A multi-element coordination composite nanofiltration membrane, a preparation method and application thereof

Abstract

This invention discloses a multi-component coordination composite nanofiltration membrane, its preparation method, and its applications, belonging to the field of membrane separation technology. To address the technical problem of uneven selective layer structure and limited performance in traditional metal-polyphenol network membranes due to excessively rapid coordination reaction rates, this invention proposes a synergistic assembly strategy. The method includes: firstly, pre-mixing a polyphenol compound and a silicon-containing compound in an aqueous solution to form a relatively large silicon-polyphenol network intermediate; then, contacting this mixture containing the intermediate with a porous support substrate membrane pre-adsorbed with polyvalent metal ions to conduct a secondary coordination reaction, thereby constructing a uniform and dense multi-component coordination network selective layer on the substrate membrane surface. The pre-coordination step regulates the overall reaction kinetics, achieving precise control of the membrane pore size. The nanofiltration membrane prepared by this invention exhibits a smaller average pore size, a higher divalent salt rejection rate, and excellent removal performance for organic pollutants such as dyes and antibiotics, showing broad application prospects in water treatment and wastewater purification.

Description

Technical Field

[0001] This invention relates to a multi-component coordination composite nanofiltration membrane, its preparation method, and its application, belonging to the field of membrane separation technology. Background Technology

[0002] Nanofiltration (NF), an emerging pressure-driven liquid-phase membrane separation technology situated between ultrafiltration (UF) and reverse osmosis (RO), exhibits great promise in wastewater treatment, water softening, and purification due to its pore size (0.5-2 nm) and charged surface, effectively retaining divalent ions and organic pollutants with molecular weights ranging from 200-2000 Da. However, polyamide (PA) nanofiltration membranes based on interfacial polymerization (IP) technology commonly rely on organic solvents such as hexane as reaction media during their preparation. These organic solvents not only pose toxicity and bioaccumulation risks, but their release during preparation and subsequent discharge of wastewater and waste solvents also carry potential threats to ecosystems and human health.

[0003] In recent years, membrane materials based on metal-phenolic networks (MPNs) have attracted widespread attention due to their simple and rapid preparation process, good interfacial adhesion, and abundant coordination structures. Natural polyphenol molecules, such as tannic acid (TA), contain a large number of catechol structures, which can rapidly coordinate with metal ions such as Fe³⁺ to form stable network structures on various substrate surfaces. This MPN structure not only endows the membrane material with good chemical stability but also allows for functionalization by adjusting coordination conditions. However, the coordination reaction rate between TA and Fe³⁺ is usually fast, easily leading to the formation of structurally inhomogeneous membrane layers in a short time. This results in increased selective layer thickness or structural defects, thus limiting further optimization of membrane separation performance. Therefore, how to regulate the formation kinetics of MPNs to achieve fine control of membrane structure remains a key research issue. Summary of the Invention

[0004] The technical problem this invention aims to solve is that the rapid coordination reaction during the construction of nanofiltration membranes using metal-polyphenol networks (MPNs) often leads to difficulties in controlling the membrane structure. This invention proposes a synergistic assembly strategy of silicon-polyphenol networks (SPNs) and metal-polyphenol networks to construct a Si-TA / Fe multi-element coordination network (MSPN) nanofiltration membrane on the substrate surface. By introducing Na₂SiO₃ and tannic acid to pre-form an SPN structure, the coordination kinetics between TA and Fe³⁺ can be controlled, achieving controllable construction of the selective layer structure.

[0005] A composite nanofiltration membrane includes: a porous support base membrane and a selective layer disposed on the surface of the porous support base membrane; the selective layer is a multi-component coordination network structure formed by the synergistic coordination of polyphenolic compounds, polyvalent metal ions and silicon-containing compounds.

[0006] The polyphenolic compound is a compound containing a catechol or pyrogallol structure, preferably tannic acid.

