A high-performance, aging-resistant c-PIM / UiO crosslinked membrane, its preparation method and its application

Abstract

This invention provides a high-performance, aging-resistant c-PIM / UiO crosslinked membrane, its preparation method, and its application, belonging to the field of gas separation membrane technology. The crosslinked membrane is a porous homogeneous membrane comprising a bromomethylated BM-PIM matrix and a porous MOF crosslinking agent, wherein the porous MOF crosslinking agent is embedded in the BM-PIM matrix. First, the bromomethylated polymer BM-PIM is prepared; second, amino-modified metal-organic framework materials (MOFs) are prepared; finally, the BM-PIM / MOF composite membrane is heat-treated using a temperature gradient method to construct multiple covalent crosslinked networks within the membrane, thus preparing the c-PIM / MOF crosslinked membrane. In the crosslinked membrane obtained by this invention, the regular channels within the porous MOF crosslinking agent and the micropores of the BM-PIM matrix serve as gas transport channels, and the two work synergistically to form a defect-free structure, resulting in a membrane with good long-term stability and high gas selectivity.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology and relates to a method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane. The obtained c-PIM / MOF crosslinked membrane can be used in, but is not limited to, gas separation systems. Background Technology

[0002] Carbon dioxide (CO2) is one of the major greenhouse gases. With increasing industrialization and energy consumption, CO2 emissions are constantly rising, which is a major cause of global warming and climate change. Controlling and recovering CO2 emission sources is one of the most effective methods to reduce atmospheric CO2 levels, and recovering CO2 from flue gas has significant environmental and economic benefits. Membrane separation of CO2 has advantages such as low energy consumption, simple operation, high selectivity, scalability, and environmental friendliness. However, the key to achieving efficient CO2 capture through membrane separation is the preparation of membrane materials that simultaneously possess high permeability and high selectivity. Novel separation membranes, represented by microporous materials, have attracted much attention due to their advantages such as easy membrane formation and nanoscale transport channels.

[0003] Self-polymerizing microporous polymers (PIMs) are highly permeable linear polymers containing inherent micropores (<2 nm) and ultramicropores (<0.7 nm). Due to the unique rigid and twisted backbone structure of PIMs, the polymer chain segments are difficult to form a dense packing structure, resulting in a large free volume between polymer chains, with a BET surface area as high as 800 m². 2 g -1 High gas permeability can be achieved. Furthermore, the bottlenecks or windows of interconnected micropores can sieve gas molecules of different sizes and shapes, providing selective gas transport channels. However, plasticization and physical aging severely limit the practical application of PIMs membranes in industrial carbon capture. Plasticization refers to the rearrangement of polymer chains under high adsorption of condensable gases (such as CO2), reducing selectivity for specific gases. Physical aging refers to the tendency of polymer chains to relax over time through continuous and spontaneous molecular rearrangement and lattice contraction, gradually increasing the polymer chain packing density. Therefore, the gas permeability of the membrane decreases significantly, thus affecting its application in gas separation.

[0004] To simultaneously mitigate the effects of plasticization and physical aging, this invention proposes to construct an intramembrane cross-linked network structure by heat-treating PIMs membranes using a temperature gradient method, thereby improving the long-term stability of the PIMs membranes. Furthermore, metal-organic frameworks (MOFs) are introduced to compensate for the loss of microporous structure within the PIMs membrane due to cross-linking, thus enhancing the gas separation performance of the PIMs. Summary of the Invention

[0005] The purpose of this invention is to provide a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material, solving the problem of difficulty in preparing high-performance, aging-resistant PIMs membranes in existing technologies. Simultaneously, a method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane is provided, characterized by the use of a temperature gradient method to construct the intramolecular and intermolecular crosslinking network of the c-PIM / MOF membrane. The preparation process is simple and can yield c-PIM / MOF crosslinked membranes with stable performance and high gas selectivity.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0007] A high-performance, aging-resistant c-PIM / MOF crosslinked membrane material is disclosed. The crosslinked membrane is a porous homogeneous membrane comprising a bromomethylated BM-PIM matrix and a porous MOF crosslinking agent. The porous MOF crosslinking agent is embedded within the BM-PIM matrix, specifically composed of a BM-PIM self-crosslinking structure and a composite of MOFs and BM-PIM crosslinking structures. In this crosslinked membrane material, the regular channels within the MOFs and the micropores of the BM-PIM serve as gas transport channels, working synergistically to form a defect-free structure. The membrane exhibits good long-term stability and high gas selectivity.

[0008] Furthermore, the thickness of the c-PIM / MOF crosslinked membrane material is 50-150 μm.

[0009] A method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material, comprising the following steps: First, preparing a casting solution. Second, preparing a BM-PIM / MOF composite membrane. Finally, heat-treating the BM-PIM / MOF composite membrane using a temperature gradient method to construct multiple covalent crosslinked networks within the membrane, thereby preparing the c-PIM / MOF crosslinked membrane material. The casting solution formulation of the crosslinked membrane contains bromomethylated BM-PIM, a porous MOF crosslinking agent, and chloroform; wherein the porous MOF crosslinking agent accounts for less than 30 wt% of the BM-PIM mass.

