An ultrafine air pollutant particulate filter membrane, its preparation method, and its application in filtering flue gas pollutants.

Abstract

This invention belongs to the field of air filtration technology, and discloses an ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants. The preparation method includes the following steps: S1, preparing a modified PP fiber membrane material; S2, preparing a PP / ZIF-8 composite membrane, making Zn... 2+ By fully reacting with 2-methylimidazole, a microstructure is constructed in which a suitable number of ZIF-8 crystals are arranged in a monolayer and uniformly distributed on the surface of PP fibers, with gaps between the crystals, forming an ultrafine air pollutant particle filter membrane. This invention also discloses an ultrafine air pollutant particle filter membrane and its application in filtering flue gas pollutants. This filter membrane exhibits good filtration effects for various ultrafine particulate matter in flue gas while maintaining good air permeability, thus resolving the technical contradiction between filtration effect and air permeability. It can be widely used in the analysis, detection, and purification of air pollutants.

Description

Technical Field

[0001] This invention belongs to the field of air filtration and new materials technology, specifically relating to an ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants. Background Technology

[0002] Particulate matter and toxic aerosols are common air pollutants. Particulate matter (PM) is typically composed of extremely small solid particles and droplets, including sulfates, nitrates, ammonia, and carbon black. PM is classified into different levels based on its size, such as PM10, PM2.5, and PM0.5. Epidemiological and toxicological studies have shown that PM contains pathogens that cause heart and respiratory diseases and can enter the lungs and bloodstream through respiration, harming human health. Therefore, long-term exposure to airborne particulate matter can lead to adverse health consequences. Currently, polypropylene (PP) masks are widely used to protect human health and prevent PM exposure due to their excellent filtration performance. Their filtration mechanisms include interception, inertial impaction, Brownian diffusion, and electrostatic particle capture. Surface charge is a key characteristic of filters for effectively removing 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 sacrifices the relative thickness, basis weight, and pressure drop of the air filter chamber, which is detrimental to the development of air filter chambers. Electrostatic charge is a key parameter for effective particulate matter removal. However, in specific environments such as humid conditions (water vapor) and those containing organic chemicals, charge is lost, making it difficult to achieve stable removal results. This can directly lead to poor health for filter users. Some studies report that PP air filter chambers have a relatively short lifespan, typically less than 4 hours under high humidity and temperature conditions, and filtration performance may degrade. Some studies have shown that cigarette smoke aerosols can cause the filtration efficiency of traditional air filter chambers to drop sharply from 92.5% to 33.3% (-Δ59.2%). Cigarette smoke aerosols significantly affect the electrostatic charge characteristics of the filter tip. Therefore, developing highly efficient and stable fiber membranes to address the health hazards caused by particulate matter pollution in complex flue gas is an important issue.

[0003] In air pollutant particulate filtration experiments, filtration efficiency represents the proportion of target particles intercepted by the filter material under specific conditions; that is, the degree of reduction in particle concentration upstream and downstream of the material. It is a core indicator for measuring the ability of a filter material or system to capture target particles, and is usually expressed as a percentage (%). Quality factor (QF), on the other hand, is a core parameter for evaluating the overall performance of filter materials, used to quantify the balance between filtration efficiency and airflow resistance. However, existing filter materials often struggle to achieve a balance between filtration efficiency and quality factor for ultrafine air pollutant particles.

[0004] To address this issue, some researchers have found that adding electrets can optimize the morphology of PP fibers and improve their electroactivity in hazardous environments, which is one of the effective methods to balance pressure drop and improve filtration efficiency. However, this method is largely ineffective for ultrafine particles. Other research results have shown that PP materials incorporating nanoparticles, such as ZnO nanorods (NR), reduced graphene oxide (rGO), manganese dioxide (MnO2), and metal-organic frameworks (MOFs), can significantly improve filtration performance and the ability to absorb pollutants in flue gas. MOFs exhibit excellent performance in air filtration applications due to their tunable porosity, high adsorption capacity, structural stability, and antibacterial properties. However, MOFs mainly exist in powder form, and their poor compatibility with polymers limits their application in air filtration materials, and their performance with ultrafine particles is also poor. 2-Methylimidazolium zinc salt (ZIF-8, zeolite imidazolium ester framework-8) is a zinc ester-based PP material containing ZnO nanorods (NR), reduced graphene oxide (rGO), reduced graphene oxide (mnO2), and reduced graphene oxide (mnO2). 2+ It is a typical porous metal-organic framework (MOF) material composed of ions and 2-methylimidazolium ligands. It has high porosity, thermal stability and chemical stability, and shows unique advantages in catalysis, gas separation and biomedicine. However, due to the complexity of its crystal structure and preparation method, it cannot be directly applied to simultaneously improve the filtration efficiency and quality factor of ultrafine pollutant particles.

[0005] In the prior art, CN 110777537A discloses a ZIF-8 / nonwoven composite material and its preparation method. This method involves directly immersing nonwoven fabric in a native ZIF-8 solution and allowing it to stand for aging, thereby allowing ZIF-8 to be deposited in situ onto the surface of the nonwoven fabric to synthesize a ZIF-8 / nonwoven composite material with a hierarchical porous structure. However, this material does not consider the compatibility between MOFs and the polymer, which can easily lead to unstable MOF particles that are prone to detachment and cannot effectively function for a long period. Furthermore, the requirement for 24 hours of aging results in a long reaction time, which is detrimental to industrial applications. Therefore, it is necessary to consider how to improve the interfacial compatibility between ZIF-8 and the polymer and reduce the reaction time to improve the practicality and stability of ZIF-8-based materials.

[0006] In the prior art, CN 118649562A describes the preparation of a ZIF-8 / PTFE composite membrane filter material by electrospraying ZIF-8 onto the surface of PTFE foam. Specifically, ZIF-8 powder is firmly embedded into the PTFE surface via electrospraying to increase the contact area and bonding strength of the material. The prepared ZIF-8 / PTFE@PPS exhibits good filtration efficiency for fine particulate matter. Figure 2 As shown. However, according to its recorded particulate matter filtration efficiency evaluation data, this material has poor filtration effect on ultrafine particles such as PM 0.3, with a removal efficiency of less than 40%. Therefore, it is evident that various composite materials in existing technologies have unsatisfactory filtration efficiency and quality factor for ultrafine particles below PM1.0, making it difficult to meet the requirements for efficient filtration, accurate detection, and reduced power consumption for these ultrafine particles. If conventional techniques are used to directly increase the quantity and density of ZIF-8 powder to improve filtration efficiency, it will inevitably lead to a significant decrease in the air permeability (quality factor) of the filter material, making it difficult to balance the overall filtration efficiency and quality factor of the filter material. Summary of the Invention

[0007] To address the shortcomings of the existing technology, the present invention aims to provide an ultrafine air pollutant particulate filter membrane, its preparation method, and its application in filtering flue gas pollutants. This PP / ZIF-8 preparation method controls the Zn content in the precursor solution. 2+ Process parameters such as concentration range and magnetic stirring speed in Zn 2+ The appropriate microstructure is constructed during the stepwise reaction with 2-methylimidazole, enabling ZIF-8 to grow oriented and monolayer on the surface of PP fibers with high production efficiency. At the same time, the final ZIF-8 crystals on the fiber membrane are of a single crystal form (dodecahedron) and are relatively uniformly distributed, with gaps between the crystals and no agglomeration. It has good filtration efficiency for various ultrafine particles in flue gas and can maintain good air permeability, thus solving the technical contradiction between filtration efficiency and air permeability, and balancing filtration efficiency and quality factor.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing an ultrafine air pollutant particulate filter membrane, characterized by comprising the following steps:

[0010] S1. Preparation of modified PP fiber membrane material

[0011] Prepare a Tris solution of appropriate concentration and adjust the pH to 8.5. Then add appropriate amounts of dopamine hydrochloride (DA) and tannic acid (TA), and stir until homogeneous to obtain a DA / TA modified solution. Immerse a 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. 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 allow it to stand for at least 10 hours to ensure the Zn content is within acceptable limits. 2+ Ions are firmly loaded onto the surface of the PP fiber membrane material; an appropriate amount of 2-methylimidazole is dissolved in methanol to prepare a 0.5-0.8 mol / L 2-methylimidazole / methanol precursor solution; after magnetically stirring the 2-methylimidazole / methanol precursor solution for 30 min, it is slowly added to the zinc acetate dihydrate / methanol precursor solution that has not been impregnated with the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution is concentrated. 2+ ZIF-8 is oriented and grown in situ on the surface of modified PP fibers by fully reacting with 2-methylimidazole. It is bonded to the surface of PP fibers through hydrogen bonds or covalent bonds. After the reaction, a suitable number of ZIF-8 crystals with dodecahedral crystal form, monolayer arrangement, and uniform distribution on the surface of PP fibers are obtained. There are gaps between each ZIF-8 crystal, which constructs a microstructure of PP / ZIF-8 composite membrane material with rough surface, pore channels and high specific surface area. After drying, ultrafine air pollutant particle filter membranes are obtained, specifically including two types of filter membranes: PP5 / ZIF-8 and PP7 / ZIF-8.

