Ultrafine air pollutant particle filtering membrane, preparation method and application in smoke pollutant filtering

Abstract

The invention belongs to the technical field of air filtration, and discloses a superfine air pollutant particle filtering membrane, a preparation method and application in smoke pollutant filtering, and the preparation method comprises the following steps: S1, preparing a modified PP fiber membrane material; s2, preparing a PP / ZIF-8 composite membrane, enabling Zn < 2 + > to fully react with 2-methylimidazole, constructing a microstructure which is formed by arranging a proper number of ZIF-8 crystals on the PP fiber surface in a single layer and is uniformly distributed, and forming a superfine air pollutant particle filtering membrane with gaps between the crystals. The invention further discloses an ultrafine air pollutant particle filtering membrane and application thereof in smoke pollutant filtering, the filtering membrane has a good filtering effect on various ultrafine particles in smoke and can keep good air permeability, and therefore the technical contradiction between the filtering effect and the air permeability is solved; the method can be widely applied to analysis, detection and purification treatment of air pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical fields of air filtration and new materials, and particularly relates to an ultra-fine air pollutant particle filtration membrane, a preparation method thereof, and an application in filtering flue gas pollutants. Background Art

[0002] Particulate matter and toxic and harmful aerosols are common air pollutants. Particulate matter (PM) usually consists of extremely small solid particles and droplets, including sulfates, nitrates, ammonia, carbon black, etc. PM can be divided into different levels according to its size, such as PM10, PM2.5, PM0.5, etc. According to relevant epidemiological and toxicological studies, PM contains some pathogens that cause heart and respiratory diseases, which can enter the human lungs and blood through breathing, endangering human health. Therefore, long-term exposure to airborne particulate matter will lead to adverse health consequences. At present, polypropylene (PP) masks have been widely used to protect human health and prevent PM exposure due to their excellent filtration performance. Its filtration mechanism includes interception, inertial impaction, Brownian diffusion, and electrostatic mechanisms to capture particles. Among them, surface charge is a key characteristic for the filter to effectively remove airborne particulate matter. However, PP fibers have some limitations, such as large fiber diameter, low porosity, and low removal efficiency for submicron particles (diameter < 1μm). Improving the removal efficiency of submicron particles will sacrifice the relative thickness, basis weight, and pressure drop of the air filtration chamber, which is not conducive to the development of the air filtration chamber. Charge is a key parameter for effective particulate matter removal. However, in specific environments such as humid environments (water vapor) and organic chemical environments, the charge will be lost, making it difficult to achieve a stable removal effect, which may directly lead to poor health conditions for filter users. Some research reports state that the service life of PP air filtration chambers is relatively short, usually less than 4 hours under high humidity and high temperature, and the filtration performance may decrease. Some studies have shown that cigarette smoke aerosol can cause the filtration efficiency of traditional air filtration chambers to drop sharply from 92.5% to 33.3% (-Δ59.2%). Cigarette smoke aerosol will significantly affect the static charge characteristics of the filter tip. Therefore, developing highly efficient and stable fiber membranes to solve the health hazards caused by particulate matter pollution in complex flue gas is an important issue.

[0003] In the air pollutant particle filtration experiment, filtration efficiency refers to the interception ratio of the filter material to the target particles under specific conditions, that is, the degree of reduction of the particle concentration upstream and downstream of the material. It is the core indicator to measure the ability of the filter material or system to capture the target particles, usually expressed as a percentage (%); while the quality factor (QF) is the core parameter for evaluating the comprehensive performance of the filter material, which is used to quantify the balance between filtration efficiency and airflow resistance. However, various filter materials in the existing technology often find it difficult to achieve both filtration efficiency and quality factor for ultrafine air pollutant particles.

[0004] To solve this problem, some researchers have found that adding electret can optimize the morphology of PP fibers and improve their electrical activity in hazardous environments. It is one of the effective ways to balance pressure drop and improve filtration efficiency, but it is basically ineffective for ultrafine particles. Other research results also show that PP materials doped with nanoparticles, such as ZnO nanorods (NR), reduced graphene oxide (rGO), manganese dioxide (MnO 2 ) and metal organic frameworks (MOFs) can significantly improve the filtration performance and the absorption capacity of pollutants in flue gas. Metal organic frameworks (MOFs) have excellent performance in air filtration applications due to their adjustable porosity, high adsorption, structural stability and antibacterial ability. However, MOFs mainly exist in the form of powders and their poor compatibility with polymers restricts their application in air filtration materials, and their application effect on ultrafine particles is also poor. 2-Methylimidazole zinc salt (ZIF-8, zeolite imidazolate framework-8) is a Zn 2+ A typical porous metal-organic framework (MOF) material composed of ions and 2-methylimidazole ligands has high porosity, thermal stability and chemical stability, and shows unique advantages in catalysis, gas separation, biomedicine and other fields. However, due to the complexity of its own crystal structure and preparation method, it cannot be directly applied to the simultaneous improvement of the filtration efficiency and quality factor of ultrafine pollutant particles.

[0005] In the prior art, a ZIF-8 / non-woven fabric composite material and a preparation method thereof disclosed in CN 110777537A synthesize a ZIF-8 / non-woven fabric composite material with a hierarchical pore structure by directly immersing the non-woven fabric in a ZIF-8 precursor solution and allowing it to stand for aging, so that ZIF-8 is in-situ deposited on the surface of the non-woven fabric. However, the compatibility between MOFs and polymers is not considered in this material, which easily leads to instability and easy shedding of MOFs particles, making it difficult to play an effective role in the long term. Moreover, it is necessary to stand for aging for 24 h, resulting in a long reaction time, which is not conducive to industrial application. Therefore, it is also necessary to consider how to improve the interfacial compatibility between ZIF-8 and polymers and reduce the reaction time to improve the practicability and stability of ZIF-8-based materials.

[0006] In the prior art, CN 118649562A prepared a ZIF-8 / PTFE composite membrane filtration material by coating ZIF-8 on the surface of PTFE foam using an electrospray spraying method. Specifically, ZIF-8 powder was firmly embedded on the PTFE surface by electrospray to increase the contact area and bonding strength of the material. The prepared ZIF-8 / PTFE@PPS has good filtration efficiency for fine particulate matter, as Figure 2 shown. However, according to the particulate filtration efficiency evaluation data recorded therein, the material has a poor filtration effect on ultrafine particulate matter such as PM 0.3, and the removal efficiency is less than 40%. It can be seen that for various composite materials in the prior art, the filtration efficiency and quality factor for ultrafine particulate matter below PM1.0 are not ideal, and it is difficult to meet the requirements of efficient filtration, precise detection, power consumption reduction, etc. for these ultrafine particulate matter. If the conventional technology is used to directly increase the quantity and density of ZIF-8 powder to improve the filtration efficiency, it will inevitably lead to a significant decrease in the air permeability (quality factor) of the filtration material, and it is difficult to balance the overall filtration efficiency and quality factor of the filtration material. Summary of the Invention

[0007] Aiming at the deficiencies of the above prior art, the purpose of the present invention is to propose a method for preparing an ultrafine air pollutant particle filtration membrane, a preparation method thereof, and an application in filtering flue gas pollutants. The preparation method of this PP / ZIF-8 controls process parameters such as the concentration range of Zn in the precursor solution and the magnetic stirring speed, and in Zn 2+ 2+During the step-by-step reaction with 2-methylimidazole, an appropriate microstructure is constructed, enabling ZIF-8 to grow directionally and in a single layer on the surface of PP fibers with high production efficiency. At the same time, the finally prepared ZIF-8 has a single crystal form (dodecahedron) on the fiber membrane and is relatively evenly distributed, with gaps between the crystals and no agglomeration phenomenon. It has good filtration efficiency for various ultrafine particulate matters in flue gas and can maintain good air permeability, thus solving the technical contradiction between filtration efficiency and air permeability and being able to balance filtration efficiency and quality factor.

