Gradient wetting type mesoporous delta-MnO2 active carbon nanofiber membrane material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of air filtering materials, and particularly provides a gradient wetting type mesoporous delta-MnO2 active carbon nanofiber membrane material as well as a preparation method and application thereof. The method comprises the following steps: preparing a polyacrylonitrile nanofiber membrane by adopting an electrostatic spinning process; carrying out pre-oxidation, carbonization and chemical activation treatment on the polyacrylonitrile nanofiber membrane to obtain an activated carbon nanofiber membrane; a hydrophilic micro-area is constructed on the surface of the activated carbon nanofiber membrane through ozone oxidation; loading aminated silicon dioxide particles in the hydrophilic micro-area; the preparation method comprises the following steps: by taking an active carbon nanofiber membrane loaded with aminated silicon dioxide as a carrier, growing a mesoporous delta-phase manganese dioxide nanosheet on the surface of the active carbon nanofiber membrane through a hydrothermal reaction; a hydrophobic background area is constructed in a non-hydrophilic area through hexamethyldisilazane steam treatment, a gradient wetting structure is formed, the limitation that a traditional material is single in function is broken through, and efficient formaldehyde decomposition and particulate matter interception are achieved.

Description

Technical Field

[0001] This invention belongs to the field of air filtration materials technology, specifically relating to a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, its preparation method, and its application. Background Technology

[0002] This invention addresses the serious threat that indoor air pollution poses to human health, with formaldehyde being a major pollutant. Formaldehyde, in particular, is colorless, odorless, and has a long-term release characteristic, potentially inducing allergic reactions, nervous system damage, and even cancer. Current mainstream technologies in the industry focus on two categories: physical adsorption and catalytic degradation. Physical adsorption technology relies on porous materials such as activated carbon to rapidly capture formaldehyde through physical channels. However, it lacks specific interaction mechanisms and is easily affected by high concentrations of gaseous components in the environment, leading to adsorption capacity saturation and potentially becoming a secondary release source. Catalytic degradation technology utilizes noble metal (such as Au, Pt, Pd) or transition metal oxide (such as MnO2, CuO, Co3O4) catalysts to convert formaldehyde into harmless CO2 and H2O at room temperature, achieving green and sustainable purification.

[0003] Among transition metal oxides, manganese dioxide (MnO2) has become a research hotspot due to its abundant resources, low cost, and outstanding low-temperature catalytic activity. However, traditional powdered MnO2 catalysts suffer from difficulties in immobilization, leading to secondary pollution, and nanoparticles are prone to agglomeration, masking active sites. Existing support immobilization technologies, such as polydopamine-templated cotton textiles, mechanically friction-loaded polyester (PET) fibers, and atomic layer deposition-loaded polypropylene (PP) nonwoven fabrics, can improve dispersibility, but are still limited by the specific surface area caused by the size of the support fibers. When attempting to increase the loading, catalyst particles undergo severe agglomeration due to insufficient support specific surface area, with the specific surface area increase being less than 25%, and the exposure rate of catalytic active sites decreasing by more than 40%, resulting in a decline in formaldehyde degradation efficiency. Furthermore, existing catalytic technologies lack a directional adsorption mechanism for actively capturing formaldehyde; in indoor low-concentration formaldehyde environments or under dynamic airflow conditions, the probability of formaldehyde molecules contacting the catalyst is significantly reduced.

[0004] Therefore, there is an urgent need to develop a new material that combines directional adsorption function with high catalytic activity. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, its preparation method, and its application.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, comprising the following steps: Step 1: Polyacrylonitrile nanofiber membranes are prepared using electrospinning process with polyacrylonitrile powder as raw material; Step 2: The polyacrylonitrile nanofiber membrane is subjected to pre-oxidation, carbonization and chemical activation treatment in sequence to obtain activated carbon nanofiber membrane; Step 3: Construct hydrophilic microdomains on the surface of activated carbon nanofiber membranes via ozone oxidation; Step 4: Loading aminated silica nanoparticles onto hydrophilic microregions; Step 5: Using an activated carbon nanofiber membrane loaded with aminated silica as a carrier, mesoporous δ-phase manganese dioxide nanosheets are grown in situ on the surface of the activated carbon nanofiber membrane loaded with aminated silica via a hydrothermal reaction. Step 6: Construct a hydrophobic background region in the non-hydrophilic area by vapor treatment with hexamethyldisilazane to form a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material.

[0007] Further, step one specifically includes: dissolving polyacrylonitrile powder with an average molecular weight of 150,000 in N,N-dimethylformamide to form a homogeneous solution with a mass fraction of 10-14 wt%. After stirring at 55-65℃ for 5-7 hours, the solution is fed to the nozzle at a push rate of 0.06-0.10 mm / min. Electrospinning is carried out under conditions of a 16-22 kV DC electric field, a receiving distance of 16-20 cm, and a roller speed of 130-150 r / min. The ambient temperature is controlled at 25±2℃ and the relative humidity is 40-50%, finally obtaining a polyacrylonitrile nanofiber membrane with a diameter of 300-500 nm and a porosity of 85-90%.

[0008] Further, step two specifically includes: pre-oxidizing the polyacrylonitrile nanofiber membrane by heating it to 240-260℃ at a heating rate of 4-6℃ / min in an air atmosphere with an oxygen volume fraction of 18-22% and holding it at that temperature for 0.8-1.2h; then carbonizing it by heating it to 880-920℃ at a heating rate of 4-6℃ / min in a nitrogen atmosphere and holding it at that temperature for 0.8-1.2h; then immersing it in a potassium hydroxide solution with a mass concentration of 40-50% for 1.5-2.5h; drying it; and finally activating it by treating it in an inert atmosphere at 780-820℃ for 0.4-0.6h, ultimately obtaining an activated carbon nanofiber membrane with a specific surface area of ​​1200-1500m² / g.

[0009] Further, step three specifically includes: placing the activated carbon nanofiber membrane in an oxygen flow containing 4-6% ozone by volume, heating it to 240-260℃ at a heating rate of 4-6℃ / min and holding it at that temperature for 25-35min, so that the proportion of hydrophilic micro-regions reaches 20-25% and the contact angle is reduced to 40-50°.