[0012] An ultrafine air pollutant particle filter membrane, characterized in that it is prepared by the method described above, by controlling the Zn content in the precursor solution. 2+ The concentration range and magnetic stirring speed in Zn 2+ During the stepwise reaction with 2-methylimidazole, a suitable number of ZIF-8 crystals are obtained, and a unique microstructure is constructed: ZIF-8 crystals are in-situ orientedly grown on the surface of DA / TA modified PP fiber membranes, and bonded to the surface of PP fibers through hydrogen bonds or covalent bonds, forming a dodecahedral crystal structure, a monolayer arrangement, and a uniform distribution on the surface of PP fibers. Intervals exist between the ZIF-8 crystals, ultimately forming a rough surface, pore channels, and a high specific surface area. The filtration efficiency for PM0.5 ultrafine particles is not less than 80%, while the quality factor is not less than 0.0075 Pa. -1 PP / ZIF-8 composite membrane material.

[0013] An application of the ultrafine air pollutant particle filter membrane in filtering flue gas pollutants involves using the ultrafine air pollutant particle filter membrane to filter ultrafine particulate matter PM1.0 and PM0.5 in flue gas, and it has high filtration efficiency and quality factor.

[0014] Compared with the existing technology, the present invention has at least the following advantages and effects:

[0015] 1. The technical solution provided by this invention controls the concentration range of Zn at room temperature. 2+ Using 2-methylimidazole as the ligand, a unique microstructure is constructed by modifying PP fiber membrane materials with -OH and through controlled reactions. During the reaction, various reaction conditions are adjusted to allow ZIF-8 to grow in situ on the surface of the modified PP fibers. The microstructure is constructed by bonding with the PP fiber surface through hydrogen bonds or covalent bonds. After the reaction, a suitable number of dodecahedral, monolayered ZIF-8 crystals are obtained and uniformly distributed on the surface of the PP fibers, with gaps between the crystals. This further forms PP / ZIF-8 composite membrane materials with rough surfaces, pore channels, and high specific surface areas, specifically including PP5 / ZIF-8 and PP7 / ZIF-8 filter membranes. This filter membrane material significantly improves the filtration efficiency and quality factor for ultrafine air pollutant particles such as PM1.0 and PM0.5. It has a good filtration effect on various ultrafine particles in flue gas and can maintain good air permeability, thus solving the technical contradiction between filtration effect (increasing the number and density of ZIF-8) and air permeability.

[0016] 2. The preparation method provided by this invention has simple operation steps and mild reaction conditions. It can prepare efficient and stable PP / ZIF-8 air filter materials at room temperature. The PP / ZIF-8 composite membrane air filter material prepared by the controlled in-situ growth method allows ZIF-8 to grow uniformly and monolayer on PP through hydrogen bonds or covalent bonds, and is firmly bonded to PP fibers to become an integral material. The modification enables PP to load ZIF-8 well. At the same time, the controlled in-situ growth also solves the problem of constructing a monolayer ZIF-8 microstructure (avoiding stacking) and preventing ZIF-8 from falling off easily during repeated use. The two can be firmly bonded together without the use of other binders.

[0017] 3. The PP / ZIF-8 composite membrane material prepared by this invention, as an ultrafine air pollutant particle filtration membrane, significantly simplifies the preparation process due to the ingenious construction of the microstructure of ZIF-8 crystals on the PP fiber surface during the controlled reaction process. This combination method of in-situ growth of ZIF-8 crystals significantly improves the stability of the composite membrane. Furthermore, the constructed monolayer distribution of dodecahedral crystals expands the application range of ZIF-8, enabling it to achieve high filtration efficiency and high-quality factor in both ultrafine air pollutant filtration and air pollution control. XRD and SEM tests characterize the prepared ZIF-8 crystals as having good crystal form and relatively uniform monolayer distribution on the PP surface, with gaps between the crystals. This facilitates the adhesion of ultrafine particles to the PP / ZIF-8 composite membrane material while ensuring the permeability of clean air.

[0018] 4. The preparation process provided by this invention is suitable for continuous industrial production, and the product quality is stable. Repeated experiments have demonstrated that, in the preparation of the PP / ZIF-8 composite membrane material, the use of a lower precursor concentration can overcome particle aggregation, ensuring that the monolayer ZIF-8 loaded on the PP surface can efficiently adsorb ultrafine pollutant particles and harmful gases, while the gaps between the crystals ensure high air permeability. The two embodiments of this invention use a lower precursor concentration (mainly Zn). 2+ The PP / ZIF-8 fibers prepared at (concentration) showed no aggregation during preparation, exhibiting a monolayer arrangement; however, in several comparative examples, the concentration of Zn in the precursor solution increased. 2+ As the concentration increases, ZIF-8 begins to accumulate in appropriate quantities on the PP fiber surface, forming multi-layered arrangements with no gaps between crystals and diverse crystal forms. This makes the PP fiber surface excessively rough, with very small gaps between the PP fibers. While this excessive roughness does not necessarily improve the material's filtration efficiency for ultrafine particles, it inevitably leads to a significant decrease in air permeability. Although the increased number of crystals increases the contact area between the crystals and the fiber surface, and also increases their bonding stability, the overall removal efficiency for ultrafine particles and the permeability of flue gas significantly decrease. Therefore, reducing the Zn content in the precursor... 2+ The concentration is controlled within the range of 0.14-0.20 mol / L, which has a decisive influence on the microstructure and performance of the final product. If the concentration is too low, the number of ZIF-8 crystals generated will be too small and it will be difficult to effectively cover the surface of PP fibers. If the concentration is too high, the number of ZIF-8 crystals generated will be too large and will form stacks. There will be no gap structure between the crystals, which will affect the air throughput. Both of these will significantly affect the filtration effect and filtration quality factor of ultrafine particles in the air.

[0019] 5. The PP / ZIF-8 composite membrane material prepared by this invention utilizes in-situ grown ZIF-8 to enhance the surface charge of PP fibers and improve the removal efficiency of particulate matter with an aerodynamic diameter of less than 1.0 μm (PM1.0) by leveraging the unbalanced polarization between metals and organic matter in ZIF-8. Compared with traditional PP materials, this polarization enhancement strengthens the removal of ultrafine particles through electrostatic interactions. Furthermore, in-situ growth maximizes the preservation of the porous structure of ZIF-8, increasing adsorption sites on the PP surface and enhancing the adsorption of small molecule gases through pore-filling. Simultaneously, retaining the network structure of the PP material enhances the removal efficiency of aerodynamic particles larger than 1.0 μm through gravity deposition and diffusion, thereby improving the effective coverage of the PP / ZIF-8 composite membrane material for airborne particles of different sizes while maintaining high filtration efficiency.

