed in a mixed solution containing 2-aminoterephthalic acid and 2-sulfoterephthalic acid, and reacted at 80~120℃ for 12~48 hours to obtain modified MOF nanoparticles with carboxylate and sulfonate groups on the surface, and the particle size is 50-200 nm.

[0012] Preferably, in S2, the concentration of the polyamine monomer in the functionalized aqueous solution is 0.5~3.0 wt%, the concentration of the modified MOF nanoparticles is 0.1~0.8 wt%, and the concentration of the ion channel modulator is 0.05~0.3 wt%.

[0013] More preferably, in S2, the polyamine monomer is selected from a mixture of piperazine, m-phenylenediamine and polyethyleneimine, and the mass ratio of the three is (2~5):(1~3):(0.5~2); the ion channel modulator is selected from at least one of 4-sulfonic acid calix[4] aromatics, cyclodextrin-sulfonic acid derivatives or crown ether-carboxylic acid derivatives.

[0014] Preferably, in S3, the polyacrylamide chloride monomer in the oil phase solution is a mixture of pyromellitic tricarboxylic acid chloride and fluorinated acrylamide chloride monomer, with a mass ratio of (3~8):1; the fluorinated acrylamide chloride monomer is at least one of pentafluorobenzoyl chloride, 2,4,6-trifluorobenzoyl chloride, tetrafluoroterephthaloyl chloride, or fluorinated aliphatic diacrylamide chloride; the interfacial polymerization reaction time is 30~120 seconds.

[0015] Preferably, in step S4, the heat treatment temperature is 60-80°C, and the time is 5-15 minutes; the metal ions used in the functional enhancement treatment are selected from Zn. 2+ Zr 4+ Al 3+ At least one of them, the processing time is 10 to 30 minutes.

[0016] A third objective of this invention is to provide an application of the high-flux, high-fouling-resistant nanofiltration membrane in the treatment of high-salinity wastewater, wherein the total dissolved solids content of the high-salinity wastewater is 5-30%, and it contains Ca. 2+ Mg 2+and SiO3 2- At least one of them. Beneficial effects

[0017] This invention addresses three core challenges in nanofiltration treatment of high-salt wastewater—the trade-off between flux and selectivity, severe membrane scaling and fouling, and poor long-term operational stability—by constructing a "modified MOF / polyamide gradient composite separation layer," achieving synergistic and significant technological advancements from the structural design perspective.

[0018] 1. Breakthrough in separation performance: Breaking the trade-off between flux and selectivity - This scheme achieves low-resistance transport of water and monovalent ions through a gradient pore structure, while the dense MOF enrichment substrate ensures efficient sieving of divalent ions, thereby significantly increasing flux while achieving excellent monovalent / divalent ion selectivity.

[0019] 2. Innovation in Anti-scaling and Anti-fouling Capabilities: From "Scale Inhibition" to "Dissociation of Scale-Causing Ions"—In this scheme, the ion recognition groups (-COOH, -SO3H) on the modified MOF surface can specifically adsorb and "store" Ca. 2+ Mg 2+ The presence of scale-inducing ions thermodynamically reduces local supersaturation on the film surface, fundamentally inhibiting the formation of hard scale such as CaSiO3. Simultaneously, fluorinated segments and hydrophilic groups construct an anti-fouling surface.

[0020] 3. Improved Long-Term Process Stability and Economic Efficiency – This solution, through the synergistic effect of functionalized components, allows the membrane performance to have a wider tolerance to fluctuations in key process parameters such as amine concentration and polymerization time (as shown in Examples 4-15), reducing the difficulty of production control. In practical applications, it can significantly reduce the amount of scale inhibitor used, extend the chemical cleaning cycle, and reduce operating energy consumption. Attached Figure Description

[0021] Figure 1 A schematic diagram of the preparation of high-flux, highly fouling-resistant nanofiltration membranes based on MOF material-controlled interfacial polymerization; Figure 2 This is a schematic diagram of the separation mechanism of a high-flux, highly fouling-resistant nanofiltration membrane. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and appendices, but the scope of protection of the present invention is not limited thereto.