[0007] The multivalent metal ion is Fe. 3+ Ti 4+ Zr 4+ Al 3+ One or more of them.

[0008] The silicon-containing compound is an alkali metal silicate, preferably sodium silicate.

[0009] The porous support base membrane is a polyacrylonitrile membrane, a polyethersulfone membrane, a polyvinylidene fluoride membrane, or a polysulfone membrane.

[0010] The composite nanofiltration membrane has an average pore size of 0.5-1.0 nm, preferably 0.52-0.82 nm.

[0011] The composite nanofiltration membrane has a molecular weight cutoff (MWCO) of 500-800 Da, preferably 600-700 Da.

[0012] The composite nanofiltration membrane exhibits a Na2SO4 rejection rate of greater than 95%, preferably greater than 98%, under operating pressure of 5 bar and 1000 ppm Na2SO4 solution conditions.

[0013] The method for preparing the composite nanofiltration membrane includes the following steps:

[0014] a) Provide a porous support base membrane;

[0015] b) Contact the porous support base membrane with a first solution containing multivalent metal ions, so that the multivalent metal ions are adsorbed on the surface of the base membrane;

[0016] c) The polyphenol compound and the silicon-containing compound are premixed in the second solution to obtain a coordination mixture containing a silicon-polyphenol network;

[0017] d) The coordination mixture is applied to the surface of the porous support base membrane treated in step b) to carry out a synergistic coordination reaction and form the selective layer.

[0018] In step c), the molar ratio of the silicon-containing compound to the polyphenol compound is 0.1:1-5:1, preferably 1:1-3:1.

[0019] In step c), the premixing time is 1-60 min, preferably 5-15 min.

[0020] In step b), the concentration of polyvalent metal ions in the first solution is 1-10 g / L; and / or in step b), the contact time is 0.5-5 min; in step d), the time of the co-coordination reaction is 0.5-5 min.

[0021] The dosage of the first and / or second solution is: per cm 2 Apply 0.05-0.5 mL to the porous support base membrane.

[0022] The composite nanofiltration membrane is used in water treatment, which includes the removal of organic pollutants and / or inorganic salts from water bodies.

[0023] The organic pollutants include dyes and / or antibiotics; the inorganic salts include divalent cationic salts and / or divalent anionic salts.

[0024] The beneficial effects of this invention are:

[0025] This study proposes a strategy for the synergistic construction of SPN and MPN to build a Si-TA / Fe multi-element coordination network (MSPN) nanofiltration membrane on the substrate surface. First, Na₂SiO₃ undergoes a coordination reaction with TA to form an SPN structure, which is then further assembled with Fe³⁺ to form the MSPN selective layer. The synergistic regulation of the SPN and MPN structures is achieved by controlling the molar ratio of Na₂SiO₃ to TA and the premixing time.

[0026] The introduction of SPN effectively slows down the coordination reaction rate, promotes the formation of a more uniform and dense selective layer, reduces the average pore size of the membrane from 0.96 nm to 0.52 nm, and decreases the MWCO from 1668 Da to 556 Da. Under optimized conditions, the prepared MSPN nanofiltration membrane achieves a Na2SO4 rejection rate of over 98% and exhibits excellent removal performance for various antibiotics and dyes, while maintaining stable long-term operating performance. Attached Figure Description

[0027] Figure 1 Preparation process of Si-TA / Fe NF film

[0028] Figure 2 (a) FTIR spectral analysis of PAN and x-Si-TA / Fe nanofiltration membranes, (b) TA structural formula, (c) reaction process of Na2SiO3, TA, and FeCl3.

[0029] Figure 3 (a) and (b) are XPS full-scan spectra of x-Si-TA / Fe nanofiltration membranes.

[0030] Figure 4 XPS scan spectra of O 1s measured on the surfaces of (a) 0-Si-TA / Fe, (b) 0.5-Si-TA / Fe, (c) 1-Si-TA / Fe, (d) 2-Si-TA / Fe and (e) 3-Si-TA / Fe nanofiltration membranes.