[0020] 6. Actual testing shows that, compared with traditional PP air filter materials, the PP / ZIF-8 composite membrane material prepared in this invention, as an air filter 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). Firstly, the PP / ZIF-8 composite membrane material modifies the hydroxyl groups loaded on the membrane surface, thereby in-situ loading 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-grown ZIF-8 exhibits excellent adsorption performance for non-polar molecules (such as volatile organic compounds VOCs), thus enabling the material to take into account both polar and non-polar substances, achieving unexpected results and making it widely applicable to the analysis, detection and purification of various air pollutants. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the self-made flue gas particulate matter filtration experimental device according to an embodiment of the present invention;

[0022] Figure 2 This is a SEM image of the original PP air filter material in an embodiment of the present invention;

[0023] Figure 3 SEM image of the cleaned PP-Cleaning air filter material prepared according to an embodiment of the present invention;

[0024] Figure 4 This is a SEM image of the PP-Tri air filter material prepared in the comparative example of this invention;

[0025] Figure 5SEM image of the PP5 / ZIF-8 air filter material prepared in the embodiments of the present invention;

[0026] Figure 6 SEM image of the PP7 / ZIF-8 air filter material prepared in the embodiments of the present invention;

[0027] Figure 7 This is a SEM image of the PP9 / ZIF-8 air filter material prepared in the comparative example of this invention;

[0028] Figure 8 This is a SEM image of the PP11 / ZIF-8 air filter material prepared in the comparative example of this invention;

[0029] Figure 9 The XRD pattern of ZIF-8 obtained in an embodiment of the present invention;

[0030] Figure 10 XRD pattern of the PP / ZIF-8 air filter membrane prepared in an embodiment of the present invention;

[0031] Figure 11 This is a schematic diagram illustrating the filtration efficiency of various membrane materials prepared in the embodiments and comparative examples of the present invention for particulate matter in flue gas.

[0032] Figure 12 This is a schematic diagram showing the air permeability test results of various membrane materials prepared in the embodiments and comparative examples of the present invention;

[0033] Figure 13 This is a schematic diagram of the quality factors of various membrane materials prepared in the embodiments and comparative examples of the present invention;

[0034] Figure 14 The above are XPS spectra of the air filter membranes prepared in the embodiments and comparative examples of the present invention before filtration.

[0035] Figure 15 XPS spectra of the air filter membranes prepared in the embodiments and comparative examples of this invention after filtration;

[0036] Figure 16 The N2 adsorption-desorption curves of PP and PP / ZIF-8 prepared in the embodiments and comparative examples of this invention are shown below.

[0037] Figure 17 This is a schematic diagram of the benzene vapor adsorption capacity curves of PP and PP / ZIF-8 prepared in the embodiments and comparative examples of the present invention.

[0038] In the picture:

[0039] 1. Positive pressure air pump; 2. Air drying chamber; 3. Gas flow meter; 4. Flue gas combustion chamber; 5. Air filter chamber; 51. Hollow half-body; 52. Air filter chamber clamp; 53. Air filter membrane; 6. Outlet buffer bottle; 7. Gas collection bottle; 8. Front-end particle counter; 9. Rear-end particle counter; 10. Differential pressure gauge; 11. Connecting pipeline. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Basic Implementation

[0042] The method for preparing an ultrafine air pollutant particle filter membrane provided in this invention includes the following steps:

[0043] S1. Preparation of modified PP fiber membrane material

[0044] Prepare a Tris solution of appropriate concentration and adjust the pH to 8.5. Then add appropriate amounts of dopamine hydrochloride (DA) and tannic acid (TA), and stir until homogeneous to obtain a DA / TA modified solution.

[0045] A PP fiber membrane is immersed in a modification solution, reacted at room temperature, and then dried to obtain a modified PP fiber membrane material; specifically:

[0046] S1-1, PP pretreatment

[0047] Take a PP film (denoted as PP in the attached diagram), and ultrasonically wash it three times each with ethanol and deionized water for 15 minutes each time to remove surface impurities and electret charges. Then dry the cleaned material and denote it as PP-Cleaning.

[0048] S1-2, PP modification

[0049] A 1.2 g / L Tris solution was prepared and the pH was adjusted to 8.5. Then, dopamine hydrochloride (DA) and tannic acid (TA) were added and stirred until homogeneous 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.

[0050] The cleaned PP film was immersed in the modification solution and reacted at room temperature for 24 h, followed by drying at 50 °C to obtain the modified PP fiber membrane material, denoted as PP-Tri or Tri-PP.

[0051] S2. Preparation of PP / ZIF-8 composite film

[0052] 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 allow it to stand for at least 10 hours to ensure the Zn content is within acceptable limits. 2+ Ions are firmly loaded onto the surface of the PP fiber membrane material;

[0053] 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;

[0054] After magnetically stirring the 2-methylimidazole / methanol precursor solution for 30 min, it was slowly added to the zinc acetate dihydrate / methanol precursor solution that had not been impregnated with the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution was reduced. 2+ ZIF-8 is in situ oriented to grow on the surface of modified PP fibers by fully reacting with 2-methylimidazole. It bonds to the PP fiber surface through hydrogen bonds or covalent bonds. After the reaction, a suitable number of dodecahedral, monolayered ZIF-8 crystals are obtained, uniformly distributed on the PP fiber surface, with gaps between each ZIF-8 crystal. This constructs a microstructure of PP / ZIF-8 composite membrane material with a rough surface, pore channels, and high specific surface area. After drying, an ultrafine air pollutant particle filter membrane is obtained. In the following specific embodiments, the ultrafine air pollutant particle filter membrane is specifically PP5 / ZIF-8 or PP7 / ZIF-8, and the specific steps include:

[0055] S2-1, Zn 2+ load

[0056] Zn(CH3COO)2·2H2O was dissolved in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14-0.20 mol / L. The modified PP fiber membrane material was completely immersed in the zinc acetate dihydrate / methanol precursor solution and allowed to stand for 12 h to ensure that the Zn... 2+ Ions are firmly loaded onto the surface of the PP fiber membrane material;

[0057] In-situ growth of S2-2 and ZIF-8

[0058] 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;

[0059] The 2-methylimidazole / methanol precursor solution was magnetically stirred at 300-1000 r / min for 10-40 min, and then slowly added to the zinc acetate dihydrate / methanol precursor solution that had not been impregnated with the modified PP fiber membrane material. This process ensured that the Zn concentration in the zinc acetate dihydrate / methanol precursor solution increased. 2+ The Zn group reacts fully with 2-methylimidazole for 6 hours to allow Zn to react completely. 2+ In situ directional growth is carried out on the surface of modified PP fibers, and the ZIF-8 crystals with dodecahedral crystal form are bonded to the surface of PP fibers through hydrogen bonds or covalent bonds to obtain a suitable number of ZIF-8 crystals with monolayer arrangement and uniform distribution on the surface of PP fibers. There are gaps (channels) between each ZIF-8 crystal. Then, a PP / ZIF-8 composite membrane material with rough surface, pore channels and high specific surface area microstructure is further constructed.

[0060] S2-3, Post-processing

[0061] After the reaction is complete, the PP / ZIF-8 composite membrane material is taken out from the solution, washed three times with fresh methanol, and then washed three times with deionized water to remove residual reactants on the surface. Finally, the cleaned membrane material is dried in a vacuum drying oven at 40-60℃ for 8-15 hours to obtain an ultrafine air pollutant particle filter membrane.

[0062] An ultrafine air pollutant particle filter membrane is prepared using the aforementioned method, by controlling the Zn content in the precursor solution. 2+ The concentration range and magnetic stirring speed in Zn 2+ During the stepwise reaction with 2-methylimidazole, a suitable amount of ZIF-8 crystals are obtained, and a unique microstructure is constructed: ZIF-8 crystals are in-situ orientedly grown on the surface of DA / TA modified PP fiber membranes, and bonded to the surface of PP fibers through hydrogen bonds or covalent bonds, forming a dodecahedral crystal structure, a monolayer arrangement, and a uniform distribution on the surface of PP fibers. Intervals exist between the ZIF-8 crystals, ultimately forming a rough surface, pore channels, and a high specific surface area. The filtration efficiency for PM1.0 and PM0.5 ultrafine particles is not less than 80%, while the quality factor is not less than 0.0075 Pa. -1 PP / ZIF-8 composite membrane material.

[0063] An application of the aforementioned ultrafine air pollutant particulate filter membrane in filtering flue gas pollutants involves using the membrane to filter ultrafine particulate matter PM1.0 and PM0.5 in flue gas, achieving high filtration efficiency and quality factor. The method includes the following steps:

[0064] A1. Setting up a filtration experimental device

[0065] A self-made filtration experimental device was set up, which consists of a positive pressure air pump 1, a gas flow meter 3, a flue gas combustion chamber 4, a front-end particle counter 8, an air filter chamber 5, an air filter membrane 53, a rear-end particle counter 9, a differential pressure gauge 10, a gas collection bottle 7, an air drying chamber 2, and an outlet buffer bottle 6, forming an experimental device for filtering ultrafine particulate matter in flue gas.

