MXene modified polyimide nanofiber composite membrane, preparation method and application thereof

Abstract

The application discloses a kind of MXene modified polyimide nanofiber composite membranes and its preparation method and application, the method is prepared by acid etching method MXene nanosheet and polyamide acid molecular chain form strong hydrogen bond and coordination effect, significantly enhance interface binding force.MXene effectively transmits load, inhibits crack propagation, substantially improves the tensile strength and toughness of composite membrane, while extending the diffusion path of particulate matter, combined with the electrostatic adsorption effect produced by MXene itself conductivity, significantly improve the interception efficiency of PM0.3~PM2.5 fine particulate matter.The thermal imidization process ensures that PI matrix is completely converted into high-temperature-resistant structure, giving the material the ability to operate stably at high temperature for a long time.The composite membrane realizes four breakthroughs of high strength, high efficiency, low resistance and high dust capacity, providing a new solution for high-performance air filtration under harsh working conditions.

Description

Technical Field

[0001] This invention belongs to the field of polyimide composite material technology, and relates to an MXene-modified polyimide nanofiber composite membrane, its preparation method and application. Background Technology

[0002] With increasingly severe global air pollution and ever-increasing demands for protection in high-end industries, high-efficiency air filtration materials, as a key barrier to protect the environment and human health, have become a focal point in the field of materials science. Among them, polyimide (PI) stands out due to its unique molecular structure: the imide bonds in its main chain and the strong conjugation effect between the carbon-oxygen double bonds and heterocycles on the aromatic ring endow the material with excellent high strength, corrosion resistance, and radiation resistance; its high aromaticity and large conjugation system also give it excellent thermal stability. The rigid molecular chain, strong intermolecular forces, and high cohesive energy make it difficult to melt, and it can maintain a stable mechanical morphology even at extreme high temperatures of 500~600℃, making it an ideal high-temperature filtration substrate.

[0003] However, despite the excellent properties of PI fibers, current technologies still face significant bottlenecks in transforming them into practical filter materials. Current research progress largely focuses on preparing PI nanofiber membranes through electrospinning or simple composites with other materials, attempting to leverage the nano-effect to improve filtration performance. However, pure PI or simple composite filter materials prepared using existing technologies generally suffer from a contradiction of high resistance and low efficiency: to intercept fine particulate matter (such as PM0.3), it is often necessary to reduce the fiber diameter or increase the membrane thickness, which directly leads to a sharp increase in airflow resistance and energy consumption; conversely, if the resistance is reduced, the mechanical interception and electrostatic adsorption capacity for fine particles is insufficient, resulting in low filtration efficiency. Furthermore, the mechanical properties of traditional PI filter materials are poor under actual working conditions, prone to fiber breakage or structural collapse, and due to the lack of specific active sites and a reasonable pore gradient design on the surface, their dust holding capacity is limited, making them extremely prone to clogging and failure, and frequent replacements increase maintenance costs. Therefore, how to simultaneously solve core technical challenges such as high filtration resistance, low fine particle removal rate, poor mechanical durability, and low dust holding capacity by structural innovation and functional modification while retaining the high temperature resistance advantage of PI has become a key direction that urgently needs to be addressed in the research and development of high-performance filter materials. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an MXene-modified polyimide nanofiber composite membrane, its preparation method, and its application, thereby solving the technical problems of high filtration resistance, low filtration efficiency of fine particulate matter, poor mechanical properties, and low dust holding capacity in existing air filter materials.

[0005] This invention is achieved through the following technical solution: A method for preparing an MXene-modified polyimide nanofiber composite membrane includes the following steps: S1: MXene nanosheets were prepared by acid etching, and polyamic acid powder was prepared by reacting dianhydride monomers and diamine monomers. S2: Polyamic acid powder is dissolved in a polar aprotic solution, and MXene nanosheets are added to it to prepare MXene / PAA spinning solution; S3: Electrospinning is performed using the MXene / PAA spinning solution to obtain an MXene / PAA nanofiber membrane; S4: The MXene / PAA nanofiber membrane is subjected to thermal imidization treatment to obtain the MXene-modified polyimide nanofiber composite membrane.

[0006] Preferably, the preparation of MXene nanosheets using the acid etching method specifically involves: Hydrochloric acid and lithium fluoride were used to prepare an etching solution. Titanium aluminum carbide powder was added, and the solution was subjected to hydrothermal reaction at 40-50 °C for 30-48 h. After centrifugation until the supernatant was neutral, the solution was ultrasonically exfoliated for 45-90 min and then freeze-dried for 24-48 h to obtain the MXene nanosheets.

[0007] Preferably, the preparation of polyamic acid powder by reacting dianhydride monomers and diamine monomers specifically involves: Under conditions of -5 to 0 °C, dianhydride monomer and diamine monomer are subjected to polycondensation reaction at a molar ratio of (1 to 1.05): (0.95 to 1) for 24 to 48 h to obtain a polyamic acid solution. The solution is slowly poured into water to solidify, and after repeated washing until the aqueous phase is clear, it is freeze-dried for 24 to 48 h to obtain polyamic acid powder.