[0008] The present invention provides the following technical solutions to achieve the above object: A preparation method of an ultrafine air pollutant particle filtration membrane, characterized by comprising the following steps: S1. Prepare a modified PP fiber membrane material Prepare a Tris solution of appropriate concentration of tris(hydroxymethyl)aminomethane and adjust the pH value to 8.5. Subsequently, add an appropriate amount of dopamine hydrochloride DA and tannic acid TA, and stir evenly to obtain a DA / TA modified solution; immerse the PP fiber membrane in the modified solution, react at room temperature and then dry to obtain a modified PP fiber membrane material (denoted as PP-Tri); S2. Prepare a PP / ZIF-8 composite membrane. Dissolve an appropriate amount of Zn(CH 3 COO) 2 ·2H 2 O in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14 - 0.20 mol / L; completely immerse the modified PP fiber membrane material in the zinc acetate dihydrate / methanol precursor solution and let it stand for more than 10 h to ensure that Zn 2+ ions are firmly loaded on the surface of the PP fiber membrane material; dissolve an appropriate amount of 2-methylimidazole in methanol to prepare a 2-methylimidazole / methanol precursor solution with a concentration of 0.5 - 0.8 mol / L; after magnetic stirring of the 2-methylimidazole / methanol precursor solution for 30 min, slowly add it to the above-mentioned zinc acetate dihydrate / methanol precursor solution immersed with the modified PP fiber membrane material, so that Zn 2+ in the zinc acetate dihydrate / methanol precursor solution reacts fully with 2-methylimidazole, enabling ZIF-8 to grow in-situ and directionally on the surface of the modified PP fiber, bind to the surface of the PP fiber through hydrogen bonds or covalent bonds, and obtain an appropriate number of ZIF-8 crystals with a dodecahedron crystal form, arranged in a single layer and evenly distributed on the surface of the PP fiber after the reaction. There are gaps between the ZIF-8 crystals, constructing a microstructure of the PP / ZIF-8 composite membrane material with a rough surface, pore channels and a high specific surface area. Take it out and dry it to obtain an ultrafine air pollutant particle filtration membrane, specifically including two types of filtration membranes, PP5 / ZIF-8 and PP7 / ZIF-8.

[0009] An ultra-fine air pollutant particle filtration membrane, characterized in that it is prepared by the method described above, by controlling the concentration range of Zn in the precursor solution 2+ and the magnetic stirring speed, during the gradual reaction of Zn 2+ with 2-methylimidazole, an appropriate number of ZIF-8 crystals are obtained and a unique microstructure is constructed: the ZIF-8 crystals are in-situ oriented and grown on the surface of the DA / TA modified PP fiber membrane, and are combined with the surface of the PP fiber through hydrogen bonds or covalent bonds, forming dodecahedral crystal forms, arranged in a single layer, and evenly distributed on the surface of the PP fiber, and there are gaps between the ZIF-8 crystals, finally forming a rough surface, pore channels and a high specific surface area, with a filtration efficiency of not less than 80% for PM0.5 ultra-fine particulate matter, and a quality factor of not less than 0.0075 Pa -1 of the PP / ZIF-8 composite membrane material.

[0010] An application of the ultra-fine air pollutant particle filtration membrane in filtering flue gas pollutants, which uses the ultra-fine air pollutant particle filtration membrane to filter ultra-fine particulate matter PM1.0 and PM0.5 in the flue gas, and has a high filtration efficiency and quality factor.

[0011] Compared with the current existing technologies, the present invention has at least the following advantages and effects: 1. The technical solution provided by the present invention takes Zn 2+ with a controlled concentration range as the main center at room temperature, uses 2-methylimidazole as a ligand, constructs a unique microstructure by -OH modification and controlled reaction of the PP fiber membrane material, adjusts various reaction conditions during the reaction to make ZIF-8 grow in-situ and oriented on the surface of the modified PP fiber, combines with the surface of the PP fiber through hydrogen bonds or covalent bonds to construct a microstructure, and after the reaction, obtains an appropriate number of ZIF-8 crystals with dodecahedral crystal forms, arranged in a single layer, and evenly distributed on the surface of the PP fiber, with gaps between the crystals, and further forms a PP / ZIF-8 composite membrane material with a rough surface, pore channels and a high specific surface area, specifically including two types of filtration membranes, PP5 / ZIF-8 and PP7 / ZIF-8, and significantly improves the filtration efficiency and quality factor of the filtration membrane material for ultra-fine air pollutant particles such as PM1.0 and PM0.5, has a good filtration effect on various ultra-fine particulate matters in the flue gas and can maintain good air permeability, thus solving the technical contradiction between the filtration effect (increasing the number and density of ZIF-8) and air permeability.

[0012] 2. The preparation method provided by the present invention has simple operation steps and mild reaction conditions. It can prepare an efficient and stable PP / ZIF-8 air filtration material at room temperature. The air filtration membrane of the PP / ZIF-8 composite membrane material prepared by the method of controlled in-situ growth enables ZIF-8 to grow uniformly and monolayer on PP in the form of hydrogen bonds or covalent bonds, firmly bind to PP fibers and become an integrated material; the modification enables PP to load ZIF-8 well, and at the same time, the controlled in-situ growth also solves the problems of constructing the microstructure of monolayer ZIP-8 (avoiding stacking) and preventing ZIF-8 from being easily detached during multiple uses, and enables the two to be firmly combined without using other binders.

[0013] 3. The PP / ZIF-8 composite membrane material prepared by the present invention, as an ultra-fine air pollutant particle filtration membrane, greatly simplifies the preparation process based on the ingenious construction of the microstructure of ZIF-8 crystals on the surface of PP fibers during the controlled reaction process; through this combination method of in-situ growth of ZIF-8 crystals, on the one hand, the stability of the composite membrane can be significantly improved, and the constructed dodecahedral crystal form with monolayer distribution can also expand the application range of ZIF-8, enabling it to have high filtration efficiency and high quality factor in ultra-fine air pollutant filtration and air pollution prevention; through XRD and SEM tests, it is characterized that the crystal form of the prepared ZIF-8 crystals is good, and the monolayer distribution on the surface of PP is relatively uniform, and there are gaps between the crystals, so that the PP / ZIF-8 composite membrane material is easy to adhere to ultra-fine particles and at the same time can ensure the passage of clean air.

[0014] 4. The preparation process provided by the present invention is suitable for industrial continuous production, and the product quality is stable. After repeated experiments, it is proved that in the process of preparing the PP / ZIF-8 composite membrane material of the present invention, using a lower precursor concentration can overcome the phenomenon of particle agglomeration, ensure that the monolayer ZIF-8 loaded on the surface of PP can play an efficient adsorption role on ultra-fine pollutant particles and harmful gases, and the gaps between the crystals can ensure high air permeability. In the two examples of the present invention, the surface of the PP / ZIF-8 fibers prepared at a lower precursor concentration (mainly the concentration of Zn 2+ did not show agglomeration during the preparation process and was arranged in a monolayer; while in multiple comparative examples, with the increase of the Zn 2+With the increase in concentration, an appropriate number of ZIF-8 begins to aggregate on the surface of PP fibers, arranging in multiple layers with no gaps between the crystals and various crystal forms, making the surface of PP fibers overly rough. The gaps between PP fibers are very small, and such an overly rough surface does not necessarily contribute to improving the filtration efficiency of the material for ultrafine particles, but will inevitably lead to a significant decrease in air permeability. Although the increase in the number of crystals increases the contact area between each crystal and the fiber surface and also increases their binding stability, overall, the removal efficiency for ultrafine particles and the gas permeability of flue gas have decreased significantly. Therefore, controlling the concentration of Zn in the precursor 2+ within the range of 0.14 - 0.20 mol / L has a decisive impact on the microstructure and properties of the final product. If the concentration is too low, the number of ZIF-8 crystals formed is too small to effectively cover the surface of PP fibers. If the concentration is too high, the number of ZIF-8 formed is excessive, resulting in stacking with no gap structure between the crystals, affecting the air passing rate, and significantly affecting its filtration effect and filtration quality factor for ultrafine particles in the air.

[0015] 5. For the PP / ZIF-8 composite membrane material prepared by the present invention, the in-situ grown ZIF-8 can enhance the surface charge of PP fibers and utilize the unbalanced polarization between metals and organic substances in ZIF-8 to improve the removal effect for particles with an aerodynamic diameter less than 1.0 μm (PM1.0) and below. Compared with traditional PP materials, these polarization enhancements can strengthen the removal of ultrafine particles through electrostatic interactions. In addition, in-situ growth can retain the porous structure of ZIF-8 to the greatest extent, increase the adsorption sites on the PP surface, and increase the adsorption of small molecule gases through the pore filling effect of the porous structure. At the same time, retaining the network structure of the PP material can strengthen the removal effect of gravity deposition, diffusion, etc. on particles with an aerodynamic diameter greater than 1.0 μm, thereby increasing the effective coverage range of the PP / ZIF-8 composite membrane material for particles with different diameters in the air and maintaining a high filtration efficiency.