[0010] Step 1: Preparation of polymer BM-PIM

[0011] 1.1) Preparation of the reactive monomer 3,3,3′,3′,7,7′-hexamethyl-5,6,5′,6′-tetrahydroxy-1,1′-spirodiindane (M-TTSBI): 3-Methylcatechol was dissolved in a mixed solution of glacial acetic acid and hydrobromic acid. After stirring at room temperature for 10–30 min, acetone was added dropwise and the mixture was refluxed at 120–150 °C for 12–20 h to obtain a reddish-brown solution. The reddish-brown solution was slowly poured into deionized water to obtain a precipitated solid. The solid was filtered to separate it and washed repeatedly with glacial acetic acid. The obtained grayish-white powder was further purified by recrystallization in methanol to obtain a white M-TTSBI powder. Finally, the M-TTSBI powder was vacuum dried to obtain the reactive monomer M-TTSBI.

[0012] 1.2) Preparation of methylated polymer PIM (M-PIM): The reactive monomer M-TTSBI obtained in step 1.1) was dissolved in solvent A with tetrafluoroterephthalonitrile and anhydrous potassium carbonate. The mixture was placed in an oil bath at 65–155 °C and reacted under nitrogen (N2) protection for 0.5–72 h. The reaction mechanism of this step is as follows: the reactive monomer M-TTSBI and tetrafluoroterephthalonitrile undergo a condensation reaction in the presence of anhydrous potassium carbonate catalyst to form the high molecular weight polymer M-PIM. After cooling to room temperature, the solid was filtered, and the potassium carbonate was removed by washing with deionized water. The obtained product was dissolved again in chloroform and then precipitated and washed multiple times in methanol to obtain the final product. The collected yellow polymer was vacuum dried to obtain polymer M-PIM.

[0013] 1.3) Preparation of bromomethylated PIM (BM-PIM): The polymer M-PIM obtained in step 1.2) was dissolved in chlorobenzene under an inert atmosphere. Then, N-bromosuccinimide and azobisisobutyronitrile were added to the reaction solution, and the mixture was refluxed at 110–135 °C for 3–4 h. After cooling, the mixture was poured into methanol to obtain a pale yellow powder. The polymer product was washed several times with 500 mL of methanol and then vacuum dried to obtain bromomethylated BM-PIM.

[0014] In step 1.1), for every 30g of 3-methylcatechol, 30-60mL of glacial acetic acid, 36-72mL of hydrobromic acid, and 15-30mL of acetone are added. The vacuum drying temperature is 70℃-80℃, and the time is 24h-72h.

[0015] In step 1.2), for every 15g of M-TTSBI from step 1.1), 8-16g of tetrafluoroterephthalonitrile and 14-28g of anhydrous potassium carbonate are added. The vacuum drying temperature is 70℃-100℃, and the time is 24h-72h.

[0016] In step 1.2), solvent A is one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0017] In step 1.3), for every 4.88g of M-PIM from step 1.2), 1.96–3.92g of N-bromosuccinimide and 0.18–0.36g of azobisisobutyronitrile are added. The vacuum drying temperature is 70°C–100°C, and the time is 24–72 hours.

[0018] Step 2: Preparation of MOF porous crosslinking agent

[0019] 2.1) At room temperature, the metal salt is added to solvent B, and after stirring and ultrasonic dispersion, a uniform metal salt solution is formed, which is prepared into a metal salt dispersion with a concentration of 0.1 to 1.5 g / L; the organic ligand is added to solvent C, and after stirring and ultrasonic dispersion, a uniform organic ligand solution is formed, which is prepared into an organic ligand dispersion with a concentration of 0.1 to 18 g / L.

[0020] 2.2) Mix the metal salt dispersion, organic ligand dispersion, and accelerator obtained in step 2.1). Seal the reaction mixture in an autoclave and heat at 70–120°C for 2–24 hours. Allow it to cool naturally to room temperature to obtain the mixture. For every 5 mL of metal salt dispersion, add 5–40 mL of organic ligand dispersion and 0.5–20 g of accelerator.

[0021] 2.3) The mixture obtained in step 2.2) is centrifuged at 8000-11000 rpm for 10-20 min and washed with solvent D 3-4 times, each time for 3-12 h. The resulting wet solid is then vacuum dried to obtain MOF nanocrystals, which are used as MOF porous crosslinking agents.

[0022] In step 2.1), solvent B is one of methanol, deionized water, and N,N-dimethylformamide, and solvent C is one of methanol, deionized water, and N,N-dimethylformamide.

[0023] In step 2.1), the metal salt is one of zinc nitrate hexahydrate, ferric chloride hexahydrate, and zirconium chloride. The organic ligand is one or more of 2-aminobenzimidazole, 2-aminoterephthalic acid, and dimethylimidazole.

[0024] In step 2.2), the accelerator is one of sodium formate and glacial acetic acid.

[0025] In step 2.3), the MOFs are one of ZIF-8-NH2, MIL-101-NH2, and UiO-66-NH2. Specifically, when the metal salt is zinc nitrate hexahydrate and the organic ligands are 2-aminobenzimidazole and dimethylimidazole, the obtained MOFs are ZIF-8-NH2; when the metal salt is ferric chloride hexahydrate and the organic ligand is 2-aminoterephthalic acid, the obtained MOFs are MIL-101-NH2; and when the metal salt is zirconium chloride and the organic ligand is 2-aminoterephthalic acid, the obtained MOFs are UiO-66-NH2.

[0026] In step 2.3), the solvent D is one or more of N,N-dimethylformamide, methanol, and ethanol. The vacuum drying temperature is 70–100°C, and the time is 24–72 hours.

