Preparation method of flower-like metal organic framework compound high-temperature-resistant composite filter membrane

Abstract

The invention relates to the technical field of nanofiber thin film materials, in particular to a preparation method of a flower-shaped metal organic framework compound high-temperature-resistant composite filter membrane. The preparation method comprises the following steps: (1) preparing a polyimide nanofiber film through electrostatic spinning; (2) interface adhesion of a metal ion-polyphenol network; (3) preparing a polyimide grafted ZIF-8 composite film; (4) soaking the polyimide nanofiber film prepared in the step (3) in a zinc nitrate aqueous solution, stirring at normal temperature, washing away redundant zinc ions, and continuously soaking in a low-concentration aqueous solution of 2-methylimidazole for coordination polymerization; and (5) repeating the steps (3)-(4) for multiple times, so that the ZIF-8 crystals grow on the surfaces of the fibers in situ in a flower-like form, and the high-temperature-resistant composite filter membrane is prepared. The composite filter membrane prepared by the preparation method is resistant to high temperature and uniform in gap distribution, the filtering efficiency reaches 99.98% or above, the piezoresistance is lower than 150 Pa, and the application effect in the field of filtering separation is remarkable.

Description

Technical Field

[0001] This invention relates to the field of nanofiber thin film materials technology, and in particular to a method for preparing a high-temperature resistant composite filter membrane of a flower-like metal-organic framework compound. Background Technology

[0002] Epidemiological surveys show that air pollution has significant negative health effects, triggering asthma and other respiratory diseases, increasing difficulty in accessing medical care, and exacerbating cardiopulmonary diseases. The "State of Air Globally" report identifies air pollution as one of the leading risk factors for death and disability, with particulate matter (PM2.5) being a major contributor. 2.5 It was rated as the sixth leading risk factor for death.

[0003] Metal-organic frameworks (MOFs) are a class of organic-inorganic hybrid crystalline materials with periodic structures, formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds or intermolecular interactions. MOFs possess high specific surface area, tunable pore size, and rich chemical activity. When combined with electrospun polyimide nanofibers, they can be used to prepare composite films with excellent air filtration performance. However, the physicochemical properties of electrospun polyimide nanofibers and MOFs are stable, making it difficult to stably graft large amounts of MOF crystals onto the fiber surface through physical blending.

[0004] To address the above issues, current methods generally involve MOF particle modification, fiber surface modification, and in-situ growth. However, due to the stable physicochemical properties of both, even after modification, interfacial compatibility remains limited, and MOFs are prone to detachment, thus affecting the stability of the composite film during its production and use. In-situ growth generates MOFs on / inside the surface of polyimide fibers, avoiding the dispersion difficulties of physical blending and strengthening interfacial bonding. However, direct in-situ growth easily leads to poor film uniformity and low loading rate, failing to fully utilize the adsorption performance of MOFs. On the other hand, excessively increasing the loading rate can easily cause MOFs to agglomerate, clog fiber pores, and reduce filtration efficiency.

[0005] Zeolite imidazole ester (ZIF) framework materials are a type of metal-organic framework (MOF) material, using Zn or Co as the metal source and imidazole or imidazole derivatives as organic ligands, exhibiting strong thermal and chemical stability. Zeolite imidazole ester framework-8 (ZIF-8) is a common ZIF material. Patent application "A mixed matrix membrane containing ZIF-8 and its preparation and application" (2017107682683) crosslinks ZIF-8 with the organic polymer polyethylene glycol methacrylate to obtain a thinner mixed matrix membrane. Patent "A mixed matrix membrane composed of a metal-organic framework and a self-porous polymer and its preparation method and application" (2019104531002) uses a composite of ZIF-8, PIM-1, and UIO-66-NH2, combining the advantages of each material in gas sieving to prepare a mixed matrix membrane exhibiting excellent gas separation performance. The patent "A Mixed Matrix Membrane of Aminated ZIF-8 and Polyvinyl Alcohol and Its Preparation Method and Application" (2021105291997) provides a method for modifying ZIF-8 by shell-ligand exchange reaction, introducing amino groups, and then preparing a mixed matrix membrane with polyvinyl alcohol to improve separation performance.