[0066] An air filter membrane 53, made of PP / ZIF-8 composite membrane material, is arranged in a planar unfolded state inside the air filter chamber 5.

[0067] The front detection tubes of the front particle counter 8 and the differential pressure gauge 10 are both set on the pipeline in front of the air filter chamber 5 (including the air filter membrane 53); the rear detection tubes of the rear particle counter 9 and the differential pressure gauge 10 are both set on the pipeline behind the air filter chamber 5 (including the air filter membrane 53); the various parts are connected in sequence by the connecting pipeline 11 to form a closed pipeline that runs through the front and rear.

[0068] The air drying chamber 2 is located between the positive pressure air pump 1 and the gas flow meter 3, and is used to dry the air flowing through it.

[0069] The air filter chamber 5 is cylindrical in shape and includes two hollow halves 51 that are symmetrically arranged vertically and horizontally interlocked (the hollow parts inside are opposite each other and sealed after interlocking) and an air filter chamber clamp 52. The air filter chamber clamp 52 (opposing screws + screw rods) clamps the two horizontally interlocked hollow halves 51 from the outside. There can be one or two sets. In this embodiment, there are two sets that are parallel to each other.

[0070] The PP / ZIF-8 composite membrane material is cut into circular air filter membranes 53, which are first vertically set on the interlocking surfaces of two hollow halves 51. Then, the air filter chamber clamp 52 clamps the two hollow halves 51 together with the interlocking surfaces of the air filter membrane 53, so that the air filter membrane 53 is kept in an unfolded and taut state in the air filter chamber 5, dividing the internal space of the air filter chamber 5 into two parts, so as to evenly filter the flue gas. After the air filter chamber clamp 52 clamps, it also seals the interlocking surfaces and the internal space of the air filter chamber 5. Each of the two hollow halves 51 has a through hole at the center position for connecting the connecting pipe 11. The flue gas enters the air filter chamber 5 through the pipe connected by the through hole, passes through the air filter membrane 53 and then exits the air filter chamber 5, and enters the outlet buffer bottle 6 and the gas collection bottle 7. In order to enhance the sealing between the interlocking surfaces and the air filter membrane 53, a sealing ring or elastic gasket can also be set between the interlocking surfaces and the air filter membrane 53.

[0071] The outlet buffer bottle 6 is located between the air filter chamber 5 and the air collection bottle 7 to expand the storage space of filtered air and help maintain the stability of the pressure difference between the pipelines on both sides of the air filter chamber 5.

[0072] according to Figure 1 As shown, the above components are connected to each other in sequence by connecting pipes 11, forming a closed pipe that runs through the front and back.

[0073] A2. Experimental Preparation

[0074] The PP / ZIF-8 composite membrane material is cut into round pieces and weighed to serve as air filter membrane 53. The air filter membrane 53 is placed in the air filter chamber 5 and kept in an unfolded and taut state.

[0075] After removing the cigarette filter, place it into the flue gas combustion chamber 4 and weigh it.

[0076] Specifically, the PP / ZIF-8 composite membrane material is cut into circular pieces with a diameter of 55 mm as air filter membrane 53 and weighed. Then, the circular pieces of PP / ZIF-8 composite membrane material (air filter membrane 53) are placed between the two hollow halves 51 of the air filter chamber 5. The screws of the air filter chamber clamp 52 are tightened, and the joint surfaces of the two hollow halves 51 and the air filter membrane 53 are clamped together to seal the interior of the air filter chamber 5 and keep the air filter membrane 53 in an unfolded state.

[0077] By connecting pipe 11, each part is connected to form the entire pipeline. Then, the positive pressure air pump 1 is turned on to conduct an air flow test to confirm that there are no leaks in the entire pipeline before proceeding to the next step.

[0078] A3. Filtration Experiment

[0079] First, control the air flow rate to 30 L / min using gas flow meter 3; light the cigarette and tighten the gas collection bottle 7, then turn on the positive pressure air pump 1 and adjust the gas flow meter 3 to ensure the oxygen requirements during combustion, so that the cigarette burns completely. The values ​​of PM10, PM2.5, PM1.0 and PM0.5 in the pipelines before and after the air filter membrane 53 are recorded by the front particle counter 8 and the rear particle counter 9, respectively. At the same time, the pressure difference before and after is recorded, and then the filtration efficiency and quality factor of particulate matter are calculated.

[0080] A4, Reuse of PP / ZIF-8 Composite Membrane Materials

[0081] Take out the air filter 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 filter membrane 53 in an oven at 50°C, and then test the filtration efficiency stability of the dried air filter membrane 53 for use in the new experiment.

[0082] This invention focuses on the balance between filtration efficiency and quality factor for ultrafine pollutant particles, using Zn at room temperature. 2+Using 2-methylimidazole as the ligand and modifying commercial PP membrane materials with -OH groups, a highly efficient and stable ZIF-8 air filter material can be prepared at room temperature. Furthermore, by controlling the Zn content in the precursor solution... 2+ The concentration range and magnetic stirring speed, among other process parameters, are used to control Zn. 2+ During the reaction with 2-methylimidazole, the production quantity, growth position, and crystal form of crystals are controlled. By using an appropriate number of crystals (neither too many nor too few) to construct a unique microstructure (single-layer arrangement, uniform distribution, and gaps between each other), this air filter membrane material can maintain good air permeability while having a good filtration effect on various ultrafine particles in flue gas. This solves the technical contradiction between filtration effect and air permeability that exists in similar materials. It can simultaneously possess high filtration efficiency and quality factor, and can be widely used in the analysis, detection, and purification of air pollutants.

[0083] See Figures 2 to 17 The following provides a detailed description using several specific embodiments, comparative examples, and test results.

[0084] Example 1

[0085] The ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants provided in this embodiment are specific selections based on the aforementioned basic embodiments. The difference lies in that the ultrafine air pollutant particle filter membrane material is specifically a PP5 / ZIF-8 air filter membrane, and its preparation method includes the following steps:

[0086] 1. Remove the middle layer of the medical surgical mask. The middle layer is mainly made of PP material (original PP, referred to as PP in the attached drawings). Wash it with ethanol and deionized water three times each by ultrasonication for 15 minutes each time to remove surface impurities and electret charges. The dried membrane material is referred to as PP-Cleaning.

[0087] 2. Prepare a 1.2 g / L Tris (tris(hydroxymethyl)aminomethane) solution and adjust its pH to 8.5; then add 2 g of dopamine hydrochloride (DA) and 4 g of tannic acid (TA), and stir until homogeneous to obtain a DA / TA modified solution; immerse the cleaned PP membrane in the modified solution and react at room temperature for 24 h; then dry in a 50℃ drying oven to obtain the modified PP membrane material, denoted as PP-Tri or Tri-PP;

[0088] 3. Dissolve an appropriate amount of Zn(CH3COO)2·2H2O in methanol to obtain Zn 2+ A 0.1425 mol / L Zn(CH3COO)2·2H2O / methanol solution was prepared at 600 r·min. −1The solution was continuously magnetically stirred at a high speed for 30 min; then the modified PP membrane (PP-Tri) was completely immersed in a Zn(CH3COO)2·2H2O / methanol solution and allowed to stand for 12 h to ensure the Zn content was within acceptable limits. 2+ The ions are firmly loaded;

[0089] 4. Prepare a 0.568 mol / L solution of 2-methylimidazole dissolved in methanol. After magnetic stirring for 30 min, slowly pour the 2-methylimidazole / methanol solution into the Zn-containing container fitted with a PP membrane. 2+ In a (CH3COO)2·2H2O / methanol solution (plastic square container); react for 6 h to allow Zn 2+ React fully with 2-methylimidazole; during the reaction, wait for Zn 2+ Once all of it is consumed, the reaction terminates, leaving behind a portion of 2-methylimidazole. After the reaction is complete, the prepared PP / ZIF-8 membrane is removed from the plastic square container and washed three times with fresh methanol, followed by three washes with deionized water to remove residual reactants from the surface. The washed PP / ZIF-8 membrane material is then dried in a vacuum drying oven at 60°C for 24 hours. The prepared PP / ZIF-8 membrane material is designated as PP5 / ZIF-8, which is the ultrafine air pollutant particle filter membrane of this embodiment.

