A metal polyphenol network / zeolitic imidazolate framework nanocomposite membrane and a preparation method and application thereof

Abstract

This invention discloses a metal polyphenol network (MPN) / zeolite imidazolium ester framework nanocomposite membrane, its preparation method, and its applications. The method includes: preparing an MPN (metal polyphenol network) induction layer on a base membrane; in-situ growing ZIF-8 (zeolite imidazolium ester framework) nanoparticles on the induction layer; etching the nanoparticles with TA (tannic acid); and then placing the membrane in an MPN deposition solution for liquid-phase deposition to obtain the metal polyphenol network / zeolite imidazolium ester framework nanocomposite membrane. This method is carried out in an aqueous solution, avoiding the use of organic solvents and meeting the requirements of green chemistry. The prepared nanocomposite membrane exhibits excellent separation and permeation performance, and can be used to sieve monovalent and polyvalent ions in aqueous solutions, making it suitable for seawater desalination based on nanofiltration technology.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology is a potential green separation technology. It's an emerging technology that utilizes the highly efficient selective permeation of membranes to separate, purify, and concentrate different components in a feed solution. It features low energy consumption, no secondary pollution, simple operation, and high separation efficiency. However, membrane separation also faces a trade-off between selectivity and permeability. How to increase membrane flux without reducing the rejection rate is one of the core problems that urgently needs to be solved in this field. Nanofiltration, with its superior separation performance compared to ultrafiltration membranes and significantly lower operating energy consumption than reverse osmosis membranes, has attracted great attention and research interest from various research institutions and membrane material manufacturers. Nanofiltration membranes have pore sizes between 0.5-2 nm and carry a surface charge. They can separate ions based on ion size or valence. The electrostatic interaction on the membrane can retain divalent and polyvalent salts while allowing monovalent salts to pass through. It can retain small molecule organic matter and high-valence salt ions with molecular weights between 150-2000 Da.

[0003] Nanocomposite membranes (TFNs) are membranes formed by incorporating nanomaterials into a polymer matrix. Nanoparticles play a crucial role in the polymer matrix; for example, porous nanoparticles provide abundant mass transfer channels, enhancing the permeation flux of the composite membrane. The mesoporous structure of the nanoparticles themselves also acts as a sieving agent, further improving the chemical and mechanical stability of the composite membrane. Therefore, combining the advantages of polymers and inorganic materials promises the potential to obtain high-performance composite membranes with both high rejection rates and high flux, as well as structural stability. However, in the traditional preparation of TFN membranes, problems often arise such as poor compatibility between nanoparticles and the separation layer material, and the aggregation of nanoparticles in the polymer matrix leading to non-selective voids. These issues severely limit the achievement of ideal separation performance in TFN membranes. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a metal polyphenol network / zeolite imidazole ester framework nanocomposite film and its preparation method.

[0005] The purpose of this invention is to provide a method for preparing a metal polyphenol network / zeolite imidazole ester framework nanocomposite film, comprising the following steps:

[0006] (1) The porous support membrane is first soaked in a polyphenol solution for a period of time, then ferrous salt aqueous solution is added, and the membrane is shaken and co-deposited for a period of time. Then, the membrane is heat-treated and the reaction continues for a period of time to obtain a membrane with an MPN induced layer.

[0007] (2) The membrane with the MPN induction layer was immersed in a mixed solution containing zinc salt and 2-methylimidazole for a period of time, then removed and washed to obtain the ZIF-8 membrane grown in situ.

[0008] (3) Immerse the ZIF-8 film in a tannic acid aqueous solution for a period of time for etching, take it out and clean it to obtain the ZIF-8 film after tannic acid etching.

[0009] (4) The ZIF-8 membrane etched with tannic acid was immersed in a mixed solution of polyphenol solution and ferrous salt aqueous solution, and co-deposited by shaking for a period of time. Then, it was heat-treated and cleaned to obtain a metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane.

[0010] In one embodiment of the present invention, the porous support membrane is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, hydrolyzed polyacrylonitrile ultrafiltration membrane, and cellulose acetate ultrafiltration membrane; more preferably, it is a polyacrylonitrile ultrafiltration membrane, and the porous support membrane is a porous support membrane washed with deionized water.

