ZIF-8 thin film composite film as well as preparation method and application thereof

Abstract

The invention discloses a ZIF-8 thin film composite film and a preparation method and application thereof, and belongs to the technical field of MOF film preparation. The preparation method provided by the invention comprises the following steps: soaking one surface of a compact separation layer of a PES ultrafiltration membrane in a metal-water phase monomer solution to anchor metal ions on the surface of the PES ultrafiltration membrane, soaking one surface of a porous support layer of the PES ultrafiltration membrane in a ligand solution, taking out and drying to obtain the PES ultrafiltration membrane with a ZIF-8 selection layer on one surface, and pouring an organic phase monomer solution on the ZIF-8 selection layer, and carrying out a bulk phase interfacial polymerization reaction on a carboxyl group of an organic phase monomer in the organic phase monomer solution and an amino group of m-phenylenediamine to obtain the ZIF-8 thin film composite film. The composite membrane has excellent water permeability and dye / salt selectivity, can be used for separating dyes in printing and dyeing wastewater, and has a good separation effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of MOF membrane preparation, and particularly relates to a ZIF-8 thin film composite membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Complex wastewater is generated in industries such as tanneries, textile mills, and printing and dyeing mills, which contains emulsified oil, organic dyes, etc. At present, there are various traditional methods for treating such polluted wastewater, such as advanced oxidation, adsorption, biological treatment, etc. Compared with traditional methods, membrane separation technology has the advantages of low energy consumption, simple operation and easy control, environmental protection, high efficiency, etc., and is widely selected. In the process of membrane application, the core of membrane separation technology is a membrane material with good dye / salt rejection rate and high water flux, which determines the selective permeability of membrane separation, process design, membrane stability, and the final applicable system of membrane separation. Metal-organic frameworks (MOFs) are a class of crystalline porous materials with a periodic network structure formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. As a kind of MOF material, ZIF-8 has become one of the preferred materials in many application fields due to its high porosity, large specific surface area, low density, strong controllability, etc.

[0003] Thin film composite membranes (TFCs) are prepared by interfacial polymerization (IP) reactions of cycloaliphatic polyamides and fully aromatic polyamides (such as piperazine) or aromatic diamines (such as m-phenylenediamine, MPD) with multifunctional aromatic acid chlorides (mainly trimesoyl chloride, TMC). Since TFC membranes have a high permeation flux while maintaining sufficient mechanical strength, they have become a widely used high-performance separation membrane design. At present, when introducing MOF nanoparticles (i.e., ZIF-8) into the preparation process of thin film composite membranes, generally, the MOF nanoparticles are dispersed in an aqueous phase or an organic phase monomer solution, and an interfacial polymerization reaction is carried out to prepare a MOF thin film composite membrane, which can improve the permeation performance and anti-fouling performance of MOF nanofiltration membranes. However, ZIF-8 usually exhibits a bulk crystal morphology with a three-dimensional framework structure. Adding ZIF-8 in the interfacial polymerization reaction may cause problems such as the accumulation and uneven dispersion of MOFs in the selective layer of the membrane and poor interfacial compatibility with the base membrane due to uneven dispersion or aggregation of MOF nanoparticles, thereby reducing the water permeability and selectivity for dyes / salts of the membrane. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a ZIF-8 thin film composite membrane, a preparation method thereof, and an application thereof to solve the problems that ZIF-8 may cause in the interfacial polymerization process, such as the accumulation and uneven dispersion of MOF in the selective layer and poor interfacial compatibility with the base membrane, while ensuring that the membrane has excellent water permeability and selectivity for dyes / salts.

[0005] In the first aspect of the present invention, a method for preparing a ZIF-8 thin film composite membrane is provided. The ZIF-8 thin film composite membrane is used for separating dyes in printing and dyeing wastewater. The preparation method includes the following steps:

[0006] S1. Dissolve zinc nitrate hexahydrate in a deionized aqueous solution containing polyvinyl alcohol (PVA) and m-phenylenediamine (MPD) to obtain a metal-aqueous phase monomer solution;

[0007] S2. Immerse one side of the dense separation layer of the PES ultrafiltration membrane in the metal-aqueous phase monomer solution to anchor metal ions on the surface of the PES ultrafiltration membrane. Then immerse the porous support layer side of the PES ultrafiltration membrane in the ligand solution. The ligand solution diffuses upward under the action of polarity, enabling the metal ions to undergo in-situ growth with the ligands in the ligand solution, nucleating heterogeneously on the surface of the PES ultrafiltration membrane to form a dense and continuous ZIF-8 thin film. Then perform a drying treatment to enable the ZIF-8 crystals to grow uniformly on the PES ultrafiltration membrane, obtaining a PES ultrafiltration membrane with a ZIF-8 selective layer on one side;

[0008] S3. Pour the organic phase monomer solution onto the ZIF-8 selective layer of the PES ultrafiltration membrane obtained in step S2, and carry out a bulk interfacial polymerization reaction between the carboxyl groups of the organic phase monomers in the organic phase monomer solution and the amino groups of m-phenylenediamine;

[0009] S4. Dry the PES ultrafiltration membrane obtained in step S3 to obtain the ZIF-8 thin film composite membrane.

[0010] In some embodiments of the present invention, in the metal-aqueous phase monomer solution, the concentration of zinc nitrate hexahydrate is 1 - 2 g / mL, the concentration of m-phenylenediamine is 1.5 - 2.5 g / mL, and the concentration of polyvinyl alcohol is 0.05 - 0.1 g / mL.

[0011] In some embodiments of the present invention, the ligand solution is an anhydrous methanol solution of 2-methylimidazole.

[0012] In some embodiments of the present invention, in the ligand solution, the concentration of 2-methylimidazole is 1 - 3 g / mL.