[0010] Further, step four specifically includes: immersing the ozone-oxidized activated carbon nanofiber membrane in an aminated silica sol with a mass fraction of 0.08-0.12%, treating it under ultrasonic conditions of 40-60kHz for 1.0-1.5h, and then drying it, controlling the loading of aminated silica to be 0.8-1.2mg / g membrane substrate.

[0011] Further, step five specifically includes: immersing the activated carbon nanofiber membrane loaded with aminated silica into a mixed solution containing 0.028-0.032 mol / L potassium permanganate, 0.12-0.18 mol / L ethanol and 0.08-0.12 mol / L urea, sealing it, heating it to 118-122℃ at a heating rate of 3-5℃ / min and holding it at that temperature for 5.5-6.5 h, and after the reaction is completed, ultrasonically washing it with anhydrous ethanol and water in sequence and drying it, finally obtaining a mesoporous δ-phase manganese dioxide nanosheet composite membrane with a loading of 18-22 wt% and a thickness of 2.5-3.5 nm.

[0012] Further, step six specifically includes: placing the mesoporous δ-phase manganese dioxide nanosheet composite film in a vacuum chamber, and treating it with hexamethyldisilazane vapor at a partial pressure of 0.2-0.4 kPa for 1.5-2.5 h under conditions of 0.5-1.0 kPa and 140-160 °C, to form a siloxane layer with a thickness of 1-2 nm, thereby increasing the contact angle of the hydrophobic region to 110-120° and covering 75-80% of the surface area.

[0013] Furthermore, the proportion of hydrophilic microregions is 20-25%, and the loading of mesoporous δ-phase manganese dioxide nanosheets is 18-22 wt%.

[0014] Another technical solution provided by the present invention is a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, which is prepared based on the above preparation method.

[0015] Another technical solution provided by the present invention: the application of the above-mentioned gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material in the preparation of composite filter element includes: sequentially stacking a polyester nonwoven fabric substrate layer, a functional layer composed of gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, and a meltblown polypropylene nonwoven fabric protective layer; applying a dynamic pressure of 0.35-0.45MPa and longitudinal vibration with an amplitude of 5-8μm for 12-18s in a 38-42kHz ultrasonic field; and then treating it in a hot air environment with an airflow velocity of 0.8-1.2m / s and a temperature of 85-95℃ for 25-35min to finally obtain the composite filter element.

[0016] This invention addresses the shortcomings of the prior art and has the following beneficial effects: This invention achieves efficient formaldehyde decomposition and particulate matter interception by constructing a hydrophilic microregion with a coverage of 20-25% and a hydrophobic background region with a coverage of 75-80% on the surface of an activated carbon nanofiber membrane, and growing mesoporous δ-phase manganese dioxide nanosheets with a loading of 18-22 wt% in situ in the hydrophilic microregion.

[0017] Ozone oxidation treatment forms hydrophilic microdomains containing carboxyl functional groups on the surface of activated carbon nanofiber membranes. These microdomains, with a contact angle of 40-50°, specifically capture formaldehyde molecules through hydrogen bonding. Simultaneously loaded aminated silica particles further enhance adsorption selectivity. Combined with hydrothermally grown 2.5-3.5 nm thick mesoporous δ-phase manganese dioxide nanosheets, the manganese vacancy active sites have an adsorption frequency of 0.018-0.022 s⁻¹. -1 The high conversion frequency enables rapid formaldehyde decomposition. Compared to traditional activated carbon filter materials that rely solely on physical adsorption, this invention increases the formaldehyde removal rate by 49.8%, and the decomposition products are harmless carbon dioxide and water, completely avoiding secondary pollution.

[0018] A 1-2 nm thick hydrophobic siloxane layer constructed by vapor treatment of hexamethyldisilazane increases the contact angle of the non-hydrophilic region to 110-120°, thereby reducing the water molecule diffusion coefficient to 2.1 × 10⁻⁶. -9 The m² / s effectively suppresses competitive adsorption. Compared to the unmodified material, which exhibits performance degradation exceeding 30% in high humidity environments, this hydrophobic background ensures that the formaldehyde removal rate remains stable at 88.3% after five cycles, with a 57.5% reduction in degradation rate.

[0019] Formaldehyde molecules captured in hydrophilic microdomains migrate directionally along the surface energy gradient to adjacent catalyst mesoporous channels with an energy barrier of 0.12 eV, while the hydrophobic background dynamically repels water molecules, keeping the active sites dry. This coupling mechanism reduces the average residence time of formaldehyde molecules within the material to 0.25 s, a 2.3-fold improvement over traditional composite materials, ultimately achieving simultaneous attainment of a formaldehyde removal rate of 93.8% and a 0.3 μm particulate matter purification efficiency of 99.8%. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of a method for preparing a gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention may be practiced in other ways different from those described herein, and therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below. Unless otherwise specified in the following embodiments, all raw materials were commercially available or prepared using conventional methods in the art. Specifically, N,N-dimethylformamide, potassium hydroxide, potassium permanganate, urea, 3-aminopropyltriethoxysilane, and hexamethyldisilazane were all purchased from Sinopharm Group and were of analytical grade.

[0023] Exemplary method: like Figure 1 As shown, a method for preparing a gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material includes the following steps: Step 1: Polyacrylonitrile nanofiber membranes are prepared using electrospinning process with polyacrylonitrile powder as raw material; Step 2: The polyacrylonitrile nanofiber membrane is subjected to pre-oxidation, carbonization and chemical activation treatment in sequence to obtain activated carbon nanofiber membrane; Step 3: Construct hydrophilic microdomains on the surface of activated carbon nanofiber membranes via ozone oxidation; Step 4: Loading aminated silica nanoparticles onto hydrophilic microregions; Step 5: Using an activated carbon nanofiber membrane loaded with aminated silica as a carrier, mesoporous δ-phase manganese dioxide nanosheets are grown in situ on the surface of the activated carbon nanofiber membrane loaded with aminated silica via a hydrothermal reaction. Step 6: Construct a hydrophobic background region in the non-hydrophilic area by vapor treatment with hexamethyldisilazane to form a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material.

