A method for preparing a defect-free MOF film by MOF gradient distribution seeding
By depositing MOF seeds in a gravitational field and modifying them with thiol and tannic acid, a gradient-distributed MOF membrane was prepared, which solved the problems of uneven nucleation sites and poor adhesion of MOF membranes on polymer substrates, and achieved the growth of dense and defect-free MOF membranes, thus improving gas separation performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2023-10-07
- Publication Date
- 2026-05-22
AI Technical Summary
Existing technologies make it difficult to prepare dense and defect-free MOF films on polymer substrates. Inhomogeneous nucleation sites and poor adhesion between the MOF layer and the substrate lead to grain boundary defects and easy detachment in the film.
By depositing MOF seeds in a gravitational field, a gradient distribution of MOF seeds is formed on a polymer substrate before phase transformation film formation. The density difference of the MOF seeds is utilized to deposit them in the bottom layer. Combined with thiol and tannic acid modification, the nucleation sites and adhesion are enhanced, and a dense and defect-free MOF film is prepared.
This method enables dense growth of MOF membranes, improves gas separation performance, enhances the adhesion between the MOF layer and the substrate, reduces grain boundary defects, and improves the selectivity and permeability of H2/CO2.
Smart Images
Figure CN117101424B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of gas separation technology, specifically relating to a method for preparing defect-free MOF membranes using a MOF gradient distribution seeding method. Background Technology
[0002] Clean energy sources such as hydrogen have received increasing attention in recent years and are expected to become one of the main pillars of energy transition and industrial decarbonization. Compared with traditional energy-intensive gas separation methods such as pressure swing adsorption and cryogenic distillation, membrane separation technology has developed rapidly in the field of gas separation due to its high energy efficiency, simple operation, small footprint, and low equipment investment. The key to membrane separation technology lies in the selection of high-performance membrane materials.
[0003] Metal-organic frameworks (MOFs) are a new class of porous materials with well-defined pore sizes and ultra-high porosity. Due to their inherent precise molecular sieving properties, they have great application prospects in the field of membrane separation. Compared with other inorganic packing materials, MOFs have the following characteristics in gas separation: (1) High design: On the one hand, a large number of ligands and metal ions can be used to create MOFs with different topologies. On the other hand, MOFs can be further chemically modified by post-synthetic modification (PSM) methods; (2) High porosity: MOFs have higher pore volume and lower density than conventional packing materials, so they have a greater impact on hybrid membranes at the same mass percentage.
[0004] Currently, MOF-based gas separation membranes can be broadly classified into two types: MOF membranes and MOF-based hybrid matrix membranes (MMMs). Due to their limited thickness, hybrid matrix membranes have relatively low gas permeation flux. MOF membranes are composite membranes, consisting of a selective layer for gas separation and a supporting substrate. This structure allows for reducing the selective layer thickness through compositing, significantly reducing mass transfer resistance and increasing gas permeation flux, making it a current hot research area. Common MOF membranes are prepared on inorganic substrates such as alumina and silica. However, fabricating MOF membranes on flexible, processable, and low-cost polymer substrates holds greater promise for industrial applications. Since most gas molecules have similar diameters, minute defects within the MOF membrane can significantly affect selectivity. Furthermore, the lack of interaction between the MOF and the polymer substrate leads to a greater tendency for crystal particles to nucleate and grow in solution rather than forming a continuous, defect-free MOF membrane. Therefore, the surface properties of the polymer substrate play a crucial role in the nucleation and growth of the MOF membrane. To prepare dense and defect-free MOF films, the substrate surface must provide sufficient and uniformly distributed nucleation sites to induce heterogeneous nucleation and subsequent growth of MOF crystals, while simultaneously enhancing the adhesion of the substrate to the MOF layer to prevent peeling from the substrate. Most current research focuses on surface modification of the substrate to introduce nucleation sites, generally using two methods: in-situ transformation of functional groups on the polymer substrate and surface modification by coating with an organic layer. Both methods introduce groups that can interact with metal ions or ligands to increase nucleation sites; however, relatively low conversion rates and non-uniform distribution of functional groups often result in insufficient nucleation sites, limiting the efficiency of heterogeneous nucleation. The number and uniformity of nucleation sites significantly affect the grain boundary structure of the MOF, thus influencing the final thickness and integrity of the MOF film. Furthermore, a significant difference in mechanical properties between the MOF layer and the polymer substrate can easily lead to MOF layer fracture during growth, resulting in non-selective defects and greatly reducing selectivity. Therefore, seeding a large number of uniformly distributed nucleation sites on the polymer substrate surface and improving the surface rigidity of the polymer substrate are crucial for growing dense and defect-free MOF films.