[0006] This application aims to develop a ZIF-8 polyimide composite nanofiber filter membrane loaded in a flower-like form, which ensures high efficiency and low resistance air filtration even under high temperature conditions, in order to address the increasingly serious air pollution problem. Summary of the Invention

[0007] This invention provides a method for preparing a high-temperature resistant composite filter membrane of flower-shaped metal-organic framework compounds, which solves the problems of unstable bonding between electrospun nanofiber membranes and metal-organic framework compounds, low filtration efficiency, and high pressure drop in the prior art. The composite filter membrane prepared by this method is resistant to high temperature, has uniform pore distribution, a filtration efficiency of over 99.98%, and a pressure resistance of less than 150 Pa, showing significant application effect in the field of filtration and separation.

[0008] The technical solution adopted in this invention is: A method for preparing a high-temperature resistant composite filter membrane of a flower-like metal-organic framework compound is provided, comprising the following steps: (1) Preparation of polyimide nanofiber films by electrospinning First, an equimolar amount of diamine and dianhydride were used to carry out a polycondensation reaction to prepare an N,N'-dimethylformamide solution of polyamic acid; then, an electrospinning process was carried out to obtain a polyamic acid nanofiber film; and finally, a programmed temperature rise process was carried out to obtain a polyimide nanofiber film. (2) Interfacial adhesion of metal ion-polyphenol network The polyimide nanofiber membrane obtained in step (1) was immersed in tannic acid aqueous solution, stirred evenly, added to zinc chloride aqueous solution and stirred, and then PBS solution was added to adjust the pH to 6.5, so that it was mixed evenly and crosslinked, and a polyimide nanofiber film wrapped with metal polyphenol network MPN was prepared, specifically a zinc ion-polyphenol network polyimide nanofiber film. (3) Preparation of polyimide-grafted ZIF-8 composite film The polyimide nanofiber film coated with zinc ion-polyphenol network obtained in step (2) was immersed in a high concentration of 2-methylimidazole aqueous solution for coordination. The reaction temperature was controlled at 50℃-70℃ and the time was 6-10h to obtain the first layer of ZIF-8 crystal. (4) The polyimide nanofiber film obtained in step (3) is immersed in an aqueous solution of zinc nitrate, stirred at room temperature to wash away excess zinc ions, and then immersed in a low-concentration aqueous solution of 2-methylimidazole for coordination polymerization. (5) Repeat steps (3)-(4) multiple times to obtain ZIF-8 polyimide composite nanofiber filter membrane loaded in a flower-like form.

[0009] Further, in step (1), the dianhydride is pyromellitic dianhydride PMDA, the diamine is N,N'-dimethylformamide DMF; the polycondensation reaction is carried out at a low temperature of 0~8℃ for 24h; the concentration of the N,N'-dimethylformamide solution of the obtained polyamic acid is 12%-18%, and the solution viscosity is 18~24 Pa·s.

[0010] Furthermore, the specific preparation steps of the N,N'-dimethylformamide solution of polyamic acid are as follows: an appropriate amount of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) are added to N,N'-dimethylformamide (DMF), and a low-temperature polycondensation reaction is carried out at 0~8℃ for 24 h.

[0011] Furthermore, in step (1), the conditions for the electrospinning process are as follows: The viscous polyamic acid solution prepared above is added to a syringe. The spinning voltage is 16~24kV, the spinning solution flow rate is 0.5~1.5mL / h, and the distance between the needle tip and the aluminum foil plate receiver is 16~25cm to obtain a polyamic acid fiber film. Then, a heating process is carried out to complete the imidization reaction to obtain a polyimide nanofiber film. The temperature rise during the program stages is as follows: ① 25~150℃, 5~15℃ / min, annealing for 30~60 min; ② 150℃~250℃, 10~20℃ / min, annealing for 30~60 min; ③ 250℃~350℃, 10~30℃ / min, annealing for 60~90 min.

[0012] Furthermore, the above-mentioned temperature rise stages are carried out in a high-temperature tubular furnace under an N2 environment.

[0013] Further, in step (2), the concentration of the tannic acid aqueous solution is 20-40 mg / mL and the amount used is 10-40 mL; the concentration of the zinc chloride aqueous solution is 10-20 mg / mL and the amount used is 10-40 mL; the concentration of the PBS solution is 0.05-0.1 mol / L and the amount used is 500-2000 mL.

