Imidazole ring-containing polyimide / zif-8 composite nanofiber membrane, and preparation method and application thereof

Abstract

The application provides an imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane and a preparation method and application thereof, and the preparation method comprises the following steps: preparing an imidazole ring-containing polyamide acid spinning solution; preparing an imidazole ring-containing polyamide acid nanofiber membrane by using the imidazole ring-containing polyamide acid spinning solution through an electrostatic spinning method; performing thermal imidization treatment on the imidazole ring-containing polyamide acid nanofiber membrane to obtain an imidazole ring-containing polyimide nanofiber membrane; and repeatedly immersing the imidazole ring-containing polyimide nanofiber membrane in a ZIF-8 solution for several times, and then drying to obtain the imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane. The imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane anchors ZIF-8 on the polyimide fiber through cation-π interaction, and effectively improves the binding force between the polyimide and ZIF-8.

Description

Technical Field

[0001] This invention belongs to the field of air filtration materials technology, and relates to an imidazole ring polyimide / ZIF-8 composite nanofiber membrane, its preparation method and application. Background Technology

[0002] With urbanization and industrialization, air pollution has become increasingly serious, and frequent smog and air pollution events pose a severe threat to people's health and lives. Therefore, researching and developing efficient air filtration technologies and materials has become an urgent task. Currently, air filtration technologies have been widely applied and promoted, including mechanical filtration, electrostatic adsorption, activated carbon adsorption, ultraviolet irradiation, and ozone oxidation. Simultaneously, research and development of novel air filtration materials has become a research hotspot, such as nanomaterials, porous materials, and functionalized materials. These materials offer advantages such as higher filtration efficiency, longer service life, and lower energy consumption.

[0003] Polyimide (PI) is a high-performance material. Electrospinning can be used to prepare nanofiber membranes with small diameters, large specific surface areas, small pore sizes, and high porosity, significantly improving the air filtration performance of fibrous materials. Furthermore, introducing nanoparticles into polymers can enhance filtration performance by increasing specific surface area and creating a spatial support effect, while simultaneously imparting a lower pressure drop. Recent studies have shown that metal-organic frameworks (MOFs), due to their ultra-high specific surface area, functional channels, high and tunable porosity, and stable and diverse structures, can achieve efficient capture of particulates and other harmful gaseous pollutants not only through size filtration but also through their unique open metal sites, functional groups, and surface charges. However, the interfacial forces between MOFs and polyimide nanofibers are weak, leading to MOFs' tendency to detach and aggregate, making it difficult to effectively and uniformly adhere to the surface of polyimide nanofiber membranes and thus hindering their full potential. Therefore, effectively improving the interfacial bonding between MOFs and polyimide fibers, and thus enabling them to adhere uniformly to the surface of polyimide fibers, is particularly important for the preparation of polyimide@MOFs composites. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides an imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane, its preparation method and application, thereby solving the technical problems in the prior art where the interfacial force between MOFs and polyimide fibers is weak, MOFs are easy to detach and agglomerate, and it is difficult to effectively and uniformly attach them to the surface of polyimide nanofiber membranes.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing an imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane includes the following steps:

[0007] S1: Diamine monomer and dianhydride monomer are added sequentially to N,N-dimethylformamide, and the mixture is stirred to prepare an imidazole-containing polyamic acid spinning solution; the diamine monomer is a mixture of imidazole-containing diamine and imidazole-free diamine;

[0008] S2: Prepare imidazole-containing polyamic acid nanofiber membranes using the imidazole-containing polyamic acid spinning solution via electrospinning.

[0009] S3: The imidazole-ring polyamic acid nanofiber membrane is subjected to thermal imidization treatment to obtain an imidazole-ring polyimide nanofiber membrane.

[0010] S4: The imidazole-ring polyimide nanofiber membrane is immersed in ZIF-8 solution and water several times in sequence to obtain an imidazole-ring polyimide nanofiber membrane with ZIF-8 grown on it. After drying, the imidazole-ring polyimide / ZIF-8 composite nanofiber membrane is obtained.

[0011] Preferably, the molar ratio of the imidazole-containing diamine to the imidazole-free diamine is (1-4):(6-9).

[0012] Preferably, the dianhydride monomer is one or a mixture of several of the following in any proportion: pyromellitic dianhydride, hexafluorodianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the imidazole-containing diamine is 2-(4-aminophenyl)-5-aminobenzimidazole; and the imidazole-free diamine is one of 4,4'-diaminodiphenyl ether, biphenyl diamine, and bisphenol A type diamine.

