A zeolitic imidazolate framework / polyimide nanofiber composite membrane material based on cobalt metal defects, and a preparation method and application thereof

Abstract

The application discloses a zeolite imidazolate framework / polyimide nanofiber composite membrane material based on cobalt metal defects and a preparation method and application thereof, constructs a nanofiber membrane with polyimide as a base, secondly, adopts an in-situ synthesis method of first impregnating a cobalt salt and then introducing a ligand, makes ZIF-67 nucleate and grow on the surface of the PI fiber, forms a firm anchoring structure, prevents particle agglomeration and ensures uniform distribution of active sites, finally, introduces controllable metal defects by immersing in a second metal salt solution, breaks the crystal symmetry to increase unsaturated coordination sites, significantly enhances the electrostatic adsorption and chemical capture capacity on fine particulate matters, simultaneously optimizes the pore structure, strengthens the interception effect under the premise of not increasing the pressure drop, and realizes the high-efficiency-low-resistance balance. The composite structure has high removal rate, low pressure drop and excellent flexibility.

Description

Technical Field

[0001] This invention belongs to the field of thin-film filtration materials technology, and relates to a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects, its preparation method and application. Background Technology

[0002] Polyimide (PI) is a high-performance polymer with a high-density imide structure in its main chain. Aromatic conjugation and imide bonds endow it with excellent mechanical strength and chemical resistance. Its high aromaticity, chain rigidity, and strong interchain forces make it difficult to melt, maintaining structural and performance stability even at high temperatures of 500–600°C. These properties make PI fibers ideal high-temperature air filtration materials, suitable for harsh environments such as industrial flue gas purification and aerospace. Metal-Organic Frameworks (MOFs) are a class of novel hybrid materials with periodic porous network structures, assembled from metal ions or metal clusters and organic ligands through coordination interactions, combining the performance advantages of both inorganic and organic components. Due to their tunable structure, high specific surface area, and porosity, MOFs have shown significant application potential in air filtration, gas adsorption and separation, and gas storage, becoming a current research hotspot in porous materials. In recent years, defect-based strategies have enabled precise control over the pore structure and surface chemistry of MOFs, effectively increasing adsorption active sites and enhancing adsorption capacity and selectivity for specific gases (such as CO2 and VOCs). However, traditional zeolite imidazole framework materials are mostly in powder form, leading to easy pulverization and difficulty in recycling. Furthermore, their regular structure results in the encapsulation of active sites, limiting their adsorption capacity for specific air pollutants. In addition, their fixed pore structure provides insufficient selective recognition of mixed gases, easily causing high filtration resistance and efficiency degradation, thus restricting their large-scale application. In contrast, electrospinning technology can prepare nanofiber membranes with continuous three-dimensional network structures. With their high specific surface area, tunable pore size, and good mechanical properties, they provide an ideal carrier for uniform loading and stable fixation of MOFs. Composite MOFs onto the fiber surface or interior can prevent particle shedding and synergistically leverage the adsorption performance of MOFs and the sieving effect of the fiber membrane, thereby significantly improving the filtration efficiency, cycle stability, and practical application potential of the composite material. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects, its preparation method, and its application. This solves the technical problems of traditional powdered zeolite imidazole framework materials being prone to pulverization and difficult to recycle, while air filter materials suffer from high filtration resistance, low filtration efficiency for fine particles, and poor mechanical properties.

[0004] This invention is achieved through the following technical solution: A method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects includes the following steps: S1: Polyimide nanofiber membranes were prepared by reacting dianhydride monomers and diamine monomers; S2: The polyimide nanofiber membrane is sequentially placed in a first metal salt solution and an organic solution of the ligand to obtain a polyimide nanofiber membrane loaded with ZIF-67; the first metal salt is a cobalt salt; S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, wherein the second metal salt is one of zinc salt, nickel salt, zirconium salt, iron salt and copper salt. After the reaction, the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material is obtained.

[0005] Preferably, step S1 is as follows: S11: A polyamic acid solution is obtained by polycondensation of dianhydride monomer and diamine monomer, followed by washing to precipitate and freeze-drying to obtain polyamic acid powder. S12: Dissolve the polyamic acid powder in a polar aprotic solvent and stir until fully dissolved to obtain a polyamic acid spinning solution; S13: Electrospinning is performed using the polyamic acid spinning solution to obtain a polyamic acid nanofiber membrane; S14: The polyamic acid nanofiber membrane is subjected to thermal imidization treatment in an inert gas atmosphere to obtain the polyimide nanofiber film.

[0006] Preferably, the molar ratio of the dianhydride monomer to the diamine monomer is (1~1.05):(0.95~1); during the mixed reaction of the dianhydride monomer and the diamine monomer, the reaction temperature is -5~0 °C and the reaction time is 24~28 h.

[0007] Preferably, during electrospinning, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving plate is 10~20 cm.

