Preparation method and application of MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane

Abstract

The invention discloses a preparation method and application of an MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane, and the preparation method comprises the following steps: calcining a dual-scale three-dimensional network PAA fiber membrane in an inert atmosphere to obtain a dual-scale three-dimensional network PI fiber membrane; dipping the dual-scale three-dimensional network PI fiber membrane in a mixed solution of zinc salt, an organic ligand and a solvent B, enabling MOFs to grow on the fiber membrane in situ, and drying to prepare the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane. The MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane is used as a filtering layer and is applied to preparation of the MOFs-based dual-scale nano-network radioactive iodine aerosol protection mask, and the MOFs-based dual-scale nano-network radioactive iodine aerosol protection mask has the characteristics of good stability, high iodine gas adsorption capacity, excellent filtering efficiency and good air permeability. The method has potential application prospects in the aspects of radioactive iodine gas adsorption and purification, radioactive aerosol protection and the like in the fields of nuclear industry and nuclear accident emergency.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyimide nanofiber membrane filtration materials in nanofiltration fiber membranes, and more specifically, the present invention relates to a preparation method and application of a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane. Background Art

[0002] A large amount of radioactive aerosols will be generated during nuclear energy development and nuclear accident emergency response. They are mainly composed of some fission products and suspended solid dust, with a particle size distribution of 0.3μm to 10μm. They contain a variety of radioactive nuclides, such as 137 Cs, 3 H. 90 Sr. 14 C. 129 I. 131 I. 133 Xe, etc. Among them, 131 I and 129 I has a higher yield, especially 129 I, which has a long half-life (T 1 / 2 =1.6×10 7 a) Thyroid targeted toxicity, high mobility and easy bioaccumulation pose a potential radiation threat to workers and the environment. In a nuclear accident, radioactive iodine is mainly released into the atmosphere in the form of aerosols, and a small amount is released in the form of gas. Conventional protection measures are difficult to deal with this type of multiphase pollution.

[0003] At present, the methods for enriching and removing radioactive iodine and aerosols from radioactive waste gas are mainly divided into wet scrubbing and dry adsorption. Wet scrubbing, such as the Iodox process, Mercurex process and alkaline solution scrubbing, has problems such as complex process system, strong equipment corrosion, high operating cost, and is prone to produce secondary waste liquid containing radioactive nuclides, which poses environmental risks. However, mainstream dry adsorption materials face dual technical bottlenecks: (1) Powder materials such as activated carbon and silver-based zeolite have limited iodine adsorption capacity (<500 mg / g) and cannot intercept submicron aerosols; (2) Although HEPA filters can intercept 0.3μm particles (efficiency ≥99.97%), they lack radioactive iodine adsorption performance, resulting in the risk of radioactive iodine gas penetration. Therefore, in nuclear emergency situations, it is of great significance to develop a fast and simple radioactive iodine aerosol protective mask.

[0004] In recent years, researchers have revealed that metal-organic frameworks (MOFs) have high specific surface areas (>2000m 2 / g), the designed pore structures and functional sites (such as amino and thiol groups) exhibit excellent performance in radioactive iodine adsorption (the iodine adsorption capacity of ZIF-8 reaches 1.25 g / g, and that of UiO-66-FA reaches 2.25 g / g). Meanwhile, electrospun fiber membranes have become one of the most promising air filtration membranes due to their advantages such as simple process, controllable fiber diameter (50 - 500 nm), and high porosity (more than 80%). Currently, electrospinning technology has been successfully applied to the preparation of various polymer fiber membranes, such as polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polyimide (PI), etc.

[0005] In addition, currently, commercially available conventional protective masks have limited filtration efficiency when filtering aerosol particles with a particle size of 0.3 μm and above, and cannot adsorb radioactive iodine gas simultaneously. This technical defect makes it difficult for conventional protective masks to effectively block the diffusion of radioactive iodine-containing aerosols under complex operating conditions or accident scenarios in nuclear power plants, posing a potential risk to the health and safety of workers. Summary of the Invention

[0006] An object of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0007] To achieve these objects and other advantages of the present invention, a preparation method of a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane is provided, including the following steps:

[0008] Step 1: Calcinate the dual-scale three-dimensional network PAA fiber membrane in an inert atmosphere to achieve a thermal imidization reaction, obtaining a dual-scale three-dimensional network PI fiber membrane;

[0009] Step 2: Immerse the dual-scale three-dimensional network PI fiber membrane in a mixed solution of zinc salt, organic ligand, and solvent B, and enable the in-situ growth of MOFs on the fiber membrane through a self-assembly method, and then place it in an oven for drying to prepare a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane.

[0010] Preferably, in Step 1, the preparation method of the dual-scale three-dimensional network PAA fiber membrane includes:

[0011] S11: Weigh 4,4'-diaminodiphenyl ether, dodecyltrimethylammonium bromide, and pyromellitic dianhydride and dissolve them in organic solvent A, and stir to dissolve to form a precursor spinning solution;

[0012] S12: Perform electrospinning on the precursor spinning solution to obtain a dual-scale three-dimensional network PAA fiber membrane.

[0013] Preferably, in S11, the organic solvent A is any one of N,N-dimethylformamide, ethanol, tetrahydrofuran, N,N-dimethylacetamide, acetone, and ether.

[0014] Preferably, in S11, the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1-5:1-5; the total concentration of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in the organic solvent A is 10%-20%; the concentration of dodecyltrimethylammonium bromide in the organic solvent A is 0-5%; the stirring and dissolving temperature is 0-10°C; the environmental humidity is 30-100%; the stirring time is 1-24 h.

[0015] Preferably, in S12, the parameters of electrospinning are: spinning voltage: 5-25 kV; the needle is an 18-30 gauge stainless steel needle; the electrode distance is 5-20 cm; the injection pump propulsion rate is 0.3-1.5 mL / h; the environmental temperature is 5-40°C; the environmental humidity is 30-100%.

[0016] Preferably, in the first step, the inert atmosphere includes one of nitrogen, argon, and helium; the thermal imidization calcination temperature is 250-550°C, the heating rate is 1-10°C / min, and the holding time is 0.5-4 h.

[0017] Preferably, in the second step, the solvent B includes one or a mixture of methanol, deionized water, ethanol, and N,N-dimethylformamide; the zinc salt includes any one or a mixture of zinc nitrate hexahydrate, zinc chloride, zinc sulfate, zinc acetate, and zinc citrate; the organic ligand includes any one of imidazole and 2-methylimidazole; the impregnation time is 1-48 h; the drying temperature is 30-80°C, and the drying time is 1-10 h; the molar ratio of the zinc salt to the organic ligand is 1:8, and the dosage ratio of the organic ligand to the solvent B is 0.04 mol of the organic ligand dissolved in every 100 mL of the solvent B.