[0027] Step 3: Preparation of c-PIM / MOF crosslinked membrane

[0028] 3.1) Preparation of BM-PIM / MOF composite membrane, as detailed below:

[0029] First, the MOF nanocrystals obtained in the second step and the BM-PIM obtained in the first step were dissolved in solvent E and stirred vigorously for 24–72 h to form a BM-PIM / MOF dispersion with a concentration of 2–4 w / w%, wherein the mass ratio of MOF nanocrystals to BM-PIM was 0.5–30 wt%. Subsequently, the BM-PIM / MOF dispersion was sonicated for 30–60 min to remove air bubbles. Finally, the BM-PIM / MOF dispersion was cast into an ultra-flat quartz disk. After the solvent was completely evaporated, the BM-PIM / MOF membrane was separated from the quartz disk and immersed in methanol for 12–48 h. The resulting BM-PIM / MOF composite membrane was then dried under vacuum.

[0030] 3.2) By heat-treating the BM-PIM / MOF composite membrane using a temperature gradient method, multiple covalent cross-linked networks within the membrane are constructed to prepare a c-PIM / MOF cross-linked membrane, as detailed below:

[0031] Under a nitrogen atmosphere, BM-PIM / MOF composite membranes were placed in a tube furnace and heat-treated at 120–280 °C for 5–20 h, followed by heat treatment at 300 °C for 0.5–1.5 h. The crosslinked membranes were labeled “c-PIM / MOF”. The reaction mechanism of this step is as follows: During the heat treatment, within the temperature range of 20–280 °C, the bromomethyl groups of BM-PIM and the amino groups of MOFs form intermolecular crosslinks through a Hofmann alkylation reaction, while maintaining the mechanical stability of the membrane. At 300 °C, the carbon-bromine bonds of the BM-PIM chain and its own benzene ring also form intramolecular crosslinks through a Friedel-Crafts alkylation reaction. This temperature gradient method drives the formation of the intramolecular crosslink network and maintains mechanical stability, which is helpful for preparing anti-plasticization and anti-aging c-PIM / MOF crosslinked membrane materials, and can also be used to prepare other polymer crosslinked membranes. Furthermore, the intermolecular crosslinking bonds between BM-PIM and MOFs occur at the self-crosslinking sites of the BM-PIM chain. The addition of MOFs can effectively compensate for the shrinkage of micropores in BM-PIM due to crosslinking and provide additional gas channels, maintaining the high gas permeability of the BM-PIM crosslinked membrane. The synergy between the dissolution-diffusion mechanism and the size sieving mechanism effectively blocks molecules (N2, CH4) larger than the channel size from passing through while promoting the passage of CO2, thereby achieving efficient CO2 separation.

[0032] In step 3.1), the solvent E is one of chloroform, tetrahydrofuran, and N,N-dimethylformamide. The vacuum drying temperature is 70–100°C, and the time is 24–72 h.

[0033] An application of a high-performance, aging-resistant c-PIM / UiO crosslinked membrane material for gas separation, salinity gradient power generation, ion exchange and other systems.

[0034] The beneficial effects of this invention are:

[0035] (1) This invention employs a temperature gradient method to drive the formation of an intramolecular crosslinking network and maintain mechanical stability. Specifically, a two-step heat treatment method based on the temperature gradient concept introduces MOFs to compensate for the loss of micropores due to crosslinking. By optimizing crosslinking conditions and regulating the gas mass transfer channels within the membrane, the long-term stability and gas separation performance of the PIMs membrane are improved. Lower temperatures (120–280°C) promote the formation of intermolecular crosslinks within the membrane while maintaining the membrane's mechanical stability. Furthermore, at higher temperatures (300°C), short-duration heat treatment promotes the formation of an intramolecular crosslinking network within the membrane.

[0036] (2) The multiple strong cross-linking nodes in the cross-linked membrane material prepared by the present invention help to suppress the movement of BM-PIM chain segments, avoid the collapse of the free volume in the membrane, and improve the anti-plasticization and anti-aging effect of the membrane.

[0037] (3) In the cross-linked membrane material prepared by the present invention, the intermolecular cross-linking bond between BM-PIM and MOFs occurs at the self-cross-linking site of the BM-PIM chain. The addition of MOFs can effectively compensate for the micropores of BM-PIM that shrink due to cross-linking and provide additional gas channels. That is, the addition of MOFs makes the composite membrane contain different types of gas transfer pathways (micropores, mesopores and free cavities), maintain the high gas permeability of the BM-PIM cross-linked membrane, and further realize the preparation of high-performance aging-resistant cross-linked membranes. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope image of c-PIM / ZIF-8 from Example 1.

[0039] Figure 2 This is a scanning electron microscope image of c-PIM / MIL-101 from Example 2.

[0040] Figure 3 This is a scanning electron microscope image of c-PIM / UiO-66 from Example 3.

[0041] Figure 4 The Fourier transform infrared spectra of c-PIM / UiO-66, BM-PIM, and UiO-66-NH2 in Example 3 are shown.

[0042] Figure 5 These are gas separation performance diagrams for Examples 1-3 and Comparative Example 1. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that while the technical solutions of this invention are described in detail below through embodiments, the scope of protection of this invention is not limited thereto.