[0016] 6. Through actual tests, compared with traditional PP air filtration materials, the PP / ZIF-8 composite membrane material prepared by the present invention as an air filtration material can significantly enhance the adsorption of polar and non-polar substances in flue gas, including nitrogen-containing compounds (nicotine, nitrosamines, nitrogen oxides) and carbon-containing compounds (polycyclic aromatic hydrocarbons, volatile organic compounds). First, the PP / ZIF-8 composite membrane material modifies the hydroxyl groups loaded on the membrane surface and in-situ loads Zn 2+Meanwhile, since the hydroxyl group (-OH) is a strongly polar group, it can form hydrogen bonds and has a strong adsorption effect on polar molecules. Secondly, the surface growth of ZIF-8 exhibits excellent adsorption performance for non-polar molecules (such as volatile organic compounds VOCs, etc.). Therefore, this material can take into account the adsorption performance of polar and non-polar substances, achieving unexpected effects and can be widely used in the analysis, detection and purification of various air pollutants. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the flue gas particulate matter filtration experimental device self-made in the embodiment of the present invention; Figure 2 It is a SEM image of the original PP air filtration material in the embodiment of the present invention; Figure 3 It is a SEM image of the cleaned PP-Cleaning air filtration material prepared in the embodiment of the present invention; Figure 4 It is a SEM image of the PP-Tri air filtration material prepared in the comparative example of the present invention; Figure 5 It is a SEM image of the PP5 / ZIF-8 air filtration material prepared in the embodiment of the present invention; Figure 6 It is a SEM image of the PP7 / ZIF-8 air filtration material prepared in the embodiment of the present invention; Figure 7 It is a SEM image of the PP9 / ZIF-8 air filtration material prepared in the comparative example of the present invention; Figure 8 It is a SEM image of the PP11 / ZIF-8 air filtration material prepared in the comparative example of the present invention; Figure 9 It is an XRD pattern of the ZIF-8 prepared in the embodiment of the present invention; Figure 10 It is an XRD pattern of the PP / ZIF-8 air filtration membrane prepared in the embodiment of the present invention; Figure 11 It is a schematic diagram of the filtration efficiency of various membrane materials prepared in the embodiment and comparative example of the present invention for particulate matter in flue gas; Figure 12 It is a schematic diagram of the test results of the air permeability of various membrane materials prepared in the embodiment and comparative example of the present invention; Figure 13 It is a schematic diagram of the quality factor of various membrane materials prepared in the embodiment and comparative example of the present invention; Figure 14 It is an XPS pattern of the air filtration membrane before filtration prepared in the embodiment and comparative example of the present invention; Figure 15 The XPS spectra after filtration by the air filtration membranes prepared in the examples and comparative examples of the present invention; Figure 16 The N 2 adsorption and desorption curves of PP and PP / ZIF-8 prepared in the examples and comparative examples of the present invention; Figure 17 Schematic diagram of the benzene vapor adsorption capacity curves of PP and PP / ZIF-8 prepared in the examples and comparative examples of the present invention.

[0018] In the figure: 1. Positive pressure air pump; 2. Air drying chamber; 3. Gas flowmeter; 4. Flue gas combustion chamber; 5. Air filtration chamber; 51. Hollow semi-body; 52. Air filtration chamber fixture; 53. Air filtration membrane; 6. Outlet buffer bottle; 7. Gas collecting bottle; 8. Front-end particle counter; 9. Back-end particle counter; 10. Differential pressure gauge; 11. Connecting pipeline. Detailed implementation manners

[0019] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Basic embodiment The preparation method of the ultra-fine air pollutant particle filtration membrane provided by the embodiment of the present invention includes the following steps: S1. Prepare the modified PP fiber membrane material Prepare a Tris solution of trimethylaminomethane with an appropriate concentration, adjust the pH value to 8.5, and then add an appropriate amount of dopamine hydrochloride DA and tannic acid TA. After stirring evenly, a DA / TA modified solution is obtained; Immerse the PP fiber membrane in the modified solution, react at room temperature and then dry to obtain the modified PP fiber membrane material; specifically: S1-1. PP pretreatment Take a PP material film (denoted as PP in the attached drawing), ultrasonically wash it with ethanol and deionized water 3 times respectively for 15 minutes each time to remove surface impurities and electret charges and then dry it. The cleaned material is denoted as PP-Cleaning; S1-2. PP modification Prepare a Tris solution with a concentration of 1.2 g / L of tris(hydroxymethyl)aminomethane, adjust the pH value to 8.5, and then add dopamine hydrochloride (DA) and tannic acid (TA). After stirring evenly, a DA / TA modified solution is obtained, where the concentration of dopamine hydrochloride (DA) is 2 g / L and the concentration of tannic acid (TA) is 4 g / L; Immerse the cleaned PP film into the modified solution, react at room temperature for 24 h, and then dry at 50 °C to obtain a modified PP fiber membrane material, denoted as PP-Tri or Tri-PP; S2. Preparation of PP / ZIF-8 composite membrane Dissolve an appropriate amount of Zn(CH 3 COO) 2 ·2H 2 O in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14 - 0.20 mol / L; completely immerse the modified PP fiber membrane material into the zinc acetate dihydrate / methanol precursor solution and let it stand for more than 10 h to ensure that Zn 2+ ions are firmly loaded on the surface of the PP fiber membrane material; Dissolve an appropriate amount of 2-methylimidazole in methanol to prepare a 2-methylimidazole / methanol precursor solution with a concentration of 0.5 - 0.8 mol / L; After magnetic stirring of the 2-methylimidazole / methanol precursor solution for 30 min, slowly add it to the above-mentioned zinc acetate dihydrate / methanol precursor solution immersed with the modified PP fiber membrane material, so that Zn in the zinc acetate dihydrate / methanol precursor solution 2+ reacts fully with 2-methylimidazole, enabling the in-situ oriented growth of ZIF-8 on the surface of the modified PP fiber, binding to the surface of the PP fiber through hydrogen bonds or covalent bonds. After the reaction, an appropriate number of ZIF-8 crystals with a dodecahedral crystal form, monolayer arrangement, and evenly distributed on the surface of the PP fiber are obtained. There are gaps between the ZIF-8 crystals, constructing a microstructure of the PP / ZIF-8 composite membrane material with a rough surface, pore channels, and a high specific surface area. Take it out and dry to obtain an ultra-fine air pollutant particle filtration membrane; in the following specific examples, the ultra-fine air pollutant particle filtration membrane is specifically PP5 / ZIF-8 and PP7 / ZIF-8, and the specific steps are as follows: S2-1. Loading of Zn 2+ Dissolve an appropriate amount of Zn(CH 3 COO) 2 ·2H 2 O in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14 - 0.20 mol / L; completely immerse the modified PP fiber membrane material into the zinc acetate dihydrate / methanol precursor solution and let it stand for 12 h to ensure that Zn 2+The ions are firmly loaded on the surface of the PP fiber membrane material; In situ growth of S2-2 and ZIF-8 Dissolve an appropriate amount of 2-methylimidazole in methanol to prepare a 2-methylimidazole / methanol precursor solution with a concentration of 0.5-0.8 mol / L; The 2-methylimidazole / methanol precursor solution was magnetically stirred at a speed of 300-1000 r / min for 10-40 min, and then slowly added to the zinc acetate dihydrate / methanol precursor solution without the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution 2+ The Zn 2+ In-situ directional growth is carried out on the surface of modified PP fibers, and the ZIF-8 crystals are combined with the surface of PP fibers through hydrogen bonds or covalent bonds to obtain a suitable number of ZIF-8 crystals with a dodecahedral crystal form, a single-layer arrangement, and uniform distribution on the surface of PP fibers, with gaps (channels) between each ZIF-8 crystal, and further a PP / ZIF-8 composite membrane material with a rough surface, pore channels, and a high specific surface area microstructure is constructed; S2-3. Post-processing After the reaction is completed, the PP / ZIF-8 composite membrane material is taken out from the solution, washed with fresh methanol three times, and then washed with deionized water three times to remove residual reactants on the surface. Finally, the washed membrane material is dried in a vacuum drying oven at 40-60°C for 8-15 h to obtain an ultrafine air pollutant particle filtration membrane.

[0021] An ultrafine air pollutant particle filter membrane is prepared by the above method, by controlling the Zn in the precursor solution 2+ The concentration range and magnetic stirring speed of Zn 2+ In the process of gradual reaction with 2-methylimidazole, a suitable number of ZIF-8 crystals are obtained and a unique microstructure is constructed: the ZIF-8 crystals are in-situ directional growth on the surface of the DA / TA modified PP fiber membrane, and are combined with the surface of the PP fiber through hydrogen bonds or covalent bonds to form a dodecahedral crystal, arranged in a single layer, and evenly distributed on the surface of the PP fiber, and there are gaps between each ZIF-8 crystal, finally forming a rough surface, pore channels and high specific surface area, and the filtration efficiency of PM1.0 and PM0.5 ultrafine particles is not less than 80%, and the quality factor is not less than 0.0075 Pa -1 PP / ZIF-8 composite membrane material.