[0018] An application of a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane, which is applied to the preparation of a MOFs-based dual-scale nanonetwork radioactive iodine aerosol protective mask. The specific method includes: selecting a non-woven fabric with good air permeability as the outer layer and the inner layer of the MOFs-based dual-scale nanonetwork radioactive iodine aerosol protective mask, using the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane as the filter layer of the MOFs-based dual-scale nanonetwork radioactive iodine aerosol protective mask, placing it in the middle of the outer layer and the inner layer, and obtaining the MOFs-based dual-scale nanonetwork radioactive iodine aerosol protective mask through a composite process.

[0019] Preferably, the composite process includes hot pressing, sewing, and adhesion.

[0020] Preferably, the MOFs-based dual-scale nanofiber network radioactive iodine aerosol protection mask is used for capturing and filtering radioactive iodine aerosol.

[0021] In order to improve the adsorption capacity of the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane for iodine and increase the saturated adsorption capacity for iodine gas, after obtaining the dual-scale three-dimensional network PI fiber membrane in Step 1, the dual-scale three-dimensional network PI fiber membrane is impregnated in a polyethyleneimine solution, 2-chloro-1-methylpyridinium iodide is added as an activator, heated to 50-80 °C, the impregnation time is 5-12 h, and after impregnation, it is dried to obtain a graft-modified dual-scale three-dimensional network PI fiber membrane. The mass fraction of the polyethyleneimine solution is 30-50 wt%, the molecular weight of polyethyleneimine is 3500-12000 g / mol, and 2-chloro-1-methylpyridinium iodide accounts for 1-4 wt% of the polyethyleneimine solution.

[0022] Meanwhile, in Step 2, bismuth nitrate pentahydrate is added to the mixed solution, and the molar ratio of bismuth nitrate pentahydrate to the zinc salt is 1:1.

[0023] The present invention has at least the following beneficial effects:

[0024] (1) The present invention reports the preparation methods of three types of masks, which are respectively applied to daily PM 2.5 protection, industrial PM 0.3 high-performance protection, and radioactive iodine aerosol protection in nuclear emergency situations.

[0025] (2) For the MOFs-based dual-scale nanofiber network radioactive iodine aerosol protection mask of the present invention, the core filter material, the dual-scale three-dimensional network nanofiber membrane, can achieve controllable adjustment of fiber diameter and pore size through the electrospinning process, enabling the mask to have excellent air permeability and ideal PM 0.3 filtration performance.

[0026] (3) For the MOFs-based dual-scale nanofiber network radioactive iodine aerosol protection mask of the present invention, compared with conventional masks, the filter layer material is a MOFs-based dual-scale three-dimensional network nanofiber membrane material, achieving a high adsorption capacity for radioactive iodine gas, and having significant application potential in the field of radioactive iodine gas protection in nuclear fuel reprocessing.

[0027] (4) For the MOFs-based dual-scale nanofiber network radioactive iodine aerosol protection mask of the present invention, compared with conventional masks, it has good hydrophobic properties and thermal stability, can be used normally at high temperatures, and has good application prospects in nuclear emergency situations.

[0028] (5) The MOFs-based dual-scale nano-network radioactive iodine aerosol protective mask of the present invention has excellent antibacterial properties compared with conventional masks, providing a strong guarantee for the health of protective personnel.

[0029] The present invention uses a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane as a filter layer when preparing a MOFs-based dual-scale nano-network radioactive iodine aerosol protective mask. In the preparation process of the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane, polyethyleneimine grafting modification and bismuth incorporation are used to further enhance the adsorption capacity of the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane for elemental iodine, thereby improving the saturated adsorption capacity for elemental iodine gas.

[0030] In summary, the present invention combines the advantages of electrospinning technology with MOFs through the "adsorption-filtration" synergistic mechanism of MOFs-based dual-scale nanofiber membranes, and has high iodine capacity, high filtration efficiency and environmental stability, providing nuclear power plant personnel with an efficient and lightweight integrated protection solution, significantly reducing the hazards of radioactive exposure.

[0031] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The SEM image and fiber diameter distribution diagram of the nano three-dimensional network PAA fiber membrane prepared in Comparative Example 1;

[0033] Figure 2 The SEM image and fiber diameter distribution diagram of the nano three-dimensional network PI fiber membrane prepared in Comparative Example 1;

[0034] Figure 3 The SEM image and fiber diameter distribution diagram of the PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Comparative Example 2;

[0035] Figure 4 This is a SEM image of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1;

[0036] Figure 5 Optical images of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 and the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane mask made in the laboratory;

[0037] Figure 6 XRD diagrams of three-dimensional network nanofiber membrane materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0038] Figure 7 FTIR infrared spectra of the three-dimensional network nanofiber membrane materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0039] Figure 8 XPS images of the three-dimensional network nanofiber membrane materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0040] Figure 9 Schematic diagram of the iodine gas purification performance of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1;

[0041] Figure 10 Schematic diagram of the purification ability of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 for flue gas aerosol;

[0042] Figure 11 Filtration efficiency of the nano three-dimensional network PI fiber membrane in Comparative Example 1 for simulated radioactive aerosols of different particle sizes;

[0043] Figure 12 Filtration efficiency of the PI / DTAB dual-scale three-dimensional network nanofiber membrane in Comparative Example 2 for simulated radioactive aerosols of different particle sizes;

[0044] Figure 13 Filtration efficiency of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane in Example 1 for simulated radioactive aerosols of different particle sizes;

[0045] Figure 14 Pressure drop change diagrams of the nano three-dimensional network PI fiber membrane, PI / DTAB dual-scale three-dimensional network nanofiber membrane, and ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane;

[0046] Figure 15 Schematic diagram of the iodine gas adsorption and purification performance of the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask prepared in Example 1;

[0047] Figure 16 Adsorption curve of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 for iodine gas;

[0048] Figure 17 Isothermal adsorption curve of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 for iodine gas;

[0049] Figure 18 Performance change diagram of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 after high-temperature and water treatment. Detailed implementation mode

[0050] The following further describes the present invention in detail with reference to the accompanying drawings, so that those skilled in the art can implement it according to the text of the specification.