[0013] Preferably, in step S1, during the stirring reaction of the diamine monomer and the dianhydride monomer, the reaction temperature is 0–25°C and the reaction time is 4–6 h.

[0014] Preferably, in step S2, the electrospinning voltage is 15-20kV, the spinning solution flow rate is 0.010-0.017mL / min, the distance between the needle and the receiving plate is 10-20cm, and the electrospinning time is 20-40min.

[0015] Preferably, in step S3, the thermal imidization process specifically involves heating to 100°C–150°C at a heating rate of 5–10°C / min, holding at that temperature for 30–60 min, then heating to 200°C–250°C at a heating rate of 5–10°C / min, holding at that temperature for 30–60 min, and finally heating to 300°C–350°C at a heating rate of 5–10°C / min, holding at that temperature for 30–60 min.

[0016] Preferably, the ZIF-8 solution is prepared by direct liquid-phase synthesis, specifically by adding soluble zinc salt and 2-methylimidazole to a solvent, stirring and reacting to obtain the ZIF-8 solution.

[0017] Preferably, in the preparation of the ZIF-8 solution, the molar ratio of the concentration of zinc ions in the soluble zinc salt to that of 2-methylimidazole and the solvent is 1:4:(400-2000).

[0018] An imidazole ring polyimide / ZIF-8 composite nanofiber membrane was prepared by the above method.

[0019] The above-mentioned application of an imidazole ring polyimide / ZIF-8 composite nanofiber membrane in the field of air filtration.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] A method for preparing an imidazole-ring-containing polyimide / ZIF-8 composite nanofiber membrane is disclosed. The method involves preparing an imidazole-ring-containing polyamic acid nanofiber membrane via electrospinning; obtaining an imidazole-ring-containing polyimide nanofiber membrane through imidization treatment; preparing a ZIF-8 solution via direct liquid-phase synthesis; and anchoring ZIF-8 onto the polyimide fibers through cation-π interactions by the imidazole ring providing π electrons and ZIF-8 providing metal ions, effectively improving the bonding force between the polyimide and ZIF-8. This invention introduces electron-rich imidazole rings into the polyimide molecular chain through molecular structure design. The imidazole rings provide π electrons to capture metal ions and form cation-π interactions, which are then used as active sites to construct MOFs. This "point-to-surface" interaction effectively enhances the interface. Compared with traditional "point-to-point" non-covalent interactions such as metal ion coordination and hydrogen bonding, the cation-π interaction has a larger interaction area and can quickly form "point-to-surface" interactions in rigid polymers. It has the advantages of simplicity, high efficiency, short interaction time, wide applicability, environmental friendliness, and low cost. Furthermore, in the material preparation process, the imidazole-ring-containing polyimide nanofiber membrane is repeatedly immersed and washed in ZIF-8 solution and water. This operation facilitates better bonding between the polyimide nanofibers and ZIF-8 particles, resulting in uniform adhesion to the polyimide fiber surface. The method described in this invention is simple, feasible, and environmentally friendly. It has significant scientific and industrial value for the controllable preparation of PI-based high-temperature air filter materials and for air purification from high-temperature pollution sources such as industrial exhaust, coal combustion, vehicle exhaust, and biomass combustion.

[0022] Furthermore, the diamine monomer is a mixture of imidazole-containing and imidazole-free diamines; the molar ratio of the imidazole-containing to the imidazole-free diamines is (1-4):(6-9); the dianhydride monomer is one or a mixture of several of pyromellitic anhydride, hexafluorodianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in any proportion. Using imidazole-containing and imidazole-free diamines as diamine monomers here makes the polymerization reaction stable and easily controlled. In addition, the molar ratio of imidazole-containing to imidazole-free diamines (1-4):(6-9) makes the viscosity of the spinning solution favorable for spinning.

[0023] Furthermore, the imidazole-containing diamine is 2-(4-aminophenyl)-5-aminobenzimidazole, and the imidazole-free diamine is one of 4,4'-diaminodiphenyl ether, biphenyl diamine, and bisphenol A type diamine, which makes the polymerization reaction stable and easy to control.

[0024] Furthermore, in step S1, during the stirring reaction of the diamine monomer and the dianhydride monomer, the reaction temperature is 0–25°C and the reaction time is 4–6 h. These conditions can reduce the heat generated during the reaction and reduce the volatilization of organic solvents.