[0014] Further, in step (2), the sample is immersed in an aqueous solution of tannic acid and stirred for 0.5 h, and then added to an aqueous solution of zinc chloride and stirred for another 2-4 h.

[0015] Further, in step (3), the high-concentration 2-methylimidazole aqueous solution refers to a 2-methylimidazole solution with a mass concentration range of 25-35% and a volume of 50-100 mL; in step (4), the low-concentration 2-methylimidazole aqueous solution refers to a 2-methylimidazole solution with a mass concentration range of 10-20% and a volume of 50-100 mL.

[0016] Furthermore, in step (4), the mass concentration of the zinc nitrate aqueous solution is 1-5%, and the amount used is 50-100 mL; the stirring time at room temperature is 20-60 min; the coordination polymerization reaction temperature is controlled at 50-70℃, and the reaction time is 6-10 hours.

[0017] Furthermore, in step (5), steps (3)-(4) are repeated 3-4 times.

[0018] This invention also provides the application of the composite filter membrane prepared by the above method in gas filtration and toxic gas adsorption.

[0019] The beneficial effects of this invention are: 1. This invention utilizes the dynamic coordination bonding between catechol groups in plant polyphenols and metal ions to form an MPN cross-linked network structure with strong adhesion, while simultaneously forming active zinc ion metal sites on the fiber surface. By precisely controlling the formulation and synthesis temperature gradient of the MOF material, organic ligands are crystallized layer by layer at the metal ion sites on the electrospun nanofibers, forming nanocrystals with a branched structure. The thickness of each crystal layer is stable, and through continuous growth, a three-dimensional flower-like structure of MOF crystals is finally formed, thereby obtaining a polyimide nanocomposite film loaded with the metal-organic framework compound ZIF-8 (zeolite imidazole ester framework-8).

[0020] 2. The introduction of a large amount of stable ZIF-8 in this invention significantly improves the porosity and specific surface area of ​​the composite film, enabling it to effectively capture and adsorb fine particulate matter and toxic gases. Due to the excellent temperature resistance of electrospun polyimide nanofibers and ZIF-8 nanocrystals, the composite structure prepared in this invention can still function normally in high-temperature environments ranging from 150°C to 260°C. More importantly, this flower-like structure significantly enhances the retention effect and collision probability of the composite film, allowing the material to maintain high filtration efficiency and low pressure drop, meeting the stringent requirements of high-temperature industrial filtration and air purification.

[0021] 3. The ZIF-8 polyimide composite nanofiber filter membrane prepared by the method of this invention, in a flower-like form, contains no organic solvents. Its filtration efficiency for impurities of different particle sizes is above 99.98%, and its piezoresistive resistance is below 150 Pa, expanding its application in the field of filtration and separation. Attached Figure Description

[0022] Figure 1 This is a physical image of the composite filter membrane prepared according to the present invention; Figure 2 Here is a SEM image of the composite filter membrane prepared according to the present invention; Figure 3 The nitrogen adsorption curve of the composite filter membrane prepared in this invention is shown. Figure 4 This is a filtration efficiency diagram of the composite filter membrane in Embodiment 1 of the present invention; Figure 5 This is a graph showing the amount of toxic gas adsorbed by the composite filter membrane in Example 1 of the present invention.

[0023] in, Figure 1 , Figure 2 In Example A, the PI nanofiber film prepared in Example 1 is represented; in Example B, the PI-metal-organic framework compound blend film prepared in Example 2 is represented; and in Example C, the flower-shaped metal-organic framework compound high-temperature resistant composite filter membrane prepared in Example 1 is represented. Detailed Implementation