[0051] It should be understood that terms such as "having", "including", and "comprising" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0052] The raw materials used in the following examples, 4,4'-diaminodiphenyl ether (ODA), dodecyltrimethylammonium bromide (DTAB), pyromellitic dianhydride (PMDA), and N,N-dimethylformamide (DMF), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 2-methylimidazole, and methanol were all purchased from Aladdin Chemical Co., Ltd. and used directly without further purification.

[0053] Example 1:

[0054] A ZIF-8@PI / DTAB dual-scale nanofiber membrane mask includes the following steps:

[0055] Step 1. Preparation of PAA / DTAB solution: Weigh 0.233 g of DTAB, 1.0113 g of ODA, and 1.146 g of PMDA using an electronic balance and add them to 5 mL of DMF solution respectively. Stir the DMF solution dissolved with ODA and DTAB evenly in an ice bath. After ODA / DTAB is completely dissolved, then quickly add the PMDA suspension to the ODA / DTAB solution. Place the mixed solution in a 0 °C water bath environment and stir for 5 h to obtain a light yellow viscous PAA / DTAB electrospinning solution with a concentration of 18 wt%.

[0056] Step 2. Preparation of PAA / DTAB fiber membrane: Perform electrospinning. Put the PAA / DTAB electrospinning solution into a plastic syringe and place the syringe in an injection pump. Use a 25-gauge metal needle during the electrospinning process, keep the speed at 0.5 mL / h, and set the voltage to 11 kV. Use a metal roller receiver wrapped with aluminum foil paper and set the rotation speed to 150 r / min for rotation. After electrospinning for 5 h, take out the aluminum foil paper loaded with the PAA / DTAB fiber membrane and set it aside for use.

[0057] Step 3. Preparation of PI / DTAB dual-scale nanofiber membrane: Place the prepared PAA / DTAB fiber membrane in a tubular furnace under a nitrogen atmosphere and complete the imidization process by heating in three stages, and naturally cool to obtain the PI / DTAB dual-scale nanofiber membrane:

[0058] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min and anneal for 30 min to remove residual solvents.

[0059] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min, and dehydrate and cyclize the hydroxyl groups.

[0060] ③ Heat from 250 °C to 350 °C at a heating rate of 10 °C / min, anneal for 60 min, and complete imidization.

[0061] Step 4: Preparation of ZIF-8@PI / DTAB double-scale nanofiber membrane: Weigh 1.487 g of Zn(NO3)2·6H2O with an electronic balance and add it to 50 mL of methanol. After the zinc salt is completely dissolved, put 40 mg of the PI / DTAB double-scale nanofiber membrane into the above solution and impregnate for 12 h. Then dissolve 3.284 g of 2-methylimidazole in 50 mL of methanol and pour it into the above impregnation solution and impregnate for another 12 h to complete the in-situ growth of self-assembly of ZIF-8. Finally, wash it 3 times with methanol and ethanol respectively, remove the unreacted impurities, and dry it in an oven at 60 °C for 1 h to obtain the ZIF-8@PI / DTAB double-scale nanofiber membrane.

[0062] Step 5: Production of ZIF-8@PI / DTAB double-scale nanofiber membrane mask: Select a fiber material with good air permeability as the outer and inner layer materials of the mask filter. Place the outer layer, ZIF-8@PI / DTAB double-scale nanofiber membrane, and inner layer materials together in sequence and obtain the mask filter through roll pressing and compounding. According to the mask design requirements, cut the mask filter into different shapes and sizes, and enter the mask production line to obtain the ZIF-8@PI / DTAB double-scale nanofiber membrane mask for nuclear emergency radioactive iodine aerosol protection.

[0063] Example 2

[0064] A ZIF-8@PI / DTAB double-scale nanofiber membrane mask, comprising the following steps:

[0065] Step 1: Preparation of PAA / DTAB solution: Weigh 0.233 g of DTAB, 1.0113 g of ODA, and 1.146 g of PMDA with an electronic balance and add them to 5 mL of DMF solution respectively. Stir the DMF solution dissolved with ODA and DTAB evenly in an ice bath. After ODA / DTAB is completely dissolved, quickly add the PMDA suspension to the ODA / DTAB solution, place the mixed solution in a 0 °C water bath environment, and stir for 5 h to obtain a light yellow viscous PAA / DTAB electrospinning solution with a concentration of 18 wt%.

[0066] Step 2: Preparation of PAA / DTAB fiber membrane: Electrospinning was carried out. The PAA / DTAB electrospinning solution was placed in a plastic syringe, and the syringe was placed in an injection pump. During the electrospinning process, a 25-gauge metal needle was used, the speed was maintained at 0.5 mL / h, and the voltage was set at 11 kV. A metal roller receiver wrapped with aluminum foil was used, and the rotation speed was set at 150 r / min. After electrospinning for 5 h, the aluminum foil loaded with the PAA / DTAB fiber membrane was taken out and reserved for use.

[0067] Step 3: Preparation of PI / DTAB fiber membrane: The obtained PAA / DTAB fiber membrane was placed in a tube furnace under a nitrogen atmosphere, and the imidization process was completed by heating in three stages. After natural cooling, a PI / DTAB dual-scale nanofiber membrane was obtained:

[0068] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min, anneal for 30 min to remove residual solvents.

[0069] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min for the dehydration cyclization of hydroxyl groups.

[0070] ③ Heat from 250 °C to 350 °C at a heating rate of 10 °C / min, anneal for 60 min to complete imidization;

[0071] 40 mg of the PI / DTAB dual-scale nanofiber membrane was immersed in 100 mL of a polyethyleneimine solution with a mass fraction of 30 wt%. The molecular weight of polyethyleneimine was 6000 g / mol, and 2-chloro-1-methylpyridinium iodide accounting for 2 wt% of the polyethyleneimine solution was added as an activator. It was heated to 60 °C, and the immersion time was 12 h. After immersion, it was dried at 60 °C to obtain a graft-modified PI / DTAB dual-scale nanofiber membrane.

[0072] Step 4: Preparation of ZIF-8@PI / DTAB dual-scale nanofiber membrane: Weighed 1.487 g of Zn(NO3)2·6H2O and 2.425 g of Bi(NO3)3·5H2O with an electronic balance and added them to 50 mL of methanol. After the zinc salt and bismuth salt were completely dissolved, 40 mg of the graft-modified PI / DTAB dual-scale nanofiber membrane was placed in the above solution and immersed for 12 h. Then, 3.284 g of 2-methylimidazole was dissolved in 50 mL of methanol and poured into the above immersion solution and immersed for another 12 h to complete the in-situ growth of the self-assembly of ZIF-8. Finally, it was washed 3 times with methanol and ethanol respectively, and after removing unreacted impurities, it was dried in an oven at 60 °C for 1 h to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane.