[0023] To ensure the accuracy and comparability of nanofiltration membrane performance evaluations in all embodiments and comparative examples, this section uniformly specifies the following standard test methods and calculation methods. All tests were conducted in cross-flow filtration devices of the same specifications (effective membrane area A = 20 cm²). Before testing, all membrane samples were pre-pressurized with ultrapure water at 0.5 MPa for 30 minutes until the flux stabilized.

[0024] 1. Basic separation performance test (1) Pure water flux

[0025] The membrane was tested at an operating pressure of 0.4 MPa, a temperature of 25 ± 1°C, and with ultrapure water as the feed solution. The pure water flux of the membrane was measured. (L·m) -2 ·h -1 ·bar -1 Calculate using the following formula in: The volume of the permeate during the test period (L); Effective membrane area (m²); The test runtime (h) is used. The applied operating pressure (bar).

[0026] (2) Salt retention rate A 2000 mg / L Na₂SO₄ solution and a NaCl solution were prepared as feed solutions, and the test was conducted at 0.4 MPa and 25°C. The conductivity of the feed solution was measured using a conductivity meter. ) and permeate ( The conductivity of the sample is calculated and converted to salt concentration. The retention rate is calculated using the following formula:

[0027] 2. Anti-scaling performance test Preparation of CaCl2 (600 mg / L as Ca 2+ ), Na2SO3 (150 mg / L as SiO3 2- Simulated wastewater containing NaCl (15000 mg / L) was used in a cross-flow circulation operation at 0.8 MPa and 25°C. Flux changes were continuously monitored, and the total operation time was 120 hours. At the end of the operation, the flux decay rate was calculated, and the amount of fouling on the membrane surface was determined by EDTA titration. The flux decay rate was calculated using the following formula: in, J 0 For the initial flux, J 120 The throughput is the result after 120 hours of operation.

[0028] 3. Anti-pollution performance test Dynamic contamination experiment: Prepare a composite contamination solution: bovine serum albumin (BSA, 500 mg / L), humic acid (HA, 50 mg / L), and Na2SO4 (2000 mg / L). Run at 0.6 MPa and 25°C for 12 hours.

[0029] Flux decay rate and flux recovery rate: record the initial flux. J 0 and post-pollution flux J 12 Then, it was backwashed with ultrapure water at 0.2 MPa for 30 minutes, and the recovery flux was tested again. J r .calculate: Flux decay rate

[0030] Flux recovery rate

[0031] 4. Long-term stability performance test Using leachate from actual solid waste incineration plants (TDS 8-18%, COD 800-2000 mg / L, Ca...) 2+ (300-700 mg / L) Run continuously for 30 days, monitoring performance daily.

[0032] Example 1 A method for preparing high-flux, highly fouling-resistant nanofiltration membranes based on MOF material-controlled interfacial polymerization includes the following steps: 1. Prepare modified MOF nanoparticles (UiO-66-COOH / SO3H) and prepare functionalized aqueous and oil phase solutions. The specific procedures are as follows: (1) Preparation of modified MOF nanoparticles

[0033] S1, Weigh 0.5 g of aminated UiO-66 (UiO-66-NH2) and disperse it in 80 mL of N,N-dimethylformamide (DMF), and sonicate for 30 minutes; S2, add 2-aminoterephthalic acid (0.52 g, 2.6 mmol) and 2-sulfoterephthalic acid (0.86 g, 3.9 mmol) (molar ratio 1:1.5) to the dispersion obtained in S1, and stir thoroughly; S3, the mixed solution obtained in S2 is transferred to a high-pressure reactor with a polytetrafluoroethylene liner and reacted at 100 °C for 24 hours; S4. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The solid product was collected by centrifugation (8000 rpm, 10 min) and washed three times with DMF and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60 °C for 12 hours to obtain modified MOF nanoparticles (denoted as UiO-66-COOH / SO3H) with both carboxylate (-COOH) and sulfonate (-SO3H) groups on the surface. The average hydrated particle size was measured to be 105 ± 15 nm.