[0013] In some embodiments of the present invention, the organic phase monomer solution is a 1,3,5-benzenetricarbonyl chloride solution.

[0014] In some embodiments of the present invention, in step S2, the time for the in-situ growth is 45 - 75 min.

[0015] In some embodiments of the present invention, step S3 specifically includes: fixing a PES ultrafiltration membrane with a ZIF-8 selective layer on a suction filtration device, with the ZIF-8 selective layer facing upward, turning on the suction pump, and then quickly pouring the organic phase monomer solution onto the membrane surface of the ZIF-8 selective layer. Under the action of the suction force, the reaction is carried out for 1-2 minutes. Under negative pressure conditions, the carboxyl groups carried by the organic phase monomers in the organic phase monomer solution react with the amino groups around the ZIF-8 selective layer to carry out bulk-phase interfacial polymerization, causing the bulk-phase interfacial polymerization reaction to penetrate the entire ZIF-8 selective layer and penetrate into the PES ultrafiltration membrane.

[0016] In some embodiments of the present invention, the drying temperature is 50-60 °C.

[0017] In the second aspect of the present invention, a ZIF-8 thin film composite membrane prepared by the above preparation method is provided.

[0018] In the third aspect of the present invention, an application of the above ZIF-8 thin film composite membrane in the treatment of printing and dyeing wastewater is provided.

[0019] One or at least a part of the following advantages are presented by the above technical solutions of the present invention compared with the prior art:

[0020] (1) By adding polyvinyl alcohol to the metal-aqueous phase monomer solution in the present invention, the metal ions are connected by polyvinyl alcohol, so that the metal ions are anchored on the hydrophobic PES ultrafiltration membrane instead of being dispersed in the solution. Furthermore, it is easy to carry out heterogeneous nucleation growth with the permeating ligands in the interfacial layer, realizing the in-situ growth of ZIF-8 on the PES substrate membrane, and avoiding the uneven dispersion and accumulation of ZIF-8 nanoparticles.

[0021] (2) In step S2 of the preparation method, the excess solvent is volatilized by drying to expose the MOF skeleton coated with the aqueous phase monomer. Through the suction filtration-assisted bulk-phase interfacial polymerization strategy, the organic phase monomer solution is injected. Under the action of negative pressure, the aqueous phase monomer pre-placed in the ZIF-8 selective layer is used to induce the organic phase monomer to penetrate into the ZIF-8 layer gap and quickly react with MPD adsorbed around the ZIF-8 nanoparticles, realizing the interfacial polymerization reaction to penetrate into the ZIF-8 layer bulk phase, resulting in the newly formed PA layer perfectly coating and penetrating the ZIF-8 nanoparticles, effectively solving the interfacial compatibility problem. At the same time, with the increase in the ligand content, the MOF undergoes sufficient coordination reaction, the MOF skeleton structure is obvious, and the membrane after bulk-phase interfacial polymerization still presents a loose state, which is beneficial to the permeation of water molecules. When the concentration of the ligand solution is 2 g / mL, the permeability of the prepared ZIF@TFC-2 membrane is 6.27 L / m 2·h·bar, and has a good separation effect. Among them, the rejection rate of Congo red is 98.88%, the rejection rate of Na2SO4 is 12.74%, and the CR / Na2SO4 selectivity ratio is 7.76138148. Brief Description of the Drawings

[0022] Figure 1 It is the surface scanning electron microscopy image of the ZIF@TFC-1 membrane prepared in Example 1;

[0023] Figure 2 It is the surface scanning electron microscopy image of the ZIF@TFC-2 membrane prepared in Example 2;

[0024] Figure 3 It is the surface scanning electron microscopy image of the ZIF@TFC-3 membrane prepared in Example 3;

[0025] Figure 4 It is the surface scanning electron microscopy image of the ZIF@TFC-4 membrane prepared in Example 4;

[0026] Figure 5 It is the surface scanning electron microscopy image of the ZIF@TFC-5 membrane prepared in Example 5;

[0027] Figure 6 It is the surface scanning electron microscopy image of the pure PA membrane prepared in Comparative Example 1;

[0028] Figure 7 It is the surface scanning electron microscopy image of the ZIF-1 membrane prepared in Comparative Example 2;

[0029] Figure 8 It is the test result diagram of the separation performance of the ZIF@TFC-1, ZIF@TFC-2 and ZIF@TFC-3 membranes;

[0030] Figure 9 It is the test result diagram of the separation performance of the ZIF@TFC-2, ZIF@TFC-4 and ZIF@TFC-5 membranes;

[0031] Figure 10 It is the test result diagram of the performance stability of the ZIF@TFC-2 membrane prepared in Example 2;

[0032] Figure 11 It is the test result diagram of the separation performance of the ZIF@TFC-2, ZIF@TFC-6 and ZIF@TFC-7 membranes. Detailed Embodiments

[0033] The following further describes the present application in detail with reference to the accompanying drawings and specific embodiments, but does not limit the present application.