[0008] Preferably, the polar aprotic solvent is a mixture of one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide in any proportion.

[0009] Preferably, in the MXene / PAA spinning solution, the mass fraction of polyamic acid is 15%~20%, and the mass fraction of MXene nanosheets is 0.2%~1.2%.

[0010] Preferably, during the electrospinning process, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving roller is 10~20 cm.

[0011] Preferably, the thermal imidization treatment specifically includes: First, the temperature is increased to 100-150 °C at a rate of 5-10 °C / min and held for 30-60 min. Then, the temperature is increased to 200-250 °C at a rate of 5-10 °C / min and held for 30-60 min. Finally, the temperature is increased to 300-350 °C at a rate of 5-10 °C / min and held for 30-60 min to complete the thermal imidization.

[0012] Preferably, the inert gas is one of helium, neon, argon, and krypton.

[0013] An MXene-modified polyimide nanofiber composite membrane was prepared by the method described above.

[0014] The above-mentioned application of an MXene-modified polyimide nanofiber composite membrane in filter materials.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing an MXene-modified polyimide nanofiber composite membrane. Firstly, the method utilizes MXene nanosheets prepared by acid etching, which possess abundant surface functional groups and can form strong hydrogen bonds and coordination interactions with polyamic acid (PAA) molecular chains, significantly enhancing interfacial adhesion. Simultaneously, MXene, as a rigid two-dimensional filler, is uniformly dispersed in the spinning solution and embedded within the fibers or attached to the surface during electrospinning, effectively transferring loads and inhibiting crack propagation, thereby significantly improving the tensile strength and toughness of the composite membrane and overcoming the poor mechanical properties of traditional materials. Secondly, the introduction of MXene regulates the fiber morphology and pore structure: its layered structure forms labyrinthine gas channels between fibers, extending the diffusion path of particulate matter. Combined with the electrostatic adsorption effect generated by the conductivity of MXene itself, this significantly improves the retention efficiency of PM0.3~PM2.5 fine particulate matter, solving the problem of low filtration efficiency. Furthermore, because MXene enhances the inter-fiber connections and optimizes the network topology, the resulting composite membrane maintains high porosity while possessing a more stable skeletal support. This allows dust to deposit more easily on the fiber surface rather than clogging the pores, thereby increasing dust holding capacity and extending service life. Finally, the thermal imidization process ensures that the PI matrix is ​​completely transformed into a high-temperature resistant structure, giving the material the ability to operate stably at high temperatures for extended periods. The thermal stability of MXene also helps to prevent the overall structure from collapsing. The entire process achieves a quadruple breakthrough in high strength, high efficiency, low resistance, and high dust holding capacity, providing a brand-new solution for high-performance air filtration under harsh operating conditions.

[0016] Furthermore, the preparation of MXene nanosheets using the acid etching method specifically involves: preparing an etching solution by mixing hydrochloric acid and lithium fluoride, adding titanium aluminum carbide powder, and performing a hydrothermal reaction at 40-50 °C for 30-48 h. After centrifugation until the supernatant is neutral, ultrasonic exfoliation is performed for 45-90 min, followed by freeze-drying for 24-48 h to obtain the MXene nanosheets. The combined process of mild LiF / HCl etching, hydrothermal reaction, ultrasonic exfoliation, and freeze-drying allows for precise control of the size and number of layers of the MXene nanosheets, avoiding excessive oxidation or structural damage. The resulting MXene surface is rich in -OH / -F functional groups, enhancing the interfacial bonding with the PAA matrix and improving the mechanical strength of the composite material. At the same time, the intact layer structure facilitates the formation of a "maze effect" in the fiber, extending the particle path, improving filtration efficiency, and reducing pressure drop.

[0017] Furthermore, the preparation of polyamic acid powder by dianhydride monomer and diamine monomer specifically involves: dianhydride monomer and diamine monomer undergoing a polycondensation reaction at a molar ratio of (1~1.05):(0.95~1) for 24~48 h at -5~0 °C to obtain a polyamic acid solution. The solution is then slowly poured into water to solidify, repeatedly washed until the aqueous phase is clear, and freeze-dried for 24~48 h to obtain polyamic acid powder. Low-temperature polycondensation (-5~0 °C) suppresses side reactions, ensuring the formation of high molecular weight PAA and guaranteeing the mechanical skeleton strength of the final PI fiber. Solidification and washing remove residual monomers and solvents, avoiding impurities in the spinning solution that could lead to fiber breakage or defects. Freeze-drying preserves the porous structure, facilitating subsequent dissolution uniformity, thereby obtaining a dense, defect-free nanofiber membrane and improving dust holding capacity and mechanical stability.