[0034] (2) Preparation of functionalized aqueous and oil phase solutions a. Preparation of functionalized aqueous solution: Accurately weigh m-phenylenediamine (MPD) and polyethyleneimine (PEI, Mw=800) and mix them at a mass ratio of 1:1, with a total mass of 0.6 g. Dissolve it together with 0.16 g of UiO-66-COOH / SO3H nanoparticles prepared in step (1) and 0.06 g of 4-sulfonic acid calix [4] aromatic hydrocarbon (as an ion channel modulator) in 20 g of deionized water. Sonicate the solution in an ice-water bath for 60 minutes to obtain a homogeneous and stable aqueous solution with a total amine monomer concentration of 3.0 wt% and a modified MOF concentration of 0.8 wt%.

[0035] b. Preparation of the oil phase solution: Accurately weigh trimesoyl chloride (TMC, 0.1 g) and 2,4,6-trifluorobenzoyl chloride (TFBC, 0.02 g), and mix them at a mass ratio of 5:1. Dissolve them in 100 g of n-hexane and shake gently to obtain an oil phase solution with a total acyl chloride concentration of 0.12 wt%.

[0036] 2. Interface aggregation and post-processing: S1: Take a commercial polyethersulfone (PES) ultrafiltration membrane (molecular weight cutoff approximately 20 kDa, effective area approximately 28 cm²) and fix it onto a polypropylene frame. Completely immerse it in the above-mentioned functionalized aqueous solution and soak it in a 40°C constant temperature water bath for 10 minutes to ensure sufficient adsorption of amine monomers and modified MOFs on the membrane pores and surface. After removal, use nitrogen to blow away excess aqueous droplets hanging on the surface to form a uniform pre-adsorption layer.

[0037] S2: Immediately place the membrane treated in S1 horizontally and uniformly coat the above oil phase solution onto the membrane surface, reacting for 120 seconds. During this period, the amine monomers in the aqueous phase and the acyl chloride monomers in the oil phase undergo a rapid interfacial condensation reaction at the liquid-liquid interface to form a polyamide separation layer. Simultaneously, the modified MOF nanoparticles are covalently anchored in the growing polymer network through the reaction of the amino groups and acyl chlorides on their surfaces.

[0038] S3: After the polymerization reaction is complete, pour off the oil phase on the membrane surface and place the membrane in a 60°C forced-air oven for 15 minutes to promote further cross-linking and curing of the polyamide network.

[0039] S4: Immerse the heat-treated membrane in a 0.1 M Zn(NO3)2 aqueous solution and allow it to stand at room temperature for 30 minutes to allow the Zn... 2+ Functional enhancement is achieved by coordinating with carboxylate and sulfonate sites in the MOF and polyamide network. Finally, the membrane is rinsed three times with deionized water to thoroughly remove unreacted monomers and residual salts. The finished membrane is stored in deionized water at 4°C for later analysis.

[0040] 3. Membrane performance characterization: The performance of the obtained composite membrane was tested according to the aforementioned performance testing method: Basic separation performance: Under an operating pressure of 0.6 MPa, the pure water flux (Jw) was measured to be 18.6 L•m. -2 •h -1 •bar -1 The rejection rate (R) for 2000 mg / L Na2SO4 solution was 98.3%, and the rejection rate for 2000 mg / L NaCl solution was 34.7%.

[0041] Anti-fouling performance: After 120 hours of dynamic operation in high-hardness simulated wastewater, the flux decay rate (JDR) was 33.7%, and the CaSiO3 scale on the membrane surface after the operation ended was 3.5 mg / cm².

[0042] Antifouling performance: After running in BSA+HA composite contaminated solution for 12 hours, the flux decline rate was 33.7%, and the flux recovery rate reached 82.3% after backwashing with pure water.

[0043] Examples 2-3: Examples 2 and 3 provide specific preparation methods for the high-flux, high-fouling-resistant nanofiltration membrane, the steps of which are exactly the same as those in Example 1, the only difference being: In step 1 (preparation of modified MOF materials), the types of matrix MOFs were replaced with MIL-101-NH2 (Example 2) and ZIF-8 (Example 3), respectively. The modification method, the grafting process of ion recognition groups (-COOH / -SO3H), and the parameters of all subsequent interfacial polymerization and post-treatment steps were kept consistent with those in Example 1 to explore the influence of different MOF frameworks on the performance of composite films.

[0044] Comparative Example 1: A commercially available DuPont FilmTec™ NF270 nanofiltration membrane without any functional modifications was selected as a control. This comparative membrane is a commercial product, and its preparation process does not involve the MOF modification, gradient structure construction, or ion recognition function design of this invention.