[0090] like Figure 5 As shown in the microstructure diagram of the PP5 / ZIF-8 membrane material prepared in this embodiment, the ZIF-8 crystal particles in this material have a dodecahedral structure on the surface of the PP fibers. There are an appropriate number of ZIF-8 crystal particles on the fiber surface, and each crystal particle is nearly uniformly distributed on the fiber surface. Furthermore, the ZIF-8 crystal particles do not exhibit aggregation or stacking on the fibers, and a large gap is maintained between each ZIF-8 crystal particle. On the one hand, this microstructure can maintain the characteristic of a large specific surface area of ​​individual crystal particles, 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 maintaining a large gap between each ZIF-8 crystal particle can maintain good air permeability of the material.

[0091] Further XRD was used to observe the changes in the crystal structure of PP after in-situ growth of ZIF-8 on PP5 / ZIF-8 film material. Figure 9 As shown in the figure, the standard spectrum of ZIF-8 and the spectrum of ZIF-8 actually prepared in the embodiment of the present invention are displayed. The comparison shows that the standard spectrum and the ZIF-8 actually prepared in this embodiment have a high degree of similarity, indicating that the ZIF-8 prepared in this embodiment has a good crystal form and high purity. Figure 10 This is the XRD pattern obtained from in-situ growth on the surface of PP fibers in this embodiment. (Observation) Figure 10It can be seen that after in-situ growth of ZIF-8 particles, the intensity of the characteristic peak at the corresponding ZIF-8 particle position on the PP fiber surface increases, indicating that ZIF-8 has been successfully grown on the PP fiber membrane surface; and with the increase of Zn... 2+ As the concentration increases, the peak shape gradually becomes sharper, indicating that the amount of ZIF-8 growing in situ on the PP surface continues to increase. Therefore, controlling the Zn concentration is crucial. 2+ The concentration can control the total number of particles generated, avoiding both too many and too few.

[0092] Further analysis of the surface composition and chemical state of the PP5 / ZIF-8 membrane material using XPS was conducted. Figure 14 As shown, the characteristic peaks of O 1s, N 1s and C 1s originate from 284.5, 398.8 and 531.5 eV of PP. A new Zn 2p peak was found at 1045 eV in the PP / ZIF-8 membrane material, indicating that ZIF-8 particles were successfully grown on the surface of the PP fiber membrane.

[0093] The application of the PP5 / ZIF-8 material in filtering flue gas pollutants provided in this embodiment differs in that it specifically includes the following steps:

[0094] 1. Cut the PP5 / ZIF-8 membrane material into circular pieces with a diameter of 55 mm (air filter membrane 53) and weigh them; according to Figure 1 As shown, after connecting each part of the filtration experimental device sequentially through the connecting pipe 11, the positive pressure air pump is first turned on to ventilate and ensure that there are no leaks in the entire pipeline. Then, the air filter membrane 53 made of PP5 / ZIF-8 is placed into the air filter chamber. Specifically, it is placed vertically on the mating surfaces of two hollow halves 51 that are symmetrically arranged vertically and horizontally interlocked. Then, the opposing screws of the air filter chamber clamp 52 are tightened to clamp the two hollow halves 51 together with the PP / ZIF-8 composite membrane material (air filter membrane 53), so that the air filter membrane 53 remains unfolded and taut, and the internal space of the air filter chamber 5 is sealed. The air filter membrane 53 divides the internal space of the air filter chamber 5 into two parts. In order to enhance the sealing of the air filter chamber 5, in this embodiment, a gasket and a sealing ring (not shown in the figure) are also provided between the mating surfaces of the two hollow halves 51 and the two sides of the air filter membrane 53. Under the clamping force of the air filter chamber clamp 52, the annular mating surfaces are sealed at all points.

[0095] 2. Conduct filtration performance tests.

[0096] Remove the cigarette filter and place it in the cigarette holder, then weigh it. Next, place the cigarette holder into the gas collecting bottle, light the cigarette, and tighten the gas collecting bottle. Turn on the positive pressure pump 1 and adjust the gas flow meter 3 to ensure the oxygen requirements for complete combustion. The experimental results are as follows: Figure 11As shown. Calculations show that the removal efficiencies of PP5 / ZIF-8 for PM0.5, PM1.0, PM2.5, PM5.0, and PM10 are 84.6%, 89.9%, 90.6%, 93.9%, and 95.6%, respectively. The pressure drop and quality factor at both ends of the air filter chamber in this embodiment are shown below. Figure 12 and Figure 13 As shown, the PP5 / ZIF-8 membrane material has a pressure drop of 0.08 kPa and a quality factor of 0.00762 Pa. -1 The filtered PP5 / ZF-8 membrane material (air filter membrane 53) was washed with water and subjected to circulation performance testing. The recovered air filter membrane 53 showed filtration efficiencies of over 85% for PM10, PM5, and PM2.5 in flue gas. Further analysis of the pore structure in the PP was conducted using BET testing, such as... Figure 16 As shown, the specific surface area of ​​the membrane material after in-situ growth of ZIF-8 increased from the original 1.881 m² / g to 105.3 m² / g. This significant increase in the specific surface area of ​​the PP / ZIF-8 membrane material is mainly attributed to the porous structure of ZIF-8, which promotes the adsorption of ultrafine particles or gases. According to the IUPAC curve classification, PP / ZIF-8 conforms to a Type I isotherm, indicating that gases undergo monolayer physical adsorption on the membrane material surface and that the material contains a large number of microporous structures.

[0097] 3. The surface composition and chemical state of the PP / ZIF-8 membrane material after adsorption were further analyzed using XPS. XPS spectra are shown below. Figure 15 The results show distinct O 1s, N 1s, C 1s, and Zn 2p peaks at 284.5, 398.8, 531.5, and 1045 eV. The Zn content in the PP / ZIF-8 membrane material remained unchanged before and after filtration, indicating that ZIF-8 is tightly attached to the PP fiber membrane through strong coordination or chemical bonds. This implies 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, with C and N growth rates of 0.66% and 3.79%, respectively. The PP / ZIF-8 membrane material captured or adsorbed nitrogen-containing compounds (nicotine, nitrosamines, nitrogen oxides) and carbon-containing compounds (polycyclic aromatic hydrocarbons, volatile organic compounds) from complex flue gas, indicating that the PP / ZIF-8 membrane material can preferentially remove nitrogen and carbon pollutants from flue gas. Oxygen-containing compounds (CO and CO2) competitively inhibit the preferential adsorption of nitrogen and carbon-containing compounds by PP / ZIF-8, resulting in a relative decrease in O content. To further evaluate the adsorption capacity of PP for carbon-containing compounds, the adsorption effect of the membrane material when benzene is used as a gaseous pollutant was tested using the static adsorption method. The results are as follows: Figure 17 As shown. By Figure 17It can be seen that the benzene vapor adsorption capacity gradually increases with increasing test pressure, and its adsorption capacity is always greater than that of PP; when the relative pressure is close to 1, the adsorption capacity of the PP / ZIF-8 membrane material for benzene vapor is 90.44 cm⁻¹. 3 / g, which is still significantly greater than PP.

[0098] Example 2

[0099] The ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants provided in this embodiment are specific selections based on the aforementioned basic embodiments. The difference lies in that the ultrafine air pollutant particle filter membrane material is specifically PP7 / ZIF-8, and the preparation method includes the following steps:

[0100] 1. Remove the middle layer of the medical surgical mask. The middle layer is mainly made of PP material. Wash it with ethanol and deionized water three times each, 15 minutes each time, to remove surface impurities and electret charges. The dried PP film material is called PP-Cleaning.