[0024] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0026] The preparation method of the high-temperature resistant composite filter membrane of the flower-like metal-organic framework compound of the present invention specifically includes the following steps: 1) Prepare the raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), tannic acid, zinc nitrate hexahydrate, and 2-methylimidazole for later use; 2) Add appropriate amounts of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) to N,N'-dimethylformamide (DMF), and heat at 0~8°C. o A low-temperature polycondensation reaction was carried out at C environment for 24 h to obtain a polyamic acid solution with a concentration of 12%-18% and a viscosity of 18-24 Pa·s. A polyamic acid solution was poured into a syringe and electrospun to obtain a polyamic acid nanofiber film. The electrospinning conditions are as follows: 3) The spinning voltage is 16~24kV, the spinning solution flow rate is 0.5~1.5mL / h, and the distance between the needle and the aluminum foil plate receiver is 16~25cm to obtain a polyamic acid nanofiber film; then, the polyamic acid nanofiber film is subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain a polyimide nanofiber film: ①25~150℃, 5~15℃ / min, annealing for 30~60 min; ②~250℃, 10~20℃ / min, annealing for 30~60 min; ③~350℃, 10~30℃ / min, annealing for 60~90 min; 4) The polyimide nanofiber membrane obtained in step 3) is immersed in 10-40 mL of 20-40 mg / mL tannic acid aqueous solution and stirred evenly for 0.5 hours; then 10-40 mL of 10-20 mg / mL zinc chloride aqueous solution is added and stirred for 2-4 hours; finally, 500-2000 mL of 0.05-0.1 mol / L PBS solution is added to adjust the pH to 6.5, so that it is mixed evenly and crosslinked, thereby preparing the MPN-coated fiber film; 5) The MPN-coated polyimide nanofiber film was immersed in 50-100 mL of 25%-30% 2-methylimidazolium aqueous solution for coordination, and the hydrothermal reaction was controlled at 50℃-70℃ for 6-10 h to obtain the first layer of ZIF-8 crystals. 6) Immerse the polyimide film obtained in step 5) in 50-100 mL of a 1-5% (w / w) aqueous solution of zinc nitrate, stir at room temperature for 20-60 min, wash away excess zinc ions, and then impregnate it in 50-100 mL of a 10%-20% (w / w) aqueous solution of 2-methylimidazole for coordination polymerization, controlling the reaction temperature at 50-70°C. o C, the reaction time is 6-10 hours.

[0027] 7) After repeating steps 5)-6) 3-4 times, a high-temperature resistant composite filter membrane loaded with flower-like metal-organic framework compounds is obtained.

[0028] The following detailed description of the preparation method of the high-temperature resistant composite filter membrane of flower-shaped metal-organic framework compound provided by the present invention will be provided through specific embodiments.

[0029] The following embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions can be performed according to experimental manuals or conventional conditions in the art, or by referring to known experimental methods in the art. Unless otherwise specified, all methods are conventional methods in the art.

[0030] In the following specific embodiments, unless otherwise specified, slight deviations may exist within the weighing accuracy range for the measurement parameters of the raw material components. For temperature and time parameters, acceptable deviations due to instrument testing accuracy or operational precision are permissible. The equipment and raw materials used are commercially available or commonly used in the art.

[0031] Example 1 The preparation method of this flower-like metal-organic framework compound high-temperature resistant composite filter membrane is as follows: 1) Prepare raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), tannic acid (TA), zinc nitrate hexahydrate (Zn(NO3)2•6H2O), and 2-methylimidazole; 2) Dissolve 21.60 g ODA and 24.88 g PMDA in 300 mL DMF and carry out a low-temperature polycondensation reaction at 0℃ for 24 h to obtain a polyamic acid solution with a concentration of 16% and a viscosity of 20 Pa·s. Pour the solution into a syringe for electrospinning. Set the electrospinning voltage to 18 kV, the flow rate to 0.8 mL / h, and the distance from the receiving plate to 16 cm to obtain a polyamic acid nanofiber film. 3) The obtained polyamic acid nanofiber film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain a polyimide nanofiber film: ① annealing at 25~150℃, 10℃ / min for 60 min; ② annealing at 150℃~250℃, 10℃ / min for 60 min; ③ annealing at 250℃~350℃, 10℃ / min for 60 min. 4) Impregnate a 5cm × 5cm polyimide nanofiber membrane prepared in the previous step with 10 mL and 40 mg mL of water. -1 Aqueous solution of tannic acid was stirred evenly for 0.5 hours; then 10 mL and 20 mg mL of the solution were added. -1Zinc chloride aqueous solution was stirred for 2 hours; finally, 500 mL of 0.1 mol / L PBS solution was added to adjust the pH to 6.5, so that it was mixed evenly and crosslinked, thereby preparing the MPN-coated fiber film. 5) The MPN-coated polyimide nanofiber film was immersed in 100 mL of 35% 2-methylimidazole aqueous solution for coordination, and the hydrothermal reaction was controlled at 60℃ for 6 hours to obtain the first layer of ZIF-8 crystals. 6) The above polyimide film was immersed in 100 mL of 2% zinc nitrate aqueous solution, stirred at room temperature for 30 min to remove excess zinc ions, and then immersed in 100 mL of 20% 2-methylimidazole aqueous solution for coordination polymerization. The reaction temperature was controlled at 60℃ and the reaction time was 6 hours.