[0034] Field emission scanning electron microscope (SEM), model Drop Shape Analyzer 100, produced by Bruker Corporation, Germany;

[0035] Ultraviolet spectrophotometer (UV), model ASAP 2010, produced by Micromeritics Instrument Corporation, USA;

[0036] The permeation rate measuring instrument is a membrane performance evaluation instrument, model SF-SA, produced by Shanghai Saifei Membrane Separation Technology Co., Ltd., China;

[0037] m-Phenylenediamine (MPD): Purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0038] n-Hexane: Specification is 99%, purchased from Aladdin Reagent Co., Ltd.;

[0039] Polyethersulfone (PES) ultrafiltration membrane: Average pore size is 20 - 30 nm, provided by Zhongyi Filter Equipment Store, Zhouwangmiao Town, Haining City, and soaked in deionized water for 6 h before use;

[0040] Congo red, methyl orange, methyl green, and methylene blue were purchased from Macklin Biochemical Co., Ltd.;

[0041] 2-Methylimidazole: Specification is 99%, purchased from Macklin Biochemical Co., Ltd.;

[0042] Zinc nitrate hexahydrate: Analytically pure, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0043] 1,3,5-Benzenetricarbonyl chloride (TMC): Specifications are all 98%, purchased from Macklin Biochemical Co., Ltd.;

[0044] Methanol: Specification is 99%, purchased from Macklin Biochemical Co., Ltd.;

[0045] Sodium sulfate, magnesium sulfate, sodium chloride, and magnesium chloride: Purchased from Macklin Biochemical Co., Ltd.;

[0046] Example 1

[0047] (1) Preparation of metal-aqueous phase monomer solution

[0048] Weigh 0.3 g of zinc nitrate hexahydrate and 0.4 g of m-phenylenediamine respectively, add them to 20 ml of deionized water containing 0.015 g of PVA, and stir them thoroughly under dark conditions to obtain the metal-aqueous phase monomer solution.

[0049] (2) Preparation of ligand solution

[0050] Add 1 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 min to obtain the ligand solution.

[0051] (3) Preparation of organic phase monomer solution

[0052] Add 0.04 g of TMC into 20 ml of pure n - hexane reagent and stir for 3 h at room temperature to obtain the organic monomer solution.

[0053] (4) Preparation of ZIF@TFC membrane

[0054] Fix the pre - wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing upwards), then pour the metal - aqueous phase monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 min, translate it into the ligand solution (with the membrane facing upwards). Based on the reverse diffusion osmosis strategy, utilize the polar effect of the ligand solution below the membrane to diffuse upwards, enabling the metal ions anchored on the membrane surface to in - situ grow with the ligand, nucleate heterogeneously on the membrane surface, and form a dense and continuous ZIF - 8 layer. After reacting for about 60 min, take out the membrane on the frame and dry it in an oven at 55 °C for 5 min to facilitate the uniform growth of ZIF - 8 crystals on the PES membrane to form the ZIF - 8 membrane.

[0055] Fix the ZIF - 8 membrane on the suction filtration device (with the membrane facing upwards), turn on the suction pump, and then quickly pour the organic phase solution onto the surface of the ZIF - 8 membrane. Under the suction force, react for 1 min. Under negative pressure conditions, carry out bulk - phase interfacial polymerization of the carboxyl groups carried by the organic phase monomer and the amino groups around ZIF - 8, causing the bulk - phase interfacial polymerization reaction to penetrate the entire ZIF - 8 selective layer and penetrate into the PES substrate, thereby obtaining a ZIF - 8 thin - film composite membrane with excellent interfacial compatibility and continuous and defect - free. Finally, place the membrane in an oven at 55 °C and dry it for 10 min to prepare the ZIF@TFC - 1 membrane.

[0056] Use SEM to scan the obtained ZIF@TFC - 1 membrane, and the obtained scanning electron micrograph is as Figure 1 shown Figure 1 (a) and (b) are planar scanning electron micrographs at 10 μm and 100 nm respectively. As can be seen from Figure 1 it, the lotus - leaf - like structure of the polyamide layer on the membrane surface of the obtained ZIF@TFC - 1 membrane is more obvious and larger. This is because when the concentration of 2 - methylimidazole in the 2 - methylimidazole solution (0.01 g / ml) is low, the ZIF - 8 layer grown by heterogeneous nucleation is thinner, the membrane surface is flatter, and thus the lotus - leaf - like protrusions on the surface of the polyamide layer are more obvious.

[0057] Example 2

[0058] (1) Preparation of metal - aqueous phase monomer solution

[0059] Weigh 0.3 g of zinc nitrate hexahydrate and 0.4 g of m-phenylenediamine separately, add them to 20 ml of deionized water containing 0.015 g of PVA, and stir them thoroughly under dark conditions to obtain a metal-aqueous phase monomer solution.

[0060] (2) Preparation of ligand solution

[0061] Add 2 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 min to obtain a ligand solution.

[0062] (3) Preparation of organic monomer solution

[0063] Add 0.04 g of TMC to 20 ml of pure n-hexane reagent and stir it at room temperature for 3 h to obtain an organic monomer solution.

[0064] (4) Preparation of ZIF@TFC membrane

[0065] Fix the pre-wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing up), then pour the metal-aqueous phase monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 min, translate it into the ligand solution (with the membrane facing up). Based on the reverse diffusion osmosis strategy, the polar action of the ligand solution below the membrane diffuses upward, enabling the metal ions anchored on the membrane surface to in-situ grow with the ligand, nucleate heterogeneously on the membrane surface, and form a dense and continuous ZIF-8 layer. After reacting for about 60 min, take out the membrane on the frame and dry it in an oven at 55 °C for 5 min to facilitate the uniform growth of ZIF-8 crystals on the PES membrane to form a ZIF-8 membrane.

[0066] Fix the ZIF-8 membrane on the suction filtration device (with the membrane facing up), turn on the suction pump, and then quickly pour the organic phase solution onto the surface of the ZIF-8 membrane. Under the suction force, react for 1 min, and polymerize the carboxyl groups carried by the organic phase monomer with the amino groups around ZIF-8 at the bulk interface, causing the bulk interface polymerization reaction to penetrate the entire ZIF-8 selective layer and penetrate into the PES substrate, thereby obtaining a ZIF-8 thin film composite membrane with excellent interfacial compatibility and continuous and defect-free. Finally, place the membrane in an oven at 55 °C and dry it for 10 min to prepare the ZIF@TFC-2 membrane.