[0018] Furthermore, in the MXene / PAA spinning solution, the mass fraction of polyamic acid is 15%~20%, and the mass fraction of MXene nanosheets is 0.2%~1.2%. Here, 15%~20% PAA ensures continuous fiber formation and sufficient mechanical strength; 0.2%~1.2% MXene is the optimal addition range. If it is too low, the reinforcement / adsorption effect will be insufficient, and if it is too high, it will easily agglomerate and cause stress concentration points, which will weaken the mechanical properties. This ratio balances the three objectives of reinforcement, toughening, and efficiency enhancement, achieving a synergistic effect of high strength and high filtration efficiency.

[0019] Furthermore, during the electrospinning process, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving roller is 10~20 cm. Here, the voltage of 16~20 kV provides sufficient electric field stretching force to form ultrafine fibers, increasing the specific surface area to capture fine particles; the flow rate of 0.010~0.017 mL / min controls the uniformity of fiber diameter; the receiving distance of 10~20 cm regulates the fiber packing density, avoiding excessive density leading to high voltage drop or excessive sparseness affecting interception efficiency, thereby achieving high efficiency and low resistance.

[0020] Furthermore, the thermal imidization treatment specifically involves: first, heating at 5-10 °C / min to 100-150 °C and holding for 30-60 min; then heating at 5-10 °C / min to 200-250 °C and holding for 30-60 min; and finally heating at 5-10 °C / min to 300-350 °C and holding for 30-60 min to complete the thermal imidization. The staged heating slowly removes the solvent and small molecule byproducts, avoiding drastic shrinkage that could lead to fiber cracking or pore collapse. The holding at each stage ensures complete imidization, imparting excellent thermal stability to the material, ensuring structural integrity under high-temperature conditions, and maintaining long-term filtration performance and dust holding capacity.

[0021] Furthermore, the inert gas is one of helium, neon, argon, and krypton, which effectively isolates oxygen, prevents PI from oxidizing and degrading at high temperatures or the functional groups on the MXene surface from being destroyed, and ensures the chemical stability and functional durability of the material, making it particularly suitable for long-term filtration applications in oxygen-containing high-temperature flue gas environments. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The images show scanning electron microscope (SEM) images of the polyimide nanofiber membrane prepared in Comparative Example 1, the MXene nanosheet prepared in Comparative Example 2, and the MXene / polyimide nanofiber membrane prepared in Example 1 at different magnifications. The images also show the fiber diameter distribution of the polyimide nanofiber membrane (top right) and the MXene / polyimide nanofiber membrane (bottom right). Figure 2The infrared spectra of the polyimide nanofiber membrane prepared in Comparative Example 1, the MXene nanosheet prepared in Comparative Example 2, and the MXene / polyimide nanofiber membrane prepared in Example 1 are shown below. Figure 3 The figures show the stress properties of the polyimide nanofiber membrane prepared in Comparative Example 1 and the MXene / polyimide nanofiber membrane prepared in Examples 1-3 of this invention. Among them, (a) is a stress-strain curve, (b) is a bar chart of tensile strength, (c) is a bar chart of elongation at break, and (d) is a bar chart of Young's modulus. Figure 4 The graphs show the filtration performance of the MXene / polyimide nanofiber membranes prepared in Examples 1-3 of this invention, where the left graph represents the filtration efficiency and the right graph represents the quality factor. Detailed Implementation

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0026] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0027] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0028] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0029] This invention provides a method for preparing MXene-modified polyimide nanofiber composite membranes. First, polyamic acid powder is prepared, then MXene and polyamic acid powder are mixed, and after electrospinning and thermal imidization treatment, MXene / polyimide nanofiber composite membrane material is obtained.

[0030] Specifically, it includes the following steps: S1: Preparation of MXene nanosheets: MXene nanosheets were prepared by acid etching. Specifically, the process of preparing MXene nanosheets by acid etching is as follows: hydrochloric acid and lithium fluoride are mixed to prepare an etching solution, titanium aluminum carbide powder is added, hydrothermal reaction is carried out at 40~50 °C for 30~48 h, centrifugation is carried out until the supernatant is neutral, followed by ultrasonic exfoliation for 45~90 min, and freeze drying for 24~48 h to obtain MXene nanosheets with a length range of 200~500 nm; S2: Preparation of polyamic acid (PAA) powder: Under -5~0 °C conditions, dianhydride monomer and diamine monomer are subjected to polycondensation reaction at a molar ratio of (1~1.05):(0.95~1) for 24~48 h to obtain polyamic acid solution. The solution is slowly poured into water to solidify, and after repeated washing until the aqueous phase is clear, it is freeze-dried for 24~48 h to obtain polyamic acid powder. S3: MXene / PAA spinning solution preparation: Dissolve polyamic acid powder in a polar aprotic solution, add MXene nanosheets to obtain MXene / PAA spinning solution; The polar aprotic solvent is a mixture of one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide in any proportion.

[0031] In the MXene / PAA spinning solution, the mass fraction of polyamic acid spinning is 15%~20%, and the mass fraction of MXene nanosheets is 0.2%~1.2%.