[0032] 7) After repeating steps 5-6 three times, a high-temperature resistant composite filter membrane with a flower-like metal-organic framework compound is obtained.

[0033] Example 2 The preparation method of this flower-like metal-organic framework compound high-temperature resistant composite filter membrane is as follows: 1) Prepare raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), tannic acid (TA), zinc nitrate hexahydrate (Zn(NO3)2•6H2O), and 2-methylimidazole; 2) Dissolve 16.20 g ODA and 18.66 g PMDA in 300 mL DMF and carry out a low-temperature polycondensation reaction at 4 °C for 24 h to obtain a polyamic acid solution with a concentration of 12% and a viscosity of 18 Pa·s. Pour the solution into a syringe for electrospinning. Set the electrospinning voltage to 20 kV, the flow rate to 1.0 mL / h, and the distance from the receiving plate to 16 cm to obtain a polyamic acid nanofiber film. 3) The obtained polyamic acid nanofiber film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain polyimide nanofiber film: ① annealing at 25~150℃, 10℃ / min for 60 min; ② annealing at 250℃, 10℃ / min for 60 min; ③ annealing at 350℃, 10℃ / min for 60 min. 4) Impregnate a 5cm×5cm polyimide nanofiber membrane with 10 mL of 30 mg / mL solution. -1 Aqueous solution of tannic acid was stirred evenly for 0.5 hours; then 10 mL and 15 mg mL of the solution were added. -1Zinc chloride aqueous solution was mixed and stirred for 2 hours; finally, 500 mL of 0.1 mol / L PBS solution was added to adjust the pH, mix it evenly and crosslink it to prepare the MPN-coated fiber film. 5) The MPN-coated polyimide nanofiber film was immersed in 100 mL of 25% 2-methylimidazole aqueous solution for coordination, and the hydrothermal reaction was controlled at 60℃ for 8 hours to obtain the first layer of ZIF-8 crystals. 6) The above polyimide film was immersed in 100 mL of 1% zinc nitrate aqueous solution, stirred at room temperature for 60 min to remove excess zinc ions, and then immersed in 100 mL of 15% 2-methylimidazole aqueous solution for coordination polymerization. The reaction temperature was controlled at 60℃ and the reaction time was 8 hours.

[0034] 7) After repeating steps 5-6 four times, a high-temperature resistant composite filter membrane with a flower-like metal-organic framework compound is obtained.

[0035] Example 3 The preparation method of this flower-like metal-organic framework compound high-temperature resistant composite filter membrane is as follows: 1) Prepare raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), tannic acid (TA), zinc nitrate hexahydrate (Zn(NO3)2•6H2O), and 2-methylimidazole; 2) 18.23 g ODA and 20.99 g PMDA were dissolved in 300 mL DMF and subjected to a low-temperature polycondensation reaction at 2 °C for 24 h to obtain a polyamic acid solution with a concentration of 18% and a viscosity of 24 Pa·s. The solution was then poured into a syringe for electrospinning. The electrospinning voltage was set to 16 kV, the flow rate to 0.6 mL / h, and the distance from the receiving plate to the syringe to 14 cm to obtain a polyamic acid nanofiber film. 3) The obtained film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain a polyimide nanofiber film: ①25~150℃, 5℃ / min, annealing for 30 min; ②~250℃, 5℃ / min, annealing for 60 min; ③~350℃, 5℃ / min, annealing for 60 min. 4) Impregnate a 5cm×5cm polyimide nanofiber membrane with 20 mL of 20 mg / mL solution. -1 Aqueous solution of tannic acid was stirred evenly for 0.5 hours; then 20 mL and 10 mg mL were added. -1Zinc chloride aqueous solution was added and stirred for 2 hours; finally, 960 mL of 0.05 mol / L PBS solution was added to adjust the pH to 6.5, so that it was mixed evenly and crosslinked, thereby preparing the MPN-coated fiber film. 5) The MPN-coated polyimide nanofiber film was immersed in 50 mL of 25% 2-methylimidazole aqueous solution for coordination, and the hydrothermal reaction was controlled at 70℃ for 6 hours to obtain the first layer of ZIF-8 crystals. 6) The above polyimide film was immersed in 50 mL of 3% zinc nitrate aqueous solution, stirred at room temperature for 60 min, and then washed away excess zinc ions. Then it was immersed in 100 mL of 10% 2-methylimidazole aqueous solution for coordination polymerization. The reaction temperature was controlled at 70℃ and the reaction time was 6 hours.