[0022] Application of the ultra-fine air pollutant particle filtration membrane in filtering flue gas pollutants, which uses the ultra-fine air pollutant particle filtration membrane to filter ultra-fine particulate matters PM1.0 and PM0.5 in the flue gas and has high filtration efficiency and quality factor. It includes the following steps: A1. Set up a filtration experiment device Set up a self-made filtration experiment device, which consists of a positive pressure air pump 1, a gas flow meter 3, a flue gas combustion chamber 4, a front-end particle calculator 8, an air filtration chamber 5, an air filtration membrane 53, a rear-end particle calculator 9, a differential pressure gauge 10, a gas collecting bottle 7, and an air drying chamber 2 and an air outlet buffer bottle 6 to form a filtration experiment device for ultra-fine particulate matters in the flue gas; The air filtration membrane 53 made of PP / ZIF-8 composite membrane material is arranged in a flat unfolded state in the air filtration chamber 5; The front-end particle calculator 8 and the front detection tube of the differential pressure gauge 10 are both arranged on the pipeline on the front side of the air filtration chamber 5 (including the air filtration membrane 53); the rear-end particle calculator 9 and the rear detection tube of the differential pressure gauge 10 are both arranged on the pipeline on the rear side of the air filtration chamber 5 (including the air filtration membrane 53); each part is connected in sequence with a connecting pipeline 11, and after being connected, a sealed pipeline that penetrates through from front to back is formed; Among them, the air drying chamber 2 is arranged between the positive pressure air pump 1 and the gas flow meter 3 to dry the flowing air; The overall shape of the air filtration chamber 5 is cylindrical, including two hollow semi-bodies 51 that are vertically arranged symmetrically front and back and horizontally buckled (the internal hollow parts face each other and are sealed after being buckled) and an air filtration chamber fixture 52; the air filtration chamber fixture 52 (opposite screws + screw rods) together clamps the two horizontally buckled hollow semi-bodies 51 from the outside, which can be one pair or two pairs. In this embodiment, they are two pairs parallel up and down; The circular air filtration membrane 53 cut from the PP / ZIF-8 composite membrane material is first vertically arranged on the buckling surface of the two hollow semi-bodies 51, and then the air filtration chamber fixture 52 clamps the joint surface of the two hollow semi-bodies 51 and the air filtration membrane 53 together, so that the air filtration membrane 53 is kept unfolded and tensioned in the air filtration chamber 5, dividing the internal space of the air filtration chamber 5 into two parts before and after, and evenly filtering the passing flue gas; after the air filtration chamber fixture 52 is clamped, the buckling surface is sealed and the internal space of the air filtration chamber 5 is sealed; through holes for connecting the connecting pipeline 11 are provided at the center positions of the two hollow semi-bodies 51, and the flue gas enters the air filtration chamber 5 from the pipeline connected to the through hole, passes through the air filtration membrane 53 and then exits the air filtration chamber 5, and enters the air outlet buffer bottle 6 and the gas collecting bottle 7; in order to enhance the sealing performance between the buckling surface and the air filtration membrane 53, a sealing ring or elastic gasket can also be set between the buckling surface and the air filtration membrane 53.

[0023] The air outlet buffer bottle 6 is arranged between the air filtration chamber 5 and the gas collecting bottle 7, and is used to expand the storage space of the filtered air and assist in maintaining the stability of the pressure difference between the pipelines on both sides of the air filtration chamber 5; According to Figure 1 As shown, the above-mentioned components are successively connected to each other by connecting pipelines 11 to form a closed pipeline that penetrates from front to back after being connected; A2. Experiment preparation The PP / ZIF-8 composite membrane material is cut into circular pieces and weighed to be used as the air filtration membrane 53. The air filtration membrane 53 is placed in the air filtration chamber 5 and kept in an unfolded and tensioned state; After removing the cigarette filter tip part, it is placed in the flue gas combustion chamber 4 and weighed; Specifically, the PP / ZIF-8 composite membrane material is cut into circular pieces with a diameter of 55 mm as the air filtration membrane 53 and weighed. Then, the circular pieces of the PP / ZIF-8 composite membrane material (air filtration membrane 53) are placed between the two hollow semi-bodies 51 of the air filtration chamber 5, and the screws of the air filtration chamber clamp 52 are tightened. At the same time, the joint surfaces of the two hollow semi-bodies 51 and the air filtration membrane 53 are clamped to make the inside of the air filtration chamber 5 airtight and keep the air filtration membrane 53 in an unfolded state; Through the connecting pipeline 11, each part is connected to form the entire pipeline, and then the positive pressure air pump 1 is turned on for ventilation test to ensure that there is no leakage in the entire pipeline, and then proceed to the next step; A3. Filtration experiment First, control the air flow rate at 30 L / min through the gas flowmeter 3; light the cigarette and tighten the gas collecting bottle 7, then turn on the positive pressure air pump 1 and adjust the gas flowmeter 3 to ensure the oxygen requirement during combustion, so that the cigarette burns fully. The front-end particle counter 8 and the rear-end particle counter 9 respectively record the values of PM10, PM2.5, PM1.0, and PM0.5 in the pipelines before and after the air filtration membrane 53, and record the pressure difference before and after at the same time, and then calculate the filtration efficiency and quality factor of the particulate matter; A4. Reuse of the PP / ZIF-8 composite membrane material Take out the air filtration membrane 53 used in the previous experiment, wash it with deionized water to remove the particulate matter adsorbed on the surface; dry the washed air filtration membrane 53 in an oven at 50 °C, and then conduct a filtration efficiency stability performance test on the dried air filtration membrane 53 for a new experiment.

[0024] The embodiment of the present invention focuses on the balance problem of the filtration efficiency and quality factor of ultrafine pollutant particles. At room temperature, with Zn 2+ as the main center and 2-methylimidazole as the ligand, by performing -OH modification on the commercial PP membrane material, a highly efficient and stable ZIF-8 air filtration material can be prepared at room temperature, and by controlling Zn in the precursor solution2+ process parameters such as the concentration range and the magnetic stirring speed to control Zn 2+ During the reaction of Zn with 2-methylimidazole, the production quantity, growth position and crystal form of the crystals are controlled. A unique microstructure (single-layer arrangement, uniform distribution and gaps between each other) is constructed using an appropriate number (neither too many nor too few) of crystals. This air filtration membrane material has a good filtration effect on various ultrafine particulate matters in flue gas and can also maintain good air permeability, thus solving the technical contradiction between the filtration effect and air permeability existing in similar materials. It can simultaneously have a high filtration efficiency and quality factor and can be widely used in the analysis, detection and purification treatment of air pollutants.

[0025] See Figures 2 to 17 , and the following will be described in detail with multiple specific examples, comparative examples and test results.

[0026] Example 1 The ultrafine air pollutant particle filtration membrane, preparation method and application in filtering flue gas pollutants provided in this example are specific selections based on the foregoing basic example. The difference lies in that the ultrafine air pollutant particle filtration membrane material is specifically a PP5 / ZIF-8 air filtration membrane, and its preparation method includes the following steps: 1. Take out the middle layer of a medical surgical mask. The middle layer is mainly made of PP material (original PP, denoted as PP in each figure). Wash it ultrasonically with ethanol and deionized water 3 times respectively for 15 minutes each time to remove surface impurities and electret charges. Denote the dried membrane material as PP-Cleaning; 2. Prepare a Tris (tris(hydroxymethyl)aminomethane) solution with a concentration of 1.2 g / L and adjust its pH value to 8.5; then add 2 g of dopamine hydrochloride (DA) and 4 g of tannic acid (TA), and stir evenly to obtain a DA / TA modified solution; immerse the washed PP membrane in the modified solution and react at room temperature for 24 h; then dry it in a drying oven at 50 °C to obtain a modified PP membrane material, denoted as PP-Tri or Tri-PP; 3. Dissolve an appropriate amount of Zn(CH 3 COO) 2 ·2H 2 O in methanol to obtain a Zn 2+ Zn(CH 3 COO) 2 ·2H 2 O / methanol solution with a concentration of 0.1425 mol / L, and continuously stir magnetically at a speed of 600 r·min −1 for 30 minutes; then completely immerse the modified PP membrane (PP-Tri) in Zn(CH 3 COO) 2·2H 2 O / methanol solution and allowed to stand for 12 h to ensure that Zn 2+ The ions are firmly loaded; 4. Prepare a 0.568 mol / L 2-methylimidazole solution dissolved in methanol. After magnetic stirring for 30 min, slowly pour the 2-methylimidazole / methanol solution into the Zn-containing PP film. 2+ (CH 3 COO 2 ·2H 2 O / methanol solution (plastic square container); react for 6 h to make Zn 2+ and 2-methylimidazole to react fully; during the reaction, wait for Zn 2+ After all the reactants are consumed, the reaction is terminated, and some 2-methylimidazole will remain. After the reaction is completed, the prepared PP / ZIF-8 membrane is taken out from the plastic square box container, and the PP / ZIF-8 membrane is washed 3 times with fresh methanol and then washed 3 times with deionized water to remove the residual reactants on the surface. The washed PP / ZIF-8 membrane material is dried in a vacuum drying oven at 60°C for 24 h, and the prepared PP / ZIF-8 membrane material is recorded as PP5 / ZIF-8, which is the ultrafine air pollutant particle filter membrane of this embodiment.