[0073] Step 5: Production of ZIF-8@PI / DTAB dual-scale nanofiber membrane mask: Select non-woven fabric with good air permeability as the outer and inner layer materials of the mask filter. Place the outer layer, ZIF-8@PI / DTAB dual-scale nanofiber membrane, and inner layer materials together in sequence, and obtain the mask filter through roll pressing and compounding. According to the mask design requirements, cut the mask filter into different shapes and sizes, and feed it into the mask production line to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask for nuclear emergency radioactive iodine aerosol protection.

[0074] Comparative Example 1:

[0075] A preparation method of a nano three-dimensional network PI fiber membrane includes the following steps:

[0076] Step 1: Preparation of PAA solution: Weigh 1.0113 g of ODA and 1.146 g of PMDA using an electronic balance and add them to 5 mL of DMF solvent respectively. Place the two in an ice bath and stir evenly. After the ODA is completely dissolved, quickly add the PMDA suspension to the ODA solution, place the mixed solution in a 0 °C water bath environment, and stir for 5 h to obtain a light yellow viscous PAA electrospinning solution with a concentration of 18 wt%.

[0077] Step 2: Preparation of nano three-dimensional network PAA fiber membrane: Conduct electrospinning. Put the PAA electrospinning solution into a plastic syringe, and place the syringe in an injection pump. Use an 18-gauge metal needle during the electrospinning process, keep the speed at 0.5 mL / h, and set the voltage to 18 kV. Use a metal roller receiver wrapped with aluminum foil paper and set the rotation speed to 150 r / min for rotation. After electrospinning for 2 h, remove the aluminum foil paper of the nano three-dimensional network PAA fiber membrane for standby.

[0078] Step 3: Preparation of nano three-dimensional network PI fiber membrane: Place the obtained nano three-dimensional network PAA fiber membrane in a tube furnace under a nitrogen atmosphere, and complete the imidization process by heating in three stages. Naturally cool to obtain a dual-scale three-dimensional network PI fiber membrane. The three-stage heating is specifically as follows:

[0079] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min, anneal for 30 min to remove residual solvents.

[0080] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min, and dehydrate and cyclize the hydroxyl groups.

[0081] ③ Heat from 250 °C to 350 °C at a heating rate of 10 °C / min, anneal for 60 min to complete imidization.

[0082] Step 4. Production of nano three-dimensional network PI fiber membrane mask: Select non-woven fabric with good air permeability as the outer and inner layer materials of the mask filter, use the nano three-dimensional network PI fiber membrane as the mask filter layer, place the three materials of the outer layer, nano three-dimensional network PI fiber membrane, and inner layer together in sequence, and obtain the mask filter through roll pressing and compounding; according to the mask design requirements, cut the mask filter into different shapes and sizes, and enter the mask production line to obtain the nano three-dimensional network PI fiber membrane for daily protection. 2.5 The nano three-dimensional network PI fiber membrane for daily protection.

[0083] Comparative Example 2:

[0084] A preparation method of a PI / DTAB dual-scale nanofiber membrane mask, comprising the following steps:

[0085] Step 1. Preparation of PAA / DTAB solution: Weigh 0.233 g of DTAB, 1.0113 g of ODA, and 1.146 g of PMDA using an electronic balance and add them to 5 mL of DMF solution respectively. Place the DMF solution dissolved with ODA / DTAB in an ice bath and stir evenly. After ODA / DTAB is completely dissolved, quickly add the PMDA suspension to the ODA / DTAB solution, place the mixed solution in a 0 °C water bath environment, and stir for 5 h to obtain a light yellow viscous PAA / DTAB electrospinning solution with a concentration of 18 wt%.

[0086] Step 2. Preparation of PAA / DTAB fiber membrane: Perform electrospinning. Put the PAA / DTAB electrospinning solution into a plastic syringe, and place the syringe in an injection pump. Use a 25-gauge metal needle during the electrospinning process, keep the speed at 0.5 mL / h, and set the voltage to 18 kV. Use a metal roller receiver wrapped with aluminum foil paper and set the rotation speed to 150 r / min for rotation. After electrospinning for 2 h, take out the aluminum foil paper loaded with the PAA / DTAB fiber membrane and set it aside for later use.

[0087] Step 3. Preparation of PI / DTAB dual-scale nanofiber membrane: Place the obtained PAA / DTAB fiber membrane in a tube furnace under a nitrogen atmosphere, complete the imidization process by heating in three stages, and naturally cool to obtain the PI / DTAB dual-scale nanofiber membrane:

[0088] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min, anneal for 30 min to remove residual solvents.

[0089] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min for hydroxyl dehydration cyclization.

[0090] ③ Heat from 250 °C to 350 °C at a heating rate of 10 °C / min, anneal for 60 min to complete imidization.

[0091] Step 4. Production of PI / DTAB dual-scale nanofiber membrane mask: Select non-woven fabric with good air permeability as the outer and inner layer materials of the mask filter. Place the outer layer, PI / DTAB dual-scale nanofiber membrane, and inner layer materials together in sequence and obtain the mask filter through roll lamination. According to the mask design requirements, cut the mask filter into different shapes and sizes, and feed it into the mask production line to obtain the industrial PM 0.3 protected PI / DTAB dual-scale nanofiber membrane mask.

[0092] Comparative Example 3

[0093] A ZIF-8@PI / DTAB dual-scale nanofiber membrane mask, comprising the following steps:

[0094] Step 1. Preparation of PAA / DTAB solution: Weigh 0.233 g of DTAB, 1.0113 g of ODA, and 1.146 g of PMDA using an electronic balance and add them to 5 mL of DMF solution respectively. Stir the DMF solution dissolved with ODA and DTAB evenly in an ice bath. After ODA / DTAB is completely dissolved, quickly add the PMDA suspension to the ODA / DTAB solution, and place the mixed solution in a 0 °C water bath environment and stir for 5 h to obtain a light yellow viscous PAA / DTAB electrospinning solution with a concentration of 18 wt%.