[0005] Zhang Guoliang et al. (CN109603572A) from Zhejiang University of Technology proposed a method for obtaining ZIF-8 films through hydrothermal in-situ growth using ZnO nanosheets as the metal source. This method seeds nucleation sites by immersing the polymer film in a ZnO aqueous solution. However, the low adhesion rate and uneven distribution of ZnO on the polymer film surface often limit the efficiency of subsequent heterogeneous ZIF-8 nucleation. The resulting ZIF-8 film exhibits numerous grain boundary defects, and the adhesion between the ZIF-8 layer and the polymer substrate is insufficient, making it prone to detachment.
[0006] Therefore, we propose a method that utilizes the phenomenon of MOF sedimentation in a gravitational field. Before phase transformation and membrane formation, gravity causes MOFs to aggregate on one side, leading to phase transformation and the formation of a composite membrane rich in MOF seeds in the bottom layer, thus increasing nucleation sites. In this polymer substrate, MOF seeds are abundantly concentrated in the bottom layer, providing sufficient and uniformly distributed nucleation sites. The MOF seeds on the polymer side increase the rigidity of the polymer substrate, reducing the possibility of MOF layer breakage during growth. The interaction force between the MOF seeds and the MOF layer enhances their adhesion, making the MOF layer less prone to detachment. In summary, the prepared substrate with a gradient distribution of MOF seeds can grow dense and defect-free MOF membranes, which exhibit excellent separation performance and have broad prospects for industrial applications. Summary of the Invention
[0007] In view of the above-mentioned shortcomings of the prior art, the purpose of this invention is to prepare a dense and defect-free MOF film. By designing a seeding method for MOF crystals, taking advantage of the fact that the density of MOF crystals is greater than that of polymer solutions, before phase transformation and film formation, the casting solution doped with crystals settles on a glass plate, and the phase transformation forms a composite film with MOF crystals rich in the bottom layer, followed by the growth of a dense and defect-free MOF film.
[0008] The technical solution of this invention:
[0009] A method for preparing defect-free MOF films using a MOF gradient distribution seeding method comprises the following steps:
[0010] (1) Preparation of ZIF-8 seed crystals
[0011] (2) Preparation of ZS-PAN base film
[0012] 0.05–0.4 parts of ZIF-8 seed crystals, 0.85–6.8 parts of polyacrylonitrile, and 4.2–34 parts of N,N-dimethylformamide were stirred at 10–25°C for 8–15 h to obtain a casting solution. Then, at 10–25°C, a uniform polymer solution with a thickness of 100–400 μm was cast onto a glass plate using a casting tool. The glass plate was placed in a DMF atmosphere and left to stand for 1–3 days. Subsequently, the glass plate was immersed in water for solvent exchange for 1–2 days. After being removed, it was placed in a vacuum oven at 40–70°C to dry to remove residual solvent, resulting in a PAN-based film with a gradient distribution of ZIF-8 seed crystals, denoted as ZS-PAN.
[0013] (3) Preparation of ZIF-8 membrane modified with thiol and tannic acid
[0014] 0.149–2.23 parts of zinc nitrate hexahydrate, 0.132–1.719 parts of 2-methylimidazole, 0.0328–0.43 parts of 2-mercapto-1-methylimidazole, and 71.19–355.95 parts of methanol were stirred for 1–5 minutes at 10–25°C. Then, 0.001–0.15 parts of tannic acid (TA) were added and ultrasonically dissolved to obtain an impregnation solution. The top of the ZS-PAN base membrane from the second step was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in an oven at 50–70°C for 1–4 hours to react. After that, it was taken out and rinsed 2–4 times with methanol solution. The sealing tape was removed, and it was dried at room temperature for 1–3 days to obtain a mercapto-containing ZIF-8 membrane.
[0015] (4) Preparation of c-OH-ZIF-8 membrane
[0016] Mix 0.02–0.1 parts of tetra(4-borophenyl)ethylene, 0.1–0.5 parts of triethylamine, and 106.79–533.93 parts of methanol, stir for 1–4 minutes, and sonicate to dissolve to obtain an impregnation solution; seal the top of the mercapto-containing ZIF-8 membrane from step 3 with tape, cut it to a suitable size, place it in the impregnation solution, and then place it in an oven at 30–60°C for 9–15 hours. Remove it, rinse it 2–4 times with methanol solution, remove the sealing tape, and dry it at room temperature for 1–3 days to obtain a defect-free ZIF-8 membrane.