[0011] In one embodiment of the present invention, the polyphenol is one or more of tannic acid, dopamine, phytic acid, and gallic acid; tannic acid is preferred.

[0012] In one embodiment of the present invention, the ferrous salt is one or more of ferrous chloride, ferrous chloride tetrahydrate, ferrous sulfate, and ferrous bromide; preferably ferrous chloride tetrahydrate.

[0013] In one embodiment of the present invention, the zinc salt is zinc nitrate or its hydrate, or zinc chloride or its hydrate.

[0014] In one embodiment of the present invention, in step (1), the soaking time of the polyphenol solution is 0 to 60 min, and is not 0, preferably 5 min.

[0015] In one embodiment of the present invention, in steps (1) and (4), the oscillating deposition time is 15–150 min, the reaction temperature is 10–60 °C, the heat treatment temperature is 30–80 °C, and the continued reaction time is 0–60 min. Further, the co-deposition time is preferably 30 min, the reaction temperature is preferably 25 °C, the heat treatment temperature is 70 °C, and the continued reaction time is 10 min.

[0016] In one embodiment of the present invention, in steps (1) and (4), the concentration of the polyphenol aqueous solution is 0.8–80 mg / mL, the concentration of the ferrous salt aqueous solution is 4.9–98 mg / mL, and the molar ratio of polyphenol to ferrous salt is 1:1–1:100. Further, the concentration of the polyphenol aqueous solution is preferably 8 mg / mL, the concentration of the ferrous salt aqueous solution is preferably 9.8 mg / mL, and the molar ratio of polyphenol to ferrous salt is preferably 1:10.

[0017] In one embodiment of the present invention, in step (1), the polyphenol aqueous solution is obtained by dissolving polyphenols in ultrapure water, and the ferrous salt aqueous solution is obtained by dissolving ferrous salt in ultrapure water.

[0018] In one embodiment of the present invention, in step (2), the concentration of the zinc nitrate aqueous solution is 0.1–1 mol / L, the concentration of the 2-methylimidazole aqueous solution is 0.1–20 mol / L, the molar ratio of zinc nitrate to 2-methylimidazole is 1:1–1:20, and the reaction time is 0–180 min and not 0. Further, the preferred concentration of the zinc nitrate aqueous solution is 0.4 mol / L, the preferred concentration of the 2-methylimidazole aqueous solution is 1.6 mol / L, the preferred molar ratio of zinc nitrate to 2-methylimidazole is 1:4, and the preferred reaction time is 3 min or more.

[0019] In one embodiment of the present invention, in step (3), the concentration of the tannic acid aqueous solution in the etching step is 0.8–80 mg / mL, and the etching time is 0–60 min. Further, the concentration of the tannic acid aqueous solution is preferably 8 mg / mL, and the etching time is preferably 40 min or more.

[0020] In one embodiment of the present invention, the metal polyphenol network is a three-dimensional network formed by the coordination assembly of polyphenols and metal ions, which can be constructed within one minute. The metal polyphenol coordination bonds exhibit strong coordination, structural diversity, hydrolytic stability, and pH dependence. Because the catechol structure present in the polyphenols can adhere to various material surfaces through covalent / non-covalent interactions, the metal polyphenol network can adhere well to the surface of nanoparticles and encapsulate them, eliminating non-selective defects between nanoparticles and the polymer matrix. The phenolic hydroxyl groups in the polyphenols interact with metal ions, inducing in-situ growth of ZIF-8, inhibiting the aggregation of ZIF-8 nanoparticles, and controlling particle size and distribution. Furthermore, the tannic acid in the polyphenols can also hydrophilically modify the surface of ZIF-8 and etch it into a hollow structure. When loaded onto a membrane, this enhances the nanofiltration performance of the nanocomposite membrane. The cavities inside ZIF-8 allow preferential flow of solution, while its low mass transfer resistance shortens the diffusion distance and increases flux.

[0021] This invention provides a metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane prepared by the above method.

[0022] The present invention also provides the application of the above-mentioned metal polyphenol network / zeolite imidazole ester framework material nanocomposite membrane in nanofiltration separation.