[0031] Figure 5 Surface and cross-sectional SEM images (magnification × 50k): Surface and cross-sectional morphology of x-Si-TA / Fe nanofiltration membrane

[0032] Figure 6 (a) and (b) pore size distribution tests of x-Si-TA / Fe nanofiltration membranes, (c) Na2SiO3 on TA-Fe 3+ The influence of coordination processes on PAN base film, (d) changes in complexes in Na2SiO3 and TA premixed solution.

[0033] Figure 7 Filtration performance of (a)-(d)x-Si-TA / Fe nanofiltration membranes for different salts

[0034] Figure 8 Surface and cross-sectional SEM images (magnification × 50k): Surface and cross-sectional morphology of Si-TA / Fe-y nanofiltration membrane

[0035] Figure 9 (a) Particle size distribution of solutions with different premixing reaction times when Na2SiO3:TA = 2:1; (b) Schematic diagram of the reaction process of Si-TA / Fe-y nanofiltration membrane.

[0036] Figure 10 (a)-(d) represent the filtration performance of Si-TA / Fe-y membranes for different salts.

[0037] Figure 11 (a) and (b) show the separation performance of 0-Si-TA / Fe and 2-Si-TA / Fe nanofiltration membranes for four antibiotics.

[0038] Figure 12 (a) Separation performance of 2-Si-TA / Fe nanofiltration membrane for five dyes; (b) Long-term stability of 2-Si-TA / Fe nanofiltration membrane. Detailed Implementation

[0039] Nanofiltration membranes are prepared through the following process ( Figure 1(1) Immerse the PAN substrate (circular, 6cm in diameter) in 5 ml of 4g / L FeCl3 solution for 1 min; (2) Wipe the FeCl3 aqueous solution remaining on the membrane with a rubber roller; (3) Add 5 ml of TA and Na2SiO3 solution with different premixing times or different molar ratios (where the concentration of TA is kept constant at 4g / L) to the PAN membrane, react for 1 min, remove the residual liquid on the membrane with ultrapure water, and let it air dry naturally. The membranes prepared with different molar ratios (Si:TA=0:1, 0.5:1, 1:1, 2:1, 3:1) are named x-Si-TA / Fe, where x is the different molar ratio of Na2SiO3; the membranes prepared with different premixing times (Si:TA=2 premixing for 1, 5, 10, 15, 30 min) are named Si-TA / Fe-y, ​​where y is the different premixing reaction time.

[0040] In the following tests, the particle size of the Si-TA network was measured using dynamic light scattering (DLS). A reaction solution with a molar ratio of Na2SiO3 (1 g / L) to TA (4 g / L) of 2:1 was diluted 10 times and placed in a clean cuvette. The particle size distribution at reaction times of 1, 5, 10, 15, and 30 min was measured using a laser particle size analyzer (ZEN 3600).