[0027] like Figure 5 As shown, from the microscopic morphology of the PP5 / ZIF-8 membrane material prepared in this embodiment, it can be seen that the ZIF-8 crystal particles in the material are dodecahedral structures on the surface of the PP fiber, and there are a suitable number of ZIF-8 crystal particles on the fiber surface. Each crystal particle is nearly uniformly distributed on the fiber surface, and the ZIF-8 crystal particles do not appear agglomeration, stacking, etc. on the fiber, and a large gap is retained between each ZIF-8 crystal particle; on the one hand, this microstructure can maintain the characteristics of a large specific surface area of ​​a single crystal particle, which is conducive to the stable and efficient adsorption of ZIF-8 on its surface; on the other hand, controlling the number of crystal particles and retaining a large gap between each ZIF-8 crystal particle can enable the material to maintain good air permeability.

[0028] XRD was further used to observe the crystal changes of PP after in-situ growth of ZIF-8 on PP5 / ZIF-8 film material. Figure 9 As shown, the figure shows the standard spectrum of ZIF-8 and the spectrum of ZIF-8 actually prepared in the embodiment of the present invention; comparison shows that the standard spectrum and the ZIF-8 actually prepared in this embodiment are highly similar, indicating that the ZIF-8 prepared in this embodiment has a good crystal form and a high purity. Figure 10 This is the XRD pattern of the in-situ growth test on the surface of PP fiber in this example. Figure 10It can be seen that after the in-situ growth of ZIF-8 particles, the intensity of the characteristic peaks corresponding to the positions of ZIF-8 particles on the surface of PP fibers increases, indicating that ZIF-8 has successfully grown on the surface of the PP fiber membrane; and as the concentration of Zn 2+ increases, the peak shape gradually becomes sharper, indicating that the number of in-situ grown ZIF-8 on the PP surface shows an increasing trend. Therefore, controlling the concentration of Zn 2+ can control the total number of generated particles and avoid excessive or insufficient amounts.

[0029] Furthermore, XPS was used to further analyze the surface composition and chemical state of the PP5 / ZIF-8 membrane material. As Figure 14 shown, the characteristic peaks of O 1s, N1s, and C1s originate from 284.5, 398.8, and 531.5 eV of PP, respectively. A new Zn 2p peak was found at 1045 eV in the PP / ZIF-8 membrane material, indicating that ZIF-8 particles have successfully grown on the surface of the PP fiber membrane.

[0030] The application of the PP5 / ZIF-8 material provided in this embodiment in filtering flue gas pollutants is different in that it specifically includes the following steps: 1. Cut the PP5 / ZIF-8 membrane material into circular pieces with a diameter of 55 mm (air filtration membrane 53) and weigh them; according to Figure 1 as shown, after sequentially connecting the various parts of the filtration experimental device through the connecting pipeline 11, first turn on the positive pressure air pump for ventilation to ensure that there is no leakage in the entire pipeline; then place the air filtration membrane 53 made of PP5 / ZIF-8 into the air filtration chamber, specifically place it vertically on the mating surface of two hollow semi-bodies 51 that are symmetrically arranged front and back and horizontally buckled, and then tighten the opposing screws of the air filtration chamber clamp 52 to clamp the two hollow semi-bodies 51 together with the PP / ZIF-8 composite membrane material (air filtration membrane 53), so that the air filtration membrane 53 remains unfolded and taut, and the internal space of the air filtration chamber 5 is sealed; the air filtration membrane 53 divides the internal space of the air filtration chamber 5 into two parts front and back; in order to strengthen the sealing of the air filtration chamber 5, in this embodiment, gaskets and sealing rings (not shown in the figure) are also provided between the mating surface of the two hollow semi-bodies 51 and the two side surfaces of the air filtration membrane 53, and under the clamping force of the air filtration chamber clamp 52, the various parts of the annular mating surface are sealed.

[0031] 2. Conduct filtration performance tests Remove the cigarette filter tip part and place it on the cigarette inserter, and weigh it. Then put the cigarette inserter into the gas collecting bottle, light the cigarette and tighten the gas collecting bottle. Turn on the positive pressure air pump 1 and adjust the gas flowmeter 3 to ensure the oxygen requirement during cigarette combustion and make the cigarette burn fully. The experimental results are as Figure 11As shown. After calculation, the removal efficiencies of PP5 / ZIF-8 for PM 0.5, PM 1.0, PM 2.5, PM 5.0 and PM 10 are 84.6, 89.9, 90.6, 93.9 and 95.6% respectively. The pressure drop at both ends and the quality factor of the air filtration chamber in this embodiment are as shown in Figure 12 and Figure 13 shown. The pressure drop of the PP5 / ZIF-8 membrane material is 0.08 KPa, and the quality factor is 0.00762 Pa -1 . The filtered PP5 / ZF-8 membrane material (air filtration membrane 53) is washed with water and its recycling performance is tested. The filtration efficiencies of the recycled air filtration membrane 53 for PM10, PM 5 and PM2.5 in flue gas are all above 85%. Further analysis of the pore structure in PP is carried out through BET test, as shown in Figure 16 shown. After in-situ growth of ZIF-8, the specific surface area of the membrane material increases from the original 1.881 m² / g to 105.3 m² / g. The specific surface area of the PP / ZIF-8 membrane material increases significantly, mainly due to the porous structure of ZIF-8 which can promote the adsorption of ultrafine particles or gases. According to the curve classification of IUPAC, PP / ZIF-8 conforms to type I isotherm, indicating that monolayer physical adsorption of gas occurs on the surface of the membrane material and there are a large number of microporous structures in the material.

[0032] 3. The surface composition and chemical state of the adsorbed PP / ZIF-8 membrane material are further analyzed by XPS. The XPS spectrum is as shown in Figure 15 shown. There are obvious O 1s, N1s, C1s and Zn 2p peaks at 284.5, 398.8 and 531.5, 1045 eV. The content of Zn element in the PP / ZIF-8 membrane material before and after filtration has not changed, indicating that ZIF-8 is tightly attached to PP through strong coordination or chemical bonds between ZIF-8 and the PP fiber membrane. This means that the ZIF-8 layer is stable and will not separate or degrade. In the PP / ZIF-8 membrane material, O decreases while C and N increase, and the growth rates of C and N are 0.66% and 3.79% respectively. The PP / ZIF-8 membrane material captures or adsorbs nitrogen-containing compounds (nicotine, nitrosamines, nitrogen oxides) and carbon-containing compounds (polycyclic aromatic hydrocarbons, volatile organic compounds) in complex flue gas, indicating that the PP / ZIF-8 membrane material can preferentially remove nitrogen and carbon pollutants in flue gas. Oxygen-containing compounds (CO and CO 2 ) can competitively inhibit the preferential adsorption of nitrogen- and carbonaceous compounds in flue gas by PP / ZIF-8, resulting in a relative decrease in the content of O. In order to further evaluate the adsorption capacity of PP for carbon-containing compounds, the adsorption effect of this membrane material is tested by static adsorption method using benzene as a gas pollutant, and the results are as shown in Figure 17 shown. As shown in Figure 17It can be seen that as the test pressure gradually increases, the benzene vapor adsorption capacity gradually increases, and the adsorption capacity is always greater than that of PP; when the relative pressure approaches 1, the adsorption capacity of the PP / ZIF-8 membrane material for benzene vapor is 90.44 cm 3 / g, which is still significantly greater than that of PP.

[0033] Example 2 The ultra-fine air pollutant particle filtration membrane, preparation method and application in filtering flue gas pollutants provided in this example are specific selections based on the foregoing basic example. The difference is that the ultra-fine air pollutant particle filtration membrane material is specifically PP7 / ZIF-8, and the preparation method includes the following steps: 1. Take out the middle layer of the medical surgical mask. The middle layer is mainly made of PP. Wash it ultrasonically with ethanol and deionized water 3 times each for 15 minutes each time to remove surface impurities and electret charges. Record the dried PP membrane material as PP-Cleaning; 2. Prepare a Tris (tris(hydroxymethyl)aminomethane) solution with a concentration of 1.2 g / L and adjust the pH value to 8.5; then add 2 g of dopamine hydrochloride (DA) and 4 g of tannic acid (TA), and stir evenly to obtain a DA / TA modified solution; Immerse the washed PP-Cleaning membrane in the modified solution and react at room temperature for 24 h; then dry it in an oven at 50 °C to obtain a modified PP membrane material; 3. Dissolve Zn(CH 3 COO) 2 ·2H 2 O in methanol and continuously stir magnetically at a speed of 600 r·min −1 for 30 min; completely immerse the modified PP membrane material in the Zn(CH 3 COO) 2 ·2H 2 O / methanol solution, and let it stand for 12 h to ensure in-situ growth and firm loading of Zn 2+ ions; 4. Prepare a 2-methylimidazole / methanol solution with a concentration of 0.8 mol / L. After magnetic stirring for 30 min, slowly pour the 2-methylimidazole / methanol solution into the above-mentioned Zn-containing (CH 2+ COO) 3 ·2H 2 O / methanol solution (plastic square box container); react for 6 h to make Zn 2 ions; 2+React fully with 2-methylimidazole; after the reaction is completed, take out the PP / ZIF-8 membrane from the plastic square box; wash the PP / ZIF-8 membrane 3 times with fresh methanol and then 3 times with deionized water to remove the residual reactants on the surface; dry the washed membrane material in a vacuum drying oven at 60 °C for 24 h; denote the modified membrane material prepared with a different precursor concentration from that in Example 1 as PP7 / ZIF-8; as Figure 6 Shown is the microscopic morphology diagram of the PP7 / ZIF-8 membrane material prepared in this example; similar to PP5 / ZIF-8, the ZIF-8 particles are in a dodecahedral structure on the surface of PP, and it can be seen that with the increase in the concentration of the precursor solution, compared with PP5 / ZIF-8, the size of individual particles decreases, while the number of ZIF-8 particles on the surface of PP increases, and there is no agglomeration or stacking phenomenon. Further, XRD is used to determine the crystal form change of PP after in-situ growth of ZIF-8, as Figure 10 Shown. After in-situ growth of ZIF-8, the characteristic peak intensity corresponding to the ZIF-8 particles increases and becomes sharp, and the peak value of PP weakens, indicating that the ZIF-8 particles have successfully grown on the surface of the PP fiber membrane, and with the increase in the concentration of the precursor solution, the number of ZIF-8 particles growing on the surface of PP also gradually increases.