[0023] The present invention also provides the application of the above-mentioned metal polyphenol network / zeolite imidazole ester framework material nanocomposite membrane in the field of seawater desalination based on nanofiltration technology.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) By growing ZIF-8 in situ on the MPN-induced layer, the aggregation of ZIF-8 nanoparticles is suppressed, and the non-selective pores generated therefrom are avoided. At the same time, the surface-induced in situ growth method can effectively control the particle size and particle size distribution, so that ZIF-8 nanoparticles are uniformly distributed in the metal polyphenol network matrix, thereby improving the utilization rate of ZIF-8 nanoparticles.

[0026] (2) By using TA to modify the surface of ZIF-8 layer to be hydrophilic and etching ZIF-8 into a hollow structure, the nanoscale pores of ZIF-8 shell are used as sieving channels, while the cavity inside ZIF-8 is used to effectively shorten the mass transfer path and reduce the mass transfer resistance of the solution across the membrane, thereby significantly improving the permeation flux of the nanocomposite membrane.

[0027] (3) In steps (3) and (4), TA can also act as a binder between the ZIF-8 layer and the MPN selective separation layer, effectively enhancing the interaction between ZIF-8 and MPN, preventing the generation of non-selective voids, and ensuring the structural compactness and structural stability of the nanocomposite separation layer.

[0028] (4) After growing ZIF-8 in situ on the base film surface, the deposition of MPN separation layer can significantly improve the deposition efficiency of MPN, shorten the deposition time from several hours to less than 30 minutes, and obtain a complete and dense separation layer in a shorter deposition time, thus achieving excellent separation performance.

[0029] The nanocomposite membrane prepared by this invention has both excellent separation and permeation performance, and can be used to sieve monovalent and polyvalent ions in aqueous solutions, and can be used in seawater desalination applications based on nanofiltration technology. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope (SEM) image of the metal polyphenol network / zeolite imidazole ester framework nanocomposite film prepared in Example 1. Figure 1 The small protrusions that are evenly and densely distributed in the middle are all zeolite imidazole ester skeletons. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The reagents used in the various embodiments of this invention are as follows: tannic acid, Sigma-Aldrich (USA); iron(II) chloride tetrahydrate, Sinopharm Chemical Reagent Co., Ltd.; 2-methylimidazole (mlm), GR, Adamas; zinc nitrate hexahydrate (Zn(NO3)2·6H2O), analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0033] The porous support membrane used in the various embodiments of the present invention is a polyacrylonitrile ultrafiltration membrane (PAN, MWCO = 40 kDa) produced by Beijing Ande Membrane Separation Technology Engineering Co., Ltd.

[0034] The metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane prepared in this invention is used for desalination. Desalination rate and water flux are two important parameters for evaluating the nanofiltration performance of nanofilms.

[0035] The aqueous nanofiltration performance of the composite membrane was evaluated using a cross-flow filtration method. Before testing, the composite membrane was pre-pressurized with ultrapure water for 1 hour to stabilize its performance. An inorganic salt solution with a concentration of 1 g / L was used as the feed solution, and the filtration performance was tested in a constant temperature water bath at 25°C and a pressure of 0.4 MPa. The aqueous nanofiltration performance of the nanocomposite membrane was evaluated by recording the permeate flux of the nanocomposite membrane and measuring the feed / filtrate concentrations.

[0036] The permeation flux (J) of the nanocomposite membrane is defined as follows:

[0037] J=V / (A×t×ΔP) (1)

[0038] Where V represents the filtrate volume in L; and A represents the test area of ​​the nanocomposite membrane in m². 2 ; t represents the time required to collect the corresponding volume of filtrate, in hours; ΔP represents the pressure applied to the surface of the nanocomposite membrane, in bars (1 MPa = 10 bar).

[0039] The retention rate (R) is defined as follows:

[0040] R(%)=(1-C p / C f(2) × 100%

[0041] Among them, C f Indicates the concentration of salt ions in the water before treatment; C p This indicates the concentration of salt ions in the solution after treatment.