[0025] Furthermore, in step S2, the electrospinning voltage is 15-20kV, the spinning solution flow rate is 0.010-0.017mL / min, the distance between the needle and the receiving plate is 10-20cm, and the electrospinning time is 20-40min. These conditions can make the fiber output uniform and stable, and the yield is high.

[0026] Furthermore, in step S3, the thermal imidization process specifically involves heating to 100℃-150℃ at a heating rate of 5-10℃ / min and holding for 30-60 minutes, then heating to 200℃-250℃ at a heating rate of 5-10℃ / min and holding for 30-60 minutes, and finally heating to 300℃-350℃ at a heating rate of 5-10℃ / min and holding for 30-60 minutes. These conditions allow the solvent in the fiber to evaporate. When the temperature reaches 250℃, the degree of imidization is close to 94%. By annealing between 300 and 350℃, "complete" imidization can be achieved.

[0027] Furthermore, the molar ratio of zinc ion concentration in the soluble zinc salt to 2-methylimidazole and solvent is 1:4:(400-2000), which makes the synthesized ZIF-8 appropriately sized and stably bound. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a process flow diagram for preparing the imidazole ring polyimide / ZIF-8 composite nanofiber membrane of the present invention;

[0030] Figure 2 This is a flowchart illustrating the synthesis process of polyimide in this invention;

[0031] Figure 3 These are SEM images of the imidazole ring-containing polyimide nanofiber membranes prepared in Examples 1-3 of this invention.

[0032] Figure 4 These are SEM images of the imidazole ring polyimide / ZIF-8 nanofiber membranes prepared in Examples 1-3 of this invention, where from left to right they correspond to Examples 1-3.

[0033] Figure 5 The images shown are SEM images and XRD test results of the ZIF-8 nanoparticles prepared in Examples 1 to 3 of this invention, where a is the SEM image and b is the XRD image. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.”

[0038] 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.

[0039] like Figure 1 As shown, this invention provides a method for preparing an imidazole-ringed polyimide / ZIF-8 composite nanofiber membrane, characterized by comprising the following steps:

[0040] S1: Add diamine monomer and dianhydride monomer sequentially to N,N-dimethylformamide (DMF solution), control the reaction temperature at 0–25℃, and stir the reaction for 4–6 hours to obtain an imidazole-containing polyamic acid spinning solution; For example... Figure 2 As shown.

[0041] Wherein, the diamine monomer is a mixture of imidazole-containing diamine and imidazole-free diamine; the molar ratio of the imidazole-containing diamine to the imidazole-free diamine is (1-4):(6-9);

[0042] The dianhydride monomer is one or a mixture of several of the following in any proportion: pyromellitic dianhydride, hexafluorodianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The imidazole-containing diamine is 2-(4-aminophenyl)-5-aminobenzimidazole, and the imidazole-free diamine is one of 4,4'-diaminodiphenyl ether, biphenyl diamine, and bisphenol A type diamine. The molar ratio of the diamine monomer to the dianhydride monomer is 1:1.

[0043] S2: Prepare imidazole-containing polyamic acid nanofiber membranes using the imidazole-containing polyamic acid spinning solution via electrospinning.

[0044] The electrospinning voltage is 15–20 kV, the spinning solution flow rate is 0.010–0.017 mL / min, the distance between the needle and the receiving plate is 10–20 cm, and the electrospinning time is 20–40 min.

[0045] S3: The imidazole-ring polyamic acid nanofiber membrane is subjected to thermal imidization treatment to obtain an imidazole-ring polyimide nanofiber membrane.

[0046] Specifically, the thermal imidization process involves heating to 100℃-150℃ at a heating rate of 5-10℃ / min, holding at that temperature for 30-60 min, then heating to 200℃-250℃ at a heating rate of 5-10℃ / min, holding at that temperature for 30-60 min, and finally heating to 300℃-350℃ at a heating rate of 5-10℃ / min, holding at that temperature for 30-60 min.