[0045] Comparative Example 2: To explore the importance of the synergistic effect between functionalized MOF and ion channel modulator in this invention, this comparative example provides a method for preparing a contrast membrane. The main difference between this method and [Example 1] is that: In step 1 (preparing the functionalized aqueous solution), no modified MOF (UiO-66-COOH / SO3H) nanoparticles or ion channel modifiers (4-sulfonic acid calix [4] aromatics) were added. The aqueous phase consisted only of m-phenylenediamine and polyethyleneimine (mass ratio 1:1, total concentration 3.0 wt%) dissolved in deionized water. The preparation of the oil phase solution (TMC and TFBC, mass ratio 5:1) and all subsequent interfacial polymerization and post-treatment steps were exactly the same as in Example 1.

[0046] Comparative Example 3: To investigate the key role of MOF surface chemical modification and its formation of gradient distribution in the separation layer, this comparative example provides a method for preparing a comparative film. The main difference between this method and Example 1 is that: (1) Use unmodified UIO-66-NH2 nanoparticles directly without grafting carboxylate and sulfonate groups.

[0047] (2) The unmodified MOF was physically blended in an aqueous solution at a concentration of 0.8 wt%, while the concentrations of other components remained unchanged.

[0048] This comparative example is designed to simulate a simple physical doping process to demonstrate the technical advantages of MOF chemical modification and gradient anchoring achieved through interfacial polymerization in this invention.

[0049] Test Example 1: The high-flux, high-fouling-resistant nanofiltration membranes prepared by Examples 1-3 and Comparative Examples 1-3 were tested according to the aforementioned performance test conditions. The results are shown in Table 1 below. Table 1 Performance test characterization of Test Example 1 serial number Types of matrix MOFs Pure water flux (LHM / bar) <![CDATA[Sodium sulfate rejection rate (%)]]> NaCl retention rate (%) Flux decay rate* (%) Surface fouling (mg / cm²) Flux recovery rate (%) Example 1 UiO-66 18.6 98.3 34.7 33.7 3.5 82.3 Example 2 MIL-101 16.8 97.8 38.6 35.8 3.9 80.8 Example 3 ZIF-8 17.6 98.1 37.7 37.7 3.8 81.3 Comparative Example 1 / 10.8 97.5 52.1 51.4 10.8 71.8 Comparative Example 2 / 8.5 88.6 63.5 66.9 11.9 56.9 Comparative Example 3 UiO-66 9.6 92.7 51.9 53.1 9.6 66.2 *After running the high-hardness simulated wastewater for 120 hours The results of Examples 1-3 and Comparative Examples 1-3 show that, compared with commercial nanofiltration membranes and composite nanofiltration membranes without aqueous and oil phase modification, the strategy proposed in this invention can effectively improve the flux and divalent salt rejection rate of the composite nanofiltration membrane while maintaining ultra-high SO42- content. 2-While improving the retention rate, it significantly increased Cl - Permeability and water flux are crucial for the salt separation and crystallization of high-salinity wastewater. In Example 1, the amount of fouling on the membrane surface was only 32% of that in Comparative Example 1. This is because the modified MOF transfers a large amount of Ca... 2+ Adsorption and storage within the membrane result in a surface ion activity product that is significantly lower than the solubility product. Comparative Example 3 (physical blend) showed better performance than conventional membranes but was far inferior to that of this invention, confirming the crucial role of MOF surface chemical modification and gradient distribution. Notably, compared to ZIF-8 and MIL-101, the UiO-66 nanofiltration membrane with surface chemical modification and gradient distribution exhibited the best performance.

[0050] Example 4: A method for preparing high-flux, highly fouling-resistant nanofiltration membranes based on MOF material-controlled interfacial polymerization, wherein the preparation method comprises the steps described in Example 1, with the difference being: In step 1 (preparing the functionalized aqueous solution), the total concentration of the polyamine monomers (m-phenylenediamine and polyethyleneimine, mass ratio 1:1) was adjusted to 0.5 wt%. The concentrations of the modified MOF (UiO-66-COOH / SO3H) and the ion channel modifier (4-sulfonic acid calix[4] aromatics) in the aqueous phase, the oil phase composition, and all subsequent interfacial polymerization and post-treatment process parameters remained unchanged.