[0034] The application of the PP7 / ZIF-8 membrane material provided in this example in filtering flue gas pollutants is different in that it specifically includes the following steps: 1. Particulate filtration performance test According to the appendix Figure 1 Connect all parts of the filtration experimental device; cut the PP7 / ZIF-8 into a diameter of 55 mm to obtain the air filtration membrane 53 and weigh it; connect the entire pipeline, turn on the positive pressure air pump for ventilation, and ensure that there is no leakage in the entire pipeline; then put the air filtration membrane 53 into the fixture, place the gasket and sealing ring, and tighten the fixture screws to seal the mating surface. 2. Remove the cigarette filter part and place it on the cigarette inserter, and weigh it. Then put the cigarette inserter into the gas collecting bottle, light the cigarette and tighten the gas collecting bottle. Turn on the positive pressure air pump (or positive pressure air pump), adjust the flow rate setting of the gas flowmeter to ensure the oxygen requirement during cigarette combustion and make the cigarette burn fully; after calculation, for the air filtration membrane 53 prepared from PP7 / ZIF-8, the removal efficiencies for PM 0.5, PM 1.0, PM 2.5, PM 5.0, and PM 10 are 80.1, 92.58, 93.46, 95.8, and 96.9% respectively, the pressure drop is 0.07 KPa, and the quality factor is 0.00820 Pa -1 . Wash the filtered air filtration membrane 53 and conduct a cyclic performance test. For the air filtration membrane 53 prepared from the recovered PP7 / ZIF-8, the filtration efficiencies for PM10, PM 5, and PM2.5 in the flue gas are above 89%.

[0035] In each of the drawings, when PP5 / ZIF-8 or PP7 / ZIF-8 is not specifically shown, PP / ZIF-8 only refers to PP5 / ZIF-8 or PP7 / ZIF-8, and does not include PP9 / ZIF-8 and PP11 / ZIF-8.

[0036] Comparative Example 1 The ultra-fine air pollutant particle filtration membrane, preparation method and application in filtering flue gas pollutants provided in this comparative example are based on Example 1, adjusting the membrane material preparation parameters to prepare a PP9 / ZIF-8 air filtration membrane and specifically applying it. Its basic content is the same as that of Example 1. The difference is that the ultra-fine air pollutant particle filtration membrane material is specifically PP9 / ZIF-8 (PP9 / ZIF-8 in each drawing). In the step of preparing the PP9 / ZIF-8 air filtration membrane, the concentration of Zn(CH 3 COO) 2 ·2H 2 O / methanol solution is 0.25 mol / L, and the concentration of 2-methylimidazole / methanol solution is 1.1 mol / L. The modified membrane material obtained with a different precursor concentration from that in Example 1 is denoted as PP9 / ZIF-8.

[0037] Figure 7 This is the microscopic morphology diagram of the PP9 / ZIF-8 membrane material prepared in this comparative example. It can be observed that similar to PP5 / ZIF-8, ZIF-8 forms a dodecahedral structure on the surface of PP, and it can be seen that the number of ZIF-8 on the surface of PP increases significantly. With the increase of the crystallization concentration, ZIF-8 particles aggregate on the surface of PP, showing multi-layer stacking and no gaps between crystals, and the air permeability of the material decreases significantly, and it is no longer possible to balance the filtration quality and filtration efficiency of ultra-fine particles.

[0038] 2. Filtration performance test for ultra-fine particles Using the same filtration experimental device and method as in Example 1, the filtration performance of the PP9 / ZIF-8 membrane material was tested. Among them, only one difference from Example 1 is that the PP9 / ZIF-8 membrane material was cut into circular pieces with a diameter of 55 mm as the air filtration membrane, and the others are the same.

[0039] After calculation, the removal efficiencies of the PP9 / ZIF-8 membrane material for PM 0.5, PM 1.0, PM 2.5, PM 5 and PM 10 are 56.86, 66.84, 68.61, 77.23 and 82.4% respectively, the pressure drop is 0.07 KPa, and the quality factor is 0.00536 Pa -1Compared with PP5 / ZIF-8 and PP7 / ZIF-8, its filtering ability for ultrafine particles is weakened, mainly because the increase in precursor concentration will lead to a sharp increase in the number of crystal particles, which will agglomerate on the PP surface, making it difficult for individual particles to exert their adsorption effect, which is not conducive to the adsorption of particles and gases. At the same time, there is almost no gap between the crystal particles. The filtered PP9 / ZF-8 membrane material discs are then washed with water and subjected to a cycle performance test. The filtration efficiency of the recycled PP9 / ZIF-8 membrane material discs for PM10, PM5 and PM2.5 in flue gas is only about 60%, and the performance is seriously degraded.

[0040] Comparative Example 2 The ultrafine air pollutant particle filter membrane, preparation method and application in filtering flue gas pollutants provided in this comparative example are based on Example 1, and the membrane material preparation parameters are adjusted to prepare and apply the PP11 / ZIF-8 air filter membrane. The basic content is the same as Example 1, except that the ultrafine air pollutant particle filter membrane material is specifically PP11 / ZIF-8 (PP11 / ZIF-8 in each figure), and in the step of preparing the PP9 / ZIF-8 air filter membrane, the Zn(CH 3 COO 2 ·2H 2 The concentration of the O / methanol solution is 0.3 mol / L, the concentration of the 2-methylimidazole / methanol solution is 1.25 mol / L, and the modified membrane material obtained by using a different precursor concentration from Example 1 is recorded as PP11 / ZIF-8.

[0041] Figure 8 This is the microscopic morphology of PP11 / ZIF-8 prepared in this comparative example. Similar to PP5 / ZIF-8, ZIF-8 forms a dodecahedral structure on the PP surface. The in-situ grown ZIF-8 is stacked in multiple layers and can completely wrap the outer surface of the entire PP fiber. The particles are severely aggregated on the PP surface, and there are no gaps between the particles.

[0042] 2. Particle filtration performance test The filtration performance of the PP11 / ZIF-8 membrane material was tested using the same filtration experimental device and method as in Example 1. The only difference from Example 1 was that the PP11 / ZIF-8 membrane material was cut into discs with a diameter of 55 mm as air filtration membranes, and the rest were the same.

[0043] The calculated removal efficiencies of PP11 / ZIF-8 for PM 0.5, PM 1.0, PM 2.5, PM 5, and PM 10 were 52.6, 74.1, 75.8, 82.8, and 86.8%, respectively, with a pressure drop of 0.07 KPa and a quality factor of 0.00505 Pa. -1The filtered PP11 / ZF-8 membrane material wafers were washed with water and subjected to a cyclic performance test. The recovered PP11 / ZIF-8 had a filtration efficiency of approximately 60% for PM10, PM5, and PM2.5 in flue gas.

[0044] Comparative Example 3 The ultra-fine air pollutant particle filtration membrane, preparation method, and application in filtering flue gas pollutants provided in this comparative example were based on Example 1. The basic content was the same as that of Example 1, except that the original PP membrane (PP in each drawing) was used to prepare the air filtration membrane, and the filtration performance was tested.

[0045] Figure 2 is the microscopic morphology diagram of the original PP membrane, which is Figure 2 It can be seen that the surface of the original PP fibers is relatively smooth, the diameter of a single fiber is relatively large, and there are no obvious holes on its surface; further analysis of the pore structure in the PP was carried out through BET testing, as Figure 16 shown. The original PP fiber membrane structure had a weak ability to adsorb nitrogen, a small adsorption capacity, and a small specific surface area, with a specific surface area of 1.881 m² / g.