[0095] Step 2. Preparation of PAA / DTAB fiber membrane: Conduct electrospinning. Put the PAA / DTAB electrospinning solution into a plastic syringe, and place the syringe in an injection pump. Use a 25-gauge metal needle during the electrospinning process, keep the speed at 0.5 mL / h, and set the voltage to 11 kV. Use a metal roller receiver wrapped with aluminum foil paper and set the rotation speed to 150 r / min for rotation. After electrospinning for 5 h, take out the aluminum foil paper loaded with the PAA / DTAB fiber membrane for standby.

[0096] Step 3. Preparation of PI / DTAB fiber membrane: Place the obtained PAA / DTAB fiber membrane in a tube furnace under a nitrogen atmosphere and complete the imidization process by heating in three stages, and naturally cool down to obtain the PI / DTAB dual-scale nanofiber membrane:

[0097] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min, anneal for 30 min to remove residual solvents.

[0098] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min, and dehydrate and cyclize the hydroxyl groups.

[0099] ③Heat from 250 °C to 350 °C at a heating rate of 10 °C / min and anneal for 60 min to complete imidization;

[0100] Immerse 40 mg of the PI / DTAB dual-scale nanofiber membrane in 100 mL of a polyethyleneimine solution with a mass fraction of 30 wt%. The molecular weight of polyethyleneimine is 6000 g / mol. Add 2-chloro-1-methylpyridinium iodide accounting for 2 wt% of the polyethyleneimine solution as an activator, heat to 60 °C, and the immersion time is 12 h. After immersion, dry at 60 °C to obtain the graft-modified PI / DTAB dual-scale nanofiber membrane.

[0101] Step 4: Preparation of ZIF-8@PI / DTAB dual-scale nanofiber membrane: Weigh 1.487 g of Zn(NO3)2·6H2O with an electronic balance and add it to 50 mL of methanol. After the zinc salt is completely dissolved, put 40 mg of the graft-modified PI / DTAB dual-scale nanofiber membrane into the above solution and immerse for 12 h. Then dissolve 3.284 g of 2-methylimidazole in 50 mL of methanol and pour it into the above immersion solution and immerse for another 12 h to complete the in-situ growth of ZIF-8 self-assembly. Finally, wash 3 times with methanol and ethanol respectively, remove unreacted impurities, and dry in an oven at 60 °C for 1 h to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane.

[0102] Step 5: Production of ZIF-8@PI / DTAB dual-scale nanofiber membrane mask: Select non-woven fabric with good air permeability as the outer and inner layer materials of the mask filter. Place the outer layer, ZIF-8@PI / DTAB dual-scale nanofiber membrane, and inner layer materials together in sequence and obtain the mask filter through roll pressing and compounding. According to the mask design requirements, cut the mask filter into different shapes and sizes and enter the mask production line to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask for nuclear emergency radioactive iodine aerosol protection.

[0103] Comparative Example 4

[0104] A ZIF-8@PI / DTAB dual-scale nanofiber membrane mask, comprising the following steps:

[0105] Step 1: Preparation of PAA / DTAB solution: Weigh 0.233 g of DTAB, 1.0113 g of ODA, and 1.146 g of PMDA with an electronic balance and add them to 5 mL of DMF solution respectively. Stir the DMF solution dissolved with ODA and DTAB evenly in an ice bath. After ODA / DTAB is completely dissolved, quickly add the PMDA suspension to the ODA / DTAB solution, place the mixed solution in a 0 °C water bath environment, and stir for 5 h to obtain a light yellow viscous PAA / DTAB electrospinning solution with a concentration of 18 wt%.

[0106] Step 2: Preparation of PAA / DTAB fiber membrane: Electrospinning is carried out. The PAA / DTAB electrospinning solution is put into a plastic syringe, and the syringe is placed in an injection pump. During the electrospinning process, a 25-gauge metal needle is used, the speed is maintained at 0.5 mL / h, and the voltage is set at 11 kV. A metal roller receiver wrapped with aluminum foil paper is used, and the rotation speed is set to rotate at 150 r / min. After electrospinning for 5 h, the aluminum foil paper loaded with the PAA / DTAB fiber membrane is taken out for standby.

[0107] Step 3: Preparation of PI / DTAB fiber membrane: The obtained PAA / DTAB fiber membrane is placed in a tube furnace under a nitrogen atmosphere, and the imidization process is completed by heating in three stages, and then naturally cooled to obtain a PI / DTAB dual-scale nanofiber membrane:

[0108] ① Heat from 25 °C to 150 °C at a heating rate of 5 °C / min, anneal for 30 min to remove residual solvents.

[0109] ② Heat from 150 °C to 250 °C at a heating rate of 5 °C / min, anneal for 30 min, and dehydrate and cyclize the hydroxyl groups.

[0110] ③ Heat from 250 °C to 350 °C at a heating rate of 10 °C / min, anneal for 60 min to complete imidization.

[0111] Step 4: Preparation of ZIF-8@PI / DTAB dual-scale nanofiber membrane: Weigh 1.487 g of Zn(NO3)2·6H2O and 2.425 g of Bi(NO3)3·5H2O with an electronic balance and add them to 50 mL of methanol. After the zinc salt and bismuth salt are completely dissolved, put 40 mg of the PI / DTAB dual-scale nanofiber membrane into the above solution and impregnate for 12 h. Then dissolve 3.284 g of 2-methylimidazole in 50 mL of methanol and pour it into the above impregnation solution and impregnate for another 12 h to complete the in-situ growth of the self-assembly of ZIF-8. Finally, wash it 3 times with methanol and ethanol respectively, remove the unreacted impurities, and dry it in an oven at 60 °C for 1 h to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane.

[0112] Step 5: Production of ZIF-8@PI / DTAB dual-scale nanofiber membrane mask: Select non-woven fabric with good air permeability as the outer and inner layer materials of the mask filter. Put the outer layer, ZIF-8@PI / DTAB dual-scale nanofiber membrane, and inner layer together in sequence, and obtain the mask filter through roll lamination; According to the mask design requirements, cut the mask filter into different shapes and sizes, and enter the mask production line to obtain the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask for nuclear emergency radioactive iodine aerosol protection.