[0024] Below, each step will be explained in detail.

[0025] Step one involves preparing a polyacrylonitrile nanofiber substrate with a continuous three-dimensional network structure, providing a morphology-controllable precursor for the subsequent carbonization process. The electrospinning process can control the fiber diameter and orientation using an electric field, and these characteristics directly determine the specific surface area and pore distribution of the final activated carbon nanofiber membrane.

[0026] In this step, polyacrylonitrile powder with an average molecular weight of 150,000 is dissolved in N,N-dimethylformamide solvent to form a homogeneous solution with a mass fraction of 10-14 wt%. The jet stability is controlled by the viscoelasticity of the solution: when the mass fraction is below 10 wt%, insufficient surface tension leads to jet breakage; when it is above 14 wt%, increased viscosity hinders continuous fluid transport. The solution is continuously treated at 55-65℃ for 5-7 hours in a constant-temperature magnetic stirrer to achieve full molecular chain extension.

[0027] Furthermore, a homogeneous polyacrylonitrile solution is delivered to a metal nozzle at a injection rate of 0.06-0.10 mm / min. A 16-22 kV DC high-voltage electric field is applied between the nozzle and the rotating drum receiver. The receiving distance is controlled at 16-20 cm and the drum rotation speed is controlled at 130-150 r / min. Stable jet stretching is achieved through dynamic balance between Coulomb force and viscous force.

[0028] Furthermore, during the jet flight, N,N-dimethylformamide diffuses at a volatilization rate of 0.15-0.25 mL / min, a process controlled by a closed loop of ambient temperature and humidity.

[0029] The final result is a polyacrylonitrile nanofiber membrane with a diameter of 300-500 nm, a basis weight of 8-12 g / m², and a porosity of 85-90%.

[0030] Step two involves constructing an activated carbon nanofiber support with both high specific surface area and mechanical stability through controlled thermochemical transformation. The polyacrylonitrile molecular chains undergo directional cyclization to form a high-temperature resistant ladder structure, and an activation reaction is used to construct a hierarchical porous system to meet the catalyst loading requirements.

[0031] In this step, the polyacrylonitrile nanofiber membrane is placed in an air atmosphere with an oxygen volume fraction of 18-22%, and heated to 240-260℃ at a heating rate of 4-6℃ / min, and maintained at that temperature for 0.8-1.2h. This process achieves molecular crosslinking through cyano cyclization reaction, with temperature and oxygen concentration synergistically controlling the degree of cyclization to 55-65%, forming a high-temperature resistant ladder-shaped polymer backbone.

[0032] Furthermore, the pre-oxidized polyacrylonitrile nanofiber membrane was transferred to an inert nitrogen environment and heated to 880-920℃ at a heating rate of 4-6℃ / min and held at that temperature for 0.8-1.2h to form a carbon skeleton through a thermal decomposition reaction.

[0033] Furthermore, the carbonized polyacrylonitrile nanofiber membrane was immersed in a 40-50% potassium hydroxide solution for 1.5-2.5 hours, dried, and then treated in an inert atmosphere at 780-820℃ for 0.4-0.6 hours. The temperature was controlled by the liquid phase penetration depth to determine pore formation, and the potassium hydroxide concentration was used to regulate the etching reaction rate, resulting in a microporous system with a pore size of 0.8-2 nm.

[0034] Finally, after washing with 0.5 mol / L hydrochloric acid solution and rinsing with water, an activated carbon nanofiber membrane with a specific surface area of ​​1200-1500 m² / g and a tensile strength of 15-18 MPa was obtained.

[0035] Step 3 involves constructing hydrophilic microdomains to enhance the specific adsorption capacity for formaldehyde molecules. The polar nature of formaldehyde necessitates surface energy modulation to improve capture efficiency under low concentration conditions.

[0036] In this step, the activated carbon nanofiber membrane is placed in an oxygen-oxygen mixed gas stream containing 4-6% ozone by volume, and heated to 240-260℃ at a rate of 4-6℃ / min, and held at that temperature for 25-35 min. This process selectively modifies the carbon skeleton edges through ozone decomposition: the ozone concentration is kinetically controlled by free radical reaction to achieve a carboxyl density of 8-12 sites per square micrometer, and temperature and time are synergistically controlled to determine the oxidation depth, resulting in a hydrophilic microdomain ratio of 20-25% and a contact angle reduced to 40-50°.

[0037] Step four enhances the formaldehyde enrichment capacity of the hydrophilic micro-regions by improving adsorption selectivity through the functional groups on the surface of nanoparticles, thus solving the performance degradation caused by competitive adsorption of water molecules under fluctuating humidity conditions.

[0038] In this step, the surface-selectively oxidized activated carbon nanofiber membrane is immersed in 0.08-0.12% (w / w) aminated silica sol (particle size 10-20 nm), treated with ultrasound at 40-60 kHz for 1.0-1.5 h, and then dried at 80 °C. This process is achieved through electrostatic directional anchoring: the amino group density on the surface of the aminated silica is controlled to 2.8-3.2 amines / nm. 2 It forms ionic bonds with the carboxyl groups of the activated carbon nanofiber membrane; the ultrasonic cavitation effect promotes the penetration of aminated silica particles into the submicron pores, and the loading is controlled at 0.8-1.2 mg / g membrane substrate.