[0008] Preferably, the ligand is one or two of 2-methylimidazole, benzimidazole, imidazole, 5,6-dimethylbenzimidazole, imidazole-2-carboxaldehyde, aldehyde imidazole, and 3-methyl-1-acetylimidazole.

[0009] Preferably, the molar ratio of the first metal salt to the ligand is (0.5~1.5):(1~8).

[0010] Preferably, the polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution and reacted at room temperature for 12-24 h.

[0011] Preferably, the molar ratio of the second metal to the first metal is (0.2~0.4):1.

[0012] A zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects was prepared by the method described above.

[0013] The above-mentioned application of a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects in filtration materials.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects. The method first constructs a nanofiber membrane using polyimide as a substrate. Polyimide itself possesses excellent thermal stability and mechanical strength, providing a flexible support framework for subsequent functional layers, fundamentally avoiding the problem of powder materials falling off or breaking under airflow impact. Second, an in-situ synthesis method is employed, first impregnating cobalt salt and then introducing ligands, allowing ZIF-67 crystals to nucleate and grow directly on the PI fiber surface, forming a robust chemical / physical anchoring structure. This not only prevents particle agglomeration and peeling but also ensures uniform distribution of active sites, improving filtration consistency. Finally, the ZIF-67-loaded membrane is immersed in a second metal salt solution, introducing controllable metal defects into the ZIF lattice. On one hand, this breaks the original crystal symmetry, increases unsaturated coordination sites on the surface, and enhances the electrostatic adsorption and chemical capture capabilities for fine particles, thereby significantly improving filtration efficiency. On the other hand, the defect structure can optimize pore tortuosity and specific surface area, strengthening the interception effect without significantly increasing pressure drop, achieving a balance between high efficiency and low resistance. Furthermore, because the entire ZIF layer is a three-dimensional composite structure continuously grown on a fiber network, rather than a simple coating or mixing, it maintains structural integrity even after long-term operation or cleaning cycles, completely solving the powder recovery problem. Ultimately, this material combines high removal rate, low pressure drop, excellent flexibility, and reusability, perfectly meeting the needs of high-end air filtration applications and marking a technological leap from passively filled to actively designed filter media.

[0015] Furthermore, the molar ratio of the dianhydride monomer to the diamine monomer is (1~1.05):(0.95~1); during the mixing and reaction of the dianhydride monomer and the diamine monomer, the reaction temperature is -5~0 °C and the reaction time is 24~28 h, to ensure that the polyimide precursor (PAA) has a narrow molecular weight distribution and high chain segment regularity, avoiding side reactions or gelation caused by high temperature, thereby obtaining a nanofiber membrane substrate with excellent mechanical properties and uniform fiber diameter, providing a stable carrier for subsequent ZIF in-situ growth.

[0016] Furthermore, during the electrospinning process, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving plate is 10~20 cm. This combination of parameters can control the jet stretching degree and solvent evaporation rate, forming a continuous, bead-free nanofiber network with moderate porosity, which not only ensures a high-throughput airflow channel but also enhances the mechanical interception capability of fine particles.

[0017] Furthermore, the molar ratio of the first metal salt to the ligand is (0.5~1.5):(1~8) to prevent excessive metal ions from causing amorphous precipitation or insufficient ligands from causing uncontrolled crystal defects, ensuring that ZIF-67 forms a dense and well-crystallized coating on the PI fiber surface and improving structural stability.

[0018] Furthermore, the polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution and reacted at room temperature for 12-24 h to ensure sufficient time to complete the ion exchange / doping process, so that the second metal can be effectively embedded into the ZIF lattice to form active defect sites, while avoiding long-term reaction that could lead to framework collapse or particle detachment.

[0019] Furthermore, the molar ratio of the second metal to the first metal is (0.2~0.4):1, which precisely controls the doping concentration. If the doping concentration is too low, the defect effect will not be obvious, while if it is too high, the ZIF topology will be destroyed. This ratio range can maximize the introduction of unsaturated coordination sites while maintaining the integrity of the framework, significantly enhancing the electrostatic capture and chemical adsorption capabilities for ultrafine particles. It is a key design to achieve a high-efficiency-low-resistance balance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Scanning electron microscope images and particle size distribution diagrams of the polyimide (PI) nanofiber membrane prepared in Comparative Example 1, the ZIF-67 powder prepared in Comparative Example 2, the ZIF-67-Ni-ZIF composite powder prepared in Comparative Example 3, the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4, and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1 at different magnifications. Figure 2Infrared spectra of the polyimide (PI) nanofiber membrane prepared in Comparative Example 1, the ZIF-67 powder prepared in Comparative Example 2, the ZIF-67-Ni-ZIF composite powder prepared in Comparative Example 3, the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4, and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1. Figure 3 The graphs show the filtration performance of the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4 and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1 for PM0.3, PM0.5, and PM2.5. The left graph represents the removal efficiency, and the right graph represents the quality factor. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] This invention provides a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects, comprising a polyimide nanofiber membrane, wherein a zeolite imidazole framework layer is grown on the surface of the nanofibers in the polyimide nanofiber membrane.