[0051] Examples 5-8: Examples 5-8 provide specific preparation methods for the high-flux, high-fouling-resistant nanofiltration membrane, the steps of which are exactly the same as those in Example 4, the only difference being: The total concentration of the polyamine monomers was adjusted to 1.0 wt% (Example 5), 1.5 wt% (Example 6), 2.0 wt% (Example 7), and 2.5 wt% (Example 8), respectively. All other material formulations and process parameters remained strictly consistent with those in Example 4.

[0052] Comparative Example 4: This comparative example provides a method for preparing a control membrane. The main difference between this method and the one in Example 4 is that: The aqueous phase used only 0.5 wt% piperazine (PIP) as a single amine monomer, without the addition of modified MOF or ion channel modifiers. The organic phase was a 0.2 wt% TMC solution in n-hexane.

[0053] Comparative Example 5: This comparative example provides a method for preparing a control membrane. The main difference between this method and the one in Example 4 is that: 0.8 wt% unmodified UiO-66-NH2 nanoparticles were physically blended into 0.5 wt% of a polyamine monomer (MPD:PEI=1:1) aqueous solution without the addition of ion channel modifiers.

[0054] Test Example 2: The composite membranes prepared by Examples 4-8 and Comparative Examples 1 and 4-5 were tested according to the aforementioned performance test conditions. The results are shown in Table 2 below. Table 2 Performance test characterization of Test Example 2 serial number Polyamine monomer content (wt%) Pure water flux (LHM / bar) <![CDATA[Na2SO4 rejection rate (%)]]> NaCl retention rate (%) Flux decay rate* (%) Surface scale content (mg / cm²) Flux recovery rate (%) Example 4 0.5 15.5 98.1 47.5 26.5 4.1 79.4 Example 5 1.0 16.8 98.2 38.6 25.8 3.9 81.8 Example 6 1.5 18.6 98.5 34.7 24.7 3.5 83.3 Example 7 2.0 19.7 98.9 28.6 23.8 2.9 86.3 Example 8 2.5 18.1 98.6 34.6 24.8 3.2 82.3 Comparative Example 1 / 10.8 97.5 52.1 51.4 10.8 71.8 Comparative Example 4 0.5 6.5 87.6 66.5 69.9 12.9 66.9 Comparative Example 5 0.5 8.6 90.7 57.9 58.1 10.6 69.2 After running the high-hardness simulated wastewater for 120 hours The results of Examples 4-8, Comparative Examples 1, and Comparative Examples 4-5 show that, compared to commercial nanofiltration membranes and composite nanofiltration membranes without aqueous and oil phase modification, the strategy proposed in this invention can effectively improve the flux and divalent salt rejection rate of the composite nanofiltration membrane while maintaining ultra-high SO42- content. 2- While improving the retention rate, it significantly increased Cl - Permeability and water flux are crucial for the salt separation and crystallization of high-salinity wastewater. Since the performance of the composite nanofiltration membrane is affected by the polyamine monomer content, we adjusted and optimized the polyamine monomer content. The results showed that the composite nanofiltration membrane exhibited optimal performance when the polyamine monomer content was 2 wt%. Notably, the amount of CaSiO3 fouling on the membrane surface in Example 7 was significantly reduced, only 27% of that in Comparative Example 1. This is because the modified MOF absorbed a large amount of Ca... 2+ Adsorption and storage within the membrane result in surface ion activity product being much lower than solubility product.

[0055] Example 9: A method for preparing high-flux, highly fouling-resistant nanofiltration membranes based on MOF material-controlled interfacial polymerization, wherein the preparation method comprises the steps described in Example 7, with the difference being: In step S3 of the interfacial polymerization and post-treatment process, after coating the surface of the aqueous phase wetted membrane with an oil phase solution containing acyl chloride monomer, the interfacial polymerization reaction time is controlled to be 30 seconds.

[0056] Examples 10-14: Examples 10-14 provide specific preparation methods for the composite membrane, the steps of which are exactly the same as those in Example 9, the only difference being: In step S3 of the interface polymerization and post-processing process, the interface polymerization reaction time is adjusted to 45 seconds (Example 11), 60 seconds (Example 12), 75 seconds (Example 13), 90 seconds (Example 14), and 105 seconds (Example 15), respectively.