[0067] Use SEM to scan the obtained ZIF@TFC-2 membrane above, and the obtained scanning electron microscope images are as Figure 2 shown Figure 2 (a), (b) are planar scanning electron microscope images at 200 nm and 10 μm respectively. From Figure 2It can be seen that when the concentration of 2-methylimidazole reaches 0.02 g / ml, the polyamide layer on the membrane surface of the ZIF@TFC-2 membrane is relatively uniform, and the leaf-like structure of the polyamide layer is more obvious. This is because when the concentration of 2-methylimidazole is appropriate, the thickness of the ZIF-8 layer formed by the reaction is moderate and the undulation is small, which leads to a more uniform and obvious polyamide layer, resulting in better dye / salt selectivity of the membrane.

[0068] Example 3

[0069] (1) Preparation of metal-aqueous phase monomer solution

[0070] Weigh 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine respectively, add them to 20 ml of deionized water containing 0.015 g of PVA, and stir them thoroughly under dark conditions to obtain the metal-aqueous phase monomer solution.

[0071] (2) Preparation of ligand solution

[0072] Add 3 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 min to obtain the ligand solution.

[0073] (3) Preparation of organic phase monomer solution

[0074] Add 0.04 g of TMC to 20 ml of pure n-hexane reagent and stir it at room temperature for 3 h to obtain the organic monomer solution.

[0075] (4) Preparation of ZIF@TFC membrane

[0076] Fix the pre-wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing up), then pour the metal-aqueous phase monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 min, translate it into the ligand solution (with the membrane facing up). Based on the reverse diffusion osmosis strategy, the polar effect of the ligand solution below the membrane diffuses upward, enabling the metal ions anchored on the membrane surface to in-situ grow with the ligand, nucleate heterogeneously on the membrane surface, and form a dense and continuous ZIF-8 layer. After reacting for about 60 min, take out the membrane on the frame and dry it in an oven at 55 °C for 5 min to facilitate the uniform growth of ZIF-8 crystals on the PES membrane to form the ZIF-8 membrane.

[0077] The ZIF-8 membrane was fixed on the filtration device (the front of the membrane was facing up), the filtration pump was turned on, and then the organic phase solution was quickly poured on the surface of the ZIF-8 membrane. Under the action of suction force, the reaction lasted for 1 minute. Under negative pressure conditions, the carboxyl groups carried by the organic phase monomers and the amino groups around ZIF-8 were polymerized at the bulk interface, so that the bulk interface polymerization reaction penetrated the entire ZIF-8 selective layer and penetrated into the PES substrate, thereby obtaining a continuous and defect-free ZIF-8 thin film composite membrane with excellent interfacial compatibility. Finally, the membrane was placed in an oven at 55°C and dried for 10 minutes to prepare the ZIF@TFC-3 membrane.

[0078] The ZIF@TFC-3 membrane obtained above was scanned by SEM, and the obtained SEM image is as follows: Figure 3 As shown, Figure 3 (a) and (b) are plane scanning electron microscope images at 200nm and 2μm respectively. Figure 3 It can be seen from the results that when the concentration of 2-methylimidazole is 0.03g / ml, the polyamide layer on the surface of the ZIF@TFC-3 membrane has large fluctuations and some overflow, and the leaf-like structure of the polyamide layer is more obvious but slightly hollow. This is because when the concentration of 2-methylimidazole is high, the ZIF-8 layer generated by the reaction is thick and has large fluctuations, which makes the polyamide layer relatively uneven, resulting in a decrease in the dye / salt selectivity of the membrane.

[0079] Example 4

[0080] (1) Preparation of metal-water monomer solution

[0081] 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine were weighed respectively, added into 20 ml of deionized water containing 0.015 g of PVA, and stirred sufficiently in the dark to obtain a metal-water phase monomer solution.

[0082] (2) Preparation of ligand solution

[0083] 2 g of 2-methylimidazole was added into 100 ml of anhydrous methanol, and the mixture was stirred for 30 min to obtain a ligand solution.

[0084] (3) Preparation of organic monomer solution

[0085] 0.04 g of TMC was added into 20 ml of pure n-hexane reagent and stirred at room temperature for 3 h to obtain an organic monomer solution.

[0086] (4) Preparation of ZIF@TFC membrane

[0087] The wet PES ultrafiltration membrane that had been soaked in deionized water was fixed on a square frame (the front of the membrane was facing up), and then the metal-water phase monomer solution was poured on the top of the membrane to allow the metal ions to be evenly anchored on the surface of the PES ultrafiltration membrane. After 10 minutes of reaction, it was translated into the ligand solution (the front of the membrane was facing up). Based on the reverse diffusion osmosis strategy, the polarity of the ligand solution below the membrane was used to diffuse upward, so that the metal ions anchored on the membrane surface and the ligands grew in situ, heterogeneously nucleated on the membrane surface and formed a dense and continuous ZIF-8 layer. After about 45 minutes of reaction, the membrane on the frame was taken out and placed in a 55°C oven for 5 minutes to allow ZIF-8 crystals to grow evenly on the PES membrane to form a ZIF-8 membrane.

[0088] The ZIF-8 membrane was fixed on the filtration device (the front of the membrane was facing upward), and the aqueous monomer solution was first poured on the surface of the ZIF-8 membrane. After standing for 2 minutes, the filtration was performed from the bottom. After the surface of the ZIF-8 membrane was slightly wet, the organic phase solution was poured on the surface of the ZIF-8 membrane. Under the action of suction force, the reaction lasted for 1 minute, and the organic phase quickly entered the gap between the ZIF-8 nanoparticles, thereby inducing an interfacial polymerization reaction around the ZIF-8 nanoparticles. The m-phenylenediamine coated on the surface of the ZIF-8 could undergo a condensation reaction with the organic phase monomer, and then the excess organic phase solution was removed. The membrane was placed in an oven at 55°C and dried for 10 minutes to form a ZIF@TFC membrane with embedded nanoparticles, and a ZIF@TFC-4 membrane was prepared.