[0044] Example 1: The method of the present invention includes the following steps:

[0045] Step 1: Preparation of polymer BM-PIM

[0046] 1.1) Preparation of the reactive monomer M-TTSBI: 30 g of 3-methylcatechol was dissolved in a mixed solution of 30 mL glacial acetic acid and 36 mL hydrobromic acid. After stirring at room temperature for 10 min, 15 mL of acetone was added dropwise and the mixture was refluxed at 120 °C for 12 h. The reddish-brown solution was slowly poured into 500 mL of deionized water to obtain a precipitated solid. The solid was filtered to separate it and washed three times repeatedly with 500 mL glacial acetic acid. The resulting grayish-white powder was further purified by recrystallization in methanol to obtain a white M-TTSBI powder. Finally, the M-TTSBI powder was dried under vacuum at 70 °C for 24 h.

[0047] 1.2) Preparation of polymer M-PIM: 15g of the reactive monomer M-TTSBI obtained in step 1.1) was dissolved in 80mL of N,N-dimethylformamide with 8g of tetrafluoroterephthalonitrile and 14g of anhydrous potassium carbonate. The mixture was placed in an oil bath at 65℃ and reacted under N2 protection for 72h. After cooling to room temperature, the solid was filtered, and the potassium carbonate was removed by washing with deionized water. The obtained product was dissolved again in chloroform and then precipitated and washed three times in methanol to obtain the final product. The collected yellow polymer was dried under vacuum at 70℃ for 24h.

[0048] 1.3) Preparation of polymer BM-PIM: 4.88 g of polymer M-PIM obtained in step 1.2) was dissolved in 100 mL of chlorobenzene under an inert atmosphere. Then, 1.96 g of N-bromosuccinimide and 0.18 g of azobisisobutyronitrile were added to the reaction solution, and the mixture was refluxed at 110 °C for 4 h. After cooling, the mixture was poured into methanol to obtain a pale yellow powder. The polymer product was washed four times with 500 mL of methanol and dried at 70 °C for 24 h.

[0049] Step 2: Preparation of MOF porous crosslinking agent

[0050] 2.1) At room temperature, zinc nitrate hexahydrate (a metal salt) was added to methanol and dispersed by stirring and ultrasonication to form a homogeneous metal salt solution, preparing a 0.1 g / L metal salt dispersion. An organic ligand was added to methanol and dispersed by stirring and ultrasonication to form a homogeneous organic ligand solution, preparing a 0.1 g / L organic ligand dispersion. The organic ligand was 2-aminobenzimidazole and dimethylimidazole in a molar ratio of 1:1.

[0051] 2.2) Mix 5 mL of metal salt dispersion, 5 mL of organic ligand dispersion and 0.5 g of accelerator sodium formate, seal the reaction mixture in an autoclave, heat at 70 °C for 2 h, and then cool naturally to room temperature.

[0052] 2.3) The resulting mixture was centrifuged at 8000 rpm for 10 min and washed three times with methanol for 3 h each time. The resulting wet solid was dried under vacuum at 70 °C for 24 h.

[0053] In step 2.3), the MOFs are ZIF-8-NH2.

[0054] Step 3: Preparation of c-PIM / MOF crosslinked membrane

[0055] 3.1) A mixture of 0.001 g of ZIF-8-NH2 nanocrystals and 0.199 g of BM-PIM was dissolved in 9.8 g of chloroform solvent and stirred vigorously for 24 h to form a BM-PIM / ZIF-8 dispersion with a concentration of 2 w / w%. The dispersion was then sonicated for 30 min to remove air bubbles. The MOF content in the membrane was 0.5 wt%. The BM-PIM / ZIF-8 dispersion was cast into an ultra-flat quartz disk. After the solvent was completely evaporated, the BM-PIM / ZIF-8 membrane was separated from the quartz disk and immersed in methanol for 12 h. The resulting BM-PIM / ZIF-8 membrane was then vacuum dried at 70 °C for 24 h.

[0056] 3.2) Under N2 atmosphere, the BM-PIM / ZIF-8 membrane was placed in a tube furnace and heat-treated at 120°C for 20 h, followed by heat treatment at 300°C for 0.5 h. The crosslinked membrane was labeled "c-PIM / ZIF-8".

[0057] In Example 1, ZIF-8-NH2 crystals were uniformly distributed in the BM-PIM matrix of the c-PIM / ZIF-8 composite film, with most ZIF-8-NH2 crystals having a size of approximately 500 nm. Furthermore, the ZIF-8-NH2 crystals were tightly bonded to the BM-PIM matrix, indicating that the interaction between the bromomethyl and amino groups promoted the formation of a defect-free interface.

[0058] Example 2: The method of the present invention includes the following steps:

[0059] Step 1: Preparation of polymer BM-PIM

[0060] 1.1) Preparation of the reactive monomer M-TTSBI: 30 g of 3-methylcatechol was dissolved in a mixed solution of 40 mL glacial acetic acid and 54 mL hydrobromic acid. After stirring at room temperature for 20 min, 25 mL acetone was added dropwise and the mixture was refluxed at 130 °C for 15 h. The reddish-brown solution was slowly poured into 500 mL of deionized water to obtain a precipitated solid. The solid was filtered to separate it and washed three times repeatedly with 500 mL glacial acetic acid. The resulting grayish-white powder was further purified by recrystallization in methanol to obtain white powder M-TTSBI. Finally, the M-TTSBI powder was dried under vacuum at 75 °C for 48 h.