[0113] SEM, XRD, FTIR infrared, and XPS characterizations were carried out on the three-dimensional network nanofiber membrane materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Figures 1-4 Respectively show the microscopic morphological characteristics of PAA (prepared in Step 2 of Comparative Example 1), PI (prepared in Step 4 of Comparative Example 1), PI / DTAB (prepared in Step 4 of Comparative Example 2), and ZIF-8@PI / DTAB (prepared in Example 1) fiber membranes. In Comparative Example 1, the original PAA and PI fibers were regular cylindrical shapes (as Figure 1 and Figure 2 shown), with smooth surfaces, and the fiber diameters were normally distributed, with the fiber diameters being about 238 nm and 193 nm respectively. After introducing DTAB (as Figure 3 shown), the fiber diameter decreased significantly, being about 111 nm. More importantly, finer secondary fiber networks (with a diameter of 37 nm) formed on the fiber surface, forming a dual-scale three-dimensional nanofiber network structure, and the fiber arrangement became denser, the pore size decreased, which was more conducive to improving the aerosol interception efficiency. In the ZIF-8@PI / DTAB fibers (as Figure 4 shown), ZIF-8 crystals grew uniformly on the fiber surface in a typical rhombic dodecahedron morphology (with a size of about 32 nm). While maintaining the integrity of the fiber structure, it significantly improved the accessibility of MOFs active sites, providing a structural guarantee for the efficient chemical adsorption of radioactive iodine, and further reducing the pore size of the fibers, which was more conducive to improving the filtration efficiency of aerosols.

[0114] Figure 5 Show the optical pictures of the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane prepared in Example 1 and the ZIF-8@PI / DTAB dual-scale three-dimensional network nanofiber membrane mask made in the laboratory. It can be seen that the fiber membrane has excellent mechanical properties and can be fully used for the production of masks.

[0115] Figure 6 Show the XRD test images of the PI fiber membrane, PI / DTAB, and ZIF-8@PI / DTAB dual-scale nanofiber membranes. The PI fiber membrane and the PI / DTAB dual-scale nanofiber membrane show amorphous phase images. In the XRD spectrum of the ZIF-8@PI / DTAB dual-scale nanofiber membrane, characteristic peaks of ZIF-8 nanocrystals were observed at 7.3, 10.4, 12.7, 14.7, 16.7, 18.0, and 26.7, corresponding to the strong diffraction peaks of the (011), (002), (112), (022), (013), (222), and (134) crystal planes of ZIF-8, which were consistent with the standard spectrum of ZIF-8, proving that ZIF-8 was successfully self-assembled and in-situ grown in the PI / DTAB dual-scale nanofiber membrane.

[0116] The chemical bond structure of the sample obtained by FTIR spectroscopy (such as Figure 7 shown). In the spectrum of the PAA / DTAB fiber membrane, typical characteristic peaks can be observed. Among them, a strong absorption peak appears at 1710 cm -1 , corresponding to the stretching vibration of C=O in carboxylic acid (-COOH). A C-O stretching vibration of the catechol group is shown at 1240 cm -1 , and an N-H stretching vibration of the catechol group is at 1544 cm -1 . After the thermal imidization reaction, these characteristic peaks of the PAA / DTAB fiber membrane disappear, and new characteristic peaks at 1780 cm -1 and 1720 cm -1 appear, corresponding to the asymmetric and symmetric stretching vibrations of C=O in the imide ring, which are typical characteristic peaks of PI. And a new characteristic peak appears at 1380 cm -1 , which belongs to the stretching vibration of C-N in the imide ring, further confirming the completion of the cyclization reaction. After self-assembled in-situ growth of ZIF-8, in the FTIR spectrum of the ZIF-8@PI / DTAB dual-scale nanofiber membrane, characteristic peaks at 1146 cm -1 , 994 cm -1 , 759 cm -1 , 694 cm -1 and 420 cm -1 are shown, which are attributed to the characteristic peaks of ZIF-8. Among them, the peak shown at 420 cm -1 belongs to the Zn-N stretching of the characteristic peak of ZIF-8. The peaks at 1146 cm -1 and 994 cm -1 are attributed to the 2-methylimidazole C-N stretching mode, and the peak at 759 cm -1 corresponds to the C-N bending vibration and C-H bending mode in 2-methylimidazole. Among them, the Zn-N bond is the functional group connecting the metal sites and the organic framework in ZIF-8. Therefore, the Zn-N bond is the key functional group in ZIF-8. To further prove the chemical composition, XPS analysis was carried out on the PI / DTAB and ZIF-8@PI / DTAB dual-scale nanofiber membranes. The full-spectrum analysis is as Figure 8 shown. The PI / DTAB diagram shows peaks of C1s, N1s, and O1s, while the ZIF-8@PVP / PAN diagram shows peaks of C1s, N1s, O1s, and Zn2p. The comparison of the FTIR spectra, XPS spectra, and XRD diagrams of the PAA fiber membrane, PI / DTAB dual-scale fiber membrane, and ZIF-8@PI / DTAB dual-scale fiber membrane illustrates the chemical structures of several fiber membranes and proves the successful in-situ growth of the MOF crystal ZIF-8 on the fiber membrane.

[0117] Application Example 1

[0118] To evaluate the air permeability of the prepared masks, tests were conducted through the ammonia air permeability experiment. The ZIF-8@PI / DTAB dual-scale fiber membrane filter material of the mask prepared in Example 1 was cut into circular specimens with a diameter of 5 cm, which were closely attached to a wide-mouth bottle filled with ammonia. A pH test paper was taken and quickly placed at the bottle mouth to observe the change of the pH test paper.

[0119] As Figure 9 shown, 1 s after the pH test paper was placed, the pH test paper quickly changed color, which can intuitively prove that the prepared ZIF-8@PI / DTAB dual-scale fiber membrane filter material has significant air permeability performance. Therefore, the prepared ZIF-8@PI / DTAB dual-scale fiber membrane mask has obvious air permeability comfort.

[0120] Application Example 2

[0121] To further evaluate the filtration performance of the prepared ZIF-8@PI / DTAB dual-scale fiber membrane mask, first, the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material prepared in Example 1 was placed in the interlayer of an intercommunicating volumetric flask. On one side, the generation of flue gas-simulated aerosol was carried out, and then the purification ability of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material for aerosol was judged by observing the change of gas concentration on both sides.

[0122] From Figure 10 it can be seen that the volumetric flask containing flue gas aerosol was filled with aerosol particles, while the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material significantly blocked the passage of aerosol. As a result, the volumetric flask on the right showed the original transparent color. This shows that the ZIF-8@PI / DTAB dual-scale nanofiber membrane has excellent aerosol filtration performance and can meet the purpose of purifying aerosol. This ZIF-8@PI / DTAB dual-scale nanofiber membrane mask has significant application potential for the protection against industrial flue gas pollution.