[0041] Effect of different molar ratios of Na2SiO3 on the film

[0042] The chemical functional groups of the PAN substrate and the x-Si-TA / Fe nanofiltration membrane were analyzed by ATR-FTIR, and the results are as follows: Figure 2 As shown in Figure a. Compared to the PAN substrate, the absorption peaks in the 1130–1200 cm⁻¹ range correspond to the stretching vibrations of COC in the TA ester group, while the absorption peaks at 754 cm⁻¹ and 1610 cm⁻¹ originate from the out-of-plane bending vibrations of CH in TA and the stretching vibrations of C=C in the aromatic ring, respectively. Furthermore, the MSPNs nanofiltration membrane exhibits absorption peaks in the 1300–1350 cm⁻¹ range. -1 The absorption peaks appearing within this range can be attributed to the stretching vibration of CO in the phenolic hydroxyl group of TA, which is 1319 cm⁻¹. -1 Offset to 1342 cm -1 (Figure S1) is because of its relationship with Fe 3+ This is due to coordination. Compared to the O-Si-TA / Fe membrane without Na₂SiO₃, the modified membrane exhibits a new absorption peak at 670 cm⁻¹ attributable to the asymmetric stretching vibration of the Si-O bond, proving that Si was successfully introduced into the nanofiltration membrane. Furthermore, with increasing Na₂SiO₃ doping concentration, the absorption peak at 1130-1200 cm⁻¹ in the spectrum... -The absorption peak intensities attributable to the CO and CC stretching vibrations in TA within the specified range are significantly reduced. This is due to the interaction between the phenolic hydroxyl functional groups of the TA molecule and Si. 4 ⁺ Coordination occurred, thus restricting the vibrations of the corresponding chemical bonds. Furthermore, the C=C stretching vibration peak (1610 cm⁻¹) attributed to the aromatic ring was observed. -1 The range of (location) widens, further proving Si 4 - Coordination with TA alters the electron cloud density of the TA aromatic ring. FTIR results indicate that the addition of Na₂SiO₃ is not a simple physical mixing process, but rather occurs through Si... 4 The coordination reaction between ⁺ and the phenolic hydroxyl group of TA, in conjunction with Fe³⁺, constructs a Si-TA / Fe selective layer.

[0043] The chemical composition of the membrane was analyzed using XPS. Full-scan spectroscopy was employed. Figure 3 From (a) and (b), it can be seen that as the molar ratio of Na₂SiO₃ increases, the content of Fe and Si elements on the film gradually increases. Figure 4 As shown in Figure ae, the high-resolution O 1s spectrum of the x-Si-TA / Fe nanofiltration membrane is fitted with four peaks: CO (532.8 eV), C=O (531.9 eV), Fe-O (530.9 eV), and Si-O (532.1 eV). With increasing Na2SiO3 doping concentration in the premixed solution, the proportion of the Si-O peak formed by its coordination with TA gradually increases, indicating that Si... 4+ The coordination reaction with TA is thus enhanced. Furthermore, the area of ​​the Fe-O peak continuously increases, due to the overall increase in alkalinity of the Si-TA SPN solution with increasing Na₂SiO₃ doping concentration. In an alkaline solution environment, Fe… 3+ The Fe group coordinates with tannic acid, thus increasing the number of coordination bonds between Fe and O. This demonstrates that the addition of Na₂SiO₃ not only coordinates with TA but also further promotes Fe coordination. 3+ Coordination with TA enables precise control of membrane pore size structure.

[0044] The effect of different amounts of Na2SiO3 added on the morphology of MSPN films was investigated. Figure 5Figures a and b show SEM images of the nanofiltration membrane surface and cross-section under different molar ratios of TA and Na₂SiO₃. A complete selective layer forms on the TA / Fe membrane surface, with some nanoparticles distributed on the surface, which is a typical structure of an MPN selective layer. After adding Na₂SiO₃, the number of particles on the membrane surface decreases, but the size increases. With increasing Na₂SiO₃ addition, both the number and size of particles on the membrane surface gradually increase. In addition, the cross-section of the membrane shows that a selective layer of uniform thickness is formed on the membrane surface. Simultaneously, with increasing Na₂SiO₃ addition, the thickness of the selective layer gradually decreases. This phenomenon is mainly due to the pre-coordination reaction between Na₂SiO₃ and TA, which alters the mechanism of selective layer formation. The specific mechanism is as follows: Figure 5 As shown in c. First, Fe 3+ The coordination ability with TA is extremely strong, and a TA / Fe MPN structure can be rapidly formed in a short time. However, the reaction rate of this process is too fast, which easily leads to inhomogeneous film structure and thus a thicker film layer. Then, after adding Na2SiO3 to the TA solution, a coordination reaction occurs to generate a Si-TA network. In this network, two different Si-O bonds can undergo exchange reactions, causing the ligands connected to the silicon center to recombine intramolecularly or intermolecularly, so that the system spontaneously forms a dynamic equilibrium oligomeric mixture. Figure 5 (d). Therefore, TA in solution exists in two forms: TA in the Si-TA network and free TA. In the presence of Fe... 3+ During the coordination reaction, the Si-TA network reacts with Fe. 3+ The reaction generates an MSPN network, with free TA and Fe. 3+ The reaction generates an MPN network. These MPNs surround the colloidal particles and effectively fill the pores on the membrane surface. This provides structural support for the nanofiltration membrane to achieve higher retention performance. Compared to coordination reactions involving only TA, the Si-TA network has a larger size and a slower diffusion rate, thus mitigating the reaction with Fe. 3+ The reaction rate is faster, resulting in a thinner selective layer, but with larger particle size. With increasing Na₂SiO₃ addition, the Si content in the solution... 4+ The size of the oligomer colloidal particles formed with TA increases, thus increasing the size of the nanoparticles on the film surface. Simultaneously, this leads to an increase in the size of the Si-TA network and Fe... 3+ The reaction speed is slower, and the resulting selective layer is thinner.