[0028] This invention also provides a method for preparing the above-mentioned zeolite imidazole framework / polyimide nanofiber composite membrane material with cobalt metal defects. S1: Polyimide nanofiber membranes were prepared by reacting dianhydride monomers and diamine monomers; Specifically, the above process is as follows: S11: Polycondensation reaction of dianhydride monomer and diamine monomer is carried out to obtain polyamic acid solution, which is then washed, precipitated and freeze-dried to obtain polyamic acid powder; The molar ratio of the dianhydride monomer to the diamine monomer is (1~1.05):(0.95~1); during the reaction of the dianhydride monomer and the diamine monomer, the reaction temperature is -5~0 °C and the reaction time is 24~28 h. The freeze-drying time is 24-48 hours.

[0029] S12: Dissolve the polyamic acid powder in a polar aprotic solvent and stir until fully dissolved to obtain a polyamic acid spinning solution; The polar aprotic solvent is a mixture of one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide in any proportion; The mass concentration of polyamic acid in the polyamic acid spinning solution is 15%~20%.

[0030] S13: Electrospinning is performed using the polyamic acid spinning solution to obtain a polyamic acid nanofiber membrane; During electrospinning, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving plate is 10~20 cm.

[0031] S14: The polyamic acid nanofiber membrane is subjected to thermal imidization treatment in an inert gas atmosphere to obtain the polyimide nanofiber film.

[0032] The thermal imidization process specifically involves: at 5~10 o Heating to 100-150°C at a heating rate of C / min o Keep warm at C for 30-60 minutes, then for 5-10 minutes. o Heating to 200-250°C at a heating rate of C / min o C, keep warm for 30-60 minutes, and finally 5-10.o Heating to 300~350°C at a heating rate of C / min o C, keep warm for 30~60 minutes.

[0033] The inert gas is one of helium, neon, argon, and krypton.

[0034] S2: The polyimide nanofiber membrane is placed in the first metal salt solution and the organic solution of the ligand in sequence to obtain a polyimide nanofiber membrane loaded with ZIF-67 (ZIF-67 / PI). The first metal salt is a cobalt salt, and the cobalt salt is cobalt nitrate hexahydrate; The ligand is one or two of 2-methylimidazolium, benzimidazole, imidazole, 5,6-dimethylbenzimidazole, imidazole-2-carboxaldehyde, aldehyde imidazole, and 3-methyl-1-acetylimidazolium.

[0035] The molar ratio of the first metal salt to the ligand is (0.5~1.5):(1~8); The polyimide nanofiber membrane was sequentially placed in a first metal salt solution and an organic solution of the ligand to obtain a polyimide nanofiber membrane loaded with ZIF-67. Specifically, the polyimide nanofiber membrane was first placed in the first metal salt solution and immersed at room temperature for 12-24 h. After being removed and dried once, it was then placed in the organic solution of the ligand and immersed at room temperature for 12-24 h. After being removed and dried a second time, the ZIF-67 / PI was obtained. S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, wherein the second metal salt is one of zinc salt, nickel salt, zirconium salt, iron salt and copper salt. After the reaction, the membrane is dried three times to obtain the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material.

[0036] In this step, the reaction time is 12-24 h at room temperature; The temperature for the first drying, second drying, and third drying is 50~100 °C, and the time is 12~36 h.

[0037] The molar ratio of the second metal to the first metal is (0.2~0.4):1.

[0038] The cobalt salt solution, the organic solution of the ligand, and the metal salt solution in this invention are prepared by adding the cobalt salt, the ligand, and the metal salt to an organic solvent and mechanically stirring for 20 to 60 minutes.

[0039] The molar ratio of the cobalt salt to the organic solvent is (0.5~1.5):(300~3000), and the molar ratio of the ligand to the organic solvent is (1~8):(300~3000).

[0040] The organic solvent is one or a mixture of methanol, ethanol, acetone, toluene, tetrahydrofuran, deionized water, N,N'-dimethylformamide, N,N'-dimethylacetamide, and dimethyl sulfoxide.

[0041] The reagents involved in this invention, namely pyromellitic anhydride (analytical grade, 96%), 4,4'-diaminodiphenyl ether (analytical grade, 98%), N,N-dimethylformamide, cobalt nitrate hexahydrate (analytical grade, 98%), nickel nitrate hexahydrate (analytical grade, 98%), and 2-methylimidazole (analytical grade, 98%), are all from Shanghai Maclean Biochemical Technology Co., Ltd.; methanol is from Chengdu Kelon Chemical Co., Ltd.