[0057] Comparative Example 6: This comparative example provides a method for preparing a control membrane. The main difference between this method and Example 9 is that: In step S2 (preparation of functionalized aqueous solution), only 2.0 wt% piperazine (PIP) is used as a single amine monomer, without adding modified MOF or ion channel modifiers. The organic phase is a 0.2 wt% TMC n-hexane solution.

[0058] Comparative Example 7: This comparative example provides a method for preparing a control membrane. The main difference between this method and the one in Example 9 is that: In step S2, 0.8 wt% of unmodified UiO-66-NH2 nanoparticles are directly physically blended into an aqueous solution of 2.0 wt% of polyamine monomer (MPD:PEI=1:1) without adding ion channel modifiers.

[0059] Test Example 3: Effect of Curing Temperature on Composite Film Properties The composite membranes prepared by Examples 9-14, Comparative Examples 1, and Comparative Examples 6-7 were tested according to the aforementioned performance test conditions. The results are shown in Table 3 below. Table 3 Performance test characterization of Test Example 3 serial number Interface aggregation time (s) Pure water flux (LHM / bar) <![CDATA[Sodium sulfate rejection rate (%)]]> NaCl retention rate (%) Flux decay rate* (%) Surface scale content (mg / cm²) Flux recovery rate (%) Example 10 30 19.7 98.4 28.6 23.8 2.9 86.3 Example 11 45 20.8 98.6 21.6 22.8 1.9 88.8 Example 12 60 22.6 99.2 16.7 16.7 1.5 90.3 Example 13 75 22.1 99.1 17.5 17.5 2.1 89.4 Example 14 90 20.8 98.2 18.6 18.8 2.9 87.8 Example 15 105 19.6 98.5 20.7 19.7 3.5 82.3 Comparative Example 1 / 10.8 97.5 52.1 51.4 10.8 71.8 Comparative Example 6 30 7.5 89.6 62.5 61.9 11.9 60.9 Comparative Example 7 30 9.6 93.7 54.9 55.1 9.6 68.2 After running the high-hardness simulated wastewater for 120 hours The results of Examples 10-15, Comparative Examples 1, and Comparative Examples 6-7 show that, compared to commercial nanofiltration membranes and composite nanofiltration membranes without aqueous and oil phase modification, the strategy proposed in this invention can effectively improve the flux and divalent salt rejection rate of the composite nanofiltration membrane. The membranes in these examples maintain ultra-high SO4 levels. 2- While improving the retention rate, it significantly increased Cl - Permeability and water flux are crucial for the salt separation and crystallization of high-salinity wastewater. Since the performance of the composite nanofiltration membrane is affected by the interfacial polymerization time, we adjusted and optimized the interfacial polymerization time. The results showed that the composite nanofiltration membrane exhibited optimal performance when the interfacial polymerization time was 60 seconds. Notably, in Example 12, the CaSiO3 scale on the membrane surface was reduced to 1.5 mg / cm², only 14% of that in Comparative Example 1. This is because the modified MOF absorbed a large amount of Ca... 2+ Adsorption and storage within the membrane result in surface ion activity product being much lower than solubility product.

[0060] Application Examples The membrane from Example 12 was used for leachate treatment at a solid waste incineration plant (design capacity 100 m³). 3 / d).

[0061] Influent TDS 12-22%, Ca 2+ 400-650 mg / L, SO3 2-80-180 mg / L, COD 1200-2500 mg / L. Operating parameters: operating pressure 0.8-1.0 MPa, recovery rate 70%.

[0062] Result: SO4 2- Retention rate ≥99%, Cl - With a permeability ≥80%, the TDS of the permeate is reduced to 3-5% before entering the subsequent RO unit. The system operated continuously for 30 days without chemical cleaning, maintaining stable flux only through periodic backwashing. Compared with traditional processes, it can significantly reduce the amount of scale inhibitor used and improve the purity of salts (Na2SO4).

[0063] The above embodiments demonstrate that the present invention achieves a synergistic improvement in nanofiltration membrane separation performance, anti-fouling properties, and stability through the gradient design of functionalized MOFs, providing an efficient and reliable technical solution for "zero discharge" of high-salinity wastewater.