[0089] The ZIF@TFC-4 membrane obtained above was scanned by SEM, and the obtained SEM image is as follows: Figure 4 As shown, Figure 4 (a) and (b) are plane scanning electron microscope images at 10 μm and 100 nm, respectively. Figure 4 It can be seen from the data that when the ligand reaction time is reduced to 45 min, the polyamide layer on the surface of the ZIF@TFC-4 membrane is more uniform, but the polyamide layer is thinner and there are residual reactants on the surface. This is because when the reaction time of 2-methylimidazole is too short, the ZIF-8 layer generated by the reaction is too thin, which leads to a thinner polyamide layer and unsaturated reaction, resulting in excessive residues on the surface, a thin ZIF@TFC-4 membrane, and poor dye / salt selectivity.

[0090] Example 5

[0091] (1) Preparation of metal-water monomer solution

[0092] 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine were weighed respectively, added into 20 ml of deionized water containing 0.015 g of PVA, and stirred sufficiently in the dark to obtain a metal-water phase monomer solution.

[0093] (2) Preparation of ligand solution

[0094] Add 2 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 min to obtain the ligand solution.

[0095] (3) Preparation of organic monomer solution

[0096] Add 0.04 g of TMC to 20 ml of pure n-hexane reagent and stir at room temperature for 3 h to obtain the organic monomer solution.

[0097] (4) Preparation of ZIF@TFC membrane

[0098] Fix the pre-wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing upwards), then pour the metal-aqueous phase monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 min, translate it into the ligand solution (with the membrane facing upwards). Based on the reverse diffusion osmosis strategy, utilize the polar effect of the ligand solution below the membrane to diffuse upwards, enabling the metal ions anchored on the membrane surface to in-situ grow with the ligand, nucleate heterogeneously on the membrane surface, and form a dense and continuous ZIF-8 layer. After reacting for about 75 min, take out the membrane on the frame and dry it in an oven at 55 °C for 5 min to facilitate the uniform growth of ZIF-8 crystals on the PES membrane to form a ZIF-8 membrane.

[0099] Fix the ZIF-8 membrane on the suction filtration device (with the membrane facing upwards), turn on the suction pump, and then quickly pour the organic phase solution onto the surface of the ZIF-8 membrane. Under the suction force, react for 1 min. Under negative pressure conditions, polymerize the carboxyl groups carried by the organic phase monomer with the amino groups around ZIF-8 at the bulk interface, causing the bulk interface polymerization reaction to penetrate through the entire ZIF-8 selective layer and penetrate into the PES substrate, thereby obtaining a ZIF-8 thin film composite membrane with excellent interface compatibility and continuous and defect-free. Finally, place the membrane in an oven at 55 °C and dry it for 10 min to prepare the ZIF@TFC-5 membrane.

[0100] Use SEM to scan the obtained ZIF@TFC-5 membrane, and the obtained scanning electron micrograph is as Figure 5 shown Figure 5 (a) and (b) are planar scanning electron micrographs at 10 μm and 100 nm respectively. From Figure 5It can be seen that when the ligand reaction time increases to 75 min, the polyamide layer on the surface of the ZIF@TFC-5 membrane is more rugged, the polyamide layer is thicker and has an obvious lotus leaf shape on the surface. This is because when the reaction time of 2-methylimidazole is longer, the ZIF-8 layer generated by the reaction is slightly thicker and uneven, resulting in a less uniform polyamide layer and poor dye / salt selectivity.

[0101] Comparative Example 1

[0102] (1) Preparation of organic phase monomer solution

[0103] 0.04 g of TMC was added into 20 ml of pure n-hexane reagent and stirred at room temperature for 3 hours to obtain an organic monomer solution.

[0104] (2) Preparation of aqueous monomer solution

[0105] Add 0.4 g of m-phenylenediamine into 20 ml of deionized water and stir at room temperature for 2 hours to obtain an aqueous monomer solution.

[0106] (3) Preparation of pure polyamide membrane

[0107] The wet PES ultrafiltration membrane that had been soaked with deionized water was fixed on a square frame (the front of the membrane was facing up), and then the m-phenylenediamine aqueous solution was poured on top to allow the metal ions to anchor in the gaps of the PES ultrafiltration membrane and react for 2 minutes. After the excess m-phenylenediamine aqueous solution was filtered out, the organic phase monomer solution was poured on top and reacted for 1 minute. After the reaction was completed, the organic phase monomer solution was removed and dried in an oven at 55°C for 5 minutes to obtain a polyamide membrane.

[0108] The polyamide membrane obtained above was scanned by SEM, and the obtained SEM image is as follows: Figure 6 As shown, Figure 6 (a) and (b) are plane scanning electron microscope images at 10 μm and 200 nm, respectively. Figure 6 It can be seen from the obtained results that the polyamide layer is clearly evenly attached to the membrane, but due to the lack of MOF layer to cooperate with it, its dye / salt retention rate flux is poor.

[0109] Comparative Example 2

[0110] (1) Preparation of aqueous monomer solution

[0111] 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine, respectively, were added into 20 ml of deionized water, and the mixture was fully stirred in the dark to obtain a ZIF-8 aqueous monomer solution.

[0112] (2) Preparation of ligand solution

[0113] Add 2 g of 2-methylimidazole to 100 ml of pure methanol reagent and stir it thoroughly to obtain a ligand solution.