[0042] This invention discloses a method for preparing a cobalt metal defect-bearing zeolite imidazole framework / polyimide nanofiber composite membrane. First, this invention employs electrospinning technology and a thermal imidization process to prepare the polyimide nanofiber membrane. It combines the multifunctionality of the zeolite imidazole framework material with the excellent properties of electrospun polyimide nanofiber membranes, enabling the zeolite imidazole framework material to undergo heterogeneous nucleation and uniform growth on the flexible polyimide nanofiber membrane. The preparation process of this invention is simple and easy to operate; the zeolite imidazole framework grows stably on the polyimide nanofiber membrane; and the prepared composite membrane material exhibits excellent thermodynamic stability and excellent mechanical properties, which is beneficial for the practical application of the material in various fields.

[0043] This invention combines electrospinning technology with in-situ growth of zeolite imidazole frameworks to obtain a stable, continuous, and flexible zeolite imidazole framework / polyimide flexible composite membrane material with certain flexibility and strength. This process produces a nanofiber membrane with a high specific surface area and a fine pore structure. This structure not only increases the contact area with air, facilitating the interception of more fine particles, but also allows for a more tortuous airflow path, effectively reducing filtration resistance. Furthermore, it solves problems such as the easy pulverization and difficulty in recycling of zeolite imidazole frameworks, insufficient exposure of active sites due to their regular structure, and insufficient selective recognition ability of mixed gases due to fixed pore structures. The preparation process of this invention is simple and easy to operate; the zeolite imidazole framework grows stably in polyimide nanofiber membranes; and the prepared composite membrane material exhibits excellent thermodynamic stability and mechanical properties, which is beneficial for applications in high-temperature air filtration, gas adsorption and separation, and catalysts.

[0044] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0045] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0046] Comparative Example 1 The preparation of polyimide nanofiber (PI) membranes includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. o Dissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0047] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0048] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 oHeating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0049] Comparative Example 2 The preparation of ZIF-67 powder includes the following steps: First, 1.164 g of cobalt nitrate hexahydrate and 1.314 g of 2-methylimidazole were weighed and dissolved separately in 100 mL of methanol. The solutions were then magnetically stirred for 30 min at room temperature until fully dissolved. Next, the 2-methylimidazole-methanol solution was rapidly added to the cobalt nitrate hexahydrate-methanol solution, and the mixture was magnetically stirred for another 30 min at room temperature. After the reaction was complete, the mixture was allowed to stand for 12 h. The resulting product was centrifuged at 8000 r / min for 5 min to collect the precipitate, which was then repeatedly washed with methanol until the supernatant was colorless. Finally, the precipitate was dried for 12 h and ground to obtain ZIF-67 powder.

[0050] Comparative Example 3 The preparation of ZIF-67-Ni-ZIF composite powder includes the following steps: 40 mg of ZIF-67 powder and 40 mg of nickel nitrate hexahydrate were weighed and dispersed together in 100 mL of methanol. The mixture was stirred continuously on a magnetic stirrer for 30 minutes at room temperature. Subsequently, it was centrifuged at 8000 r / min for 5 minutes, and the solid precipitate was collected. The precipitate was washed repeatedly with methanol until the supernatant was colorless and transparent. Finally, the obtained solid was dried at room temperature for 12 hours and ground to obtain ZIF-67-Ni-ZIF composite powder.

[0051] Comparative Example 4 The preparation of ZIF-67 / PI nanofiber composite membrane material includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1°C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect occurred, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect occurred, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0052] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0053] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide (PI) nanofiber membrane.

[0054] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate and 1.312 g of 2-methylimidazole were dissolved in 200 mL of methanol, respectively. After stirring at room temperature for 30 min, methanol solutions of cobalt nitrate hexahydrate and 2-methylimidazole were obtained, respectively. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. It was then immersed in the methanol solution of 2-methylimidazole for 12 h, and then removed and dried again, yielding the ZIF-67 / PI nanofiber composite membrane material. Figure 1 As shown, a stable and continuous zeolite imidazole framework layer is grown on the surface of the nanofibers in the polyimide nanofiber film.

[0055] Comparative Example 5 The preparation of ZIF-67 / PI nanofiber composite membrane material includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. oDissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0056] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0057] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0058] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate and 2.624 g of 2-methylimidazole were dissolved in 200 mL of methanol and stirred at room temperature for 30 min to obtain methanol solutions of cobalt nitrate hexahydrate and 2-methylimidazole, respectively. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. It was then immersed in the methanol solution of 2-methylimidazole for 12 h and removed and dried to obtain ZIF-67 / PI nanofiber composite membrane material.

[0059] Comparative Example 6 The preparation of ZIF-67 / PI nanofiber composite membrane material includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1 °C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect appeared, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect appeared, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and then freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0060] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0061] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0062] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate and 5.248 g of 2-methylimidazole were dissolved in 200 mL of methanol and stirred at room temperature for 30 min to obtain methanol solutions of cobalt nitrate hexahydrate and 2-methylimidazole, respectively. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. It was then immersed in the methanol solution of 2-methylimidazole for 12 h and removed and dried to obtain ZIF-67 / PI nanofiber composite membrane material.