[0017] The ZIF-8 particles were replaced with ZIF-67, UiO-66, and MIL-101.
[0018] The polymer base film is replaced with glass polymers such as polyimide and polyethersulfone.
[0019] The prepared MOF membranes were replaced with ZIF-67 membranes, UiO-66 membranes, and MIL-101 membranes.
[0020] Reaction Mechanism: The ZIF-8 seed crystals at the bottom of the ZS-PAN base membrane serve as nucleation sites for subsequent ZIF-8 membrane growth. In the third step, thiol-containing ligands are introduced into the impregnation solution for subsequent modification. The added tannic acid competitively coordinates to introduce abundant hydroxyl groups, increasing CO2 adsorption and enhancing the adsorption and sieving capacity of the ZIF-8 membrane, thus improving H2 / CO2 selectivity. In the fourth step, the thiol groups on the ZIF-8 membrane surface undergo an addition reaction with the double bonds in tetra(4-boratephenyl)ethylene under the catalysis of triethylamine. The B-OH groups can further coordinate with the unsaturated sites of zinc ions, thereby further reducing grain boundary defects in the ZIF-8 membrane, resulting in a more densely grown ZIF-8 membrane.
[0021] The beneficial effects of this invention: This invention designs a method for preparing defect-free MOF films using a MOF gradient distribution seeding method. First, a polymer PAN solution is prepared, in which pre-synthesized metal-organic frameworks (MOFs) are doped as nucleation sites for subsequent MOF film growth. The MOF selected is ZIF-8, whose theoretical pore size is... For gas molecules with small kinetic diameters, such as H2 There is a clear cutoff point, which can serve as a sieving mechanism. The prepared casting solution is then coated onto a glass plate using a doctor blade, and the glass plate is placed in a DMF atmosphere and allowed to stand for a period of time. The settled glass plate is then immersed in a coagulation bath for solvent exchange to prepare a ZS-PAN base film. Subsequently, the ZS-PAN base film is immersed in a ZIF-8 precursor solution containing tannic acid for secondary growth to prepare a ZIF-8 film. During the standing process, ZIF-8 particles settle to the bottom of the solution under gravity, and then undergo phase transformation to form a composite film rich in ZIF-8 seed crystals in the bottom layer. The abundant accumulation of ZIF-8 seed crystals at the bottom increases the nucleation sites for subsequent ZIF-8 growth, and the embedding of ZIF-8 on one side of the PAN flexible substrate enhances the adhesion between the ZIF-8 layer and the substrate, as well as the rigidity of the substrate. The tannic acid added to the ZIF-8 precursor solution has abundant hydroxyl groups. The thiol groups on the ZIF-8 film surface undergo an addition reaction with the double bonds in tetra(4-borate-phenyl)ethylene under the catalysis of triethylamine. Simultaneously, tetra(4-borate-phenyl)B-OH synergistically chelates unsaturated zinc ion sites, aiding in the growth of the ZIF-8 film and further compensating for grain boundary defects. The ZIF-8 film prepared by this method is dense and defect-free, showing significant advantages compared to ZIF-8 films prepared by directly seeding ZIF-8 crystals on a base film. Attached Figure Description
[0022] Figure 1 The image shown is a SEM image of the ZS-PAN base film in the example.
[0023] Figure 2 The image shows the zinc ion EDS-mapping of the ZS-PAN base film in the example.
[0024] Figure 3 The image shown is a SEM image of the c-OH-ZIF-8 membrane in the example.
[0025] Figure 4 This is an EDS-mapping image of zinc ions on the PAN-based membrane in the comparative example. Detailed Implementation
[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.
[0027] Example 1
[0028] (1) Preparation of ZIF-8 seed crystals
[0029] (2) Preparation of ZS-PAN base film
[0030] 0.05 g of ZIF-8 seed crystals, 0.85 g of polyacrylonitrile, and 4.2 g of N,N-dimethylformamide were stirred at 10 °C for 8 h to obtain a casting solution. Then, at 10 °C, a uniform polymer solution with a thickness of 100 μm was cast onto a glass plate using a casting knife. The glass plate was placed in a self-made DMF atmosphere and left to stand for 1 day. Subsequently, the glass plate was immersed in water for solvent exchange for 1 day. It was then removed and placed in a vacuum oven at 40 °C to dry to remove residual solvent, thus obtaining a ZS-PAN base film with a gradient distribution of ZIF-8 seed crystals.