[0032] S4: Electrospinning to form a film: Using the MXene / PAA spinning solution prepared in step S3, electrospinning is carried out under the process conditions of spinning voltage of 16~20 kV, spinning solution flow rate of 0.010~0.017 mL / min, and needle-to-receiving roller distance of 10~20 cm to obtain MXene / PAA nanofiber membrane. S5: Thermal imidization treatment: The fiber membrane prepared in step S4 is placed in an inert gas. First, the temperature is raised to 100-150 °C at 5-10 °C / min and held for 30-60 min. Then, the temperature is raised to 200-250 °C at 5-10 °C / min and held for 30-60 min. Finally, the temperature is raised to 300-350 °C at 5-10 °C / min and held for 30-60 min to complete the thermal imidization and obtain the MXene / PI nanofiber composite membrane.

[0033] The inert gas is one of helium, neon, argon, and krypton.

[0034] The MXene / polyimide nanofiber composite membrane material prepared by the above method is mainly used in the field of high-temperature air filtration.

[0035] This invention uses pyromellitic anhydride, 4,4'-diaminodiphenyl ether, and N,N-dimethylformamide as raw materials to prepare polyamic acid salt materials. By utilizing the various active groups on the surface of MXene materials and doping them into the polyamic acid salt solution, a high-temperature resistant MXene / polyimide nanofiber composite membrane material is prepared through electrospinning and thermal imidization treatment. This composite material can perform air filtration at high temperatures, showing great application potential in the field of high-temperature air filtration. The material uses MXene nanosheets as the functional reinforcing phase and polyimide nanofibers as the structural matrix. Hydrogen bonding and chemical bonding significantly enhance the interfacial adhesion between the two phases, thereby greatly improving the mechanical strength and structural stability of the composite material. Simultaneously, the MXene sheets form a micro-nano rough structure on the fiber surface and inside, effectively increasing the fiber specific surface area and pore control capability, enabling the composite membrane to maintain high porosity and air permeability while possessing excellent particulate matter retention performance and high-temperature dimensional stability. This invention not only provides a new approach for the design of high-performance high-temperature resistant filter materials but also provides a new perspective for MXene… The controllable preparation and engineering application of polymer nanocomposites provide important technical references.

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] Comparative Example 1 The preparation of polyimide nanofiber (PI) membranes includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. o Dissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0039] (2) Preparation of PAA nanofiber membrane: Adjust the concentration of spinning solution and use electrospinning equipment to carry out the spinning process (ambient humidity is 30%, distance between needle tip and receiving plate is 16 cm) to prepare PAA fibers. The specific process is as follows: Weigh 3 g of the PAA powder prepared above and dissolve it in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% is obtained. Set the electrospinning voltage to 17 kV and the flow rate to 0.015 mL / min to carry out electrospinning and obtain PAA nanofiber membrane.

[0040] (3) Preparation of polyimide nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 oHeating to 320°C at a heating rate of C / min o C, heat for 30 min to obtain polyimide nanofiber membrane.

[0041] Comparative Example 2 Preparation of MXene nanosheets: Monolayer / few-layer MXene nanosheets were prepared using a lithium fluoride (LiF) / hydrochloric acid (HCl) etching method to selectively remove aluminum (Al) between MAX (Ti3AlC2) layers. The detailed steps were as follows: First, 150 mL of 12 M concentrated hydrochloric acid (HCl) was added to 50 mL of deionized water and mixed thoroughly to prepare a 9 M HCl solution. Then, 40 mL of HCl was placed in a polytetrafluoroethylene (PTFE) container, and 3.2 g of LiF was added. The mixture was stirred at room temperature for 20 min to completely dissolve the LiF, yielding an HF solution. Finally, 2 g of Ti3AlC2 was added to the above solution, and the mixture was stirred at 40 °C. o C. Magnetic stirring for 48 h. After stirring, the mixture was washed repeatedly by centrifugation with deionized water (4500 r / min, 5 min) until the pH of the mixed suspension was approximately 6. The lower precipitate was collected. It was redispersed in deionized water, shaken vigorously, and sonicated at 500 W for 1 h. The suspension was then centrifuged at 4500 r / min for 30 min. The supernatant was collected, and a dark green MXene / water dispersion (5 mg / mL) was prepared. Finally, it was freeze-dried for 48 h and ground to obtain MXene nanosheets.

[0042] Example 1 The preparation of MXene / polyimide nanofiber membranes includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. o Dissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0043] (2) Preparation of MXene / PAA nanofiber membrane: The concentration of the spinning solution was adjusted, and the spinning process was carried out using an electrospinning device (ambient humidity was 30%, and the distance between the needle tip and the receiving plate was 16 cm) to prepare MXene / PAA fibers. The specific process is as follows: 3 g of the PAA powder prepared above was weighed and dissolved in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% was obtained. MXene nanosheets were added to make the mass concentration of MXene nanosheets 0.3 wt%. The mixture was stirred for 4 h to obtain the MXene / PAA spinning solution. The solution was then placed in a refrigerator for defoaming. After complete defoaming, electrospinning was carried out using a 22G spinning needle. The electrospinning voltage was set to 17 kV and the flow rate was 0.015 mL / min to obtain the MXene / PAA nanofiber membrane.