[0046] Evaluation of the filtration efficiency of the original PP membrane for particulate matter in flue gas. According to the same method as in Example 1, the original PP membrane was prepared into an air filtration membrane and placed in a filtration experimental device for testing. Through calculation, the removal efficiencies of the PP membrane material for PM0.5, PM1.0, PM2.5, PM5.0, and PM10 were 39.5, 68.09, 69.91, 79.1, and 84.4% respectively, the pressure drop was 0.19 Kpa, and the quality factor was 0.0014 Pa -1 。The air filtration membrane prepared from the filtered PP membrane was washed with water and subjected to a cyclic performance test. The recovered PP air filtration membrane had a filtration efficiency of approximately 50% for PM10, PM5, and PM2.5 in flue gas. The surface composition and chemical state of the PP air filtration membrane after filtering flue gas were further analyzed by XPS. The PP air filtration membrane had obvious O 1s, N1s, and C1s peaks at 284.5, 398.8, and 531.5 eV. The O and N in PP increased while C decreased, and the increase rates of O and N were 2.04 and 0.12 respectively. Further testing of the adsorption effect of the PP air filtration membrane on benzene vapor showed that the results were as Figure 17 shown. As the test pressure gradually increased, the benzene vapor adsorption amount gradually increased. When the relative pressure was close to 1, the benzene vapor adsorption amount of the PP air filtration membrane was 84.97 cm 3 / g.

[0047] Comparative Example 4 The ultra-fine air pollutant particle filtration membrane, preparation method and application in filtering flue gas pollutants provided in this comparative example are based on Example 1. The difference lies in that a cleaned PP membrane material (PP-Cleaning in each drawing) is used to prepare the air filtration membrane, and the filtration performance is tested.

[0048] Figure 2 is the microscopic morphology diagram of the cleaned PP. It can be seen from Figure 2 that the surface of the cleaned PP-Cleaning becomes rough, and the diameter of a single fiber decreases.

[0049] Using the same filtration experimental device and method as in Example 1, the filtration performance of the PP-Cleaning membrane material was tested. By calculation, the removal efficiencies of the cleaned PP-Cleaning membrane material for PM 0.5, PM 1.0, PM 2.5, PM 5.0 and PM10 are 34.64, 69.37, 71.78, 81.06 and 86.08% respectively, the pressure drop is 0.19 Kpa, and the quality factor is 0.00124 Pa -1 . As Figure 4 shown, the XRD pattern of the cleaned PP is consistent with the original, indicating that the crystal structure does not change. The filtered cleaned PP was washed with water and the cyclic performance was tested. The filtration efficiencies of the recovered cleaned PP-Cleaning for PM10, PM5 and PM2.5 in the flue gas are about 50%.

[0050] Comparative Example 5 The ultra-fine air pollutant particle filtration membrane, preparation method and application in filtering flue gas pollutants provided in this comparative example are based on Example 1. The difference lies in that a Tris-modified PP membrane material (PP-Tri, or Tri-PP in each drawing) is used to prepare the air filtration membrane, and the filtration performance is tested.

[0051] Figure 3 is the microscopic morphology diagram of the Tris-modified PP. It can be seen from Figure 3 that the surface of the PP-Tri becomes rougher after hydroxyl modification, and a large number of oxidized self-polymerized dopamine particles appear on its surface. As Figure 16 shown, compared with the original PP, the specific surface area of the PP-Tri fiber membrane after surface hydroxyl modification decreases to 1.5576 m² / g, probably because a small amount of polydopamine particles block the PP pores.

[0052] The modified PP membrane material was tested using the same apparatus and method as in Example 1. By calculation, the removal efficiencies of the PP membrane material modified with surface hydroxyl groups for PM 0.5, PM 1.0, PM 2.5, PM 5.0, and PM 10 were 70.32, 85.71, 86.69, 91.19, and 93.51%, respectively, the pressure drop was 0.14 KPa, and the quality factor was 0.0035 Pa -1 . As Figure 4 shown, the XRD pattern of the modified PP-Tri membrane material after surface hydroxyl modification was consistent with that of the original PP. The filtered PP-Tri air filter membrane was washed with water and subjected to a cyclic performance test. The filtration efficiencies of the recovered PP-Tri for PM10, PM 5, and PM2.5 in flue gas could still be maintained above 70%.

[0053] In summary, for the PP / ZIF-8 air filter membranes prepared in Example 1 and Example 2 of the present invention, precursor concentrations within a suitable concentration range were used to control the number of particles, avoiding the appearance of too few or too many particles; by increasing the specific surface area and leaving gaps between the crystals, the loaded ZIF-8 could take into account both the filtration efficiency and the quality factor for ultrafine particles, achieving an enhanced surface charge of the PP fibers without changing the pressure drop, increasing the surface polarization effect, and improving the removal effect for ultrafine flue gas particles with an aerodynamic diameter below 1.0 μm; for the prepared air filter membranes PP5 / ZIF-8 and PP7 / ZIF-8, the filtration efficiencies for PM1.0 and PM0.5 in flue gas could reach over 90%, and after in-situ growth of a single layer of ZIF-8 particles, the membrane material had a lower pressure drop, with the lowest pressure drop reaching 0.07 Kpa. Compared with traditional PP air filter materials, the PP5 / ZIF-8 and PP7 / ZIF-8 air filter materials prepared in the present invention could significantly enhance the adsorption of polar and non-polar substances in flue gas, including nitrogen-containing compounds (nicotine, nitrosamines, nitrogen oxides) and carbon-containing compounds (polycyclic aromatic hydrocarbons, volatile organic compounds); at the same time, washing with water, drying, and reusing could maintain good pressure drop and ultrafine particle filtration efficiency, and could be reused multiple times to reduce the comprehensive cost.

[0054] In the above Examples 1 and 2, after in-situ growth of ZIF-8 on PP fibers of PP5 / ZIF-8 and PP7 / ZIF-8, the specific surface area increased from the original 1.881 m² / g to 105.3 m² / g. The porous structure mainly consisted of micropores with an average pore diameter of about 1.9 nm. A porous network could be formed on the PP surface by introducing ZIF-8. In addition, the unbalanced metal ions and positive charges generated by surface defects on the ZIF-8 surface would polarize the PM surface and enhance the electrostatic interaction. Therefore, the porosity and enhanced electrostatic interaction of the PP material after in-situ growth of ZIF-8 were enhanced, improving the adsorption efficiency of the composite membrane material for ultrafine particles, including PM 0.5, PM 1.0, and PM 2.5. The surface of the original PP was relatively smooth, resulting in poor filtration effect for ultrafine particles in flue gas. As the concentration of Zn 2+ increased in the precursor ligand solution for generating ZIF-8, in Comparative Examples 1-2, as the number of ZIF-8 particles on the PP surface gradually increased and stacking occurred, the material surface became significantly rough. On the one hand, the air permeability deteriorated. On the other hand, the rough surface did not necessarily increase its filtration efficiency for ultrafine particles, but instead showed a significant decrease.

[0055] Therefore, for PP5 / ZIF-8 and PP7 / ZIF-8 prepared in Examples 1-2 of the present invention, the particles in-situ grown on the PP fiber surface were uniformly dispersed, having the best filtration performance for ultrafine particles. The filtration efficiency for 1.0 and 0.5 in flue gas could reach over 90%, and the PP5 / ZIF-8 and PP7 / ZIF-8 membrane materials had a low pressure drop, with the lowest pressure drop able to reach 0.07 Kpa. Comparative Examples 1-2 demonstrated that as the concentration of Zn 2+ gradually increased and exceeded the set threshold, a large number of crystal particles aggregated severely on the PP surface, not only making it difficult to effectively exert the adsorption performance of a single in-situ grown particle, but also directly leading to a decrease in its filtration performance. Therefore, only by using a precursor solution that meets the concentration control requirements can PP5 / ZIF-8 and PP7 / ZIF-8 be obtained. The concentration ranges of Zn 2+ participating in the reaction with 2-methylimidazole must be strictly restricted. Zn 2+Too much or too little cannot achieve the technical effects of the present invention. In addition, by verifying the adsorption effect of the air filtration material prepared by the present invention on benzene vapor, the adsorption capacity of PP5 / ZIF-8 for benzene vapor is always greater than that of PP, indicating that the air filtration material synthesized by the present invention also has potential application space for toxic and harmful pollutants. Each of the above embodiments of the present invention utilizes the porous property and the property of enhancing surface polarity of ZIF-8 to in-situ load it on the surface of PP, which can significantly reduce the pressure drop of the PP fiber membrane while improving the removal effect on ultrafine particles, thus solving the technical contradiction between filtration effect and air permeability, and can be widely applied to the analysis, detection and purification of air pollutants, having good development prospects.

[0056] It should be noted that in other embodiments of the present invention, within the scope of the steps, components, concentrations, ratios, process parameters and conditions recorded in the present invention, other different solutions obtained by specific selection can all achieve the technical effects recorded in the present invention, so the present invention will not list them one by one.