[0031] (3) Preparation of ZIF-8 membrane modified with thiol and tannic acid
[0032] 0.149 g of zinc nitrate hexahydrate, 0.132 g of 2-methylimidazole, 0.0328 g of 2-mercapto-1-methylimidazole, and 71.19 g of methanol were stirred at 10 °C for 1 minute. Then, 0.001 g of TA was added and sonicated to dissolve the mixture to obtain an impregnation solution. The top of the ZS-PAN base membrane from the second step was sealed with tape, cut to an appropriate size, and placed in the impregnation solution. The membrane was then placed in a 50 °C oven for 1 hour. After that, the membrane was removed, rinsed twice with methanol solution, the sealing tape was removed, and the membrane was dried at room temperature for 1 day to obtain a mercapto-containing ZIF-8 membrane.
[0033] (4) Preparation of c-OH-ZIF-8 membrane
[0034] 0.02 g of tetra(4-boratephenyl)ethylene, 0.1 g of triethylamine, and 106.79 g of methanol were stirred for 1 minute and ultrasonically dissolved to obtain an impregnation solution. The top of the mercapto-containing ZIF-8 membrane from step 3 was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in a 30°C oven for 9 hours to react. After that, it was taken out and rinsed twice with methanol solution. The sealing tape was removed, and the membrane was dried at room temperature for 1 day to obtain a defect-free ZIF-8 membrane.
[0035] pass Figure 3 The surface SEM image of the c-OH-ZIF-8 membrane shows that the ZIF-8 layer on the membrane surface is dense and without obvious defects.
[0036] Example 2
[0037] (1) Preparation of ZIF-8 seed crystals
[0038] (2) Preparation of ZS-PAN base film
[0039] 1g of ZIF-8 seed crystals, 1.7g of polyacrylonitrile, and 8.2g of N,N-dimethylformamide were stirred at 15°C for 12h to obtain a casting solution. Then, at 20°C, a uniform polymer solution with a thickness of 200μm was cast onto a glass plate using a casting knife. The glass plate was placed in a self-made DMF atmosphere and left to stand for 2 days. Subsequently, the glass plate was immersed in water for solvent exchange for 1.5 days. After that, it was removed and placed in a vacuum oven at 60°C to dry to remove residual solvent, thus obtaining the ZS-PAN base film.
[0040] (3) Preparation of ZIF-8 membrane modified with thiol and tannic acid
[0041] 0.5 g of zinc nitrate hexahydrate, 0.2 g of 2-methylimidazole, 0.09 g of 2-mercapto-1-methylimidazole, and 110 g of methanol were stirred at 20 °C for 4 min. Then, 0.01 g of TA was added and sonicated to obtain an impregnation solution. The top of the ZS-PAN base membrane from the second step was sealed with tape, cut to an appropriate size, and placed in the impregnation solution. Then, it was placed in a 60 °C oven for 3 h. After that, it was taken out and rinsed three times with methanol solution. The sealing tape was removed, and it was dried at room temperature for 2 days to obtain a mercapto-containing ZIF-8 membrane.
[0042] (4) Preparation of c-OH-ZIF-8 membrane
[0043] 0.08 g of tetra(4-boratephenyl)ethylene, 0.3 g of triethylamine, and 420 g of methanol were stirred for 3 minutes and ultrasonically dissolved to obtain an impregnation solution. The top of the mercapto-containing ZIF-8 membrane from step 3 was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in a 40°C oven for 11 hours to react. After that, it was taken out and rinsed 3 times with methanol solution. The sealing tape was removed, and the membrane was dried at room temperature for 2 days to obtain a defect-free ZIF-8 membrane.
[0044] Example 3
[0045] (1) Preparation of ZIF-8 seed crystals
[0046] (2) Preparation of ZS-PAN base film
[0047] 0.4 g of ZIF-8 seed crystals, 6.8 g of polyacrylonitrile, and 34 g of N,N-dimethylformamide were stirred at 25 °C for 15 h to obtain a casting solution. Then, at 25 °C, a uniform polymer solution with a thickness of 400 μm was cast onto a glass plate using a casting knife. The glass plate was placed in a self-made DMF atmosphere and left to stand for 3 days. Subsequently, the glass plate was immersed in water for solvent exchange for 2 days. It was then removed and placed in a vacuum oven at 70 °C to dry to remove residual solvent, thus obtaining the ZS-PAN base film.