[0042] Example 1

[0043] (1) Weigh an appropriate amount of tannic acid and dissolve it in 30 mL of ultrapure water to obtain a polyphenol aqueous solution with a polyphenol concentration of 8 mg / mL; weigh an appropriate amount of ferrous chloride tetrahydrate and dissolve it in 30 mL of ultrapure water to obtain a ferrous salt aqueous solution with a ferrous chloride concentration of 9.8 mg / mL. Immerse the polyacrylonitrile ultrafiltration membrane in the polyphenol aqueous solution for 5 minutes; then add the ferrous salt aqueous solution and quickly transfer it to a water bath constant temperature shaker, and shake and co-deposit for 30 minutes in a water bath at 25℃; after co-deposition, transfer it to an oven and react at 70℃ for 10 minutes. Finally, take out the membrane and wash it with ultrapure water to obtain the MPN induced layer membrane.

[0044] (2) Weigh an appropriate amount of zinc nitrate hexahydrate and dissolve it in 30 mL of ultrapure water to obtain a zinc nitrate aqueous solution with a concentration of 0.4 mol / L; weigh an appropriate amount of 2-methylimidazole and dissolve it in 30 mL of ultrapure water to obtain a 2-methylimidazole aqueous solution with a concentration of 1.6 mol / L. Mix the 0.4 mol / L zinc nitrate aqueous solution and the 1.6 mol / L 2-methylimidazole aqueous solution in equal volumes to obtain a mixed solution of zinc nitrate hexahydrate and 2-methylimidazole. Immerse the obtained MPN-induced layer membrane in the mixed solution of zinc nitrate hexahydrate and 2-methylimidazole for 3 min to grow a ZIF-8 layer in situ.

[0045] (3) Weigh an appropriate amount of tannic acid and dissolve it in 30 mL of ultrapure water to obtain a polyphenol aqueous solution with a polyphenol concentration of 8 mg / mL. Immerse the ZIF-8 membrane in the polyphenol aqueous solution for 10 minutes, then remove the membrane and wash it with ultrapure water to obtain a TA-etched ZIF-8 membrane.

[0046] (4) Mix the above 8 mg / mL polyphenol aqueous solution with 9.8 mg / mL ferrous salt aqueous solution in equal volumes to prepare a mixed solution of polyphenol aqueous solution and ferrous salt aqueous solution; then immerse the TA-etched ZIF-8 membrane obtained in (3) into the mixed solution of polyphenol aqueous solution and ferrous salt aqueous solution, and quickly transfer it into a water bath constant temperature shaker, and co-deposit it under a water bath at 25°C for 30 minutes; after co-deposition, transfer it into an oven and react it at 70°C for 10 minutes. Finally, take out the membrane and wash it with ultrapure water to obtain a metal polyphenol network / zeolite imidazole ester framework material nanocomposite membrane.

[0047] Figure 1 This indicates the successful synthesis of a metal polyphenol network / zeolite imidazole ester framework nanocomposite film.

[0048] Examples 2-6

[0049] Adjust the MPN separation layer deposition time in step (4) as shown in Table 1, and the remaining implementation conditions are as in Example 1.

[0050] Test Example 1

[0051] The metal polyphenol network / zeolite imidazole ester framework nanocomposite films prepared in Examples 1-6 were tested. The results are shown in Table 1.

[0052] Table 1. Water flux and retention rate of the metal polyphenol network / zeolite imidazolate framework nanocomposite membranes prepared in Examples 1-6

[0053]

[0054] As shown in Table 1, the water flux of the obtained metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane decreases with increasing deposition time, which may be due to the increased thickness of the separation layer. The retention rate gradually increases with increasing deposition time because the separation layer is more complete and dense, and its density remains constant while its thickness increases, leading to a higher retention rate. Furthermore, compared with the existing method (CN111203107A), we can achieve the same retention effect in a shorter time, thus shortening the deposition time of the separation layer.

[0055] Examples 7-10

[0056] Adjust the etching time of the ZIF-8 layer by TA in step (3) (as shown in Table 2), and the other implementation conditions are as in Example 1.

[0057] Test Example 2

[0058] The metal polyphenol network / zeolite imidazole ester framework nanocomposite films prepared in Examples 7-10 were tested. The results are shown in Table 2.