[0045] Before testing the separation performance of the Si-TA / Fe nanofiltration membrane, the pore size distribution of the membrane was characterized. For example... Figure 6As shown in figures a and b, the average pore size of the unmodified MPNs nanofiltration membrane is 0.96 nm, and the MWCO is 1668 Da. After modification with Na2SiO3 (Na2SiO3:TA=3), the average pore size of the nanofiltration membrane decreases to 0.58 nm, and the MWCO is 609 Da. This is mainly due to the Si... 4+ SPNs are pre-formed through a coordination reaction with TA, and then the SPNs react with Fe along with the free TA. 3+ The reaction generates a nanofiltration membrane selective layer. SPNs and Fe 3+ The reaction generates the large framework of the MSPN selective layer, while free TA and Fe... 3+ The reaction-generated MPN repairs the defects in the MSPN network. In contrast, Fe... 3+ An excessively rapid reaction rate with TA can easily lead to inhomogeneous membrane structure and defects. Furthermore, increasing the addition of Na₂SiO₃ raises the pH of the premixed solution, and the resulting alkaline environment promotes Fe production. 3+ It forms a six-coordinate structure with free TA in solution, resulting in a higher coordination number and further reducing the pore size. The hydrophilicity and surface potential of the membrane are then characterized. Figure 6 As shown in Figure c, with the increase of Na2SiO4 addition, the water contact angle on the membrane surface gradually increases, indicating that the hydrophilicity gradually weakens. Figure 6 As shown in Figure d, the surface potentials of both the 0-Si-TA / Fe and 2-Si-TA / Fe films are negative within a pH range of 4-10. Under the same pH conditions, the potential of the 0-Si-TA / Fe film is more negative than that of the 2-Si-TA / Fe film. This is because the addition of Na₂SiO₃ allows for the addition of more Fe. 3+ It participates in the coordination reaction, thus allowing more positive charges to enter the selective layer and neutralize some of the negative charges.

[0046] To investigate the effect of Na₂SiO₃ addition on the separation performance of MPNs membranes, four single salt solutions with a concentration of 1000 ppm were used to test the filtration performance of MPNs membranes with different Na₂SiO₃ additions. Figure 7 As shown, the MPNs membrane modified with Na2SiO3 exhibited increased rejection rates for all four salts, while simultaneously decreasing permeability, indicating an effective reduction in the average pore size and enhanced separation selectivity. With increasing Na2SiO3 content, the membrane rejection rate for Na2SO4 increased from 84.98% (0-Si-TA / Fe) to 98.25% (2-Si-TA / Fe). This is mainly due to the introduction of Na2SiO3 promoting the formation of a multi-component coordination structure in the MSPN, resulting in a more uniform and dense particle distribution on the membrane surface, and the MPN filling the defects in the MSPN, thereby significantly reducing the average pore size of the membrane. Figure 6(b) In addition, the membrane showed the greatest increase in MgSO4 rejection rate, from 54.6% to 90.2%. This is due to the combined effect of reduced pore size and reduced negative charge on the membrane surface, leading to improved MgSO4 rejection. 2+ The repulsive effect is higher than that of Na. + In summary, a molar ratio of Na₂SiO₃ to TA of 2 results in good salt separation performance.