[0061] 1.2) Preparation of polymer M-PIM: 15g of the reactive monomer M-TTSBI obtained in step 1.1) was dissolved in 80mL of N,N-dimethylacetamide with 12g of tetrafluoroterephthalonitrile and 21g of anhydrous potassium carbonate. The mixture was placed in an oil bath at 120℃ and reacted under N2 protection for 24h. After cooling to room temperature, the solid was filtered, and the potassium carbonate was removed by washing with deionized water. The obtained product was dissolved again in chloroform and then precipitated and washed three times in methanol to obtain the final product. The collected yellow polymer was dried under vacuum at 80℃ for 48h.

[0062] 1.3) Preparation of polymer BM-PIM: 4.88 g of polymer M-PIM obtained in step 1.2) was dissolved in 100 mL of chlorobenzene under an inert atmosphere. Then, 2.94 g of N-bromosuccinimide and 0.27 g of azobisisobutyronitrile were added to the reaction solution, and the mixture was refluxed at 120 °C for 3.5 h. After cooling, the mixture was poured into methanol to obtain a pale yellow powder. The polymer product was washed four times with 500 mL of methanol and dried at 85 °C for 48 h.

[0063] Step 2: Preparation of MOF porous crosslinking agent

[0064] 2.1) At room temperature, ferric chloride hexahydrate (a metal salt) was added to deionized water and dispersed by stirring and ultrasonication to form a homogeneous metal salt solution, preparing a metal salt dispersion of 0.8 g / L. An organic ligand was added to deionized water and dispersed by stirring and ultrasonication to form a homogeneous organic ligand solution, preparing an organic ligand dispersion of 10 g / L. The organic ligand was 2-aminoterephthalic acid.

[0065] 2.2) Mix 5 mL of metal salt dispersion, 20 mL of organic ligand dispersion and 10 g of accelerator sodium formate. Seal the reaction mixture in an autoclave and heat at 110 °C for 20 h. Then let it cool naturally to room temperature.

[0066] 2.3) The resulting mixture was centrifuged at 10,000 rpm for 15 min and washed three times with ethanol for 6 h each time. The resulting wet solid was then dried under vacuum at 80 °C for 48 h.

[0067] In step 2.3), the MOFs are MIL-101-NH2.

[0068] Step 3: Preparation of c-PIM / MOF crosslinked membrane

[0069] 3.1) A mixture of 0.045 g of MIL-101-NH2 nanocrystals and 0.255 g of BM-PIM was dissolved in 9.7 g of tetrahydrofuran solvent and stirred vigorously for 48 h to form a BM-PIM / MIL-101 dispersion with a concentration of 3 w / w%. The dispersion was then sonicated for 45 min to remove air bubbles. The MOF content in the membrane was 15 wt%. The BM-PIM / MIL-101 dispersion was cast into an ultra-flat quartz disk. After the solvent was completely evaporated, the BM-PIM / MIL-101 membrane was separated from the quartz disk and immersed in methanol for 24 h. The resulting BM-PIM / MIL-101 membrane was then vacuum dried at 80 °C for 48 h.

[0070] 3.2) Under N2 atmosphere, the BM-PIM / MIL-101 membrane was placed in a tube furnace and heat-treated at 250°C for 10 h, followed by heat treatment at 300°C for 1 h. The crosslinked membrane was labeled "c-PIM / MIL-101".

[0071] In Example 2, the MIL-101-NH2 crystals in the c-PIM / MIL-101 composite film were uniformly distributed within the BM-PIM matrix, with most of the MIL-101-NH2 crystals having a size of approximately 100 nm. Furthermore, the MIL-101-NH2 crystals were tightly bonded to the BM-PIM matrix, indicating that the interaction between the bromomethyl and amino groups promoted the formation of a defect-free interface.

[0072] Example 3: The method of the present invention includes the following steps:

[0073] Step 1: Preparation of polymer BM-PIM

[0074] 1.1) Preparation of the reactive monomer M-TTSBI: 30 g of 3-methylcatechol was dissolved in a mixed solution of 60 mL glacial acetic acid and 72 mL hydrobromic acid. After stirring at room temperature for 30 min, 30 mL acetone was added dropwise and the mixture was refluxed at 150 °C for 20 h. The reddish-brown solution was slowly poured into 500 mL deionized water to obtain a precipitated solid. The solid was filtered to separate it and washed three times repeatedly with 500 mL glacial acetic acid. The resulting grayish-white powder was further purified by recrystallization in methanol to obtain white powder M-TTSBI. Finally, the M-TTSBI powder was dried under vacuum at 80 °C for 72 h.

[0075] 1.2) Preparation of polymer M-PIM: 15g of the reactive monomer M-TTSBI obtained in step 1.1) was dissolved in 80mL of N-methylpyrrolidone along with 16g of tetrafluoroterephthalonitrile and 28g of anhydrous potassium carbonate. The mixture was placed in an oil bath at 155℃ and reacted under N2 protection for 0.5h. After cooling to room temperature, the solid was filtered, and the potassium carbonate was removed by washing with deionized water. The obtained product was dissolved again in chloroform and then precipitated and washed three times in methanol to obtain the final product. The collected yellow polymer was dried under vacuum at 100℃ for 72h.