Claims

1. A method for preparing a high-flux, highly fouling-resistant nanofiltration membrane, characterized in that, Includes the following steps: S1, Preparation of modified MOF nanoparticles: Select a matrix MOF containing amino groups on its surface, and graft at least two different ion recognition groups onto its surface by ligand modification to obtain modified MOF nanoparticles. S2, Preparation of functionalized aqueous solution: Dissolve the polyamine monomer, the modified MOF nanoparticles described in S1 and the ion channel modifier in deionized water and disperse them evenly to obtain the functionalized aqueous solution; S3, interfacial polymerization reaction: The porous support membrane is immersed in the functionalized aqueous solution prepared in S2, so that the aqueous components are adsorbed on its surface, and then it is contacted with an oil solution containing polyacrylamide chloride monomer to carry out an interfacial polymerization reaction. S4, Post-treatment: After removing the oil phase, the membrane after the reaction is heat-treated, then immersed in an aqueous solution containing metal ions for functional enhancement treatment, and after cleaning, the high-flux, high-fouling-resistant nanofiltration membrane is obtained.

2. The preparation method according to claim 1, characterized in that, In S1, the matrix MOF is selected from at least one of UiO-66-NH2, MIL-101-NH2 or ZIF-8; the ion recognition group is selected from at least two of carboxylate, sulfonate and phosphate groups.

3. The preparation method according to claim 1, characterized in that, In S1, the ligand modification method is as follows: the matrix MOF is dispersed in a mixed solution containing 2-aminoterephthalic acid and 2-sulfoterephthalic acid, and reacted at 80~120℃ for 12~48 hours to obtain modified MOF nanoparticles with carboxylate and sulfonate groups on the surface, and the particle size is 50-200nm.

4. The preparation method according to claim 1, characterized in that, In S2, the concentration of the polyamine monomer in the functionalized aqueous solution is 0.5~3.0 wt%, the concentration of the modified MOF nanoparticles is 0.1~0.8 wt%, and the concentration of the ion channel modulator is 0.05~0.3 wt%.

5. The preparation method according to claim 4, characterized in that, In S2, the polyamine monomer is selected from a mixture of piperazine, m-phenylenediamine and polyethyleneimine, with a mass ratio of (2~5):(1~3):(0.5~2); the ion channel modulator is selected from at least one of 4-sulfonic acid calix[4] aromatics, cyclodextrin-sulfonic acid derivatives or crown ether-carboxylic acid derivatives.

6. The preparation method according to claim 1, characterized in that, In S3, the polyacrylamide chloride monomer in the oil phase solution is a mixture of pyromellitic tricarboxylic acid chloride and fluorinated acrylamide chloride monomer, with a mass ratio of (3~8):1; the fluorinated acrylamide chloride monomer is at least one of pentafluorobenzoyl chloride, 2,4,6-trifluorobenzoyl chloride, tetrafluoroterephthaloyl chloride, or fluorinated aliphatic diacrylamide chloride; the interfacial polymerization reaction time is 30~120 seconds.

7. The preparation method according to claim 1, characterized in that, In S4, the heat treatment temperature is 60~80℃, and the time is 5~15 minutes; the metal ions used in the functional enhancement treatment are selected from Zn. 2+ Zr 4+ Al 3+ At least one of them, the processing time is 10 to 30 minutes.

8. A high-flux, highly fouling-resistant nanofiltration membrane prepared by the method according to any one of claims 1-7, characterized in that, It includes a porous support layer and a composite separation layer loaded thereon; the composite separation layer is a MOF / polyamide composite layer with a three-dimensional gradient structure, wherein the modified MOF nanoparticles are anchored in the polyamide network by chemical bonds and are distributed in a gradient direction in the thickness direction of the separation layer.

9. The high-flux, high-fouling-resistant nanofiltration membrane according to claim 8, characterized in that, The thickness of the composite separation layer is 80~180 nm.

10. The application of the high-flux, high-fouling-resistant nanofiltration membrane according to claim 8 or 9 in the treatment of high-salinity wastewater, characterized in that, The total dissolved solids content of the high-salinity wastewater is 5-30%, containing Ca. 2+ Mg 2+ and SiO3 2- At least one of them.

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