[0063] Example 1 The preparation of a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1°C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect appeared, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect appeared, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0064] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0065] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0066] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate, 1.312 g of 2-methylimidazole, and 1.163 g of nickel nitrate hexahydrate were dissolved in 200 mL of methanol, respectively. After stirring at room temperature for 30 min, methanol solutions of cobalt nitrate hexahydrate, 2-methylimidazole, and nickel nitrate hexahydrate were obtained. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. Next, it was immersed in the methanol solution of 2-methylimidazole for 12 h, then removed and dried, yielding a ZIF-67 / polyimide nanofiber composite membrane material. Finally, the ZIF-67 / polyimide nanofiber composite membrane material was immersed in the methanol solution of nickel nitrate hexahydrate for 4 h, then removed and dried, yielding a ZIF67-Ni-ZIF / PI nanofiber composite membrane material.

[0067] Example 2 The preparation of a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1°C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect appeared, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect appeared, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0068] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0069] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0070] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate, 2.624 g of 2-methylimidazole, and 0.582 g of nickel nitrate hexahydrate were dissolved in 200 mL of methanol, respectively. After stirring at room temperature for 30 min, methanol solutions of cobalt nitrate hexahydrate, 2-methylimidazole, and nickel nitrate hexahydrate were obtained. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. Next, it was immersed in the methanol solution of 2-methylimidazole for 12 h, and then removed and dried again, yielding a ZIF-67 / polyimide nanofiber composite membrane material. Finally, the ZIF-67 / polyimide nanofiber composite membrane material was immersed in the methanol solution of nickel nitrate hexahydrate for 4 h, and then removed and dried, yielding a ZIF67-Ni-ZIF / PI nanofiber composite membrane material.

[0071] Example 3 The preparation of a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1°C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect appeared, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect appeared, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0072] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0073] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0074] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate, 5.248 g of 2-methylimidazole, and 1.163 g of nickel nitrate hexahydrate were dissolved in 200 mL of methanol, respectively. After stirring at room temperature for 30 min, methanol solutions of cobalt nitrate hexahydrate, 2-methylimidazole, and nickel nitrate hexahydrate were obtained. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. Next, it was immersed in the methanol solution of 2-methylimidazole for 12 h, then removed and dried, yielding a ZIF-67 / polyimide nanofiber composite membrane material. Finally, the ZIF-67 / polyimide nanofiber composite membrane material was immersed in the methanol solution of nickel nitrate hexahydrate for 4 h, then removed and dried, yielding a ZIF67-Ni-ZIF / PI nanofiber composite membrane material.

[0075] Example 4 The preparation of a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was stirred and dissolved at a low temperature of 1°C. Then, 11.22 g of pyromellitic anhydride (PMDA) was weighed and added in four portions, with an interval of 10 min between each addition. The beaker and flask walls were rinsed with the remaining 20 mL of DMF. The mixture was stirred for 6 h. The reaction ended after the rod-climbing effect appeared, and a PAA solution was obtained. When the PAA solution was stretched and oriented along the stirring shaft and wrapped around the shaft during the stirring process, i.e., when the rod-climbing effect appeared, the PAA was slowly poured into 2 L of deionized water to precipitate and was washed multiple times. The solution was then placed in a refrigerator for pre-freezing and freeze-dried for 48 h to obtain PAA solid. After grinding, the solid was stored at low temperature for later use.

[0076] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0077] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 oHeating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0078] (4) Growth of zeolite imidazole framework 1.164 g of cobalt nitrate hexahydrate, 1.312 g of 2-methylimidazole, and 0.582 g of nickel nitrate hexahydrate were dissolved in 200 mL of methanol, respectively. After stirring at room temperature for 30 min, methanol solutions of cobalt nitrate hexahydrate, 2-methylimidazole, and nickel nitrate hexahydrate were obtained. The prepared polyimide nanofiber membrane was first immersed in the methanol solution of cobalt nitrate hexahydrate for 12 h, then removed and dried. Next, it was immersed in the methanol solution of 2-methylimidazole for 12 h, then removed and dried, yielding a ZIF-67 / polyimide nanofiber composite membrane material. Finally, the ZIF-67 / polyimide nanofiber composite membrane material was immersed in the methanol solution of nickel nitrate hexahydrate for 4 h, then removed and dried, yielding a ZIF67-Ni-ZIF / PI nanofiber composite membrane material.

[0079] Table 1. Filtration performance data of ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4 of the present invention for PM0.3 at different spinning times.