[0076] 1.3) Preparation of polymer BM-PIM: 4.88 g of polymer M-PIM obtained in step 1.2) was dissolved in 100 mL of chlorobenzene under an inert atmosphere. Then, 3.92 g of N-bromosuccinimide and 0.36 g of azobisisobutyronitrile were added to the reaction solution, and the mixture was refluxed at 135 °C for 3 h. After cooling, the mixture was poured into methanol to obtain a pale yellow powder. The polymer product was washed five times with 500 mL of methanol and dried at 100 °C for 72 h.

[0077] Step 2: Preparation of MOF porous crosslinking agent

[0078] 2.1) At room temperature, zirconium chloride metal salt was added to N,N-dimethylformamide solvent, and dispersed by stirring and ultrasonication to form a homogeneous metal salt solution, preparing a dispersion with a concentration of 1.5 g / L. An organic ligand was added to N,N-dimethylformamide solvent, and dispersed by stirring and ultrasonication to form a homogeneous organic ligand solution, preparing a dispersion with a concentration of 18 g / L. The organic ligand was 2-aminoterephthalic acid.

[0079] 2.2) Mix 5 mL of metal salt solution, 40 mL of organic ligand solution and 20 g of accelerator glacial acetic acid. Seal the reaction mixture in an autoclave and heat at 120 °C for 24 h. Allow it to cool naturally to room temperature.

[0080] 2.3) The resulting mixture was centrifuged at 11,000 rpm for 20 min and washed four times with solvent D, each time for 12 h. The resulting wet solid was then dried under vacuum at 100 °C for 72 h. The solvent D was a mixed solution of N,N-dimethylformamide and methanol, with a volume ratio of N,N-dimethylformamide to methanol of 1:1.

[0081] In step 2.3), the MOFs are UiO-66-NH2.

[0082] Step 3: Preparation of c-PIM / MOF crosslinked membrane

[0083] 3.1) A mixture of 0.12 g of UiO-66-NH2 nanocrystals and 0.28 g of BM-PIM was dissolved in 9.6 g of N,N-dimethylformamide solvent and stirred vigorously for 72 h to form a BM-PIM / UiO-66 dispersion with a concentration of 4 w / w%. The dispersion was then sonicated for 60 min to remove air bubbles. The MOF content in the membrane was 30 wt%. The BM-PIM / UiO-66 dispersion was cast into an ultra-flat quartz disk. After the solvent was completely evaporated, the BM-PIM / UiO-66 membrane was separated from the quartz disk and immersed in methanol for 48 h. The resulting BM-PIM / UiO-66 membrane was then vacuum dried at 100 °C for 72 h.

[0084] 3.2) Under N2 atmosphere, the BM-PIM / UiO-66 membrane was placed in a tube furnace and heat-treated at 280°C for 5 h, followed by heat treatment at 300°C for 1.5 h. The crosslinked membrane was labeled "c-PIM / UiO-66".

[0085] In Example 3, the UiO-66-NH2 crystals in the c-PIM / UiO-66 composite film were uniformly distributed within the BM-PIM matrix, with most UiO-66-NH2 crystals having a size of approximately 120 nm. Furthermore, the UiO-66-NH2 crystals were tightly bonded to the BM-PIM matrix, indicating that the interaction between the bromomethyl and amino groups promoted the formation of a defect-free interface.

[0086] Comparative Example 1: Compared with Example 1, the difference is that MOFs are absent, while other conditions are the same as in Example 1. The specific steps are as follows:

[0087] Step 1: Preparation of polymer BM-PIM

[0088] 1.1) Preparation of the reactive monomer M-TTSBI: 30 g of 3-methylcatechol was dissolved in a mixed solution of 30 mL glacial acetic acid and 36 mL hydrobromic acid. After stirring at room temperature for 10 min, 15 mL acetone was added dropwise and the mixture was refluxed at 120 °C for 12 h. The reddish-brown solution was slowly poured into 500 mL of deionized water to obtain a precipitated solid. The solid was filtered to separate it and washed three times with 500 mL glacial acetic acid. The resulting grayish-white powder was further purified by recrystallization in methanol to obtain white powder M-TTSBI. Finally, the M-TTSBI powder was dried under vacuum at 70 °C for 24 h.

[0089] 1.2) Preparation of polymer M-PIM: 15g of the reactive monomer M-TTSBI obtained in step 1.1) was dissolved in 80mL of N,N-dimethylformamide with 8g of tetrafluoroterephthalonitrile and 14g of anhydrous potassium carbonate. The mixture was placed in an oil bath at 65℃ and reacted under N2 protection for 72h. After cooling to room temperature, the solid was filtered, and the potassium carbonate was removed by washing with deionized water. The obtained product was dissolved again in chloroform and then precipitated and washed three times in methanol to obtain the final product. The collected yellow polymer was dried under vacuum at 70℃ for 24h.

[0090] 1.3) Preparation of polymer BM-PIM: 4.88 g of polymer M-PIM obtained in step 1.2) was dissolved in 100 mL of chlorobenzene under an inert atmosphere. Then, 1.96 g of N-bromosuccinimide and 0.18 g of azobisisobutyronitrile were added to the reaction solution, and the mixture was refluxed at 110 °C for 4 h. After cooling, the mixture was poured into methanol to obtain a pale yellow powder. The polymer product was washed four times with 500 mL of methanol and dried at 70 °C for 24 h.