[0123] Application Example 3

[0124] To further verify the filtration performance of several masks prepared in the examples, this study used a nanoparticle aerosol generator to carry out aerosol interception efficiency tests. The experimental procedure is as follows: The fiber membrane filter materials of the three masks prepared in Example 1, Comparative Example 1, and Comparative Example 2 were cut into circular specimens with a diameter of 5 cm and fixed in the test cavity by precision jigs. The actual effective filtration area was 15.904 cm 2. The test system uses a dual-channel particle counter to monitor the upstream and downstream aerosol concentrations respectively, and selects nano-silica particles in the particle size range of 300 nm to 10 μm as the test medium for simulating radioactive aerosols. During the experiment, the face velocity is controlled by adjusting the airflow parameters, and the concentration changes of particles with different particle sizes before and after filtration are recorded synchronously. The pressure loss value obtains the pressure drop parameters on both sides of the membrane structure in real time through a differential pressure sensor, and the average value of each group of data is processed through three parallel experiments. The filtration performance parameters are calculated according to the following mathematical formula:

[0125] Filtration efficiency = 1 - (number of upstream aerosol particles) / (number of downstream aerosol particles)

[0126] The quality factor is calculated by the following formula:

[0127] Quality factor = -ln(1 - filtration efficiency) / pressure drop

[0128] Where Figure 11 shows the change in the filtration efficiency of the PI mask filter material prepared in Comparative Example 1 for aerosol particles with different particle sizes at a face velocity of 5 cm / s. It can be seen that the filtration efficiency of the PI mask filter material for PM 0.3 is 97.61%. As the particle size of the aerosol particles increases, the filtration efficiency also gradually increases. For aerosol particles with a particle size greater than 3 μm, the filtration efficiency reaches 99.99%. Therefore, the PI mask has obvious advantages and application potential for daily protection. Figure 12 is the change in the filtration efficiency of the PI / DTAB dual-scale nanofiber membrane mask filter material prepared in Comparative Example 2 for aerosol particles with different particle sizes at a face velocity of 5 cm / s. It can be seen that the filtration efficiency of the PI / DTAB dual-scale nanofiber membrane mask for PM 0.3 is 99.99%. For aerosol particles with a particle size greater than 1 μm, the filtration efficiency reaches 100%. This is because after adding DTAB, the chargeability of the spinning solution is enhanced, the fiber diameter is significantly reduced, and thus the fiber pore size is significantly reduced, significantly enhancing the filtration efficiency of the PI / DTAB dual-scale nanofiber membrane mask. Therefore, the PI / DTAB dual-scale nanofiber membrane mask has obvious advantages and application potential for the protection of industrial nano-scale aerosol particles. Figure 13 is the change in the filtration efficiency of the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask filter material prepared in Example 1 for aerosol particles with different particle sizes at a face velocity of 5 cm / s. It can be seen that the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask for PM 0.3The filtration efficiency is 99.99%, and for aerosol particles with a particle size greater than 1 μm, the filtration efficiency reaches 100%. More importantly, due to the excellent iodine adsorption functionality of the MOF crystal ZIF-8, the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask has excellent application potential for nanoscale radioactive iodine aerosols in nuclear accident emergencies. At the same time, the pressure drop changes of three types of masks were measured, as Figure 14 shown. At a face velocity of 5 cm / s, the pressure drop of the PI mask is only 97 Pa, indicating excellent air permeability. After adding DTAB, the chargeability of the spinning solution is enhanced, significantly reducing the fiber diameter, thus significantly reducing the fiber pore size, and increasing the pressure drop of the PI / DTAB dual-scale nanofiber membrane mask, but it is only 119 Pa. After self-assembling and in-situ growing ZIF-8 crystals, the pore size of the fiber membrane continues to decrease, and the pressure drop also rises slowly, but it is only 131 Pa. The three types of masks of the present invention not only have remarkable filtration efficiency but also excellent pressure drop performance. They have significant application potential in daily protection, industrial nanoscale aerosol protection, and the application of nuclear power plants and the protection of iodine aerosols in nuclear accident emergencies.

[0129] Application Example 4:

[0130] To intuitively and significantly prove the iodine gas adsorption and purification performance of the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask prepared in Example 1, the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material prepared in Example 1 was placed in the interlayer of an interconnected volumetric flask. 20 mg of iodine was placed on one side, and then it was placed in an oven at 75 °C. The purification ability of the fiber membrane for iodine gas was judged by observing the color change of the gas on both sides.

[0131] As Figure 15 shown, after adding iodine to the left volumetric flask, an obvious purple gas was formed. However, after passing through the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material in the interlayer of the interconnected volumetric flask, it can be seen that the iodine gas was quickly adsorbed and purified by the fiber membrane, enabling the right volumetric flask to continue to remain transparent without being contaminated by iodine gas. This shows that the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material has remarkable iodine gas purification performance and excellent application potential in nuclear emergencies.

[0132] Application Example 4:

[0133] To further explore the adsorption kinetics of the ZIF-8@PI / DTAB dual-scale nanofiber membrane material for iodine gas, in the present invention, the stable isotope (I2) of non-radioactive iodine with almost the same chemical properties is used to replace radioactive iodine. A 20 mg fiber membrane sample and I2 are placed together in a glass container and put into a constant-temperature oven at 75 °C under normal pressure to simulate the environmental temperature of waste gas treatment in a reprocessing plant. After adsorption for a certain period of time, the container is taken out and cooled to room temperature. The iodine adsorption performance of the two fiber membrane samples is calculated and compared through the following formula.

[0134] Iodine adsorption capacity = (mass after reaction - mass before reaction) / mass before reaction;

[0135] Meanwhile, to deeply study the I2 gas adsorption performance of this nanofiber membrane material at different concentrations, a series of isothermal adsorption experiments were carried out in the present invention. Take 20 mg of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material prepared according to Example 1, and different concentrations of iodine gas environments are prepared by adding different masses of iodine. Subsequently, experiments are carried out at 75 °C to explore the adsorption capacity of this material for iodine gas under different iodine concentration conditions. After the experiment is carried out for 12 h, by measuring its mass change, its iodine capture performance is further calculated.

[0136] The capture and purification ability of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material prepared in Example 1 for iodine gas was studied through different adsorption times. As Figure 16 shown, the saturated adsorption capacity of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material for iodine gas reaches 2931 mg / g, which is twice the reported adsorption capacity of ZIF-8 powder. This is attributed to the fact that the fiber structure avoids the agglomeration of ZIF-8 crystals. More importantly, it improves the diffusion path of iodine, enhances the charge transfer process, and further improves the adsorption kinetics, and can reach adsorption equilibrium in about 120 min. It can be seen from the fitting curves of the two adsorption kinetic models that the adsorption curve is more in line with the pseudo-second-order adsorption kinetics.