[0114] (3) Preparation of ZIF-1 membrane

[0115] Fix the pre-wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing upwards), then pour the MOF aqueous monomer solution above it to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 minutes, based on the reverse diffusion osmosis strategy, for the next step, translate the PES ultrafiltration membrane anchored with the aqueous phase to the ligand solution (with the membrane facing upwards). Utilize the upward diffusion of the polarity of the ligand solution below the membrane to enable the metal ions anchored on the membrane surface to react with the ligand solution, nucleate heterogeneously on the membrane surface, and form a dense MOF layer. After reacting for approximately 60 minutes, remove the aqueous monomer within the frame, and then place the membrane in an oven at 55 °C for drying for 15 minutes to facilitate the uniform growth of ZIF-8 crystals on the PES membrane, thus preparing the ZIF-1 membrane.

[0116] Use SEM to scan the obtained ZIF-1 membrane above, and the obtained scanning electron micrographs are as Figure 7 shown, Figure 7 (a) and (b) are SEM images of the surface of the ZIF-1 membrane at 10 μm and 100 nm respectively. It can be seen that ZIF-8 crystals are uniformly loaded on the membrane, but due to the lack of defect repair by the PA layer, its dye / salt selectivity is poor.

[0117] Comparative Example 3

[0118] (1) Preparation of metal-aqueous monomer solution

[0119] Weigh 0.3 g of zinc nitrate hexahydrate and 0.4 g of m-phenylenediamine respectively, add them to 20 ml of deionized water, and stir them thoroughly under dark conditions to obtain a metal-aqueous monomer solution.

[0120] (2) Ligand solution preparation

[0121] Add 2 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 minutes to obtain a ligand solution.

[0122] (3) Preparation of organic monomer solution

[0123] Add 0.04 g of TMC to 20 ml of pure n-hexane reagent and stir it at room temperature for 3 hours to obtain an organic monomer solution.

[0124] (4) Preparation of ZIF@TFC membrane

[0125] The wet PES ultrafiltration membrane that had been soaked in deionized water was fixed on a square frame (the front of the membrane faced upward), and then the metal-water phase monomer solution was poured on top of the membrane. Since the base membrane is hydrophobic, the metal ions will not be evenly anchored on the surface of the PES ultrafiltration membrane. After reacting for 10 minutes, it was transferred to the ligand solution (the front of the membrane faced upward). Based on the reverse diffusion osmosis strategy, the polarity of the ligand solution below the membrane was utilized to diffuse upward. Most of the ligands homogeneously nucleated with the free metal ions in the solution, but the interface layer MOF membrane had large-area defects and could not form a membrane.

[0126] Comparative Example 4

[0127] (1) Preparation of metal-water monomer solution

[0128] 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine were weighed respectively, added into 20 ml of deionized water containing 0.015 g of PVA, and stirred sufficiently in the dark to obtain a metal-water phase monomer solution.

[0129] (2) Preparation of ligand solution

[0130] 2 g of 2-methylimidazole was added into 100 ml of anhydrous methanol, and the mixture was stirred for 30 min to obtain a ligand solution.

[0131] (3) Preparation of organic monomer solution

[0132] 0.04 g of TMC was added into 20 ml of pure n-hexane reagent and stirred at room temperature for 3 h to obtain an organic monomer solution.

[0133] (4) Preparation of ZIF@TFC membrane

[0134] Fix the wet PES ultrafiltration membrane pre-soaked in deionized water on a square frame (with the membrane facing upwards), then pour the metal-aqueous monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 minutes, translate it into the ligand solution (with the membrane facing upwards). Based on the reverse diffusion and osmosis strategy, utilize the polar effect of the ligand solution below the membrane to diffuse upwards, enabling the metal ions anchored on the membrane surface to in-situ grow with the ligand, nucleate heterogeneously on the membrane surface, and form a dense and continuous ZIF-8 layer. After reacting for approximately 60 minutes, take out the membrane on the frame, fix it on a suction filtration device (with the membrane facing upwards), turn on the suction pump, and then quickly pour the organic phase solution onto the surface of the ZIF-8 membrane. Under the action of the suction force, react for 1 minute, and under negative pressure conditions, conduct interfacial polymerization between the carboxyl groups carried by the organic phase monomer and the amino groups around ZIF-8, thereby obtaining the ZIF-8 thin film composite membrane. Finally, place the membrane in an oven at 55 °C and dry it for 10 minutes to prepare the ZIF@TFC-8 membrane. Since a relatively thick aqueous monomer layer adheres to the surface layer of the MOF, most of the organic phase undergoes interfacial polymerization reaction with the surface layer aqueous monomer and does not penetrate into the MOF framework.

[0135] Comparative Example 5

[0136] (1) Preparation of metal-aqueous monomer solution

[0137] Weigh 0.3 g and 0.4 g of zinc nitrate hexahydrate and m-phenylenediamine respectively, add them to 20 ml of deionized water containing 0.015 g of PVA, and stir them thoroughly under dark conditions to obtain the metal-aqueous monomer solution.

[0138] (2) Preparation of ligand solution

[0139] Add 2 g of 2-methylimidazole to 100 ml of anhydrous methanol and stir it thoroughly for 30 minutes to obtain the ligand solution.

[0140] (3) Preparation of organic monomer solution

[0141] Add 0.04 g of TMC to 20 ml of pure n-hexane reagent and stir it at room temperature for 3 hours to obtain the organic monomer solution.