[0101] 2. Prepare a 1.2 g / L Tris (tris(hydroxymethyl)aminomethane) solution and adjust the pH to 8.5; then add 2 g of dopamine hydrochloride (DA) and 4 g of tannic acid (TA), and stir until homogeneous to obtain a DA / TA modified solution; immerse the cleaned PP-Cleaning membrane in the modified solution and react at room temperature for 24 h; then dry in a 50℃ drying oven to obtain the modified PP membrane material;

[0102] 3. Dissolve 0.2 mol / L Zn(CH3COO)2·2H2O in methanol at a speed of 600 r·min −1 The mixture was continuously magnetically stirred at a high speed for 30 min; the modified PP film material was then completely immersed in a Zn(CH3COO)2·2H2O / methanol solution and allowed to stand for 12 h to ensure the Zn content was within acceptable limits. 2+ In-situ ion growth and firm loading;

[0103] 4. Prepare a 0.8 mol / L 2-methylimidazole / methanol solution. After magnetic stirring for 30 min, slowly pour the 2-methylimidazole / methanol solution into the Zn-containing container loaded with the modified PP membrane. 2+ In a (CH3COO)2·2H2O / methanol solution (plastic square container); react for 6 h to allow Zn 2+The PP / ZIF-8 membrane was reacted with 2-methylimidazole until fully reacted. After the reaction was complete, the membrane was removed from the plastic box. The membrane was washed three times with fresh methanol and then three times with deionized water to remove residual reactants. The washed membrane material was dried in a vacuum drying oven at 60°C for 24 hours. The modified membrane material prepared using a different precursor concentration than that in Example 1 was designated as PP7 / ZIF-8. Figure 6 The image shows the microstructure of the PP7 / ZIF-8 membrane material prepared in this embodiment. Similar to PP5 / ZIF-8, ZIF-8 particles exhibit a dodecahedral structure on the PP surface. It can be observed that as the precursor solution concentration increases, the size of individual particles decreases compared to PP5 / ZIF-8, while the number of ZIF-8 particles on the PP surface increases, without aggregation or stacking. Further XRD was used to determine the crystal structure changes of PP after in-situ ZIF-8 growth, such as… Figure 10 As shown, the characteristic peak intensity corresponding to ZIF-8 particles increased and became sharper after in-situ growth of ZIF-8, while the peak value of PP weakened, indicating that ZIF-8 particles were successfully grown on the surface of PP fiber membrane. Furthermore, the number of ZIF-8 particles grown on the PP surface gradually increased with the increase of precursor solution concentration.

[0104] The application of the PP7 / ZIF-8 membrane material provided in this embodiment for filtering flue gas pollutants differs in that it specifically includes the following steps:

[0105] 1. Particulate matter filtration performance test

[0106] According to the appendix Figure 1 Connect the various parts of the filtration experimental apparatus; cut PP7 / ZIF-8 into 55 mm diameter pieces to obtain air filter membrane 53 and weigh it; connect the entire pipeline, turn on the positive pressure air pump to ventilate, and confirm that there are no leaks in the entire pipeline; then put the air filter membrane 53 into the clamp, put on the gasket and sealing ring, tighten the clamp screws, and seal the mating surface.

[0107] 2. Remove the cigarette filter and place it on the cigarette holder, then weigh it. Next, place the cigarette holder into the gas collection bottle, light the cigarette, and tighten the gas collection bottle. Turn on the positive pressure air pump (or positive pressure pump), adjust the flow rate setting of the gas flow meter to ensure the oxygen requirements for cigarette combustion, allowing for complete combustion. Calculations show that the air filter membrane 53 prepared by PP7 / ZIF-8 has removal efficiencies of 80.1%, 92.58%, 93.46%, 95.8%, and 96.9% for PM 0.5, PM 1.0, PM 2.5, PM 5.0, and PM 10, respectively, with a pressure drop of 0.07 kPa and a quality factor of 0.00820 Pa. -1The filtered air filter membrane 53 was washed with water and subjected to a cycle performance test. The air filter membrane 53 prepared from the recycled PP7 / ZIF-8 had a filtration efficiency of over 89% for PM10, PM5 and PM2.5 in flue gas.

[0108] In the accompanying drawings, unless PP5 / ZIF-8 or PP7 / ZIF-8 is specifically indicated, PP / ZIF-8 refers only to PP5 / ZIF-8 or PP7 / ZIF-8, excluding PP9 / ZIF-8 and PP11 / ZIF-8.

[0109] Comparative Example 1

[0110] The ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants provided in this comparative example are based on Example 1. The membrane material preparation parameters are adjusted to prepare the PP9 / ZIF-8 air filter membrane and its specific application are described. The basic content is the same as that of Example 1. The difference is that the ultrafine air pollutant particle filter membrane material is specifically PP9 / ZIF-8 (PP9 / ZIF-8 in the figures). In the step of preparing the PP9 / ZIF-8 air filter membrane, the concentration of the Zn(CH3COO)2·2H2O / methanol solution is 0.25 mol / L, and the concentration of the 2-methylimidazole / methanol solution is 1.1 mol / L. The modified membrane material obtained by using a different precursor concentration than that in Example 1 is referred to as PP9 / ZIF-8.

[0111] Figure 7 The image shows the microstructure of the PP9 / ZIF-8 membrane material prepared in this comparative example. As can be seen, similar to PP5 / ZIF-8, ZIF-8 forms a dodecahedral structure on the PP surface. It can also be seen that the number of ZIF-8 on the PP surface increases significantly. With the increase of crystallization concentration, ZIF-8 particles aggregate on the PP surface, resulting in multi-layer stacking with no gaps between crystals. The air permeability of the material decreases significantly, making it impossible to maintain both the filtration quality and filtration efficiency for ultrafine particles.

[0112] 2. Testing of ultrafine particulate matter filtration performance

[0113] The filtration performance of the PP9 / ZIF-8 membrane material was tested using the same filtration experimental apparatus and method as in Example 1. The only difference from Example 1 was that the PP9 / ZIF-8 membrane material was cut into 55 mm diameter discs to serve as air filter membranes; all other aspects were the same.

[0114] Calculations showed that the removal efficiencies of the PP9 / ZIF-8 membrane material for PM0.5, PM1.0, PM2.5, PM5, and PM10 were 56.86%, 66.84%, 68.61%, 77.23%, and 82.4%, respectively, with a pressure drop of 0.07 kPa and a quality factor of 0.00536 Pa. -1 Compared to PP5 / ZIF-8 and PP7 / ZIF-8, its filtration capacity for ultrafine particles is weakened. This is mainly because the increased precursor concentration leads to a sharp increase in the number of crystal particles, which agglomerate on the PP surface, making it difficult for individual particles to exert their adsorption effect, which is not conducive to the adsorption of particulate matter and gas. At the same time, there are almost no gaps between the crystal particles. Then, the filtered PP9 / ZF-8 membrane material discs were washed with water and subjected to cycle performance tests. The recovered PP9 / ZIF-8 membrane material discs had a filtration efficiency of only about 60% for PM10, PM5 and PM2.5 in flue gas, which is a serious performance degradation.

[0115] Comparative Example 2

[0116] The ultrafine air pollutant particle filter membrane, its preparation method, and its application in filtering flue gas pollutants provided in this comparative example are based on Example 1. The membrane material preparation parameters are adjusted, a PP11 / ZIF-8 air filter membrane is prepared, and then applied. The basic content is the same as that of Example 1. The difference is that the ultrafine air pollutant particle filter membrane material is specifically PP11 / ZIF-8 (PP11 / ZIF-8 in each figure). In the step of preparing the PP9 / ZIF-8 air filter membrane, the concentration of the Zn(CH3COO)2·2H2O / 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 using a different precursor concentration than that in Example 1 is denoted as PP11 / ZIF-8.

[0117] Figure 8 The image shows the microstructure 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 multi-layered and can completely cover the outer surface of the entire PP fiber. The particles are severely aggregated on the PP surface with no gaps between them.

[0118] 2. Particulate matter filtration performance test

[0119] The filtration performance of the PP11 / ZIF-8 membrane material was tested using the same filtration experimental apparatus and method as in Example 1. The only difference from Example 1 was that the PP11 / ZIF-8 membrane material was cut into 55 mm diameter discs to serve as air filter membranes; all other aspects were the same.