[0047] The effect of different premixing reaction times of Na2SiO3 and TA on membrane performance

[0048] Since the coordination process between Na2SiO3 and TA is a dynamic process, the degree of reaction between Na2SiO3 and TA increases with time, which in turn affects the structure of the SPN network. Therefore, the effect of the reaction time between Na2SiO3 and TA on the performance of the MSPN membrane was investigated. Figure 8 The surface and cross-sectional morphology of the nanofiltration membrane under different premixing times for Na₂SiO₃:TA (2:1) are shown. The figures show that with increasing reaction time, the size of the nanoparticles on the membrane surface gradually becomes more uniform, and their distribution becomes more even, while the thickness of the selective layer remains essentially unchanged. This is because with increasing reaction time, the degree of reaction between Na₂SiO₃ and TA gradually increases, more TA undergoes coordination reactions with Na₂SiO₃, the number of SPNs increases, and the particle size gradually increases before stabilizing. Figure 9 a). The greater the number of SPN particles and the larger the particle size, the better it interacts with Fe. 3+ The reaction between them is more uniform. Figure 9 (b) Therefore, the number of nanoparticles on the membrane surface increases and their size becomes more uniform.

[0049] Next, the effect of Na₂SiO₃ and TA premixing time on the separation performance of the nanofiltration membrane was investigated. Figure 10 It can be seen that with the extension of the Na2SiO3 and TA premixing time, the retention capacity of the nanofiltration membrane for the four salts first increases, and then gradually decreases after the premixing reaction time exceeds 10 min, while the membrane permeability gradually improves. This is attributed to the effect of the Na2SiO3 and TA premixing time on SPN. With the increase of reaction time, the number of SPNs increases, and the particle size gradually increases. First, the increase in the number and particle size of SPNs can effectively slow down the reaction rate, making the generated MSPN network more uniform and the retention performance higher. Then, the further increase in the number of SPNs leads to a decrease in the number of free TA, which in turn reduces the number of MPN particles filling the gaps between SPN particles. Therefore, the membrane flux increases, but the permeability decreases. The optimal conditions are a Na2SiO3 to TA molar ratio of 2:1 and a premixing reaction time of 10 min.