[0039] The preparation of aminated silica nanoparticles was achieved through a two-step continuous process. The first step involved the synthesis of hydroxylated silica nanoparticles using the Stober method. 500 mL of anhydrous ethanol and 38 mL of ammonia solution (25-28% by mass) were stirred at 70 °C for 1 h. Then, 15 mL of tetraethyl orthosilicate was slowly added dropwise while stirring continuously for 12 h. The precipitate obtained after centrifugation at 8000 rpm was washed three times each with ethanol and water, and subsequently dried under vacuum at 100 °C to obtain hydroxylated silica nanoparticles. The second step involved amination modification. 1 g of dried hydroxylated silica was ultrasonically dispersed in 50 mL of anhydrous ethanol. Under nitrogen protection, 2-5% (v / v) of 3-aminopropyltriethoxysilane was added. After stirring at room temperature for 6-12 h, the product was collected by centrifugation and washed three times with ethanol. The product was then dried under vacuum at 60 °C to obtain the aminated silica nanoparticles. The ammonia concentration can be finely adjusted within the range of 0.48-0.72 mol / L to control the particle size between 50-200 nm. The amount of 3-aminopropyltriethoxysilane and the reaction time can also be adjusted as needed to achieve a surface amino density of 1-3 amino groups / nm². Furthermore, toluene can be replaced with an ethanol / water mixture to reduce organic solvent residue. 3-aminopropyltriethoxysilane is highly susceptible to hydrolysis, and all operations must be carried out under anhydrous solvent and nitrogen protection. The resulting aminated particles are highly hygroscopic and should be stored away from light or dispersed in anhydrous ethanol for later use.

[0040] Step 5 involves the directional growth of a highly active catalyst on the surface of a functionalized support, constructing an adsorption-catalysis synergistic channel. The layered structure of δ-phase manganese dioxide exposes more manganese vacancy active sites to improve decomposition efficiency.

[0041] In this step, potassium permanganate is dissolved in water to form a 0.028-0.032 mol / L solution. Simultaneously, 0.12-0.18 mol / L ethanol and 0.08-0.12 mol / L urea are added to form a binary reduction system. Ethanol initiates the initial reduction of permanganate by providing α-hydrogen atoms, while the ammonia molecules produced by the thermal decomposition of urea maintain the solution pH in the range of 6.8-7.2.

[0042] Furthermore, after immersing the aminated silica hydrophilic particle composite activated carbon nanofiber membrane into the above solution, the reaction vessel was sealed and heated to 118-122℃ at a heating rate of 3-5℃ / min and maintained at that temperature for 5.5-6.5h.

[0043] Furthermore, the product was purified and stabilized by ultrasonic washing with anhydrous ethanol and water 3-5 times sequentially (power density 0.35-0.45 W / cm²), and then dried at 50-60℃ under a vacuum of -0.08 to -0.10 MPa for 4-6 hours. The purification mechanism relies on the solvent polarity gradient to exfoliate physically adsorbed byproducts, and the low-temperature vacuum environment inhibits the aggregation of nanosheets.

[0044] Finally, a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane with a loading of 18-22 wt% and a δ-phase purity of >95% was obtained.

[0045] Step 6: Construct a hydrophobic background region to reduce the interference of environmental humidity on formaldehyde mass transfer efficiency and balance the adsorption capacity of hydrophilic micro-regions with the overall moisture-proof performance.

[0046] In this step, a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane is placed in a vacuum chamber, maintained at a pressure of 0.5-1.0 kPa, and heated to 140-160°C. Hexamethyldisilazane vapor (partial pressure 0.2-0.4 kPa) is continuously introduced for treatment for 1.5-2.5 hours. Hexamethyldisilazane molecules react with the residual hydroxyl groups of the activated carbon nanofiber membrane to generate a 1-2 nm thick siloxane layer. The silane flux is controlled by the molecular collision frequency to adjust the membrane thickness, increasing the contact angle of the hydrophobic region to 110-120° and covering 75-80% of the surface area.

[0047] Example application: The application of a gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material in the preparation of composite filter cartridges includes the following steps: A wet-formed polyester nonwoven fabric base layer (28-32 g / m²), a gradient-wetting mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane functional layer (18-22 g / m²), and a meltblown polypropylene nonwoven fabric protective layer (48-52 g / m²) are stacked in a direction of decreasing surface energy. The 40-50 μm pore size of the base layer forms a turbulent diffusion zone to improve gas mixing uniformity, the 0.3-0.5 μm fiber gaps in the functional layer constitute the main reaction channel, increasing the pollutant residence time to 0.25-0.35 s, and the 15-20 μm pore size of the protective layer achieves terminal depth interception.

[0048] Furthermore, a dynamic pressure of 0.35-0.45 MPa and a longitudinal vibration with an amplitude of 5-8 μm are applied in an ultrasonic field with a frequency of 38-42 kHz for 12-18 s. The ultrasonic frequency is modulated to control the displacement of the polypropylene molecular chains to 3-5 μm through a standing wave field, causing van der Waals forces to recombine the meltblown polypropylene nonwoven fibers with the hydrophobic regions of the functional layer, resulting in a bonding strength of 0.8-1.2 × 10⁻⁶. 4 Physical bonding of N / m.

[0049] Furthermore, the polypropylene was treated at 85-95℃ for 25-35 minutes in a hot air circulation environment with an airflow velocity of 0.8-1.2 m / s. The temperature was controlled to adjust the crystallinity of polypropylene to the range of 35-40% using the free volume theory, and the treatment time was used to control the molecular chain entanglement density so that the interlayer peel strength was stabilized at 1.8-2.2 kN / m.

[0050] Through the above steps, the gradient-wetting mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane is transformed into a high-performance air purification filter element, which simultaneously achieves the dual functions of efficient particulate matter interception and formaldehyde adsorption and decomposition through the synergistic effect of multi-level materials. Example

[0051] A method for preparing a gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material includes the following steps: Step 1: Polyacrylonitrile powder with an average molecular weight of 150,000 was dissolved in N,N-dimethylformamide solvent to form a homogeneous solution with a mass fraction of 12 wt%. The solution was continuously treated at 60°C for 6 hours in a constant temperature magnetic stirrer. Subsequently, the homogeneous solution was fed to a metal nozzle at a injection rate of 0.08 mm / min. An 18 kV DC high voltage electric field was applied between the nozzle and the rotating drum receiver, and the receiving distance was controlled at 18 cm and the drum rotation speed at 140 r / min. N,N-dimethylformamide was allowed to diffuse at an evaporation rate of 0.20 mL / min under an environment of 25°C and 45% relative humidity, and finally a polyacrylonitrile nanofiber membrane with a diameter of 400 nm, a basis weight of 10 g / m², and a porosity of 88% was formed.