[0057] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention, or modify it into equivalent embodiments with equivalent changes. All equivalent changes made according to the components, ratios and processes of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A method for preparing an ultrafine air pollutant particle filtration membrane, characterized in that: The steps include: S1. Preparation of modified PP fiber membrane material Prepare a Tris solution of appropriate concentration, adjust the pH value to 8.5, then add appropriate amounts of dopamine hydrochloride DA and tannic acid TA, stir evenly to obtain a DA / TA modified solution; The PP fiber membrane is immersed in the modified solution, reacted at room temperature and then dried to obtain a modified PP fiber membrane material; S2. Preparation of PP / ZIF-8 composite film Dissolve an appropriate amount of Zn (CH3COO)2·2H2O in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14-0.20 mol / L; completely immerse the modified PP fiber membrane material in the zinc acetate dihydrate / methanol precursor solution and let it stand for more than 10 h to ensure that Zn 2+ The ions are firmly loaded on the surface of the PP fiber membrane material; Dissolve an appropriate amount of 2-methylimidazole in methanol to prepare a 2-methylimidazole / methanol precursor solution with a concentration of 0.5-0.8 mol / L; The 2-methylimidazole / methanol precursor solution was magnetically stirred for 30 minutes and then slowly added to the zinc acetate dihydrate / methanol precursor solution without the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution 2+ After fully reacting with 2-methylimidazole, ZIF-8 is allowed to grow in situ on the surface of the modified PP fiber, and is bonded to the surface of the PP fiber through hydrogen bonds or covalent bonds. After the reaction, an appropriate number of ZIF-8 crystals with a dodecahedral crystal form, a single-layer arrangement, and uniform distribution on the surface of the PP fiber are obtained, and there are gaps between each ZIF-8 crystal, so as to construct a PP / ZIF-8 composite membrane material microstructure with a rough surface, pore channels and a high specific surface area. After being taken out and dried, an ultrafine air pollutant particle filtration membrane is obtained.

2. The method for preparing the ultrafine air pollutant particle filtration membrane according to claim 1, characterized in that: The step S1 comprises: S1-1. PP pretreatment Take the PP film, wash it with ethanol and deionized water ultrasonically for 3 times, 15 min each time, to remove surface impurities and electret charge, and dry it. The cleaned material is recorded as PP-Cleaning. S1-2, PP modification A 1.2 g / L tris (hydroxymethyl)aminomethane (Tris) solution was prepared, and the pH value was adjusted to 8.5, followed by adding dopamine hydrochloride (DA) and tannic acid (TA), and stirring to obtain a DA / TA modified solution, wherein the concentration of dopamine hydrochloride (DA) was 2 g / L and the concentration of tannic acid (TA) was 4 g / L; The cleaned PP film was immersed in the modified solution, reacted at room temperature for 24 h, and then dried at 50 °C to obtain a modified PP fiber membrane material, which was recorded as PP-Tri.

3. The method for preparing the ultrafine air pollutant particle filtration membrane according to claim 1, characterized in that: The step S2 comprises: S2-1, Zn 2+ Load Dissolve Zn (CH3COO)2·2H2O in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14-0.20 mol / L; completely immerse the modified PP fiber membrane material in the zinc acetate dihydrate / methanol precursor solution and let it stand for 12 hours to ensure that Zn 2+ The ions are firmly loaded on the surface of the PP fiber membrane material; In situ growth of S2-2 and ZIF-8 Dissolve an appropriate amount of 2-methylimidazole in methanol to prepare a 2-methylimidazole / methanol precursor solution with a concentration of 0.5-0.8 mol / L; The 2-methylimidazole / methanol precursor solution was magnetically stirred at a speed of 300-1000 r / min for 10-40 min, and then slowly added to the zinc acetate dihydrate / methanol precursor solution without the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution 2+ After fully reacting with 2-methylimidazole for 6 hours, ZIF-8 is allowed to grow in situ on the surface of the modified PP fiber, and is bonded to the surface of the PP fiber through hydrogen bonds or covalent bonds, thereby obtaining ZIF-8 crystals with a dodecahedral crystal form, a single-layer arrangement, and uniform distribution on the surface of the PP fiber, with gaps between the crystals, and further forming a PP / ZIF-8 composite membrane material with a rough surface, pore channels, and a high specific surface area; S2-3. Post-processing After the reaction is completed, the PP / ZIF-8 composite membrane material is taken out from the solution, washed with fresh methanol three times, and then washed with deionized water three times to remove residual reactants on the surface. Finally, the washed PP / ZIF-8 composite membrane material is dried in a vacuum drying oven at 40-60°C for 8-15 h to obtain an ultrafine air pollutant particle filter membrane.

4. An ultra-fine air pollutant particle filtration membrane, characterized in that: It is prepared by the method described in any one of claims 1 to 3, and has a filtration efficiency of not less than 80% for PM0.5 ultrafine particles, and a quality factor of not less than 0.0075Pa -1 PP / ZIF-8 composite membrane material.

5. Use of the ultrafine air pollutant particle filtration membrane according to claim 4 in filtering flue gas pollutants, characterized in that: The ultrafine air pollutant particle filter membrane is used to filter ultrafine particles PM1.0 and PM0.5 in flue gas, and has a high filtering efficiency and quality factor.

6. The use according to claim 5, characterized in that: It includes the following steps: A1. Set up the filtration experimental device An ultrafine particle filtration experimental device in flue gas is set up, which is composed of a positive pressure air pump, a gas flow meter, a flue gas combustion chamber, a front-end particle counter, an air filter chamber, an air filter membrane, a rear-end particle counter, a differential pressure gauge and a gas collecting bottle. An air filter membrane prepared by a PP / ZIF-8 composite membrane material is unfolded and set in the air filter chamber; the front-end particle counter and the front detection tube of the differential pressure gauge are both set on the pipeline on the front side of the air filter chamber; the rear-end particle counter and the rear detection tube of the differential pressure gauge are both set on the pipeline on the rear side of the air filter chamber; each part is connected in turn with a connecting pipeline to form a closed pipeline that runs through the front and back after being connected; A2. Experimental Preparation The PP / ZIF-8 composite membrane material is cut into discs and weighed, and used as air filter membranes, and placed in an air filter chamber and kept in an unfolded state; After removing the filter part of the cigarette, put it into the smoke combustion chamber and weigh it; Connect the entire pipeline, turn on the positive pressure air pump to perform a ventilation test, and make sure there is no leakage in the entire pipeline; A3. Filtration experiment Light the cigarette and tighten the gas collecting bottle, then turn on the positive pressure air pump and adjust the gas flow meter to ensure the oxygen requirement when the cigarette burns so that the cigarette burns fully. The front-end particle counter and the rear-end particle counter respectively record the values ​​of PM10, PM2.5, PM1.0 and PM0.5 in the pipelines before and after the air filter membrane, and record the pressure difference before and after the air filter chamber at the same time, and then calculate the filtration efficiency and quality factor of the particulate matter.

7. The use according to claim 6, characterized in that: In step A1, the filtration experimental device further includes: an air drying chamber, an air filtration chamber fixture, and an air outlet buffer bottle; The air drying chamber is arranged between the positive pressure air pump and the gas flow meter to dry the air flowing through; The air filter chamber comprises two hollow halves which are symmetrically arranged vertically and horizontally buckled. The PP / ZIF-8 composite membrane material is vertically arranged on the buckling surfaces of the two hollow halves. Then, the two hollow halves and the PP / ZIF-8 composite membrane material are clamped together from the outside by the air filter chamber clamp to keep the PP / ZIF-8 composite membrane material unfolded and to seal the internal space of the air filter chamber. A through hole for connecting a pipeline is provided at the center of the two hollow halves. The gas outlet buffer bottle is arranged between the air filter chamber and the gas collecting bottle, and is used to assist in maintaining the stability of the pressure difference of the pipelines on both sides of the air filter chamber.

8. The use according to claim 6, characterized in that: In step A2, the PP / ZIF-8 composite membrane material is cut into discs with a diameter of 55 mm and weighed. Then, the PP / ZIF-8 composite membrane material disc is used as an air filter membrane and placed between the two hollow halves of the air filter chamber. The screws of the air filter chamber clamp are tightened, and the joint surfaces of the two hollow halves and the air filter membrane are clamped at the same time, so that the interior of the air filter chamber is sealed and the air filter membrane remains in an unfolded state.

9. The use according to claim 6, characterized in that: It also includes the following steps: In step A3, the air flow rate is controlled to be 30 L / min by a gas flow meter.

10. The use according to claim 6, characterized in that: The method also includes the following steps: A4, reuse of PP / ZIF-8 composite membrane material The PP / ZIF-8 composite membrane material discs used in the previous experiment were taken out and washed with deionized water to remove the particles adsorbed on the surface; the washed PP / ZIF-8 composite membrane material discs were dried in an oven at 50°C, and then the filtration efficiency stability performance of the dried PP / ZIF-8 composite membrane material discs was tested for use in new experiments.

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