[0036] 7) After repeating steps 5-6 four times, a high-temperature resistant composite filter membrane with a flower-like metal-organic framework compound is obtained.

[0037] Example 4 The preparation method of this flower-like metal-organic framework compound high-temperature resistant composite filter membrane is as follows: 1) Prepare raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), tannic acid (TA), zinc nitrate hexahydrate (Zn(NO3)2•6H2O), and 2-methylimidazole; 2) Dissolve 15.95 g ODA and 16.33 g PMDA in 300 mL DMF, and then... o A low-temperature polycondensation reaction was carried out at C environment for 24 h to obtain a polyamic acid solution with a concentration of 14% and a viscosity of 22 Pa·s. The solution was poured into a syringe for electrospinning. The electrospinning voltage was set to 22 kV, the flow rate was 1.0 mL / h, and the distance from the receiving plate was 16 cm to obtain a polyamic acid nanofiber film. 3) The obtained polyamic acid nanofiber film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain a polyimide nanofiber film: ① annealing at 25~150℃, 5℃ / min for 30 min; ② annealing at 250℃, 5℃ / min for 60 min; ③ annealing at 350℃, 5℃ / min for 60 min. 4) Impregnate a 5cm×5cm polyimide nanofiber membrane with 40 mL of 40 mg / mL solution. -1 Aqueous solution of tannic acid was stirred evenly for 0.5 hours; then 40 mL and 20 mg mL of [unspecified solution] were added. -1Zinc chloride aqueous solution was mixed and stirred for 4 hours; finally, 2000 mL of 0.1 mol / L PBS solution was added to adjust the pH to 6.5, so that it was mixed evenly and crosslinked, thereby preparing the MPN-coated fiber film. 5) The MPN-coated polyimide nanofiber film was immersed in 50 mL of 30% 2-methylimidazole aqueous solution for coordination, and the hydrothermal reaction was controlled at 50℃ for 10 hours to obtain the first layer of ZIF-8 crystals. 6) The above polyimide film was immersed in 50 mL of 5% zinc nitrate aqueous solution, stirred at room temperature for 20 min and then washed away excess zinc ions. Then it was immersed in 50 mL of 10% 2-methylimidazole aqueous solution for coordination polymerization. The reaction temperature was controlled at 50℃ and the reaction time was 10 hours.

[0038] 7) After repeating steps 5-6 four times, a high-temperature resistant composite filter membrane with a flower-like metal-organic framework compound is obtained.

[0039] Comparative Example 1: Preparation of Control Sample - PI Nanofiber Thin Film 1) Prepare the raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and N,N'-dimethylformamide (DMF). 2) Dissolve 21.60 g ODA and 24.88 g PMDA in 300 mL DMF and carry out a low-temperature polycondensation reaction at 0℃ for 24 h to obtain a polyamic acid solution with a concentration of 16% and a viscosity of 20 Pa·s. Pour the solution into a syringe for electrospinning. Set the electrospinning voltage to 18 kV, the flow rate to 0.8 mL / h, and the distance from the receiving plate to 16 cm to obtain a polyamic acid nanofiber film. 3) The obtained polyamic acid nanofiber film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain a polyimide nanofiber film: ①25~150℃, 10℃ / min, annealing for 60 min; ②~200℃, 10℃ / min, annealing for 60 min; ③~300℃, 10℃ / min, annealing for 60 min.