[0047] S4: The imidazole-containing polyimide nanofiber membrane is sequentially immersed in ZIF-8 solution and water several times to obtain an imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it. After drying, the imidazole-containing polyimide / ZIF-8 composite nanofiber membrane is obtained. Here, the ZIF-8 solution is prepared by direct liquid-phase synthesis, specifically by adding a soluble zinc salt and 2-methylimidazole to a solvent, stirring and reacting to obtain the ZIF-8 solution. More specifically, the soluble zinc salt is one of Zn(NO3)2·6(H2O) and (CH3COO)2Zn, and the solvent is at least one of water and methanol. Furthermore, during the preparation of the ZIF-8 solution, the molar ratio of zinc ions in the soluble zinc salt to 2-methylimidazole and the solvent is 1:4:(400~2000). Specifically, during the impregnation process, the imidazole-ringed polyimide nanofiber membrane is first impregnated in a ZIF-8 solution to carry out a cationic-π coordination reaction. Then, it is transferred to water, which can be deionized water, and this process is repeated 7–8 times to ensure uniform growth of ZIF-8 on the imidazole-ringed polyimide nanofibers and to remove excess ZIF-8 particles deposited on the membrane. Finally, during drying, the oven temperature is 60–100℃, and the drying time is 12–24 hours.

[0048] The composite nanofiber membrane prepared by the method of this invention exhibits strong interfacial forces, is not easily detached, and is uniformly distributed. Furthermore, this invention uses ZIF-8 to prepare imidazole ring polyimide / ZIF-8 air filter materials, which, in addition to possessing the advantages of other MOF materials (large specific surface area, structural and pore diversity, and functional tunability), also exhibit high thermal and chemical stability. The resulting filter materials can be used in fields requiring high-temperature resistance, such as thermal power generation, waste incineration, steel smelting, and cement production.

[0049] 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.

[0050] 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.

[0051] Example 1

[0052] Preparation of imidazole-containing polyimide nanofiber membrane: First, weigh 0.699 g of 4,4'-diaminodiphenyl ether (ODA) and add it to a beaker. Add 6 mL of DMF and stir to dissolve. Then weigh 0.366 g of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and add 6 mL of DMF to dissolve. Then weigh 1.2 g of pyromellitic anhydride (PMDA) and slowly add it while stirring for 6 h to obtain a yellow transparent solution, which is the imidazole-containing polyamic acid solution.

[0053] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 16kV and the flow rate to 0.017mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0054] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 150°C at a heating rate of 10°C / min and held for 30 min, then raised to 250°C at a heating rate of 10°C / min and held for 60 min, and finally raised to 320°C at a heating rate of 5°C / min and held for 30 min to obtain an imidazole ring polyimide nanofiber membrane.

[0055] Preparation of imidazole ring polyimide / ZIF-8: Add 16.8 mL of deionized water and 16.3 mL of methanol to a beaker and stir for 10 min. Add 1 g of zinc nitrate to the methanol-water solution and stir for 10 min. Then add 1.0964 g of 2-methylimidazole to the methanol-water solution and stir for 30 min to obtain a milky white ZIF-8 solution.

[0056] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution (1-2 min) and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0057] Example 2

[0058] Preparation of imidazole-containing polyimide nanofiber membrane: First, weigh 0.699 g of 4,4'-diaminodiphenyl ether (ODA) and add it to a beaker. Add 6 mL of DMF and stir to dissolve. Then weigh 0.366 g of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and add 6 mL of DMF to dissolve. Then weigh 1.2 g of pyromellitic anhydride (PMDA) and slowly add it while stirring for 6 h to obtain a yellow transparent solution, which is the imidazole-containing polyamic acid solution.

[0059] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 16kV and the flow rate to 0.017mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0060] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 150°C at a heating rate of 10°C / min and held for 30 min, then raised to 250°C at a heating rate of 10°C / min and held for 60 min, and finally raised to 320°C at a heating rate of 5°C / min and held for 30 min to obtain an imidazole ring polyimide nanofiber membrane.

[0061] Preparation of imidazole ring polyimide / ZIF-8: Add 33.6 mL of deionized water and 32.6 mL of methanol to a beaker and stir for 10 min. Add 1 g of zinc nitrate to the methanol-water solution and stir for 10 min. Then add 1.0964 g of 2-methylimidazole to the methanol-water solution and stir for 30 min to obtain a milky white ZIF-8 solution.

[0062] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution (1-2 min) and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0063] Example 3

[0064] Preparation of imidazole-containing polyimide nanofiber membrane: First, weigh 0.699 g of 4,4'-diaminodiphenyl ether (ODA) and add it to a beaker. Add 6 mL of DMF and stir to dissolve. Then weigh 0.366 g of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and add 6 mL of DMF to dissolve. Then weigh 1.2 g of pyromellitic anhydride (PMDA) and slowly add it while stirring for 6 h to obtain a yellow transparent solution, which is the imidazole-containing polyamic acid solution.