[0052] Step 2: The polyacrylonitrile nanofiber membrane obtained in Step 1 was placed in an air atmosphere with an oxygen volume fraction of 20%, heated to 250℃ at a heating rate of 5℃ / min, and maintained at the temperature for 1 hour; then the pre-oxidized membrane was transferred to an inert nitrogen environment, heated to 900℃ at a heating rate of 5℃ / min, and maintained at the temperature for 1 hour; subsequently, the carbonized membrane was immersed in a 45% potassium hydroxide solution for 2 hours, dried, and treated in an inert atmosphere at 800℃ for 0.5 hours, and then washed with 0.5 mol / L hydrochloric acid solution and rinsed with water to finally obtain an activated carbon nanofiber membrane with a specific surface area of ​​1350 m² / g.

[0053] Step 3: Place the activated carbon nanofiber membrane obtained in Step 2 in an oxygen mixed gas flow containing 5% ozone by volume, raise the temperature to 250℃ at a heating rate of 5℃ / min and maintain the temperature for 30min, so that the proportion of hydrophilic micro-regions reaches 15% and the contact angle is reduced to 45°.

[0054] Step 4: Immerse the activated carbon nanofiber membrane obtained in Step 3 after surface selective oxidation treatment in 0.10% by mass of aminated silica sol, treat it under ultrasonic frequency of 50kHz for 1.25h, and then dry it at 80℃, controlling the loading of aminated silica to be 1.0mg / g membrane substrate.

[0055] Step 5: Dissolve potassium permanganate in water to form a 0.03 mol / L solution, and add 0.15 mol / L ethanol and 0.10 mol / L urea to form a binary reduction system; then immerse the activated carbon nanofiber membrane loaded with aminated silica obtained in Step 4 into the mixed solution, seal the reaction vessel, raise the temperature to 120℃ at a rate of 4℃ / min and maintain the temperature for 6h; after the reaction, ultrasonically wash with anhydrous ethanol and water 4 times in sequence, and dry at 55℃ and vacuum degree -0.09MPa for 5h to finally obtain a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane with a loading of 15wt%.

[0056] Step Six: Place the mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane obtained in Step Five in a vacuum chamber, maintain the pressure at 0.8 kPa and heat to 150°C, and continuously introduce hexamethyldisilazane vapor at a partial pressure of 0.3 kPa for 2 hours to raise the contact angle of the hydrophobic region to 115° and cover 78% of the surface area, thus completing the preparation of the gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material. Example

[0057] Unlike Example 1, in step five of this example, the concentration of potassium permanganate solution was adjusted to 0.035 mol / L, and the hydrothermal reaction time was extended to 7 h to obtain a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane with a loading of 20 wt%. The remaining steps and parameters are exactly the same as in Example 1. Example

[0058] Unlike Example 1, in step five of this example, the concentration of potassium permanganate solution was adjusted to 0.040 mol / L, the concentration of urea was increased to 0.12 mol / L, and the hydrothermal reaction time was extended to 8 h to obtain a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane with a loading of 25 wt%. The remaining steps and parameters are exactly the same as in Example 1. Example

[0059] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 35 minutes, which increases the proportion of hydrophilic micro-regions to 25% and reduces the contact angle to 42°. The remaining step parameters are exactly the same as in Example 1. Example

[0060] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 35 minutes to achieve a hydrophilic micro-region ratio of 25%; at the same time, in step five, the concentration of potassium permanganate solution is adjusted to 0.035 mol / L and the hydrothermal reaction is extended to 7 hours to achieve a loading of 20 wt%. The remaining step parameters are exactly the same as those in Example 1. Example

[0061] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 35 minutes to achieve a hydrophilic micro-region ratio of 25%; at the same time, in step five, the potassium permanganate solution concentration is adjusted to 0.040 mol / L, the urea concentration is increased to 0.12 mol / L, and the hydrothermal reaction is extended to 8 hours to achieve a loading of 25 wt%. The remaining step parameters are exactly the same as in Example 1. Example

[0062] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 40 minutes, the ozone volume fraction is increased to 6%, the proportion of hydrophilic micro-regions is increased to 35%, and the contact angle is reduced to 38°. The remaining step parameters are exactly the same as in Example 1. Example

[0063] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 40 min and the ozone volume fraction is increased to 6%, so that the proportion of hydrophilic micro-regions reaches 35%; at the same time, in step five, the concentration of potassium permanganate solution is adjusted to 0.035 mol / L and the hydrothermal reaction is extended to 7 h, so that the loading reaches 20 wt%. The remaining step parameters are exactly the same as those in Example 1. Example

[0064] Unlike Example 1, in step three of this example, the ozone oxidation treatment time is extended to 40 min and the ozone volume fraction is increased to 6%, so that the proportion of hydrophilic micro-regions reaches 35%. At the same time, in step five, the concentration of potassium permanganate solution is adjusted to 0.040 mol / L, the concentration of urea is increased to 0.12 mol / L, and the hydrothermal reaction is extended to 8 h, so that the loading reaches 25 wt%. The remaining step parameters are exactly the same as those in Example 1.

[0065] Comparative Example 1: Polyacrylonitrile powder with an average molecular weight of 150,000 was dissolved in N,N-dimethylformamide solvent to form a homogeneous solution with a mass fraction of 12 wt%. This solution was continuously treated at 60 °C for 6 h in a constant-temperature magnetic stirrer. The homogeneous polyacrylonitrile solution was then fed to a metal nozzle at a feed rate of 0.08 mm / min. An 18 kV DC high-voltage electric field was applied between the nozzle and a rotating drum receiver, with the receiving distance controlled at 18 cm and the drum rotation speed at 140 r / min. Under conditions of 25 °C and 45% relative humidity, N,N-dimethylformamide was allowed to diffuse at an evaporation rate of 0.20 mL / min, forming a polyacrylonitrile nanofiber membrane with a diameter of 400 nm, a basis weight of 10 g / m², and a porosity of 88%.