[0080] Example 4 A method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects. S1: A polycondensation reaction of dianhydride monomer and diamine monomer at a molar ratio of 1:0.95 was carried out at -5°C for 28 h to obtain a polyamic acid solution. After washing to precipitate and freeze-drying for 24 h, polyamic acid powder was obtained. The polyamic acid powder was dissolved in N,N'-dimethylformamide and stirred until fully dissolved to obtain a polyamic acid spinning solution with a mass concentration of 15%. S13: Electrospinning was performed using the polyamic acid spinning solution to prepare a polyamic acid nanofiber membrane. During electrospinning, the spinning voltage was 16 kV, the spinning solution flow rate was 0.010 mL / min, and the distance between the needle and the receiving plate was 10 cm. S14: The polyamic acid nanofiber membrane was subjected to thermal imidization treatment in a helium atmosphere to obtain the polyimide nanofiber film. The thermal imidization treatment process specifically involved: at 5... o Heating to 100°C at a heating rate of C / mino Keep warm at C for 60 minutes, then at 5°C. o Heating to 200°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 300°C at a heating rate of C / min o C, keep warm for 60 min; S2: First, the polyimide nanofiber membrane is placed in a first metal salt solution and immersed at room temperature for 12 h. After being removed and dried once, it is then placed in an organic solution of the ligand and immersed at room temperature for 12 h. After being removed and dried a second time, the ZIF-67 / PI is obtained. The first metal salt is cobalt nitrate hexahydrate, the ligand is 2-methylimidazole, and the molar ratio of the first metal salt to the ligand is 0.5:1. S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, the second metal salt being an iron salt, and the reaction time is 12 h at room temperature. After three drying cycles, the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material is obtained.

[0081] The first, second, and third drying processes were performed at 50 °C for 36 h, with the molar ratio of the second metal to the first metal being 0.2:1. The cobalt salt solution, the organic solution of the ligand, and the metal salt solution were prepared by adding the cobalt salt, ligand, and metal salt to an organic solvent and mechanically stirring for 20 min. The molar ratio of the cobalt salt to the organic solvent was 0.5:300, and the molar ratio of the ligand to the organic solvent was 1:300. The organic solvent was methanol.

[0082] Example 6 A method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects. S1: The molar ratio is 1.05: 1) The dianhydride monomer and diamine monomer undergo a polycondensation reaction at 0°C for 28 h to obtain a polyamic acid solution. After washing to precipitate and freeze-drying for 48 h, polyamic acid powder is obtained. The polyamic acid powder is dissolved in N,N'-dimethylacetamide and stirred until fully dissolved to obtain a polyamic acid spinning solution with a mass concentration of 20%. Electrospinning is performed using the polyamic acid spinning solution to prepare a polyamic acid nanofiber membrane. During electrospinning, the spinning voltage is 20 kV, the spinning solution flow rate is 0.017 mL / min, and the distance between the needle and the receiving plate is 20 cm. The polyamic acid nanofiber membrane is subjected to thermal imidization treatment in a helium atmosphere to obtain the polyimide nanofiber film. The thermal imidization treatment process specifically involves: at 10... o Heating to 150°C at a heating rate of C / min oKeep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 30 minutes, and finally at 10 o Heating to 350°C at a heating rate of C / min o C, keep warm for 30 minutes; S2: First, the polyimide nanofiber membrane is placed in a first metal salt solution and immersed at room temperature for 24 h. After being removed and dried once, it is then placed in an organic solution of the ligand and immersed at room temperature for 24 h. After being removed and dried a second time, the ZIF-67 / PI is obtained. The first metal salt is cobalt nitrate hexahydrate, the ligand is benzimidazole, and the molar ratio of the first metal salt to the ligand is 1.5:8. S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, the second metal salt being zirconium salt. The reaction time is 24 h at room temperature, and the membrane is dried three times to obtain the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material.

[0083] The first, second, and third drying processes were performed at 100 °C for 12 hours, with a molar ratio of the second metal to the first metal of 0.4:1. The cobalt salt solution, the organic solution of the ligand, and the metal salt solution were prepared by adding the cobalt salt, ligand, and metal salt to an organic solvent and mechanically stirring for 60 minutes. The molar ratio of the cobalt salt to the organic solvent was 1.5:3000, and the molar ratio of the ligand to the organic solvent was 8:3000; the organic solvent was ethanol.

[0084] Example 7 A method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects. S1: A polycondensation reaction of dianhydride monomer and diamine monomer in a molar ratio of 1:1 was carried out at -2 °C for 25 h to obtain a polyamic acid solution. After washing to precipitate and freeze-drying for 30 h, polyamic acid powder was obtained. The polyamic acid powder was dissolved in N-methylpyrrolidone and stirred until fully dissolved to obtain a polyamic acid spinning solution with a mass concentration of 18%. Electrospinning was performed using the polyamic acid spinning solution to prepare a polyamic acid nanofiber membrane. During electrospinning, the spinning voltage was 18 kV, the spinning solution flow rate was 0.015 mL / min, and the distance between the needle and the receiving plate was 15 cm. The polyamic acid nanofiber membrane was subjected to thermal imidization treatment in a helium atmosphere to obtain the polyimide nanofiber film. The thermal imidization treatment process specifically involved: at 8... o Heating to 120°C at a heating rate of C / min oKeep warm at C for 40 minutes, then at 8 o Heating to 220°C at a heating rate of C / min o C, keep warm for 40 minutes, and finally at 8 o Heating to 330°C at a heating rate of C / min o C, keep warm for 40 minutes.