[0065] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 16kV and the flow rate to 0.017mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0066] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 150°C at a heating rate of 10°C / min and held for 30 min, then raised to 250°C at a heating rate of 10°C / min and held for 60 min, and finally raised to 320°C at a heating rate of 5°C / min and held for 30 min to obtain an imidazole ring polyimide nanofiber membrane.

[0067] Preparation of imidazole ring polyimide / ZIF-8: Add 50 mL of deionized water and 48.8 mL of methanol to a beaker and stir for 10 min. Add 1 g of zinc nitrate to the methanol-water solution and stir for 10 min. Then add 1.0964 g of 2-methylimidazole to the methanol-water solution and stir for 30 min to obtain a milky white ZIF-8 solution.

[0068] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution (1-2 min) and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0069] Example 4

[0070] Preparation of imidazole ring-containing polyimide nanofiber membrane: First, 2-(4-aminophenyl)-5-aminobenzimidazole and 4,4'-diaminodiphenyl ether in a molar ratio of 1:9 were stirred with pyromellitic dianhydride at 0℃ for 4 h to obtain an imidazole ring-containing polyamic acid solution.

[0071] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 15kV and the flow rate to 0.010mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0072] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 100°C at a heating rate of 5°C / min and held for 30 min, then raised to 200°C at a heating rate of 5°C / min and held for 30 min, and finally raised to 300°C at a heating rate of 5°C / min and held for 30 min to obtain an imidazole ring polyimide nanofiber membrane.

[0073] Preparation of imidazole ring polyimide / ZIF-8: Add zinc nitrate, 2-methylimidazolium, and deionized water-methanol solution in a molar ratio of 1:4:1600 to a beaker, stir for 30 min, and obtain a milky white ZIF-8 solution;

[0074] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution for 2 minutes and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0075] Example 5

[0076] Preparation of imidazole ring-containing polyimide nanofiber membrane: First, 2-(4-aminophenyl)-5-aminobenzimidazole and biphenyl diamine in a molar ratio of 2:8 were stirred with hexafluorodianhydride at 10°C for 5 h to obtain an imidazole ring-containing polyamic acid solution.

[0077] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 18kV and the flow rate to 0.013mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0078] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 120°C at a heating rate of 8°C / min and held for 45 min, then raised to 230°C at a heating rate of 8°C / min and held for 45 min, and finally raised to 320°C at a heating rate of 5°C / min and held for 45 min to obtain an imidazole ring polyimide nanofiber membrane.

[0079] Preparation of imidazole ring polyimide / ZIF-8: Add zinc nitrate, 2-methylimidazolium, and deionized water-methanol solution in a molar ratio of 1:4:1800 to a beaker, stir for 30 min to obtain a milky white ZIF-8 solution;

[0080] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution for 2 minutes and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0081] Example 6

[0082] Preparation of imidazole ring polyimide nanofiber membrane: First, 2-(4-aminophenyl)-5-aminobenzimidazole and bisphenol A type diamine in a molar ratio of 4:6 were stirred with 3,3',4,4'-benzophenone tetracarboxylic dianhydride at 15°C for 5.5 h to obtain an imidazole ring polyamic acid solution.

[0083] The obtained imidazole-containing polyamic acid solution was poured into an electrospinning syringe, and the electrospinning voltage was set to 20kV and the flow rate to 0.015mL / min. Electrospinning was then performed to obtain an imidazole-containing polyamic acid nanofiber film.

[0084] The above-mentioned film was subjected to staged heating treatment in a high-temperature tube furnace under N2 environment: the temperature was raised to 140℃ at a heating rate of 10℃ / min and held for 50 min, then raised to 240℃ at a heating rate of 8℃ / min and held for 45 min, and finally raised to 350℃ at a heating rate of 6℃ / min and held for 60 min to obtain an imidazole ring polyimide nanofiber membrane.

[0085] Preparation of imidazole ring polyimide / ZIF-8: Add zinc nitrate, 2-methylimidazolium, and deionized water-methanol solution in a molar ratio of 1:4:2000 to a beaker, stir for 30 min, and obtain a milky white ZIF-8 solution;

[0086] The imidazole-containing polyimide nanofiber membrane prepared above was immersed in ZIF-8 solution for 2 minutes and then washed with deionized water. This process was repeated 7-8 times to ensure uniform growth of ZIF-8 on the imidazole-containing polyimide nanofiber and to remove excess ZIF-8 particles deposited on the membrane. The imidazole-containing polyimide nanofiber membrane with ZIF-8 grown on it was dried in an oven at 60°C and then cooled to obtain imidazole-containing polyimide / ZIF-8 air filter material.