[0050] Applications of Si-TA / Fe nanofiltration membranes

[0051] To evaluate the application potential of nanofiltration membranes in removing antibiotics from surface water, the filtration performance of nanofiltration membranes for four antibiotic solutions—benzylampicin, amoxicillin, tetracycline, and rifampin—was tested. Orange II (OII, Mw = 350.32 Da), Media Yellow 10 (MY 10, Mw = 366.26 Da), Soap Yellow (MY, Mw = 375.38 Da), Acid Fuchs Red (AF, Mw = 585.54 Da), Congo Red (CR, Mw = 696.66 Da), Rifampin (98%, Mw = 822.94 Da), Tetracycline (98%, Mw = 444.45 Da), Amoxicillin (> 99%, Mw = 365.4 Da), and Benzylampicin (98%, Mw = 349.4 Da) were used to evaluate the separation performance of the composite nanofiltration membrane for organic matter and antibiotics. Figure 11 As shown, after modification with Na2SiO3, the flux of the nanofiltration membrane for filtering four antibiotics decreased slightly, but the rejection rate increased significantly. The rejection rates for benzylampicin, amoxicillin, tetracycline, and rifampin increased from 57.87% to 92.71%, 61.16% to 95.15%, 71.62% to 96.74%, and 92.58% to 99.76%, respectively. This indicates that the membrane has good separation performance for antibiotics. In addition, the separation performance of the 2-Si-TA / Fe nanofiltration membrane for five dyes (MY 10, OⅡ, AF, MY, CR) was also tested. Figure 12 As shown in Figure a, with the increase of dye molecular weight, the retention rate of the 2-Si-TA / Fe-10 nanofiltration membrane for dye increases. This phenomenon is related to... Figure 5 The membrane pore size distribution results shown are consistent, indicating that the separation mechanism is dominated by size sieving. Furthermore, the long-term stability of the 2-Si-TA / Fe-10 nanofiltration membrane was evaluated using a 200 ppm Congo red solution, as shown... Figure 12 As shown in b, after 120 h of intermittent filtration and immersion in pure water, the membrane's rejection rate for Congo red solution remained above 99%, and the permeability remained at 5.2 L / m². -2 h -1 bar -1 This indicates that the 2-Si-TA / Fe-10 nanofiltration membrane has good long-term stability.

Claims

1. A composite nanofiltration membrane, characterized in that, include: Porous support base membrane; And a selection layer disposed on the surface of the porous support base film; the selection layer is a multi-component coordination network structure formed by the synergistic coordination of polyphenolic compounds, polyvalent metal ions and silicon-containing compounds.

2. The composite nanofiltration membrane according to claim 1, characterized in that, The polyphenolic compound is a compound containing a catechol or pyrogallol structure, preferably tannic acid.

3. The composite nanofiltration membrane according to claim 1 or 2, characterized in that, The multivalent metal ion is Fe. 3+ Ti 4+ Zr 4+ Al 3+ One or more of them.

4. The composite nanofiltration membrane according to any one of claims 1, characterized in that, The silicon-containing compound is an alkali metal silicate, preferably sodium silicate; the porous supporting substrate membrane is a polyacrylonitrile membrane, a polyethersulfone membrane, a polyvinylidene fluoride membrane, or a polysulfone membrane.

5. The composite nanoemulsion membrane according to any one of claims 1, characterized in that, The composite nanofiltration membrane has an average pore size of 0.5-1.0 nm, preferably 0.52-0.82 nm; and a molecular weight cutoff of 500-1700 Da, preferably 600-700 Da.

6. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, Includes the following steps: a) Provide a porous support base membrane; b) Contact the porous support base membrane with a first solution containing multivalent metal ions, so that the multivalent metal ions are adsorbed on the surface of the base membrane; c) The polyphenol compound and the silicon-containing compound are premixed in the second solution to obtain a coordination mixture containing a silicon-polyphenol network; d) The coordination mixture is applied to the surface of the porous support base membrane treated in step b) to carry out a synergistic coordination reaction and form the selective layer.

7. The preparation method according to claim 6, characterized in that, In step c), the molar ratio of the silicon-containing compound to the polyphenol compound is 0.1:1-5:1, preferably 1:1-3:1; the premixing time is 1-60 min, preferably 5-15 min.

8. The preparation method according to any one of claims 6, characterized in that: In step b), the concentration of polyvalent metal ions in the first solution is 1-10 g / L; and / or in step b), the contact time is 0.5-5 min; and / or in step d), the time for the co-coordination reaction is 0.5-5 min; the amount of the first solution and / or the second solution used is: per cm 2 Apply 0.05-0.5 mL to the porous support base membrane.

9. The application of the composite nanofiltration membrane according to claim 1 in water treatment, characterized in that, The water treatment includes the removal of organic pollutants and / or inorganic salts from the water body.

10. The application according to claim 9, characterized in that, The organic pollutants include dyes and / or antibiotics; the inorganic salts include divalent cationic salts and / or divalent anionic salts.

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