[0137] Meanwhile, the saturated adsorption capacities of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter materials prepared in Example 2, Comparative Example 3, and Comparative Example 4 for iodine gas reached 3375 mg / g, 2952 mg / g, and 3019 mg / g respectively. It can be seen that the saturated adsorption capacity of the ZIF-8@PI / DTAB dual-scale nanofiber membrane prepared in Example 2 for iodine gas is significantly higher than that of Example 1, and is also significantly higher than that of Comparative Example 3 and Comparative Example 4.

[0138] Isothermal adsorption curve ( Figure 17) As shown, with the increase in the concentration of I2, the iodine gas adsorption capacity of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material increases significantly until it reaches equilibrium. This phenomenon indicates that the concentration difference promotes the rapid adsorption of iodine gas onto the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material until the binding sites of ZIF-8 reach adsorption saturation. According to the fitting results of the two adsorption models, it is more in line with the Langmuir model. This shows that the capture of iodine by the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material is independent of each other, and the adsorption process tends to monolayer adsorption.

[0139] To test the adsorption stability of the material in a high-temperature and high-humidity environment, the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material was placed in an oven at 75 °C, 100 °C, and 200 °C for 2 h and then an iodine gas adsorption experiment was carried out, as Figure 18 shown. The ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material maintained its adsorption performance and remained at about 2900 mg / g under different temperature treatments. To verify the water stability of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material, the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material was immersed in pure water for 6 h, 12 h, and 48 h, then placed in a fume hood to air dry naturally and then an adsorption experiment was carried out. From Figure 18 it can be seen that the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material maintained its adsorption performance and still remained at about 2900 mg / g after being immersed in pure water for different times, indicating that the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material has excellent water stability. In a high-temperature and high-humidity environment, it will not affect the iodine gas adsorption performance of the ZIF-8@PI / DTAB dual-scale nanofiber membrane filter material. According to the experimental results of the above several application examples, the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask not only has excellent filtration performance, low air permeability and pressure drop, but also has remarkable iodine gas adsorption and purification ability. Therefore, the ZIF-8@PI / DTAB dual-scale nanofiber membrane mask has excellent application potential for protecting against iodine-containing radioactive iodine aerosols in nuclear energy development and nuclear accident emergencies.

[0140] The equipment quantity and processing scale described here are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be apparent to those skilled in the art.

[0141] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A preparation method of a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane, characterized in that It includes the following steps: Step 1: Calcinate the dual-scale three-dimensional network PAA fiber membrane in an inert atmosphere to achieve thermal imidization reaction, and obtain the dual-scale three-dimensional network PI fiber membrane; Step 2: Immerse the dual-scale three-dimensional network PI fiber membrane in a mixed solution of zinc salt, organic ligand, and solvent B, and in-situ grow MOFs on the fiber membrane through a self-assembly method, and then place it in an oven for drying to prepare the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane.

2. The preparation method of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 1, wherein, In the said Step 1, the preparation method of the dual-scale three-dimensional network PAA fiber membrane includes: S11: Weigh 4,4'-diaminodiphenyl ether, dodecyltrimethylammonium bromide, and pyromellitic dianhydride and dissolve them in organic solvent A, and stir to dissolve to form a precursor spinning solution; S12: Electrospin the precursor spinning solution to obtain the dual-scale three-dimensional network PAA fiber membrane.

3. The preparation method of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 2, characterized in that, In the said S11, the organic solvent A is any one of N,N-dimethylformamide, ethanol, tetrahydrofuran, N,N-dimethylacetamide, acetone, and ether.

4. The preparation method of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 2, characterized in that, In the said S11, the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1-5:1-5; the total concentration of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in organic solvent A is 10%-20%; the concentration of dodecyltrimethylammonium bromide in organic solvent A is 0%-5%; the stirring and dissolving temperature: 0-10°C; the environmental humidity: 30%-100%; the stirring time is 1-24 h.

5. The preparation method of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 2, wherein, In the said S12, the parameters of electrospinning are: spinning voltage: 5-25 kV; the needle is an 18-30 gauge stainless steel needle; the electrode distance: 5-20 cm; the injection pump propulsion rate: 0.3-1.5 mL / h; the environmental temperature: 5-40°C; the environmental humidity: 30%-100%.

6. The preparation method of the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 1, characterized in that, In the said Step 1, the inert atmosphere includes one of nitrogen, argon, and helium; the thermal imidization calcination temperature is 250-550°C, the heating rate is 1-10°C / min, and the holding time is 0.5-4 h.

7. The preparation method of the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 1, characterized in that, In the said Step 2, the solvent B includes one or a mixture of methanol, deionized water, ethanol, and N,N-dimethylformamide; the zinc salt includes any one or a mixture of zinc nitrate hexahydrate, zinc chloride, zinc sulfate, zinc acetate, and zinc citrate; the organic ligand includes any one of imidazole and 2-methylimidazole; the impregnation time is 1-48 h; the drying temperature is 30-80°C, and the drying time is 1-10 h; the molar ratio of zinc salt to organic ligand is 1:8, and the dosage ratio of organic ligand to solvent B is to dissolve 0.04 mol of organic ligand per 100 mL of solvent B.

8. Application of a MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane, wherein the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane is prepared from the MOFs-based dual-scale polyimide three-dimensional network nanofiber membrane according to any one of claims 1-7, characterized in that The MOF-based dual-scale polyimide three-dimensional network nanofiber membrane is applied to the preparation of an MOF-based dual-scale nano-network radioactive iodine aerosol protective mask. The specific method includes: selecting a non-woven fabric with good air permeability as the outer layer and the inner layer of the MOF-based dual-scale nano-network radioactive iodine aerosol protective mask, and using the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane as the filter layer of the MOF-based dual-scale nano-network radioactive iodine aerosol protective mask, placing it in the middle of the outer layer and the inner layer, and obtaining the MOF-based dual-scale nano-network radioactive iodine aerosol protective mask through a composite process.

9. Use of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 8, characterized in that, The composite process includes hot pressing, sewing, and adhesion.

10. Use of the MOF-based dual-scale polyimide three-dimensional network nanofiber membrane according to claim 8, characterized in that, The MOF-based dual-scale nano-network radioactive iodine aerosol protective mask is used to capture and filter radioactive iodine aerosols.

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