[0066] Polyacrylonitrile nanofiber membranes were placed in an air atmosphere containing 20% ​​oxygen by volume and heated to 250℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The pre-oxidized polyacrylonitrile nanofiber membranes were then transferred to an inert nitrogen environment and heated to 900℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The carbonized polyacrylonitrile nanofiber membranes were then immersed in a 45% potassium hydroxide solution for 2 hours, dried, and treated at 800℃ in an inert atmosphere for 0.5 hours. After washing with 0.5 mol / L hydrochloric acid solution and rinsing with water, an activated carbon nanofiber membrane with a specific surface area of ​​1350 m² / g was obtained.

[0067] Comparative Example 2: Polyacrylonitrile powder with an average molecular weight of 150,000 was dissolved in N,N-dimethylformamide solvent to form a homogeneous solution with a mass fraction of 12 wt%. This solution was continuously treated at 60 °C for 6 h in a constant-temperature magnetic stirrer. The homogeneous polyacrylonitrile solution was then fed to a metal nozzle at a feed rate of 0.08 mm / min. An 18 kV DC high-voltage electric field was applied between the nozzle and a rotating drum receiver, with the receiving distance controlled at 18 cm and the drum rotation speed at 140 r / min. Under conditions of 25 °C and 45% relative humidity, N,N-dimethylformamide was allowed to diffuse at an evaporation rate of 0.20 mL / min, forming a polyacrylonitrile nanofiber membrane with a diameter of 400 nm, a basis weight of 10 g / m², and a porosity of 88%.

[0068] Polyacrylonitrile nanofiber membranes were placed in an air atmosphere containing 20% ​​oxygen by volume and heated to 250℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The pre-oxidized polyacrylonitrile nanofiber membranes were then transferred to an inert nitrogen environment and heated to 900℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The carbonized polyacrylonitrile nanofiber membranes were then immersed in a 45% potassium hydroxide solution for 2 hours, dried, and treated at 800℃ in an inert atmosphere for 0.5 hours. After washing with 0.5 mol / L hydrochloric acid solution and rinsing with water, an activated carbon nanofiber membrane with a specific surface area of ​​1350 m² / g was obtained.

[0069] The activated carbon nanofiber membrane was placed in an oxygen mixed gas flow containing 5% ozone by volume, and heated to 250℃ at a heating rate of 5℃ / min and held at that temperature for 35 minutes, so that the proportion of hydrophilic micro-regions reached 25% and the contact angle was reduced to 42°.

[0070] Activated carbon nanofiber membranes with selective surface oxidation treatment were immersed in 0.10% (w / w) aminated silica sol, treated with ultrasonic frequency of 50 kHz for 1.25 h, and then dried at 80 °C, with the aminated silica loading controlled to reach 1.0 mg / g membrane substrate.

[0071] Comparative Example 3: Polyacrylonitrile powder with an average molecular weight of 150,000 was dissolved in N,N-dimethylformamide solvent to form a homogeneous solution with a mass fraction of 12 wt%. This solution was continuously treated at 60 °C for 6 h in a constant-temperature magnetic stirrer. The homogeneous polyacrylonitrile solution was then fed to a metal nozzle at a feed rate of 0.08 mm / min. An 18 kV DC high-voltage electric field was applied between the nozzle and a rotating drum receiver, with the receiving distance controlled at 18 cm and the drum rotation speed at 140 r / min. Under conditions of 25 °C and 45% relative humidity, N,N-dimethylformamide was allowed to diffuse at an evaporation rate of 0.20 mL / min, forming a polyacrylonitrile nanofiber membrane with a diameter of 400 nm, a basis weight of 10 g / m², and a porosity of 88%.

[0072] Polyacrylonitrile nanofiber membranes were placed in an air atmosphere containing 20% ​​oxygen by volume and heated to 250℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The pre-oxidized polyacrylonitrile nanofiber membranes were then transferred to an inert nitrogen environment and heated to 900℃ at a rate of 5℃ / min, then held at that temperature for 1 hour. The carbonized polyacrylonitrile nanofiber membranes were then immersed in a 45% potassium hydroxide solution for 2 hours, dried, and treated at 800℃ in an inert atmosphere for 0.5 hours. After washing with 0.5 mol / L hydrochloric acid solution and rinsing with water, an activated carbon nanofiber membrane with a specific surface area of ​​1350 m² / g was obtained.

[0073] Potassium permanganate was dissolved in water to form a 0.035 mol / L solution. A binary reduction system was constructed by adding 0.15 mol / L ethanol and 0.10 mol / L urea. An activated carbon nanofiber membrane was immersed in the solution, and the reaction vessel was sealed. The temperature was increased to 120°C at a rate of 4°C / min and maintained at this temperature for 7 hours. The membrane was then ultrasonically washed four times with anhydrous ethanol and water, and dried for 5 hours under a vacuum of 55°C and -0.09 MPa to obtain a mesoporous δ-phase manganese dioxide nanosheet composite activated carbon nanofiber membrane with a loading of 20 wt%.

[0074] Comparative Example 4: 100-200μm coconut shell granular activated carbon was impregnated in a 10% phenolic resin solution for 1 hour and then dried and cured at 120℃. The resin-loaded granular activated carbon was filled into a mold and pressed under 15MPa pressure for 3 minutes to form a filter element blank with a thickness of 2mm. The filter element blank was placed in a tube furnace and heated to 700℃ at 10℃ / min under a nitrogen atmosphere and maintained at that temperature for 1 hour. The activated filter element was impregnated in a 5wt% phosphoric acid solution for 30 minutes and then dried at 105℃.

[0075] Experimental Example 1: Samples: The composite materials prepared in Examples 1-9 and Comparative Examples 1-4 were used as functional layers with a thickness of 0.10 mm. These layers were placed between a polyester nonwoven fabric base layer with a thickness of 0.20 mm and a meltblown polypropylene nonwoven fabric protective layer with a thickness of 0.25 mm. A dynamic pressure of 0.40 MPa and longitudinal vibration with an amplitude of 5 μm were applied in a 40 kHz ultrasonic field for 15 s. The samples were then treated in a hot air environment with an airflow velocity of 1.0 m / s and a temperature of 90 °C for 30 min to obtain composite filter element samples.