[0044] (3) Preparation of MXene / PI nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o At temperature C, heat for 30 minutes to obtain MXene-modified polyimide nanofiber (MXene / PI-1) membrane.

[0045] Example 2 A method for preparing an MXene / polyimide nanofiber composite membrane material, comprising a polyimide nanofiber membrane, includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. oDissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0046] (2) Preparation of MXene / PAA nanofiber membrane: The concentration of the spinning solution was adjusted, and the spinning process was carried out using an electrospinning device (ambient humidity was 30%, and the distance between the needle tip and the receiving plate was 16 cm) to prepare MXene / PAA fibers. The specific process is as follows: 3 g of the PAA powder prepared above was weighed and dissolved in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% was obtained. MXene nanosheets were added to make the mass concentration of MXene nanosheets 0.7 wt%. The mixture was stirred for 4 h to obtain the MXene / PAA spinning solution. The solution was then placed in a refrigerator for defoaming. After complete defoaming, electrospinning was carried out using a 22G spinning needle. The electrospinning voltage was set to 17 kV and the flow rate was 0.015 mL / min to obtain the MXene / PAA nanofiber membrane.

[0047] (3) Preparation of MXene / PI nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o At temperature C, heat for 30 minutes to obtain MXene-modified polyimide nanofiber (MXene / PI-2) membrane.

[0048] Example 3 A method for preparing an MXene / polyimide nanofiber composite membrane material, comprising a polyimide nanofiber membrane, includes the following steps: (1) Preparation of precursor polyamic acid (PAA) solid: In 120 mL of DMF solution, PMDA and ODA were added at a molar mass ratio of 1.03:1. The specific steps are as follows: First, 100 mL of DMF and 10 g of 4,4'-diaminodiphenyl ether (ODA) were weighed and added to a three-necked flask. The mixture was then heated at low temperature for 1 minute. o Dissolve the PAA solution by stirring at C. Then, weigh 11.22 g of pyromellitic anhydride (PMDA) and add it in four portions, 10 min apart. Rinse the beaker and flask walls with the remaining 20 mL of DMF. Stir for 6 h, and stop the reaction when the climbing effect occurs, to obtain a PAA solution. When the PAA solution is stretched and oriented along the stirring shaft and wrapped around the shaft during stirring, i.e., when the climbing effect occurs, slowly pour the PAA into 2 L of deionized water to precipitate it. After washing several times, pre-freeze it in a refrigerator, then freeze-dry it for 48 h to obtain solid PAA, grind it, and store it at low temperature for later use.

[0049] (2) Preparation of MXene / PAA nanofiber membrane: The concentration of the spinning solution was adjusted, and the spinning process was carried out using an electrospinning device (ambient humidity was 30%, and the distance between the needle tip and the receiving plate was 16 cm) to prepare MXene / PAA fibers. The specific process is as follows: 3 g of the PAA powder prepared above was weighed and dissolved in 7 mL of DMF solution. After stirring at low temperature for 4 h, a light yellow PAA spinning solution with a mass concentration of 30% was obtained. MXene nanosheets were added to make the mass concentration of MXene nanosheets 1.1 wt%. The solution was stirred for 4 h to obtain the MXene / PAA spinning solution. The solution was placed in a refrigerator for defoaming. After complete defoaming, electrospinning was carried out using a 22G spinning needle. The electrospinning voltage was set to 17 kV and the flow rate was 0.015 mL / min to obtain the MXene / PAA nanofiber membrane.

[0050] (3) Preparation of MXene / PI nanofiber membrane: The above-mentioned film was subjected to a staged heating reaction in a high-temperature tube furnace under Ar environment and then treated: at 5 o Heating to 150°C at a heating rate of C / min o Keep warm at C for 30 minutes, then at 10 o Heating to 250°C at a heating rate of C / min o C, keep warm for 60 minutes, and finally at 5 o Heating to 320°C at a heating rate of C / min o At temperature C, heat for 30 minutes to obtain MXene-modified polyimide nanofiber membrane (MXene / PI-3).