[0059] Table 2. Water flux and retention rate of the metal polyphenol network / zeolite imidazolate framework nanocomposite membranes prepared in Examples 7-10

[0060]

[0061] As shown in Table 2, the sodium sulfate rejection rate of the membrane did not change significantly with the extension of etching time, while the flux increased. This is because the synthesized ZIF-8 tends to have a hollow structure under TA etching, which can reduce mass transfer resistance and improve the flux of the composite membrane. During the etching process, TA can promote the detachment of weakly bound nanoparticles from the membrane surface, making the surface more uniform. Furthermore, within the same filtration time, the rate of water molecule permeation increased significantly, while the rate of salt ion permeation remained relatively unchanged. Therefore, the concentration of salt ions in the filtrate decreased relatively, resulting in an increase in rejection rate.

[0062] Examples 11-15

[0063] Adjust the growth time of the ZIF-8 layer in step (2) as shown in Table 3, and the other implementation conditions are as in Example 1.

[0064] Test Example 3

[0065] The metal polyphenol network / zeolite imidazole ester framework nanocomposite films prepared in Examples 11-15 were tested. The results are shown in Table 3.

[0066] Table 3. Water flux and retention rate of the metal polyphenol network / zeolite imidazolate framework nanocomposite membranes prepared in Examples 11-15

[0067]

[0068]

[0069] As shown in Table 3, after a certain growth time, the ZIF-8 layer becomes thicker and denser as the growth time of ZIF-8 increases, resulting in an increase in the overall thickness of the membrane, which leads to a decrease in flux and a certain increase in rejection rate.

[0070] Examples 16-19

[0071] Adjust the concentration of TA in step (3) as shown in Table 4, and the other implementation conditions are as in Example 1.

[0072] Test Example 4

[0073] The metal polyphenol network / zeolite imidazole ester framework nanocomposite films prepared in Examples 16-19 were tested. The results are shown in Table 4.

[0074] Table 4. Water flux and retention rate of the metal polyphenol network / zeolite imidazolate framework nanocomposite membranes prepared in Examples 16-19

[0075]

[0076] As shown in Table 4, since tannic acid is an acidic substance, when the concentration of tannic acid increases, the pH value in the reaction solution decreases, which accelerates the etching rate of ZIF-8. However, when the pH value in the solution is too low, the ZIF-8 structure collapses, thus increasing the flux and decreasing the rejection rate.

[0077] Comparative Example 1 (existing reported simple MPN membrane)

[0078] A suitable amount of tannic acid was dissolved in 30 mL of ultrapure water to obtain a polyphenol aqueous solution with a polyphenol concentration of 8 mg / mL. A suitable amount of ferrous chloride tetrahydrate was dissolved in 30 mL of ultrapure water to obtain a ferrous chloride salt solution with a ferrous chloride concentration of 9.8 mg / mL. The polyacrylonitrile ultrafiltration membrane was immersed in the polyphenol aqueous solution for 5 minutes. Then, the ferrous salt aqueous solution was added, and the membrane was quickly transferred to a water bath constant temperature shaker. Co-deposition was carried out at 25°C for 60 minutes and 120 minutes. After co-deposition, the membrane was transferred to an oven and reacted at 70°C for 10 minutes. Finally, the membrane was removed and washed with ultrapure water to obtain the MPN membrane.

[0079] The obtained MPN film was tested. The results are shown in Table 5.

[0080] Table 5 shows the water flux and rejection rate of the MPN membrane obtained in Comparative Example 1.

[0081]

[0082] As can be seen, the present invention can significantly improve the deposition efficiency of MPN by growing ZIF-8 in situ on the base film surface and then depositing the MPN separation layer, shortening the deposition time from several hours to less than 30 minutes. A complete and dense separation layer can be obtained in a shorter deposition time, achieving excellent separation performance.

[0083] Comparative Example 2 (Existing reported method of directly incorporating MOF into the separation layer)

[0084] A method for preparing a ZnCoMOF / PVDF nanofiltration membrane includes the following steps:

[0085] S1: Weigh out 100 parts of polyvinylidene fluoride (PVDF), 5-10 parts of N-vinylpyrrolidone (NVP), 47-50 parts of N,N-dimethylformamide (DMF), and 38-40 parts of acetone according to the weight ratio. Divide N,N-dimethylformamide (DMF) into two equal parts. Dissolve PVDF and N-vinylpyrrolidone (NVP) in one of the mixed solutions of N,N-dimethylformamide (DMF) and acetone. Stir magnetically at 60-70°C for 12-14 hours to form solution A.