[0040] Comparative Example 2: Preparation of PI-metal-organic framework compound blend films (as a control) 1) Prepare raw materials: pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), N,N'-dimethylformamide (DMF), zinc nitrate hexahydrate, and 2-methylimidazole; 2) Dissolve 21.60 g ODA and 24.88 g PMDA in 300 mL DMF and carry out a low-temperature polycondensation reaction at 0℃ for 24 h to obtain a polyamic acid solution with a concentration of 16% and a viscosity of 20 Pa·s. Pour the solution into a syringe for electrospinning. Set the electrospinning voltage to 18 kV, the flow rate to 0.8 mL / h, and the distance from the receiving plate to 16 cm to obtain a polyamic acid nanofiber film. 3) The obtained polyamic acid nanofiber film was subjected to a staged heating reaction in a high-temperature tube furnace under N2 environment to obtain polyimide nanofiber film: ①25~150℃, 10℃ / min, annealing for 60 min; ②~200℃, 10℃ / min, annealing for 60 min; ③~300℃, 10℃ / min, annealing for 60 min. 4) Preparation of the metal-organic framework compound ZIF-8 via hydrothermal synthesis: 14.71 g of dimethylimidazole was dissolved in 50 g of deionized water, and 0.78 g of zinc nitrate hexahydrate was dissolved in another 10 g of deionized water. The mixture was then stirred to obtain a milky white emulsion. The emulsion was poured into a polytetrafluoroethylene reactor and heated at 60°C. o ZIF-8 crystals were obtained by reacting C in an oil bath environment for 24 h, followed by centrifugation, washing, and drying. 5) A 5cm × 5cm polyimide film and 0.5g ZIF-8 crystals were mixed in 500mL of aqueous solution. After stirring at room temperature for 4 hours, excess crystals were washed away. o After drying, C yields PI-metal-organic framework compound blend films.

[0041] Taking the high-temperature resistant composite filter membrane of flower-shaped metal-organic framework compound prepared in Example 1 as an example, its performance was tested in comparison with the products of Comparative Examples 1 and 2.

[0042] See Figure 1 The images shown are physical images of the composite filter membranes prepared in Example 1 and Comparative Examples 1 and 2. It can be seen that the fiber membranes prepared by the method of this invention have a smooth surface and are more flexible.

[0043] See Figure 2 The figures show SEM images of the composite filter membranes prepared in Example 1 and Comparative Examples 1 and 2. As can be seen from the figures, the PI nanofibers have a smooth surface (…). Figure 2 In section A, simple blending can only allow a small amount of MOF crystals to adhere to the fiber surface. Figure 2 (B) After grafting crystals, a large number of flower-like ZIF-8 crystal clusters appeared on the fiber surface, solving the problem of difficult process preparation of nanofiber films rich in MOF crystals. Figure 2 (C)

[0044] Figure 3The nitrogen adsorption curves of the composite filter membranes prepared in Example 1 and Comparative Examples 1 and 2 are shown. BET calculations show that the specific surface area of ​​the prepared PI fiber film is 10.88 cm². 3 / g, the specific surface area of ​​the blended fiber film is 37.69cm². 3 / g, the specific surface area of ​​the flower-like metal-organic framework compound composite nanofiber film reaches as high as 528.54 cm². 3 / g, approximately 53 times that of the original PI fiber membrane, and the specific surface area is also increased by 14 times compared to simple blending treatment.

[0045] Figure 4 This is a filtration efficiency graph of the composite filter membrane prepared according to the embodiments of the present invention. Regardless of the room temperature of 25°C or the high temperature of 260°C, when the dust particle size is 0.3, 0.5, 1.0, 2.5, 5.0 and 10.0 μm, the filtration efficiency of the flower-shaped metal-organic framework compound composite film prepared by the present invention is above 99.99%.

[0046] Figure 5 This is an adsorption diagram of toxic gases (VOCs) on the composite filter membrane prepared by the present invention. The flower-shaped metal-organic framework compound composite nanofiber filter membrane prepared in the embodiments of the present invention has adsorption capacities of aniline, benzene, and toluene of 467 mg / g, 201 mg / g, and 443 mg / g, respectively, which far exceed the adsorption capacity of PI nanofiber film for VOCs.

[0047] The preparation method of the flower-shaped metal-organic framework compound high-temperature resistant composite filter membrane provided by the present invention has been described in detail above. The specific embodiments described above should not be construed as limiting the scope of protection of the present invention. Any substitutions, improvements, or modifications made to the embodiments of the present invention by those skilled in the art will fall within the scope of protection of the present invention.