[0076] Test conditions: 1. Formaldehyde removal performance test: The test was conducted in a 1m³ Teflon-coated stainless steel sealed chamber. A pre-installed variable frequency fan maintained an airflow speed of 1.00±0.05m / s. The environmental parameters were stabilized at 25.0±0.5℃ and relative humidity of 60±2% using a temperature and humidity controller. 2. Particulate matter filtration performance test: The TSI8130 automatic filter material tester was used to test the upstream and downstream particle concentrations under the standard test flow rate of 5.3 cm / s, using sodium chloride solid particles with an aerodynamic diameter of 0.30 ± 0.02 μm as the test aerosol.

[0077] Test items and methods: 1. Formaldehyde removal rate (η): Formaldehyde removal rate is defined as the percentage decrease in formaldehyde concentration within 150 minutes, reflecting the material's immediate formaldehyde purification capability. During the test, 0.10 ± 0.01 ppm of standard formaldehyde gas was injected into the sealed chamber. A VXV100-CH2O-G formaldehyde analyzer was used to record the concentration every 5 minutes, continuing for 150 minutes. The concentration was then calculated using the formula η = (C0 - C...). 150 The removal rate is calculated as () / C0×100%.

[0078] 2. Formaldehyde removal rate retention rate after five cycles (η5): The formaldehyde removal rate retention rate after five cycles characterizes the long-term stability of the material and is defined as the percentage of the formaldehyde removal rate in the fifth cycle relative to the initial test value. After the initial η test, the sample is heat-treated in a 60℃ forced-air drying oven for 60 minutes, then purged with 99.99% high-purity nitrogen for 10 minutes to remove residues. This formaldehyde removal rate test procedure is repeated five times, and finally, η5 = η5. th / η1 st Calculate the retention rate by multiplying by 100%.

[0079] 3.0.3μm particulate matter purification efficiency (E): The 0.3μm particulate matter purification efficiency reflects a material's ability to intercept particles of the most easily penetrating size, defined as the percentage difference between the downstream and upstream particle concentrations. During testing, a sodium chloride aerosol with a median diameter of 0.30μm and a geometric standard deviation <1.8 was generated in a TSI8130 instrument. The test flow rate was controlled at 5.3cm / s, and a laser particle counter was used to simultaneously detect the upstream and downstream particle number concentrations. The efficiency was calculated using the formula E=(1-C). d / C u )×100% calculates the efficiency value.

[0080] The experimental results are shown in the table below: Table 1 Comparison of Experimental Results

[0081] Where X1 represents the proportion of hydrophilic microregions and X2 represents the δ-MnO2 loading.

[0082] The combination of 25% hydrophilic microdomains and 20wt% mesoporous δ-phase manganese dioxide nanosheets resulted in a formaldehyde removal rate peak of 93.8%, significantly higher than other examples and comparative examples. This is because the hydrophilic microdomains enhance the formaldehyde molecule capture probability through the hydrogen bond network formed by carboxyl groups and aminated silica particles, while the manganese vacancy active sites of the mesoporous δ-phase manganese dioxide nanosheets accelerate the oxidative decomposition of formaldehyde. Delving into the molecular-scale mechanism, the spatial overlap between the 25% hydrophilic microdomains and the mesoporous δ-phase manganese dioxide nanosheets reaches 91%, forming an adsorption and catalytic cascade channel: after the adsorption energy of formaldehyde molecules drops to -0.85 eV in the hydrophilic microdomains, they migrate directionally along the surface energy gradient with a 0.12 eV energy barrier to the adjacent catalyst mesoporous channels, a process that increases the local formaldehyde concentration by 8.5 times. The 3.0 nm thickness of the mesoporous δ-phase manganese dioxide nanosheets corresponding to the 20wt% loading ensures a mesopore patency rate greater than 95%, avoiding pore blockage problems caused by high loading.

[0083] When the proportion of hydrophilic microdomains deviates from 25% or the loading of mesoporous δ-phase manganese dioxide nanosheets deviates from 20 wt%, the two variables mutually inhibit each other, leading to performance degradation. For example, in Example 7, the proportion of hydrophilic microdomains was increased to 35%. Excessive carboxyl groups covered the oxygen vacancies on the surface of the mesoporous δ-phase manganese dioxide nanosheets, hindering formaldehyde molecules from contacting the active sites, resulting in a formaldehyde removal rate of 66.4%. At the same time, the overloaded hydrophilic groups enhanced the competitive adsorption of water molecules, increasing the water vapor competitive adsorption ratio to 1.08. Conversely, in Example 3, the loading of mesoporous δ-phase manganese dioxide nanosheets was increased to 25 wt%. The excessively thick nanosheet layer blocked the submicron pores of the activated carbon nanofiber membrane, not only increasing the formaldehyde mass transfer resistance by 40% but also causing spatial separation between the hydrophilic microdomains and the catalyst, with an overlap rate of only 65%, ultimately reducing the formaldehyde removal rate to 71.4%. This is because the hydrophilic microdomains need to match the catalyst distribution density to construct an efficient reaction channel, and any imbalance in either variable will disrupt the adsorption and catalytic coupling mechanism.

[0084] Example 5 showed that the formaldehyde removal rate remained at 82.8% after the fifth cycle, with a 57.5% reduction in attenuation compared to competing products. This was due to the hydrophobic siloxane layer formed by hexamethyldisilazane modification: the hydrophobic region's contact angle of 115° reduced the water molecule diffusion coefficient to 2.1 × 10⁻⁻⁶. 9 The flow rate (m² / s) is only one-quarter that of the hydrophilic region, thus inhibiting the formation of hydrogen bond networks by water molecules on the surface of mesoporous δ-phase manganese dioxide nanosheets. Molecular dynamics simulations further confirmed that the hydrophobic layer forces a 4.2-fold increase in the migration path of water molecules, while formaldehyde molecules can rapidly cross the energy barrier difference at the hydrophilic-hydrophobic interface to the catalyst active site. This design enabled Example 5 to maintain the dry state of the catalytic active site in a high humidity environment, while in Comparative Example 4, which lacked hydrophobic protection, the manganese oxidation state decreased from 3.92 to 3.45 after five cycles due to continuous poisoning of the active site by water molecules.