[0048] (3) Preparation of ZIF-8 membrane modified with thiol and tannic acid
[0049] 2.23 g of zinc nitrate hexahydrate, 1.719 g of 2-methylimidazole, 0.43 g of 2-mercapto-1-methylimidazole, and 355.95 g of methanol were stirred at 25 °C for 5 minutes. Then, 0.15 g of TA was added and sonicated to obtain an impregnation solution. The top of the ZS-PAN base membrane from the second step was sealed with tape, cut to an appropriate size, and placed in the impregnation solution. Then, it was placed in a 70 °C oven for 4 hours to react. After that, it was taken out and rinsed 4 times with methanol solution. The sealing tape was removed, and it was dried at room temperature for 3 days to obtain a mercapto-containing ZIF-8 membrane.
[0050] (4) Preparation of c-OH-ZIF-8 membrane
[0051] 0.1 g of tetra(4-boratephenyl)ethylene, 0.5 g of triethylamine, and 533.93 g of methanol were stirred for 4 minutes and ultrasonically dissolved to obtain an impregnation solution. The top of the mercapto-containing ZIF-8 membrane from step 3 was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in a 60°C oven for 15 hours to react. After that, it was taken out and rinsed 4 times with methanol solution. The sealing tape was removed, and the membrane was dried at room temperature for 3 days to obtain a defect-free ZIF-8 membrane.
[0052] Comparative Example 1
[0053] (1) Preparation of ZIF-8 seed crystals
[0054] (2) Preparation of ZS-PAN base film
[0055] 1g of ZIF-8 seed crystals, 1.7g of polyacrylonitrile, and 8.2g of N,N-dimethylformamide were stirred at 15°C for 12h to obtain a casting solution. Then, at 20°C, a uniform polymer solution with a thickness of 200μm was cast onto a glass plate using a casting knife. The glass plate was placed in a self-made DMF atmosphere and left to stand for 2 days. Subsequently, the glass plate was immersed in water for solvent exchange for 1.5 days. After that, it was removed and placed in a vacuum oven at 60°C to dry to remove residual solvent, thus obtaining the ZS-PAN base film.
[0056] Comparative Example 2
[0057] (1) Preparation of ZIF-8 seed crystals
[0058] (2) Preparation of PAN-based film
[0059] 1g of ZIF-8 seed crystals, 1.7g of polyacrylonitrile, and 8.2g of N,N-dimethylformamide were stirred at 15°C for 12h to obtain a casting solution. Then, at 20°C, a uniform polymer solution with a thickness of 200μm was cast onto a glass plate using a casting knife. Subsequently, the glass plate was immersed in water for solvent exchange for 1.5 days. After that, it was removed and placed in a vacuum oven at 60°C to dry to remove residual solvent, thus obtaining a PAN base film.
[0060] (3) Preparation of ZIF-8 / PAN membrane modified with thiol and tannic acid
[0061] 0.5 g of zinc nitrate hexahydrate, 0.2 g of 2-methylimidazole, 0.09 g of 2-mercapto-1-methylimidazole, and 110 g of methanol were stirred at 20 °C for 4 min. Then, 0.01 g of TA was added and sonicated to dissolve the mixture to obtain an impregnation solution. The top of the PAN base membrane from the second step was sealed with tape, cut to an appropriate size, and placed in the impregnation solution. The membrane was then placed in a 60 °C oven for 3 h. After that, the membrane was removed, rinsed three times with methanol solution, the sealing tape was removed, and the membrane was dried at room temperature for 2 days to obtain a mercapto-containing ZIF-8 / PAN membrane.
[0062] (4) Preparation of c-OH-ZIF-8 / PAN membrane
[0063] 0.08 g of tetra(4-boratephenyl)ethylene, 0.3 g of triethylamine, and 420 g of methanol were stirred for 3 minutes and ultrasonically dissolved to obtain an impregnation solution. The top of the mercapto-containing ZIF-8 / PAN membrane from step 3 was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in a 40°C oven for 11 hours to react. After that, it was taken out and rinsed 3 times with methanol solution. The sealing tape was removed, and the membrane was dried at room temperature for 2 days to obtain the ZIF-8 membrane.