[0048] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a high-temperature resistant composite filter membrane of a flower-like metal-organic framework compound, characterized in that, The following steps are included: (1) Preparation of polyimide nanofiber films by electrospinning First, a polycondensation reaction was carried out using diamine and dianhydride to prepare an N,N'-dimethylformamide solution of polyamic acid; Then, an electrospinning process was carried out to obtain a polyamic acid nanofiber film; after a programmed temperature rise process, a polyimide nanofiber film was obtained. (2) Interfacial adhesion of metal ion-polyphenol network The polyimide nanofiber membrane obtained in step (1) was immersed in tannic acid aqueous solution, stirred evenly, added to zinc chloride aqueous solution and stirred, and then PBS solution was added to adjust the pH so that it was mixed evenly and crosslinked to prepare a polyimide nanofiber film wrapped with metal polyphenol network MPN. (3) Preparation of polyimide-grafted ZIF-8 composite film The polyimide nanofiber film coated with zinc ion-polyphenol network obtained in step (2) was immersed in a high concentration of 2-methylimidazole aqueous solution for coordination. The reaction temperature was controlled at 50℃-70℃ and the time was 6-10h to obtain the first layer of ZIF-8 crystal. (4) The polyimide nanofiber film obtained in step (3) is immersed in an aqueous solution of zinc nitrate, stirred at room temperature to wash away excess zinc ions, and then immersed in a low-concentration aqueous solution of 2-methylimidazole for coordination polymerization. (5) Repeat steps (3)-(4) multiple times to obtain ZIF-8 polyimide composite nanofiber filter membrane loaded in a flower-like form.

2. The preparation method according to claim 1, characterized in that, In step (1), the dianhydride is pyromellitic dianhydride PMDA, and the diamine is N,N'-dimethylformamide DMF; the polycondensation reaction is carried out at a low temperature of 0~8℃ for 24h; the concentration of the N,N'-dimethylformamide solution of the obtained polyamic acid is 12%-18%, and the solution viscosity is 18~24 Pa·s.

3. The preparation method according to claim 2, characterized in that, The specific preparation steps of N,N'-dimethylformamide solution of polyamic acid are as follows: Add appropriate amounts of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) to N,N'-dimethylformamide (DMF) and carry out a low-temperature polycondensation reaction at 0~8℃ for 24 h.

4. The preparation method according to claim 1, characterized in that, In step (1), the conditions for the electrospinning process are as follows: A polyamic acid N,N'-dimethylformamide solution was added to a syringe. The spinning voltage was 16~24kV, the spinning solution flow rate was 0.5~1.5mL / h, and the distance between the needle and the aluminum foil plate receiver was 16~25cm to obtain a polyamic acid fiber film. Then, a subsequent heating process was carried out to complete the imidization reaction to obtain a polyimide nanofiber film. The programmed heating was carried out as follows: ①25~150℃, 5~15℃ / min, annealing for 30~60 min; ②150℃~250℃, 10~20℃ / min, annealing for 30~60 min; ③250℃~350℃, 10~30℃ / min, annealing for 60~90 min.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the tannic acid aqueous solution is 20-40 mg / mL, and the amount added is 10-40 mL; the concentration of the zinc chloride aqueous solution is 10-20 mg / mL, and the amount added is 10-40 mL; the concentration of the PBS solution is 0.05-0.1 mol / L, and the amount added is 500-2000 mL.

6. The preparation method according to claim 1, characterized in that, In step (3), the high-concentration 2-methylimidazole aqueous solution refers to a 2-methylimidazole solution with a mass concentration range of 25-35%, and its dosage is 50-100 mL; in step (4), the low-concentration 2-methylimidazole aqueous solution refers to a 2-methylimidazole solution with a mass concentration range of 10-20%, and its dosage is 50-100 mL.

7. The preparation method according to claim 1, characterized in that, In step (4), the mass concentration of zinc nitrate aqueous solution is 1-5%, and the amount added is 50-100 mL; the stirring time at room temperature is 20-60 min; the reaction temperature of coordination polymerization is controlled at 50-70℃, and the reaction time is 6-10 hours.

8. The preparation method according to claim 1, characterized in that, In step (5), repeat steps (3)-(4) 3-4 times.

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