[0085] S2: First, the polyimide nanofiber membrane is placed in a first metal salt solution and immersed at room temperature for 20 h. After being removed and dried once, it is then placed in an organic solution of the ligand and immersed at room temperature for 20 h. After being removed and dried a second time, the ZIF-67 / PI is obtained. The first metal salt is cobalt nitrate hexahydrate, and the ligand is 3-methyl-1-acetylimidazole. The molar ratio of the first metal salt to the ligand is 1:5. S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, the second metal salt being zinc salt, and the reaction time is 20 hours at room temperature. After three drying cycles, the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material is obtained.

[0086] The first, second, and third drying processes are performed at 80 °C for 25 h, with the molar ratio of the second metal to the first metal being 0.3:1. The cobalt salt solution, the organic solution of the ligand, and the metal salt solution are prepared as follows: the cobalt salt, ligand, and metal salt are respectively added to an organic solvent and mechanically stirred for 40 min. The molar ratio of the cobalt salt to the organic solvent is 1:1000, and the molar ratio of the ligand to the organic solvent is 5:1000. The organic solvent is N,N'-dimethylformamide.

[0087] Figure 1Scanning electron microscope (SEM) images and particle size distribution diagrams at different magnifications are shown for the polyimide (PI) nanofiber membrane prepared in Comparative Example 1, the ZIF-67 powder prepared in Comparative Example 2, the ZIF-67-Ni-ZIF composite powder prepared in Comparative Example 3, the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4, and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1. As can be seen from the figures, pure PI nanofibers exhibit a smooth, continuous network structure with a diameter of approximately 358.92 nm; ZIF-67 is a regular dodecahedral crystal with an average particle size of approximately 702.23 nm; the ZIF-Ni-67 particle size formed after the introduction of Ni slightly increases to 763.60 nm. The nm value indicates that metal doping may affect crystal growth. When ZIF-67 or ZIF-Ni-67 is loaded onto the PI fiber surface, a beaded or particle-attached composite structure is formed. Among them, the particles in ZIF-Ni-67 / PI are more dense and uniformly distributed, suggesting that Ni modification enhances the interfacial bonding. The particle size distribution of ZIF-Ni-67 / PI is φ=753.17±4.99 nm, exhibiting excellent structural uniformity. The EDS spectrum and elemental surface scan on the far right further confirm that Co and Ni elements are uniformly distributed on the fiber surface in ZIF-Ni-67 / PI, verifying the successful construction of bimetallic active sites.

[0088] Figure 2 The figures show the infrared spectra of the polyimide (PI) nanofiber membrane prepared in Comparative Example 1, the ZIF-67 powder prepared in Comparative Example 2, the ZIF-67-Ni-ZIF composite powder prepared in Comparative Example 3, the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4, and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1. As can be seen from the figures, comparing pure ZIF-67 and Ni-doped ZIF67-Ni-ZIF, both spectra on the left side show peak values ​​around 3125 cm⁻¹. -1 and 2922 cm -1 The presence of a CH stretching vibration peak at 1579 cm⁻¹ indicates a complete organic ligand skeleton; -1 The absorption peak at the N=C bond confirms the presence of the imidazole ring structure; however, the key difference lies in the low-frequency region, with ZIF67-Ni-ZIF showing an absorption peak at 417 cm⁻¹. -1 A new MN bond characteristic peak appears at this location, and the original ZIF-67 peak at 637 cm⁻¹... -1 The shift or weakening of the MO peak at this location indicates that Ni 2+ Successfully replaced part of Co 2+ It enters the crystal lattice, forming bimetallic active centers and altering the local coordination environment. Further analysis of the composite material using the right-hand spectra reveals that the PI substrate reaches a depth of 1718 cm⁻¹. -1 A strong C=O imide carbonyl peak is observed at 1498 cm⁻¹. -1and 1367 cm -1 Corresponding to C=N and CNC skeleton vibration respectively, 725 cm -1 These are out-of-plane bending vibrations of the imide ring; when ZIF-67 or ZIF67-Ni-ZIF is loaded onto PI, these characteristic peaks are retained but their intensity is reduced, while an additional peak of approximately 753 cm⁻¹ is added. -1 The broadened absorption band at 425 cm⁻¹ is attributed to Imidering vibrational coupling caused by hydrogen bonds or coordination between ZIF particles and PI fibers; especially in ZIF67-Ni-ZIF / PI at 425 cm⁻¹. -1 The MN peak is more pronounced at 1000–1500 cm⁻¹, suggesting that Ni modification enhances the interfacial bonding between the MOF and the polymer substrate. Furthermore, all composites show improved bonding at 1000–1500 cm⁻¹. -1 The increased peak shape in the ZIF region reflects the synergistic effect of multiple components. FTIR not only verified the integrity of the chemical structure of each component, but also strongly demonstrated through characteristic peak shifts, the appearance of new peaks, and changes in relative intensity that Ni doping alters the internal electron distribution of ZIF and promotes its chemical compatibility with the PI matrix. The stronger interfacial interaction helps stabilize particle adhesion and reduce shedding, thereby improving long-term operational reliability.