[0120] Calculations showed that the removal efficiencies of PP11 / ZIF-8 for PM0.5, PM1.0, PM2.5, PM5, and PM10 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. -1 The filtered PP11 / ZF-8 membrane material discs were washed with water and subjected to circulation performance tests. The recovered PP11 / ZIF-8 had a filtration efficiency of about 60% for PM10, PM5 and PM2.5 in flue gas.

[0121] Comparative Example 3

[0122] 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. The basic content is the same as that of Example 1. The difference is that the air filter membrane is prepared using the original PP membrane (PP in each figure) and the filtration performance is tested.

[0123] Figure 2 This is a microscopic morphology image of the original PP film, created by... Figure 2 It can be seen that the surface of the original PP fibers is relatively smooth, the diameter of individual fibers is relatively large, and no obvious pores appear on the surface; further analysis of the pore structure in PP using BET testing, such as... Figure 16 As shown, the original PP fiber membrane structure has a weak ability to adsorb nitrogen, a small adsorption capacity, and a small specific surface area of ​​1.881 m² / g.

[0124] The filtration efficiency of the original PP membrane for particulate matter in flue gas was evaluated. Following the same method as in Example 1, the original PP membrane was prepared as an air filter membrane and placed in a filtration experimental apparatus for testing. Calculations showed that 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, with a pressure drop of 0.19 kPa and a quality factor of 0.0014 Pa. -1 The air filter membrane prepared from the filtered PP membrane was washed with water and subjected to cycle performance testing. The filtration efficiency of the recovered PP air filter membrane for PM10, PM5, and PM2.5 in flue gas was approximately 50%. XPS analysis was used to further analyze the surface composition and chemical state of the PP air filter membrane after flue gas filtration. The PP air filter membrane exhibited significant O 1s, N 1s, and C 1s peaks at 284.5, 398.8, and 531.5 eV. O and N increased while C decreased in PP, with O and N increases at rates of 2.04 and 0.12, respectively. Further testing of the PP air filter membrane's adsorption effect on benzene vapor yielded the following results: Figure 17As shown, the benzene vapor adsorption capacity gradually increases with increasing test pressure. When the relative pressure approaches 1, the adsorption capacity of the PP air filter membrane for benzene vapor is 84.97 cm⁻¹. 3 / g.

[0125] Comparative Example 4

[0126] 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. The difference is that the air filter membrane is prepared using cleaned PP membrane material (PP-Cleaning in each figure) and the filtration performance is tested.

[0127] Figure 2 To clean the microstructure of PP, by Figure 2 It can be seen that the surface of PP-Cleaning becomes rough after cleaning, and the diameter of individual fibers decreases.

[0128] The filtration performance of the PP-Cleaning membrane material was tested using the same filtration experimental apparatus and method as in Example 1. Calculations showed that the removal efficiencies of the cleaned PP-Cleaning membrane material for PM0.5, PM1.0, PM2.5, PM5.0, and PM10 were 34.64%, 69.37%, 71.78%, 81.06%, and 86.08%, respectively, with a pressure drop of 0.19 kPa and a quality factor of 0.00124 Pa. -1 .like Figure 4 As shown, the XRD pattern of the cleaned PP is consistent with that of the original, indicating that the crystal structure remains unchanged. The filtered cleaned PP was then washed with water and subjected to a circulation performance test. The recovered cleaned PP-Cleaning showed a filtration efficiency of approximately 50% for PM10, PM5, and PM2.5 in flue gas.

[0129] Comparative Example 5

[0130] 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. The difference is that Tris-modified PP membrane material (PP-Tri or Tri-PP in the figures) is used to prepare the air filter membrane, and the filtration performance is tested.

[0131] Figure 3 Microstructure images of Tris-modified PP, from Figure 3 It can be seen that the surface of PP-Tri after hydroxyl modification becomes rougher, and a large number of oxidized self-polymerized dopamine particles appear on its surface. For example... Figure 16As shown, compared to the original PP, the specific surface area of ​​the PP-Tri fiber membrane modified with surface hydroxyl groups decreased to 1.5576 m² / g, which may be due to a small amount of polydopamine particles clogging the PP pores.

[0132] The modified PP membrane material was tested using the same apparatus and method as in Example 1. Calculations showed that the removal efficiencies of the surface-hydroxyl-modified PP membrane material for PM0.5, PM1.0, PM2.5, PM5.0, and PM10 were 70.32%, 85.71%, 86.69%, 91.19%, and 93.51%, respectively, with a pressure drop of 0.14 kPa and a quality factor of 0.0035 Pa. -1 .like Figure 4 As shown, the XRD pattern of the modified PP-Tri membrane material after surface hydroxyl modification is consistent with that of the original PP. The filtered PP-Tri air filter membrane was washed with water and subjected to a cycle performance test. The recovered PP-Tri still maintained a filtration efficiency of over 70% for PM10, PM5, and PM2.5 in flue gas.

[0133] In summary, the PP / ZIF-8 air filter membranes prepared in Examples 1 and 2 of this invention use a precursor concentration within a suitable range to control the particle number and avoid the phenomenon of too few or too many particles. By increasing the specific surface area and leaving gaps between the crystals, the loaded ZIF-8 can simultaneously achieve both filtration efficiency and quality factor for ultrafine particles. This achieves the effect of increasing the removal efficiency of ultrafine flue gas particles with an aerodynamic diameter of less than 1.0 μm by enhancing the surface charge of PP fibers and improving surface polarization without changing the pressure drop. The prepared air filter membranes PP5 / ZIF-8 and PP7 / ZIF-8 can achieve a filtration efficiency of more than 90% for PM1.0 and PM0.5 in flue gas. Furthermore, the membrane material has a low pressure drop after in-situ growth of monolayer ZIF-8 particles, 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 this invention 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). At the same time, water washing, drying and reuse can maintain good pressure drop and ultrafine particulate filtration efficiency, and can be reused multiple times to reduce overall costs.

[0134] In Examples 1 and 2 above, 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 was mainly micropores with an average pore size of about 1.9 nm. Introducing ZIF-8 can form a porous network on the PP surface. Furthermore, the positive charge generated by the unbalanced metal ions and surface defects on the ZIF-8 surface polarizes the PM surface, enhancing electrostatic interactions. Therefore, the in-situ growth of ZIF-8 enhances the porosity and electrostatic interactions of the PP material, improving the adsorption efficiency of the composite membrane material for ultrafine particles, including PM 0.5, PM 1.0, and PM 2.5. The original PP surface is relatively smooth and has a poor filtration effect for ultrafine particles in flue gas. With the addition of Zn in the precursor ligand solution for ZIF-8 formation... 2+ As the concentration increased, in Comparative Examples 1-2, the number of ZIF-8 particles on the PP surface gradually increased and layering occurred, making the material surface significantly rougher. On the one hand, the air permeability decreased, and on the other hand, the rough surface did not necessarily increase its filtration efficiency for ultrafine particles; instead, it significantly decreased.

[0135] Therefore, the PP5 / ZIF-8 and PP7 / ZIF-8 membranes prepared in Examples 1-2 of the present invention exhibit uniform dispersion of particles grown in situ on the surface of PP fibers, resulting in the best filtration performance for ultrafine particles. The filtration efficiency for 1.0 and 0.5 g / L flue gas can reach over 90%, and the PP5 / ZIF-8 and PP7 / ZIF-8 membrane materials also exhibit low pressure drop, with a minimum pressure drop reaching 0.07 kPa. Comparative Examples 1-2 demonstrate that with the increase of Zn content in the precursor... 2+ As the concentration gradually increases and exceeds the set threshold, a large number of crystal particles aggregate severely on the PP surface. This not only makes it difficult to effectively utilize the adsorption capacity of individual in-situ grown particles but also directly leads to a decrease in 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, which is beneficial for the Zn involved in the reaction. 2+ The concentration range for 2-methylimidazole must be strictly limited, Zn 2+Too much or too little material will not achieve the technical effect of this invention. Furthermore, by verifying the adsorption effect of the air filter material prepared by this invention on benzene vapor, the adsorption capacity of PP5 / ZIF-8 for benzene vapor is consistently greater than that of PP, indicating that the air filter material synthesized by this invention also has potential application space for toxic and harmful pollutants. The above embodiments of this invention utilize the porosity and enhanced surface polarity of ZIF-8 to in-situ load it onto the PP surface, which can significantly reduce the pressure drop of the PP fiber membrane while improving the removal effect of ultrafine particles, thus resolving the technical contradiction between filtration effect and air permeability. It can be widely used in the analysis, detection, and purification of air pollutants and has good development prospects.