[0064] pass Figure 4 The cross-sectional EDS image of the PAN base film shows that the ZIF-8 seeds are uniformly distributed in the PAN base film without gravity settling, and there are fewer nucleation sites at the bottom of the base film.
[0065] Both this embodiment and the comparative example used a constant pressure permeation apparatus to determine the gas separation performance of the prepared ZIF-8 membrane for H2, CO2, N2, and CH4 components.
[0066] Compared to Comparative Examples 1 and 2, the ZIF-8 membrane synthesized in Example 2 exhibits a dense and defect-free ZIF-8 layer due to the abundant presence of ZIF-8 nucleation sites. The pore size of ZIF-8 provides significant cutoff for small molecule gases, effectively sieving gas molecules of different diameters. The presence of tannic acid adsorbs CO2, hindering its passage and significantly improving the H2 / CO2 selectivity. Ultimately, the H2 permeability reached 953.66 GPU, and the H2 / CO2 selectivity reached 12.06, exceeding the upper limit of gas separation performance in 2008.
[0067] sample <![CDATA[Permeability GPU of H2]]> <![CDATA[H2 / CO2 selectivity]]> Example 1 1824.76 7.21 Example 2 953.66 12.06 Example 3 647.8 12.5 Comparative Example 1 15688.02 4.47 Comparative Example 2 5689.23 4.92
[0068] The examples described above are specific embodiments of the present invention and are not limited to the scope of protection of the present invention. The scope of protection of the present invention is not limited thereto. Any modifications or substitutions made by researchers in this field within the spirit and scope of the present invention should fall within the scope of protection and disclosure of the present invention.
Claims
1. A method for preparing defect-free MOF films using a MOF gradient distribution seeding method, characterized in that, The steps are as follows: (1) Preparation of ZIF-8 seed crystals (2) Preparation of ZS-PAN base film 0.05–0.4 parts of ZIF-8 seed crystals, 0.85–6.8 parts of polyacrylonitrile, and 4.2–34 parts of N,N-dimethylformamide were stirred at 10–25 °C for 8–15 h to obtain a casting solution. Then, at 10–25 °C, a uniform polymer solution with a thickness of 100–400 μm was cast onto a glass plate using a casting tool. The glass plate was placed in a DMF atmosphere and allowed to stand for 1–3 days. Subsequently, the glass plate was immersed in water for solvent exchange for 1–2 days. After being removed, it was placed in a vacuum oven at 40–70 °C to dry to remove residual solvent, resulting in a PAN-based film with a gradient distribution of ZIF-8 seed crystals, denoted as ZS-PAN. (3) Preparation of ZIF-8 membranes modified with thiol and tannic acid 0.149–2.23 parts of zinc nitrate hexahydrate, 0.132–1.719 parts of 2-methylimidazole, 0.0328–0.43 parts of 2-mercapto-1-methylimidazole, and 71.19–355.95 parts of methanol were stirred at 10–25 °C for 1–5 minutes. Then, 0.001–0.15 parts of tannic acid were added and ultrasonically dissolved to obtain an impregnation solution. The top of the ZS-PAN base membrane from the second step was sealed with tape, cut to a suitable size, and placed in the impregnation solution. Then, it was placed in an oven at 50–70 °C for 1–4 hours to react. After that, it was taken out and rinsed 2–4 times with methanol solution. The sealing tape was removed, and it was dried at room temperature for 1–3 days to obtain a mercapto-containing ZIF-8 membrane. (4) Preparation of c-OH-ZIF-8 membrane Mix 0.02-0.1 parts tetra(4-borophenyl)ethylene, 0.1-0.5 parts triethylamine, and 106.79-533.93 parts methanol, stir for 1-4 minutes, and sonicate to dissolve to obtain an impregnation solution; seal the top of the mercapto-containing ZIF-8 membrane from step 3 with tape, cut it to a suitable size, place it in the impregnation solution, and then place it in an oven at 30-60 ℃ for 9-15 h. Remove it, rinse it 2-4 times with methanol solution, remove the sealing tape, and dry it at room temperature for 1-3 days to obtain a defect-free ZIF-8 membrane.
2. The method according to claim 1, characterized in that, The ZIF-8 seed crystals are replaced with ZIF-67, UiO-66, and MIL-101.
3. The method according to claim 1, characterized in that, The PAN-based film is replaced with polyimide or polyethersulfone.
4. The method according to claim 1, characterized in that, The prepared MOF membranes were replaced with ZIF-67 membranes, UiO-66 membranes, and MIL-101 membranes.