[0086] S2: Weigh 0.5-1.0 parts of Zn(NO3)2·6H2O and 0.5-1.0 parts of Co(NO3)2·6H2O according to the weight ratio, and stir them to dissolve in another part of N,N-dimethylformamide (DMF) to form solution B;

[0087] S3: Stir and mix the solution A prepared in step S1 and the solution B prepared in step S2 until they are homogeneous to form solution C;

[0088] S4: The solution C prepared in step S3 is spun into a ZnCo MOF / PVDF nanofiltration membrane using in-situ electrospinning technology.

[0089] Compared to the ZnCo MOF / PVDF nanofiltration membranes obtained above, the advantages of this invention are as follows: This invention grows MOF in situ, solving the problem of MOF agglomeration and uneven distribution when incorporated into the separation layer. Furthermore, it improves the utilization rate of MOF. With methods that directly incorporate MOF into the separation layer, most of the MOF is wasted, with only a small portion successfully incorporated. The ZIF-8 grown in situ in this patent is uniformly distributed and does not agglomerate, effectively reducing defects in the separation layer.

[0090] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a metal polyphenol network / zeolite imidazole ester framework nanocomposite film, characterized in that, Includes the following steps: (1) The porous support membrane is first soaked in polyphenol aqueous solution for a period of time, then ferrous salt aqueous solution is added, and the membrane is shaken and co-deposited for a period of time. Then, the membrane is heat-treated and the reaction continues for a period of time to obtain a membrane with MPN induced layer. (2) The membrane with the MPN induction layer was immersed in a mixed solution containing zinc salt and 2-methylimidazole for a period of time, then removed and washed to obtain the ZIF-8 membrane grown in situ. (3) Immerse the ZIF-8 membrane in a tannic acid aqueous solution for a period of time for etching, remove and clean it to obtain the ZIF-8 membrane after tannic acid etching. (4) The ZIF-8 membrane etched with tannic acid was immersed in a mixed solution of polyphenol aqueous solution and ferrous salt aqueous solution, and co-deposited by shaking for a period of time. Then, it was heat-treated and reacted for a period of time. After washing, a metal polyphenol network / zeolite imidazole ester skeleton material nanocomposite membrane was obtained.

2. The method for preparing a metal polyphenol network / zeolite imidazole ester framework nanocomposite film as described in claim 1, characterized in that, The porous support membrane is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, hydrolyzed polyacrylonitrile ultrafiltration membrane, and cellulose acetate ultrafiltration membrane; the polyphenol is one or more of tannic acid, dopamine, phytic acid, and gallic acid; and the ferrous salt is one or more of ferrous chloride, ferrous sulfate, and ferrous bromide.

3. The method as described in claim 1, characterized in that, In step (1), the soaking time of the polyphenol aqueous solution is 0 to 60 min, and is not 0.

4. The method as described in claim 1, characterized in that, In steps (1) and (4), the deposition time is 15~150 min, the reaction temperature is 10~60 ℃, the heat treatment temperature is 30~80 ℃, and the reaction time continues for 10~60 min.

5. The method as described in claim 1, characterized in that, In steps (1) and (4), the concentration of polyphenol aqueous solution is 0.8~80 mg / mL, the concentration of ferrous salt aqueous solution is 4.9~98 mg / mL, and the molar ratio of polyphenol to ferrous salt is 1:1~1:

100.

6. The method as described in claim 1, characterized in that, In step (2), the mixed solution is a mixture of zinc nitrate aqueous solution and 2-methylimidazole aqueous solution. The concentration of zinc nitrate aqueous solution is 0.1~1 mol / L, the concentration of 2-methylimidazole aqueous solution is 0.1~20 mol / L, the molar ratio of zinc nitrate to 2-methylimidazole is 1:1~1:20, and the reaction time is 0~180 min and not 0.

7. The method according to any one of claims 1-6, characterized in that, In step (3), the concentration of tannic acid aqueous solution is 0.8~80 mg / mL, and the etching time is 10~60 min.

8. A metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane prepared by the method according to any one of claims 1-7.

9. The application of the metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane according to claim 8 in nanofiltration separation.

10. The application of the metal polyphenol network / zeolite imidazole ester framework nanocomposite membrane according to claim 8 in seawater desalination.

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