[0051] Example 4 A method for preparing an MXene-modified polyimide nanofiber composite membrane includes the following steps: S1: Hydrochloric acid and lithium fluoride were used to prepare an etching solution. Titanium aluminum carbide powder was added and hydrothermally reacted at 40 °C for 48 h. After centrifugation until the supernatant was neutral, ultrasonic exfoliation was performed for 45 min. After freeze-drying for 24 h, MXene nanosheets with a length range of 200 nm were obtained. S2: Under -5 °C conditions, dianhydride monomer and diamine monomer are subjected to polycondensation reaction at a molar ratio of 1:0.95 for 24 h to obtain polyamic acid solution. The solution is slowly poured into water to solidify. After repeated washing until the aqueous phase is clear, it is freeze-dried for 24 h to obtain polyamic acid powder. S3: Polyamic acid powder is dissolved in a polar aprotic solution N,N'-dimethylformamide to obtain a polyamic acid spinning solution with a mass fraction of 15%. MXene nanosheets are added to the solution to make the mass fraction of MXene nanosheets 0.2%, thus obtaining an MXene / PAA spinning solution. S4: Using the prepared MXene / PAA spinning solution, electrospinning was carried out under the process conditions of spinning voltage of 16 kV, spinning solution flow rate of 0.010 mL / min, and needle-to-receiving roller distance of 10 cm to obtain MXene / PAA nanofiber membrane. S5: The MXene / PAA nanofiber membrane was placed in an inert helium gas atmosphere. First, the temperature was increased to 100 °C at 5 °C / min and held for 30 min. Then, the temperature was increased to 200 °C at 5 °C / min and held for 30 min. Finally, the temperature was increased to 300 °C at 5 °C / min and held for 30 min to complete the thermal imidization and obtain the MXene / PI nanofiber composite membrane.

[0052] Example 5 A method for preparing an MXene-modified polyimide nanofiber composite membrane includes the following steps: S1: Hydrochloric acid and lithium fluoride were used to prepare an etching solution. Titanium aluminum carbide powder was added and hydrothermally reacted at 50 °C for 48 h. After centrifugation until the supernatant was neutral, ultrasonic exfoliation was performed for 90 min. After freeze-drying for 48 h, MXene nanosheets with a length range of 500 nm were obtained. S2: Under 0 °C conditions, dianhydride monomer and diamine monomer were subjected to polycondensation reaction at a molar ratio of 1.05:1 for 48 h to obtain polyamic acid solution. The solution was slowly poured into water to solidify. After repeated washing until the aqueous phase was clear, it was freeze-dried for 48 h to obtain polyamic acid powder. S3: Polyamic acid powder is dissolved in a polar aprotic solution N,N'-dimethylacetamide to obtain a polyamic acid spinning solution with a mass fraction of 20%. MXene nanosheets are added to the solution to make the mass fraction of MXene nanosheets 1.2%, thus obtaining an MXene / PAA spinning solution. S4: Using the prepared MXene / PAA spinning solution, electrospinning was carried out under the process conditions of spinning voltage of 20 kV, spinning solution flow rate of 0.017 mL / min, and needle-to-receiving roller distance of 20 cm to obtain MXene / PAA nanofiber membrane. S5: The MXene / PAA nanofiber membrane was placed in an inert argon atmosphere. First, the temperature was increased to 150 °C at 10 °C / min and held for 60 min. Then, the temperature was increased to 250 °C at 10 °C / min and held for 60 min. Finally, the temperature was increased to 350 °C at 10 °C / min and held for 60 min to complete the thermal imidization and obtain the MXene / PI nanofiber composite membrane.

[0053] Example 6 A method for preparing an MXene-modified polyimide nanofiber composite membrane includes the following steps: S1: Hydrochloric acid and lithium fluoride were used to prepare an etching solution. Titanium aluminum carbide powder was added and hydrothermally reacted at 45 °C for 40 h. After centrifugation until the supernatant was neutral, ultrasonic exfoliation was performed for 50 min. After freeze-drying for 35 h, MXene nanosheets with a length range of 300 nm were obtained. S2: Under -3 °C conditions, dianhydride monomer and diamine monomer are subjected to polycondensation reaction at a molar ratio of 1:1 for 35 h to obtain polyamic acid solution. The solution is slowly poured into water to solidify, and after repeated washing until the aqueous phase is clear, it is freeze-dried for 35 h to obtain polyamic acid powder. S3: Polyamic acid powder is dissolved in a polar aprotic solution dimethyl sulfoxide to obtain a polyamic acid spinning solution with a mass fraction of 18%. MXene nanosheets are added to the solution to make the mass fraction of MXene nanosheets 1%, thus obtaining an MXene / PAA spinning solution. S4: Using the prepared MXene / PAA spinning solution, electrospinning was carried out under the process conditions of spinning voltage of 18 kV, spinning solution flow rate of 0.015 mL / min, and needle-to-receiving roller distance of 15 cm to obtain MXene / PAA nanofiber membrane. S5: The MXene / PAA nanofiber membrane was placed in an inert argon atmosphere. First, the temperature was increased to 120 °C at 8 °C / min and held for 50 min. Then, the temperature was increased to 230 °C at 8 °C / min and held for 50 min. Finally, the temperature was increased to 330 °C at 8 °C / min and held for 50 min to complete the thermal imidization and obtain the MXene / PI nanofiber composite membrane.