[0142] (4) Preparation of ZIF@TFC membrane

[0143] Fix the pre-wetted PES ultrafiltration membrane soaked in deionized water on a square frame (with the membrane facing upwards), then pour the metal-aqueous monomer solution above the membrane to evenly anchor metal ions on the surface of the PES ultrafiltration membrane. After reacting for 10 min, translate it into the ligand solution (with the membrane facing upwards). Based on the reverse diffusion osmosis strategy, utilize the polar effect of the ligand solution below the membrane to diffuse upwards, enabling the in-situ growth of the metal ions anchored on the membrane surface with the ligand, nucleating heterogeneously on the membrane surface and generating a dense and continuous ZIF-8 layer. After reacting for approximately 60 min, take out the membrane on the frame and place it in an oven at 55 °C for drying for 5 min to facilitate the uniform growth of ZIF-8 crystals on the PES membrane to form a ZIF-8 membrane.

[0144] Pour the organic phase solution on the surface of the ZIF-8 membrane and react for 1 min. The carboxyl groups carried by the organic phase monomers undergo interfacial polymerization with the amino groups around ZIF-8 to form a ZIF-8 thin film composite membrane. Finally, place the membrane in an oven at 55 °C and dry for 10 min to prepare the ZIF@TFC-9 membrane. Due to the compactness of MOF, compared with the negative pressure condition, under the normal organic phase immersion condition, the organic phase undergoes interfacial polymerization reaction with the surface aqueous phase monomers and will not penetrate into the MOF framework.

[0145] Test Example 1

[0146] Cut different types of ZIF@TFC membranes into the same size as the test membrane cell area and place them in the membrane cell. The samples are pre-pressed at 1 bar for 2 hours to reach stability, and then the permeation rate and rejection rate of the membrane for different dyes and salt solutions are recorded at the same intervals. Take the average value and test the performance stability of the membrane over a long period of time.

[0147] Performance Determination Method

[0148] For the determination method of dye / salt rejection performance, refer to the literature Liu Y, Wang X P, Zong Z A, et al. Thinfilm nanocomposite membrane incorporated with 2D-MOF nanosheets for highlyefficient reverse osmosis desalination[J]. Journal of Membrane Science, 2022, 653(5):120520. The prepared nanofiltration membranes are respectively tested for the flux and rejection rate of the membrane using a cross-flow filtration device. The effective area of the test membrane cell is 1.06 cm 2 , and the concentrations of both the dye and the salt are 100 ppm. The samples are pre-pressed at 1 bar for 2 hours to reach a stable condition. The permeability and rejection of the membrane are measured within 20 min.

[0149] The permeability (P) of the membrane can be calculated from the formula as follows.

[0150] where V (L) is the volume of the permeate passing through the membrane, A (m 2 ) is the effective area of the membrane under test, t (h) is the test time, Δp (bar) is the transmembrane pressure during the test, and the unit of P is (Lm -2 h -1 bar -1 ).

[0151] The concentrations of the dyes in the feed inlet and permeate were measured by ultraviolet / visible spectroscopy (Shimadzu), and the concentration of the salt was measured by a FE38 conductivity meter (Mettler Toledo). The concentrations were calculated based on the standard curves of the dyes and salts. According to the formula the rejection rate (R%) of the dyes and salts was calculated, where C P is the permeate solution and C f is the feed solution.

[0152] The water fluxes and dye / salt of the ZIF@TFC-1 membrane, ZIF@TFC-2 membrane, and ZIF@TFC-3 membrane obtained in Example 1, Example 2, and Example 3 above were measured respectively. The measurement data results are shown in the following table and Figure 8 as follows:[[]]

[0153]

[0154]

[0155] Figure 8 are the separation performance test result diagrams of the ZIF@TFC-1, ZIF@TFC-2, and ZIF@TFC-3 membranes; (a) and (b) show the water permeation amount and rejection rate of congo red, methyl green, methyl orange, and methylene blue, and (c) and (d) show the water permeation amount and rejection rate of MgSO4, Na2SO4, NaCl, and MgCl2.

[0156] Figure 8 As can be seen from the above table and Figure 8 the ZIF@TFC-2 membrane has the best dye rejection rate compared to the ZIF@TFC-1 and ZIF@TFC-3 membranes; compared to the salt rejection rates of the ZIF@TFC-1, ZIF@TFC-2, and ZIF@TFC-3 membranes, the salt rejection rate of the ZIF@TFC-1 is the lowest. However, in terms of the comparison of dye / salt selectivity, the ZIF@TFC-2 membrane has the best separation selectivity performance.

[0157] Test Example 2

[0158] The water fluxes, dyes / salts of the ZIF@TFC-2 membrane, ZIF@TFC-4 membrane, and ZIF@TFC-5 membrane obtained from Example 2, Example 4, and Example 5 respectively were measured, and the measurement data results are shown in the following table and Figure 9 as follows:

[0159]

[0160] Figure 9 are the separation performance test result diagrams of the ZIF@TFC-2, ZIF@TFC-4, and ZIF@TFC-5 membranes; among them, Figures (a) and (b) are the water permeation amounts and rejection rates of Congo red, methyl green, methyl orange, and methylene blue, and Figures (c) and (d) are the water permeation amounts and rejection rates of MgSO4, Na2SO4, NaCl, and MgCl2.

[0161] From the above table and Figure 9 it can be clearly seen that both the dye / salt selectivity and flux of ZIF@TFC-2 are superior to those of the other two membranes. Therefore, through experimental data, it is obtained that under the premise that other conditions remain unchanged, the ZIF@TFC-2 membrane prepared when the reaction time of the metal and the ligand is 60 min is the optimal one.

[0162] Test Example 3

[0163] At a pressure of 0.1 bar, the concentrations of the dye and the salt were both set to 100 ppm to test the long-term time stability of the membrane; secondly, by increasing the test pressure, the change in the permeation rate of the membrane was tested, and the results are as Figure 10 follows: Figure 10 is the performance stability test result diagram of the ZIF@TFC-2 membrane prepared in Example 2. Among them, Figure (a) is the stability test result of the membrane water permeation amount under different pressures, Figure (b) is the long-term time stability test result of the separation performance of the ZIF@TFC-2 membrane for Congo red, and Figure (c) is the long-term stability test result of the separation performance of the ZIF@TFC-2 membrane for Na2SO4.