[0091] Step 2: Preparation of c-PIM membrane

[0092] 2.1) 0.2 g of BM-PIM was dissolved in 9.8 g of chloroform and stirred vigorously for 24 h to form a BM-PIM dispersion with a concentration of 2 w / w%. The dispersion was then sonicated for 60 min to remove air bubbles. The BM-PIM dispersion was cast into an ultra-flat quartz disk. After the solvent was completely evaporated, the BM-PIM membrane was separated from the quartz disk and immersed in methanol for 48 h. The resulting BM-PIM membrane was then vacuum dried at 70 °C for 24 h.

[0093] 3.2) Under N2 atmosphere, the BM-PIM membrane was placed in a tube furnace and heat-treated at 280°C for 5 h, followed by heat treatment at 300°C for 1.5 h. The crosslinked membrane was labeled "c-PIM".

[0094] The c-PIM / MOF crosslinked membranes prepared in the above embodiments were tested for CO2, N2, and CH4 fluxes. The results are shown in the table below.

[0095] Table 1. Gas separation performance of examples and comparative examples

[0096]

[0097] As shown in Table 1, the c-PIM / MOF composite membrane obtained by this invention exhibits excellent gas separation performance. Comparing Examples 1-3 with added MOFs with Comparative Example 1 (without MOFs), it can be seen that the CO2 flux in Examples 1-3 is above 3846.2 Barrer, showing a certain improvement compared to Comparative Example 1. This is because the introduction of MOFs creates additional channels, resulting in different types of gas mass transfer pathways (micropores, mesopores, and free cavities) within the composite membrane, thus facilitating gas molecule passage. The ideal selectivity of CO2 / N2 and CO2 / CH4 in Examples 1-3 is approximately 1.2-2.1 times higher than that in Comparative Example 1. This is because MOF particles can enhance the selectivity of CO2 / N2 and CO2 / CH4 based on the size and interaction differences of CO2, N2, and CH4 molecules. The combination of temperature gradient method and channel compensation effectively achieves the construction of intramolecular and intermolecular cross-linked networks within the membrane. Furthermore, MOFs effectively provide additional gas transport channels while avoiding the formation of interface defects, achieving the goal of improving long-term stability while maintaining a certain level of gas separation performance. Therefore, this improved temperature gradient thermal crosslinking method has great potential as a synthesis technique for constructing high-performance gas separation membranes from various PIMs.

[0098] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material, characterized in that, The preparation method involves first preparing a casting solution; second, preparing a BM-PIM / MOF composite membrane; and finally, heat-treating the BM-PIM / MOF composite membrane using a temperature gradient method to construct multiple covalent cross-linked networks within the membrane, thereby preparing a c-PIM / MOF cross-linked membrane material. The casting solution formulation for the cross-linked membrane includes bromomethylated BM-PIM, a porous MOF cross-linking agent, and chloroform. The porous MOF cross-linking agent comprises less than 30 wt% of the BM-PIM mass, and is one of ZIF-8-NH2, MIL-101-NH2, or UiO-66-NH2.

2. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of polymer BM-PIM 1.1) Preparation of the reactive monomer 3,3,3′,3′,7,7′-hexamethyl-5,6,5′,6′-tetrahydroxy-1,1′-spirodiindane, i.e., M-TTSBI: 3-methylcatechol was added to a mixed solution of glacial acetic acid and hydrobromic acid, stirred at room temperature, and then acetone was added dropwise. After stirring under reflux at 120~150 °C for 12~20 h, the reactive monomer M-TTSBI was obtained after post-treatment. 1.2) Preparation of polymer methylated PIM, namely M-PIM: The reactive monomer M-TTSBI obtained in step 1.1) is dissolved in solvent A with tetrafluoroterephthalonitrile and anhydrous potassium carbonate, and the mixture is placed in an oil bath at 65~155 °C and reacted under nitrogen protection for 0.5~72 h. After post-treatment, M-PIM is obtained. 1.3) Preparation of bromomethylated PIM, namely BM-PIM: The M-PIM obtained in step 1.2) is dissolved in chlorobenzene under an inert atmosphere, and then N-bromosuccinimide and azobisisobutyronitrile are added to the reaction solution and reacted at 110~135 °C for 3~4 h. After post-treatment, BM-PIM is obtained. Step 2: Preparation of porous MOF crosslinking agent 2.1) At room temperature, the metal salt is added to solvent B and dispersed by stirring and ultrasonication to form a uniform metal salt solution; the organic ligand is added to solvent C and dispersed by stirring and ultrasonication to form a uniform organic ligand solution. 2.2) Mix the metal salt dispersion, organic ligand dispersion and accelerator obtained in step 2.1), seal the reaction mixture in an autoclave, heat at 70~120 °C for 2~24 h, and cool naturally to room temperature to obtain the mixture; 2.3) After centrifuging the mixture obtained in step 2.2), wash it multiple times with solvent D. After vacuum drying the resulting wet solid, MOF nanocrystals are obtained and used as porous MOF crosslinking agents. Step 3: Preparation of c-PIM / MOF crosslinked membrane 3.1) Preparation of BM-PIM / MOF composite membrane, as detailed below: First, the MOF nanocrystals obtained in the second step and the BM-PIM obtained in the first step are dissolved in solvent E and stirred vigorously for 24-72 h to form a BM-PIM / MOF dispersion with a concentration of 2-4 w / w%, wherein the mass ratio of MOF nanocrystals to BM-PIM is 0.5-30 wt%. Then, the BM-PIM / MOF dispersion is ultrasonically treated to remove air bubbles. Finally, the BM-PIM / MOF dispersion is cast to obtain a BM-PIM / MOF composite film. 3.2) By heat-treating the BM-PIM / MOF composite membrane using a temperature gradient method, multiple covalent cross-linked networks within the membrane are constructed to prepare a c-PIM / MOF cross-linked membrane, as detailed below: Under N2 atmosphere, the BM-PIM / MOF composite membrane was placed in a tube furnace and heat-treated at 120~280 °C for 5~20 h, followed by heat treatment at 300 °C for 0.5~1.5 h; the crosslinked membrane was labeled "c-PIM / MOF".

3. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 2, characterized in that, In the first step described above: In step 1.1), for every 30 g of 3-methylcatechol, add 30-60 mL of glacial acetic acid, 36-72 mL of hydrobromic acid, and 15-30 mL of acetone; the stirring time is 10-30 min. In step 1.2), for every 15g of M-TTSBI from step 1.1), 8-16g of tetrafluoroterephthalonitrile and 14-28g of anhydrous potassium carbonate are added; solvent A is one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. In step 1.3), for every 4.88g of M-PIM from step 1.2), 1.96~3.92g of N-bromosuccinimide and 0.18~0.36g of azobisisobutyronitrile are added.

4. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 2, characterized in that, In the first step described above: 1.1) The post-processing procedure is as follows: the solution after reaction is slowly poured into deionized water to obtain a solid precipitate. The solid precipitate is separated by filtration and washed repeatedly with glacial acetic acid. The obtained grayish-white powder is purified by recrystallization in methanol to obtain M-TTSBI white powder. Finally, the M-TTSBI powder is vacuum dried to obtain the reactive monomer M-TTSBI. The vacuum drying temperature is 70°C ~ 80°C and the time is 24h ~ 72h. 1.2) The post-processing process is as follows: After the reaction is cooled to room temperature, the solid is filtered and washed with deionized water to remove potassium carbonate; the obtained product is dissolved again in chloroform and then precipitated and washed multiple times in methanol to obtain a yellow polymer; it is then vacuum dried to obtain M-PIM, wherein the vacuum drying temperature is 70°C ~ 100°C and the time is 24h ~ 72h. 1.3) The post-processing process is as follows: After the reaction is cooled to room temperature, the mixture is poured into methanol to obtain a light yellow powder. After washing with methanol several times, it is vacuum dried to obtain BM-PIM. The vacuum drying temperature is 70°C ~ 100°C and the time is 24h ~ 72h.

5. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 2, characterized in that, In the second step mentioned above: In section 2.1), the metal salt is one of zinc nitrate hexahydrate, ferric chloride hexahydrate, and zirconium chloride, and the concentration of the metal salt solution is 0.1~1.5 g / L; the organic ligand is one or more of 2-aminobenzimidazole, 2-aminoterephthalic acid, and dimethylimidazole, and the concentration of the organic ligand dispersion is 0.1~18 g / L; solvent B is one of methanol, deionized water, and N,N-dimethylformamide, and solvent C is one of methanol, deionized water, and N,N-dimethylformamide. In step 2.2), 5-40 mL of organic ligand dispersion and 0.5-20 g of accelerator are added to every 5 mL of metal salt dispersion; the accelerator is one of sodium formate and glacial acetic acid. In step 2.3), the solvent D is one or more of N,N-dimethylformamide, methanol, and ethanol; the centrifugation speed is 8000~11000 rpm and the time is 10~20 min; the vacuum drying temperature is 70~100 °C and the time is 24~72 h.

6. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 2, characterized in that, In the second step, when the metal salt is zinc nitrate hexahydrate and the organic ligands are 2-aminobenzimidazole and dimethylimidazole, the obtained MOFs are ZIF-8-NH2; when the metal salt is ferric chloride hexahydrate and the organic ligand is 2-aminoterephthalic acid, the obtained MOFs are MIL-101-NH2; and when the metal salt is zirconium chloride and the organic ligand is 2-aminoterephthalic acid, the obtained MOFs are UiO-66-NH2.

7. The method for preparing a high-performance, aging-resistant c-PIM / MOF crosslinked membrane material according to claim 2, characterized in that, In step 3.1), the BM-PIM / MOF dispersion is cast into an ultra-flat quartz disk. After the solvent is completely evaporated, the BM-PIM / MOF membrane is separated from the quartz disk, immersed in methanol for 12-48 hours, and then removed and vacuum dried to obtain the BM-PIM / MOF composite membrane. The vacuum drying temperature is 70-100 °C and the time is 24-72 hours. The solvent E is one of chloroform, tetrahydrofuran, and N,N-dimethylformamide.

8. A high-performance, aging-resistant c-PIM / UiO crosslinked membrane, characterized in that, It is prepared by the preparation method of the high-performance aging-resistant c-PIM / MOF crosslinked membrane material according to any one of claims 1-7.

9. The high-performance, aging-resistant c-PIM / UiO crosslinked membrane according to claim 8, characterized in that, The thickness of the c-PIM / MOF crosslinked membrane material is 50-150 μm.

10. An application of the high-performance, aging-resistant c-PIM / MOF crosslinked membrane material as described in claim 8 or 9, characterized in that, It is used in gas separation, salinity gradient power generation, and ion exchange systems.

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