[0054] Figure 1 The images show scanning electron microscope (SEM) images at different magnifications of the polyimide (PI) nanofiber membrane prepared in Comparative Example 1, the MXene nanosheets prepared in Comparative Example 2, and the MXene / polyimide nanofiber membrane prepared in Example 1. The images also show the fiber diameter distribution of the polyimide (PI) nanofiber membrane (top right) and the MXene / polyimide nanofiber membrane (bottom right). By comparing the microstructures of the pure PI fiber membrane, MXene nanosheets, and the MXene / PI composite fiber membrane, the correlation mechanism between material structure and performance is revealed. First, the pure PI fiber membrane exhibits a uniform network structure with a concentrated fiber diameter distribution (~0.3 μm) and a smooth surface, indicating good film-forming properties and structural uniformity. The MXene nanosheets (inset in the upper left corner) exhibit a typical two-dimensional layered structure with clear edge edges and a size of approximately 200 nm, providing a high specific surface area and interfacial interaction basis for subsequent composite formation. The key lies in the MXene / PI composite fiber membrane, whose fiber diameter is significantly increased to ~1.1 μm, and its surface roughness is markedly improved, forming a denser three-dimensional network structure between the fibers. This structural change stems from the effective encapsulation of MXene nanosheets within the PI fibers or their attachment to the surface during electrospinning. This enhances the physical entanglement between fibers and introduces more surface-active sites. The fiber diameter distribution diagram shows that although the composite membrane's diameter distribution is slightly wider than that of the pure PI membrane, it still maintains a unimodal distribution, indicating that the introduction of MXene does not disrupt the fiber continuity but rather optimizes the fiber formation process by controlling the solution conductivity and viscosity. This structural feature of thickened fibers, roughened surface, and denser network provides the composite membrane with a longer particle interception path and stronger physical sieving capacity. It forms the microstructural basis for improved filtration efficiency, increased dust holding capacity, and enhanced mechanical properties, while also providing structural support for the macroscopic performance of MXene's functionality.

[0055] Figure 2The infrared spectra of the polyimide nanofiber membrane prepared in Comparative Example 1, the MXene nanosheets prepared in Comparative Example 2, and the MXene / polyimide nanofiber membrane prepared in Example 1 are shown below. By comparing the characteristic absorption peaks of pure polyimide (PI), MXene nanosheets, and the MXene / PI composite membrane, these infrared spectra confirm that MXene was successfully incorporated into the PI matrix and formed a composite structure. Specifically, the composite membrane exhibits a peak at 3447 cm⁻¹. -1 The broad peak at 1778 cm⁻¹ is attributed to the overlapping stretching vibrations of the -OH groups on the PI and MXene surfaces, indicating a hydrogen bond interaction between them; -1 With 1619 cm -1 The strong peak at 550 cm⁻¹ corresponds to the characteristic stretching vibration of C=O in the PI backbone, confirming that the imide ring structure of the composite PI remains intact; more importantly, at 550 cm⁻¹... -1 A characteristic peak attributable to the Ti-O bond in MXene was observed at 1377 cm⁻¹, which is completely absent in the pure PI spectrum, directly proving that MXene was successfully introduced into the composite system; in addition, a characteristic peak at 1377 cm⁻¹ was observed. -1 The presence of CNC bonds further corroborates the imidization process of PI. Notably, the relative intensities of the PI characteristic peaks in the composite film changed, suggesting that the addition of MXene may have slightly affected the stacking or orientation of the PI molecular chains through interfacial interactions. Overall, the infrared spectroscopy clearly demonstrates a triple chain of evidence: the retention of the PI framework structure, the introduction of MXene characteristic functional groups, and the existence of interfacial interactions between the two. This provides molecular-level structural support for the excellent mechanical properties and filtration function of the composite material.

[0056] Figure 3The figures show the stress-strain performance of the polyimide nanofiber membrane prepared in Comparative Example 1 and the MXene / polyimide nanofiber membranes prepared in Examples 1-3 of this invention. (a) is a stress-strain curve, (b) is a tensile strength histogram, (c) is a elongation at break histogram, and (d) is a Young's modulus histogram. These figures comprehensively demonstrate the comparison of the mechanical properties of the MXene / PI composite membrane and the pure PI membrane, revealing the mechanism by which MXene doping regulates the strength and toughness of the material. As can be seen from the stress-strain curve in (a), the composite membranes with appropriate MXene doping (MXene / PI-1, -2) exhibit higher yield stress and longer elongation at break than the pure PI membrane, indicating that they possess both high strength and good toughness. However, MXene / PI-3 shows a stress plateau in the high-strain region, suggesting that excessive filler may induce local defects. The bar charts (b) and (c) further quantify this trend: the tensile strength and elongation at break of the MXene / PI-2 sample both reached their peak values, increasing by approximately 30% and 50% respectively compared to pure PI. This confirms that MXene, at low doping levels, efficiently transfers the load to the high-modulus sheets through hydrogen bonds and van der Waals forces, effectively suppressing microcrack propagation. Simultaneously, the sheets are oriented along the fiber axis, exerting a fiber reinforcement effect. However, when the MXene content is too high (e.g., MXene / PI-3), its aggregation disrupts the continuity of the PI molecular chains, leading to a simultaneous decrease in strength and toughness. Figure (d) also shows that MXene reinforcement moderately improves the material's rigidity, but the modulus of MXene / PI-3 decreases, further confirming the negative effects of excessive filler. Overall, this chart systematically demonstrates that MXene, with optimized doping ratios, can significantly improve the comprehensive mechanical properties of composite membranes, providing a guarantee for the structural stability of high-temperature filtration materials.