[0089] Figure 3The graphs show the filtration performance of the ZIF-67 / PI nanofiber composite membrane material prepared in Comparative Example 4 and the ZIF67-Ni-ZIF / PI nanofiber composite membrane material prepared in Example 1 for PM0.3, PM0.5, and PM2.5. The left graph represents the removal efficiency, and the right graph represents the quality factor. As shown in the graphs, the left graph indicates that both materials possess ultra-high filtration efficiency (>98%), with ZIF67-Ni-ZIF / PI performing better across the three particle sizes: 98.76% for PM0.3, 99.17% for PM0.5, and a high 99.91% for PM2.5, showing a significant improvement, especially for the most difficult-to-capture submicron-sized PM0.3. Simultaneously, its pressure drop is only 118 Pa, slightly lower than the 120.3 Pa of ZIF-67 / PI, indicating that it achieves lower airflow resistance while maintaining high efficiency, demonstrating the advantages of structural uniformity and pore size control. The quality factor in the right graph further comprehensively evaluates the performance; a higher value indicates stronger filtration efficiency per unit pressure drop. ZIF67-Ni-ZIF / PI outperformed the control group across all particle size ranges. This indicates that the introduction of Ni not only enhances particle trapping capacity but also optimizes fiber surface roughness and charge distribution, strengthening the synergistic effect of electrostatic adsorption and mechanical interception. The figure visually demonstrates that, compared to traditional ZIF-67 / PI, the bimetallic ZIF67-Ni-ZIF / PI, with its more uniform particle loading, stronger interfacial bonding, and optimized pore structure, achieves highly efficient trapping of ultrafine particles while maintaining low resistance. It is particularly suitable for scenarios with stringent air quality requirements, such as medical protective equipment or industrial dust removal, providing a solid performance basis for its potential as a next-generation high-performance air filtration material.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects, characterized in that, Includes the following steps: S1: Polyimide nanofiber membranes were prepared by reacting dianhydride monomers and diamine monomers; S2: The polyimide nanofiber membrane is sequentially placed in a first metal salt solution and an organic solution of the ligand to obtain a polyimide nanofiber membrane loaded with ZIF-67; the first metal salt is a cobalt salt; S3: The polyimide nanofiber membrane loaded with ZIF-67 is placed in a second metal salt solution, wherein the second metal salt is one of zinc salt, nickel salt, zirconium salt, iron salt and copper salt. After the reaction, the cobalt metal defect zeolite imidazole framework / polyimide nanofiber composite membrane material is obtained.

2. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, Step S1 is: S11: A polyamic acid solution is obtained by polycondensation of dianhydride monomer and diamine monomer, followed by washing to precipitate and freeze-drying to obtain polyamic acid powder. S12: Dissolve the polyamic acid powder in a polar aprotic solvent and stir until fully dissolved to obtain a polyamic acid spinning solution; S13: Electrospinning is performed using the polyamic acid spinning solution to obtain a polyamic acid nanofiber membrane; S14: The polyamic acid nanofiber membrane is subjected to thermal imidization treatment in an inert gas atmosphere to obtain the polyimide nanofiber film.

3. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 2, characterized in that, The molar ratio of the dianhydride monomer to the diamine monomer is (1~1.05):(0.95~1); during the mixed reaction of the dianhydride monomer and the diamine monomer, the reaction temperature is -5~0 °C and the reaction time is 24~28 h.

4. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, During electrospinning, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving plate is 10~20 cm.

5. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, The ligand is one or two of 2-methylimidazolium, benzimidazole, imidazole, 5,6-dimethylbenzimidazole, imidazole-2-carboxaldehyde, aldehyde imidazole, and 3-methyl-1-acetylimidazolium.

6. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, The molar ratio of the first metal salt to the ligand is (0.5~1.5):(1~8).

7. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, The polyimide nanofiber membrane loaded with ZIF-67 was placed in a second metal salt solution and reacted at room temperature for 12-24 h.

8. The method for preparing a zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects according to claim 1, characterized in that, The molar ratio of the second metal to the first metal is (0.2~0.4):

1.

9. A zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the zeolite imidazole framework / polyimide nanofiber composite membrane material based on cobalt metal defects as described in claim 9 in filter materials.

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