[0136] It should be noted that in other embodiments of the present invention, other different solutions obtained by making specific selections within the range of steps, components, concentrations, ratios, process parameters and conditions described in the present invention can all achieve the technical effects described in the present invention, so the present invention will not list them one by one.

[0137] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention using the methods and techniques disclosed above, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. All equivalent changes made to the components, proportions, and processes of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an ultrafine air pollutant particulate filter membrane, characterized in that, Includes the following steps: S1. Preparation of modified PP fiber membrane material Prepare a Tris solution of appropriate concentration and adjust the pH to 8.

5. Then add appropriate amounts of dopamine hydrochloride (DA) and tannic acid (TA), and stir until homogeneous to obtain a DA / TA modified solution. The PP fiber membrane was immersed in the modification solution, reacted at room temperature, and then dried to obtain the 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 allow it to stand for at least 10 hours to ensure the Zn... 2+ Ions are firmly loaded onto 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 magnetically stirring the 2-methylimidazole / methanol precursor solution for 30 min, it was slowly added to the zinc acetate dihydrate / methanol precursor solution that had not been impregnated with the modified PP fiber membrane material, so that the Zn in the zinc acetate dihydrate / methanol precursor solution was reduced. 2+ ZIF-8 is fully reacted with 2-methylimidazole to allow it to grow in situ on the surface of modified PP fibers. It binds to the surface of PP fibers through hydrogen bonds or covalent bonds. After the reaction, a suitable number of ZIF-8 crystals with dodecahedral crystal form, arranged in a single layer and uniformly distributed on the surface of PP fibers are obtained. There are gaps between each ZIF-8 crystal, which constructs a microstructure of PP / ZIF-8 composite membrane material with rough surface, pore channels and high specific surface area. After drying, an ultrafine air pollutant particle filter membrane is obtained.

2. The method for preparing the ultrafine air pollutant particulate filter membrane according to claim 1, characterized in that, Step S1 includes: S1-1, PP pretreatment Take a PP film and ultrasonically wash it three times each with ethanol and deionized water for 15 minutes each time to remove surface impurities and electret charges. Then dry it. The cleaned material is recorded as PP-Cleaning. S1-2, PP modification A 1.2 g / L Tris solution was prepared and the pH was adjusted to 8.

5. Then, dopamine hydrochloride (DA) and tannic acid (TA) were added and stirred until homogeneous 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 modification solution and reacted at room temperature for 24 h, followed by drying at 50 °C to obtain the modified PP fiber membrane material, denoted as PP-Tri.

3. The method for preparing the ultrafine air pollutant particulate filter membrane according to claim 1, characterized in that, Step S2 includes: S2-1, Zn 2+ load Zn(CH3COO)2·2H2O was dissolved in methanol to prepare a zinc acetate dihydrate / methanol precursor solution with a concentration of 0.14-0.20 mol / L. The modified PP fiber membrane material was completely immersed in the zinc acetate dihydrate / methanol precursor solution and allowed to stand for 12 hours to ensure the Zn content was within acceptable limits. 2+ Ions are firmly loaded onto 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 300-1000 r / min for 10-40 min, and then slowly added to the zinc acetate dihydrate / methanol precursor solution that had not been impregnated with the modified PP fiber membrane material. This process ensured that the Zn concentration in the zinc acetate dihydrate / methanol precursor solution increased. 2+ After reacting with 2-methylimidazole for 6 hours, ZIF-8 is oriented and grown in situ on the surface of modified PP fibers. It is bonded to the surface of PP fibers through hydrogen bonds or covalent bonds to obtain ZIF-8 crystals with a dodecahedral crystal form, arranged in a single layer and uniformly distributed on the surface of PP fibers. There are gaps between the crystals. This is further used to form a PP / ZIF-8 composite membrane material with a rough surface, pore channels and high specific surface area. S2-3, Post-processing After the reaction is complete, the PP / ZIF-8 composite membrane material is taken out from the solution, washed three times with fresh methanol, and then washed three times with deionized water to remove residual reactants on the surface. Finally, the cleaned PP / ZIF-8 composite membrane material is dried in a vacuum drying oven at 40-60℃ for 8-15 hours to obtain an ultrafine air pollutant particle filter membrane.

4. An ultrafine air pollutant particle filter 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, while having a quality factor of not less than 0.0075 Pa. -1 PP / ZIF-8 composite membrane material.

5. The application of the ultrafine air pollutant particulate filter membrane according to claim 4 in filtering flue gas pollutants, characterized in that, It uses the aforementioned ultrafine air pollutant particle filter membrane to filter ultrafine particulate matter PM1.0 and PM0.5 in flue gas, and has high filtration efficiency and quality factor.

6. The application according to claim 5, characterized in that, It includes the following steps: A1. Setting up a filtration experimental device An experimental apparatus for filtering ultrafine particulate matter in flue gas was set up, consisting of a positive pressure air pump, a gas flow meter, a flue gas combustion chamber, a front-end particulate analyzer, an air filter chamber, an air filter membrane, a rear-end particulate analyzer, a differential pressure gauge, and a gas collection bottle. The air filter membrane, made of PP / ZIF-8 composite membrane material, was unfolded and placed in the air filter chamber. The front detection tubes of the front-end particulate analyzer and the differential pressure gauge were both placed on the pipeline at the front of the air filter chamber. The rear detection tubes of the rear-end particulate analyzer and the differential pressure gauge were both placed on the pipeline at the rear of the air filter chamber. All parts were connected in sequence with connecting pipes to form a closed pipeline that runs through the entire system. A2. Experimental Preparation The PP / ZIF-8 composite membrane material was cut into round pieces and weighed. These were used as air filter membranes and placed in the air filter chamber while remaining in an unfolded state. After removing the cigarette filter, place it into the combustion chamber and weigh it. Connect the entire pipeline, turn on the positive pressure air pump to conduct an air flow test, and confirm that there are no leaks in the entire pipeline. A3. Filtration Experiment Light a cigarette and tighten the gas collection bottle. Then turn on the positive pressure air pump and adjust the gas flow meter to ensure the oxygen requirements for cigarette combustion, allowing the cigarette to burn completely. Record the values ​​of PM10, PM2.5, PM1.0, and PM0.5 in the pipes before and after the air filter membrane using the front and rear particulate counters, respectively. Simultaneously record the pressure difference before and after the air filter chamber, and then calculate the particulate filtration efficiency and quality factor.

7. The application according to claim 6, characterized in that, In step A1, the filtration experimental apparatus also includes: an air drying chamber, an air filtration chamber clamp, and an outlet buffer bottle; The air drying chamber is located between the positive pressure air pump and the gas flow meter and is used to dry the air flowing through it. The air filter chamber includes two hollow halves arranged symmetrically in the front and back and horizontally interlocked. PP / ZIF-8 composite membrane material is vertically arranged on the interlocking surface 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, so that the PP / ZIF-8 composite membrane material is kept unfolded and the internal space of the air filter chamber is sealed. Each of the two hollow halves has a through hole at the center for connecting the pipeline. The outlet buffer bottle is located between the air filter chamber and the air collection bottle to help maintain the stability of the pressure difference between the pipelines on both sides of the air filter chamber.

8. The application according to claim 6, characterized in that, In step A2, the PP / ZIF-8 composite membrane material is cut into circular pieces with a diameter of 55 mm and weighed. Then, the circular pieces of PP / ZIF-8 composite membrane material are used as air filter membranes 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 together to seal the interior of the air filter chamber and keep the air filter membrane in an unfolded state.

9. The application 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 application according to claim 6, characterized in that, It also includes the following steps: reuse of A4 and PP / ZIF-8 composite membrane materials. Take out the PP / ZIF-8 composite membrane material discs used in the previous experiment, wash them with deionized water to remove adsorbed particles from the surface; dry the washed PP / ZIF-8 composite membrane material discs in an oven at 50℃, and then test the filtration efficiency and stability of the dried PP / ZIF-8 composite membrane material discs for use in the new experiment.

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