[0057] Figure 4The graphs show the filtration performance of the MXene / polyimide nanofiber membranes prepared in Examples 1-3 of this invention. The left graph represents the filtration efficiency, and the right graph represents the quality factor. This graph systematically demonstrates the filtration performance of the MXene / PI composite membranes under different particle sizes, revealing the synergistic optimization mechanism of MXene doping on filtration efficiency and pressure drop. The left graph shows that the three composite membranes exhibit excellent filtration efficiency for PM0.3, PM0.6, and PM2.5, generally exceeding 98%. Among them, MXene / PI-2 achieves efficiencies of 99.8% and 99.9% for PM0.3 and PM0.6 particle sizes, respectively, indicating that the introduction of MXene enhances the electrostatic adsorption and physical sieving capabilities of the fiber surface. The right graph shows the quality factor (QF) as a comprehensive evaluation index. MXene / PI-2 achieves QF values ​​of 0.0186, 0.0293, and 0.0713 for PM0.3, PM0.6, and PM2.5, respectively, effectively controlling the pressure drop while maintaining high filtration efficiency. This performance improvement stems from the labyrinthine pore structure formed by MXene sheets within the fiber network, which extends the migration path of particles, while its surface functional groups enhance the capture ability of fine particles. However, the performance of MXene / PI-3 slightly decreases at high doping levels, suggesting that excessive MXene may induce agglomeration, leading to decreased porosity or localized blockage, thus validating the existence of an optimal doping ratio. Overall, this figure confirms that the MXene / PI composite membrane achieves highly efficient capture of submicron-sized particles while maintaining low resistance, demonstrating excellent comprehensive filtration performance.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an MXene-modified polyimide nanofiber composite membrane, characterized in that, Includes the following steps: S1: MXene nanosheets were prepared by acid etching, and polyamic acid powder was prepared by reacting dianhydride monomers and diamine monomers. S2: Polyamic acid powder is dissolved in a polar aprotic solution, and MXene nanosheets are added to it to prepare MXene / PAA spinning solution; S3: Electrospinning is performed using the MXene / PAA spinning solution to obtain an MXene / PAA nanofiber membrane; S4: The MXene / PAA nanofiber membrane is subjected to thermal imidization treatment to obtain the MXene-modified polyimide nanofiber composite membrane.

2. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, The preparation of MXene nanosheets using the acid etching method is specifically as follows: Hydrochloric acid and lithium fluoride were used to prepare an etching solution. Titanium aluminum carbide powder was added, and the solution was subjected to hydrothermal reaction at 40-50 °C for 30-48 h. After centrifugation until the supernatant was neutral, the solution was ultrasonically exfoliated for 45-90 min and then freeze-dried for 24-48 h to obtain the MXene nanosheets.

3. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, The preparation of polyamic acid powder by reacting dianhydride monomers and diamine monomers specifically involves: Under conditions of -5 to 0 °C, dianhydride monomer and diamine monomer are subjected to polycondensation reaction at a molar ratio of (1 to 1.05): (0.95 to 1) for 24 to 48 h to obtain a polyamic acid solution. The solution is slowly poured into water to solidify, and after repeated washing until the aqueous phase is clear, it is freeze-dried for 24 to 48 h to obtain polyamic acid powder.

4. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, The polar aprotic solvent is a mixture of one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide in any proportion.

5. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, In the MXene / PAA spinning solution, the mass fraction of polyamic acid is 15%~20%, and the mass fraction of MXene nanosheets is 0.2%~1.2%.

6. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, During the electrospinning process, the spinning voltage is 16~20 kV, the spinning solution flow rate is 0.010~0.017 mL / min, and the distance between the needle and the receiving roller is 10~20 cm.

7. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, The thermal imidization treatment specifically includes: First, the temperature is increased to 100-150 °C at a rate of 5-10 °C / min and held for 30-60 min. Then, the temperature is increased to 200-250 °C at a rate of 5-10 °C / min and held for 30-60 min. Finally, the temperature is increased to 300-350 °C at a rate of 5-10 °C / min and held for 30-60 min to complete the thermal imidization.

8. The method for preparing an MXene-modified polyimide nanofiber composite membrane according to claim 1, characterized in that, The inert gas is one of helium, neon, argon, and krypton.

9. An MXene-modified polyimide nanofiber composite membrane, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the MXene-modified polyimide nanofiber composite membrane as described in claim 9 in filter materials.

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