[0087] Furthermore, the technical solution of the present invention will be explained with reference to the accompanying drawings.

[0088] Figure 3 These are SEM images of the imidazole-ring-containing polyimide nanofiber membranes prepared in Examples 1-3 of this invention. Figure 3 It can be seen that the imidazole ring polyimide nanofiber membrane before impregnation is smooth and without clumps.

[0089] Figure 4 These are SEM images of the imidazole-ringed polyimide / ZIF-8 nanofiber membranes prepared in Examples 1-3 of this invention. Figure 4 It can be seen that ZIF-8 particles are uniformly distributed on the fibers of the impregnated imidazole-containing polyimide / ZIF-8 nanofiber membrane, indicating that ZIF-8 is successfully combined with the imidazole-containing polyimide fibers.

[0090] Figure 5 The images shown are SEM images and XRD test results of the ZIF-8 nanoparticles prepared in Examples 1-3 of this invention. Figure 5 This confirms the successful preparation of ZIF-8.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0092] 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 an imidazole-ringed polyimide / ZIF-8 composite nanofiber membrane, characterized in that, Includes the following steps: S1: Add diamine monomer and dianhydride monomer sequentially to N,N-dimethylformamide, stir and react to obtain a polyamic acid spinning solution containing imidazole ring; the diamine monomer is a mixture of imidazole cyclic diamine and imidazole cyclic diamine; the molar ratio of imidazole cyclic diamine to imidazole cyclic diamine is (1~4):(6~9); S2: Prepare imidazole-containing polyamic acid nanofiber membranes using the imidazole-containing polyamic acid spinning solution via electrospinning. S3: The imidazole-ring polyamic acid nanofiber membrane is subjected to thermal imidization treatment to obtain an imidazole-ring polyimide nanofiber membrane. S4: The imidazole-ring polyimide nanofiber membrane is immersed in ZIF-8 solution and water several times in sequence to obtain an imidazole-ring polyimide nanofiber membrane with ZIF-8 grown on it. After drying, the imidazole-ring polyimide / ZIF-8 composite nanofiber membrane is obtained. ZIF-8 solution was prepared by direct liquid-phase synthesis, specifically by adding soluble zinc salt and 2-methylimidazole to a solvent, stirring and reacting to obtain the ZIF-8 solution. In the preparation of ZIF-8 solution, the concentration of zinc ions in the soluble zinc salt and the molar ratio of 2-methylimidazole and solvent are 1:4:(400~2000).

2. The method for preparing an imidazole ring-containing polyimide / ZIF-8 composite nanofiber membrane according to claim 1, characterized in that, The dianhydride monomer is one or a mixture of several of the following in any proportion: pyromellitic dianhydride, hexafluorodianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the imidazole-containing diamine is 2-(4-aminophenyl)-5-aminobenzimidazole; and the imidazole-free diamine is one of 4,4'-diaminodiphenyl ether, biphenyl diamine, and bisphenol A type diamine.

3. The method for preparing an imidazole-ringed polyimide / ZIF-8 composite nanofiber membrane according to claim 1, characterized in that, In step S1, during the stirring reaction of the diamine monomer and the dianhydride monomer, the reaction temperature is 0~25℃ and the reaction time is 4~6h.

4. The method for preparing an imidazole-ringed polyimide / ZIF-8 composite nanofiber membrane according to claim 1, characterized in that, In step S2, the electrospinning voltage is 15~20kV, the spinning solution flow rate is 0.010~0.017mL / min, the distance between the needle and the receiving plate is 10~20cm, and the electrospinning time is 20~40min.

5. The method for preparing an imidazole-ringed polyimide / ZIF-8 composite nanofiber membrane according to claim 1, characterized in that, In step S3, the thermal imidization process specifically involves heating to 100℃~150℃ at a heating rate of 5~10℃ / min, holding at that temperature for 30~60min, then heating to 200℃~250℃ at a heating rate of 5~10℃ / min, holding at that temperature for 30~60min, and finally heating to 300℃~350℃ at a heating rate of 5~10℃ / min, holding at that temperature for 30~60min.

6. A composite nanofiber membrane containing imidazole ring polyimide / ZIF-8, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. The application of the imidazole ring polyimide / ZIF-8 composite nanofiber membrane as described in claim 6 in the field of air filtration.

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