[0164] Figure 10 (a) shows that with the CR dye as the stock solution, as the test pressure of the ZIF@TFC-2 membrane increases, the permeability of the membrane is continuously increasing, and it can increase from 4.59 Lm -2 h -1 bar -1 to 6.15 Lm -2 h -1 bar -1 . Secondly, with the CR dye as the stock solution and Na2SO4 as the stock solution respectively, as the test time increases, the stability of the permeability and rejection rate of the ZIF@TFC-2 membrane was tested, and the results are as Figure 10(b) and (c). The experimental results show that, under the condition that other test conditions remain unchanged, with the increase of the test time, the water permeation amount and rejection rate of the ZIF@TFC-2 membrane for dyes and salts first slightly decrease in a relatively short time, and then remain relatively stable during the subsequent relatively long time. This is because the Congo red molecules on the membrane surface are enriched through dye adsorption and accumulation in the early stage, resulting in a decrease in the membrane permeability. However, due to the good water solubility of the dye molecules, the adsorption-desorption process is dynamic. When equilibrium is reached, the permeability of the dye solution remains stable. Although the permeability of the membrane decreases to a certain extent, the rejection reaction to the dye hardly changes.

[0165] Test Example 4

[0166] The water fluxes and dye / salts of the ZIF@TFC-2 membrane, PA membrane, and ZIF-1 membrane obtained in the above Examples 2, 6, and 7 were measured respectively. The measurement data results are as shown in the following table and Figure 11 as follows:

[0167]

[0168] Figure 11 Figure for the separation performance test results of the ZIF@TFC-2, ZIF@TFC-6, and ZIF@TFC-7 membranes. Among them, Figures (a) and (b) are the water permeation amounts and rejection rates for Congo red, methyl green, methyl orange, and methylene blue, and Figures (c) and (d) are the water permeation amounts and rejection rates for MgSO4, Na2SO4, NaCl, and MgCl2.

[0169] From the above table and Figure 11 , it can be clearly seen that when the PA layer or MOF layer is missing, the dye / salt selectivity decreases and the flux significantly increases.

[0170] This specific embodiment is only an explanation of the present application and does not limit the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A preparation method of a ZIF-8 thin film composite membrane, the ZIF-8 thin film composite membrane being used for separating dyes in printing and dyeing wastewater, characterized in that, The preparation method includes the following steps: S1. Dissolve zinc nitrate hexahydrate in a deionized aqueous solution containing polyvinyl alcohol and m-phenylenediamine to obtain a metal-aqueous phase monomer solution; S2. Immerse one side of the dense separation layer of the PES ultrafiltration membrane in the metal-aqueous phase monomer solution to anchor metal ions on the surface of the PES ultrafiltration membrane. Then immerse the porous support layer side of the PES ultrafiltration membrane in the ligand solution. The ligand solution diffuses upward under the action of polarity, enabling in-situ growth of the metal ions with the ligands in the ligand solution, and heterogeneous nucleation occurs on the surface of the PES ultrafiltration membrane to form a dense and continuous ZIF-8 thin film. Then perform a drying treatment to uniformly grow ZIF-8 crystals on the PES ultrafiltration membrane, obtaining a PES ultrafiltration membrane with a ZIF-8 selective layer on one side; S3. Pour the organic phase monomer solution onto the ZIF-8 selective layer of the PES ultrafiltration membrane obtained in step S2, and carry out a bulk-phase interfacial polymerization reaction between the carboxyl groups of the organic phase monomers in the organic phase monomer solution and the amino groups of m-phenylenediamine; S4. Dry the PES ultrafiltration membrane obtained by treating in step S3 to obtain the ZIF-8 thin film composite membrane.

2. The preparation method according to claim 1, characterized in that, In the metal-aqueous phase monomer solution, the concentration of zinc nitrate hexahydrate is 1 - 2 g / mL, the concentration of m-phenylenediamine is 1.5 - 2.5 g / mL, and the concentration of polyvinyl alcohol is 0.05 - 0.1 g / mL.

3. The preparation method according to claim 1, characterized in that, The ligand solution is an anhydrous methanol solution of 2-methylimidazole.

4. The preparation method according to claim 2, characterized in that, In the ligand solution, the concentration of 2-methylimidazole is 1 - 3 g / mL.

5. The preparation method according to claim 1, characterized in that, The organic phase monomer solution is a 1,3,5-benzenetricarbonyl chloride solution.

6. The preparation method according to claim 5, characterized in that, In step S2, the time for the in-situ growth is 45 - 75 min.

7. The preparation method according to claim 1, characterized in that, Step S3 specifically is: Fix the PES ultrafiltration membrane with a ZIF-8 selective layer on a suction filtration device, with the ZIF-8 selective layer facing upward. Turn on the suction pump, and then quickly pour the organic phase monomer solution onto the membrane surface of the ZIF-8 selective layer. Under the action of suction, react for 1 - 2 min, and under negative pressure conditions, carry out a bulk-phase interfacial polymerization between the carboxyl groups carried by the organic phase monomers in the organic phase monomer solution and the amino groups around the ZIF-8 selective layer, causing the bulk-phase interfacial polymerization reaction to penetrate the entire ZIF-8 selective layer and penetrate into the PES ultrafiltration membrane.

8. The preparation method according to claim 1, characterized in that, The drying temperature is 50 - 60 °C.

9. A ZIF-8 thin film composite membrane prepared by the preparation method according to any one of claims 1 - 8.

10. An application of the ZIF-8 thin film composite membrane as described in claim 9 in the treatment of printing and dyeing wastewater.

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