[0085] Although loading with mesoporous δ-phase manganese dioxide nanosheets increased the fiber surface roughness from 0.38 μm to 0.52 μm, the root mean square height difference of the nanosheets at a loading of 20 wt% was controlled within 40 nm, without significantly altering the basic filtration structure of the activated carbon nanofiber membrane. More importantly, gradient wetting achieved an interlayer bonding strength of 1.2 × 10⁻⁶ through ultrasonic interfacial coupling. 4 N / m ensures that the functional layer has no fiber displacement under airflow impact, making the particulate matter interception efficiency fluctuation less than 0.1%.

[0086] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material, characterized in that, Includes the following steps: Step 1: Polyacrylonitrile nanofiber membranes are prepared using electrospinning process with polyacrylonitrile powder as raw material; Step 2: The polyacrylonitrile nanofiber membrane is subjected to pre-oxidation, carbonization and chemical activation treatment in sequence to obtain activated carbon nanofiber membrane; Step 3: Construct hydrophilic microdomains on the surface of the activated carbon nanofiber membrane by ozone oxidation; Step 4: Load aminated silica nanoparticles onto the hydrophilic microregions; Step 5: Using an activated carbon nanofiber membrane loaded with aminated silica as a carrier, mesoporous δ-phase manganese dioxide nanosheets are grown in situ on the surface of the activated carbon nanofiber membrane loaded with aminated silica via a hydrothermal reaction. Step 6: Construct a hydrophobic background region in the non-hydrophilic area by vapor treatment with hexamethyldisilazane to form a gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material.

2. The preparation method according to claim 1, characterized in that, Step one specifically includes: dissolving polyacrylonitrile powder with an average molecular weight of 150,000 in N,N-dimethylformamide to form a homogeneous solution with a mass fraction of 10-14 wt%. After stirring at 55-65℃ for 5-7 hours, the solution is fed to the nozzle at a push rate of 0.06-0.10 mm / min. Electrospinning is carried out under conditions of 16-22 kV DC electric field, receiving distance of 16-20 cm, and roller speed of 130-150 r / min. The ambient temperature is controlled at 25±2℃ and the relative humidity is 40-50%, and finally a polyacrylonitrile nanofiber membrane with a diameter of 300-500 nm and a porosity of 85-90% is obtained.

3. The preparation method according to claim 1, characterized in that, Step two specifically includes: pre-oxidizing the polyacrylonitrile nanofiber membrane by heating it to 240-260℃ at a heating rate of 4-6℃ / min in an air atmosphere with an oxygen volume fraction of 18-22% and holding it at that temperature for 0.8-1.2h; then carbonizing it by heating it to 880-920℃ at a heating rate of 4-6℃ / min in a nitrogen atmosphere and holding it at that temperature for 0.8-1.2h; then immersing it in a potassium hydroxide solution with a mass concentration of 40-50% for 1.5-2.5h; drying it; and finally activating it by treating it in an inert atmosphere at 780-820℃ for 0.4-0.6h, ultimately obtaining an activated carbon nanofiber membrane with a specific surface area of ​​1200-1500m² / g.

4. The preparation method according to claim 1, characterized in that, Step 3 specifically includes: placing the activated carbon nanofiber membrane in an oxygen flow containing 4-6% ozone by volume, heating it to 240-260℃ at a heating rate of 4-6℃ / min and holding it at that temperature for 25-35min, so that the proportion of hydrophilic micro-regions reaches 20-25% and the contact angle is reduced to 40-50°.

5. The preparation method according to claim 1, characterized in that, Step four specifically includes: immersing the ozone-oxidized activated carbon nanofiber membrane in an aminated silica sol with a mass fraction of 0.08-0.12%, treating it under ultrasonic conditions of 40-60kHz for 1.0-1.5h, and then drying it, controlling the loading of aminated silica to be 0.8-1.2mg / g membrane substrate.

6. The preparation method according to claim 1, characterized in that, Step five specifically includes: immersing the activated carbon nanofiber membrane loaded with aminated silica into a mixed solution containing 0.028-0.032 mol / L potassium permanganate, 0.12-0.18 mol / L ethanol, and 0.08-0.12 mol / L urea; sealing the solution; heating it to 118-122℃ at a rate of 3-5℃ / min and holding it at that temperature for 5.5-6.5 h; after the reaction is complete, ultrasonically washing the membrane with anhydrous ethanol and water in sequence and then drying it to finally obtain a mesoporous δ-phase manganese dioxide nanosheet composite membrane with a loading of 18-22 wt% and a thickness of 2.5-3.5 nm.

7. The preparation method according to claim 1, characterized in that, Step six specifically includes: placing the mesoporous δ-phase manganese dioxide nanosheet composite film in a vacuum chamber, and treating it with hexamethyldisilazane vapor at a partial pressure of 0.2-0.4 kPa for 1.5-2.5 hours under conditions of 0.5-1.0 kPa pressure and 140-160°C to form a siloxane layer with a thickness of 1-2 nm, thereby increasing the contact angle of the hydrophobic region to 110-120° and covering 75-80% of the surface area.

8. The preparation method according to any one of claims 1, characterized in that, The hydrophilic microregions account for 20-25%, and the loading of the mesoporous δ-phase manganese dioxide nanosheets is 18-22 wt%.

9. A gradient-wetting mesoporous δ-MnO2@activated carbon nanofiber membrane material, characterized in that, Prepared according to the preparation method described in any one of claims 1-8.

10. An application of the gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material according to claim 9 in the preparation of composite filter cartridges, characterized in that, The process involves sequentially stacking a polyester nonwoven fabric substrate layer, a functional layer composed of gradient wetting type mesoporous δ-MnO2@activated carbon nanofiber membrane material, and a meltblown polypropylene nonwoven fabric protective layer; applying a dynamic pressure of 0.35-0.45MPa and longitudinal vibration with an amplitude of 5-8μm for 12-18s in a 38-42kHz ultrasonic field; and then treating it in a hot air environment with an airflow velocity of 0.8-1.2m / s and a temperature of 85-95℃ for 25-35 minutes to finally obtain the composite filter element.

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