A composite filter membrane for efficient collection of aerosol pathogens and its preparation method

Abstract

This invention provides a composite filter membrane for efficient collection of aerosol pathogens and its preparation method. The composite filter membrane comprises, from top to bottom, a coarse layer, an electrostatic layer, and an activated carbon enrichment layer. The coarse layer is made of PP fiber membrane, the electrostatic layer is made of electret-treated PP fiber membrane with a surface potential >1.0 kV, and the activated carbon enrichment layer uses activated carbon particles with a SiO2 film deposited on their surface. The SiO2 passivates the activated carbon, reducing the chemisorption intensity. The composite filter membrane of this invention has a hierarchical pore structure, enabling multi-layer gradient filtration, accelerating the diffusion of viruses to adsorption sites. Furthermore, the silica film deposited on the activated carbon surface acts as an inert barrier, achieving both low chemisorption intensity and biocompatibility protection.

Description

Technical Field

[0001] This invention belongs to the field of air filtration material technology, and in particular relates to a composite filter membrane for efficient collection of aerosol pathogens and its preparation method. Background Technology

[0002] Existing detection technologies, such as gas-liquid phase sampling, have insufficient capture efficiency for aerosols (<50%) and cannot distinguish between live and inactivated pathogens, resulting in a false negative rate as high as 30%. Furthermore, traditional filter materials have limitations; strong chemical adsorption or mechanical damage can lead to pathogen inactivation. For example, glass fiber membranes, while possessing high retention rates (PM0.3 capture rate >95%), suffer from strong adsorption, making elution difficult (virus recovery rate <60%), and the silicates released from fiber breakage interfere with nucleic acid detection. Meltblown polypropylene filter media relies on electrostatic adsorption, but in high humidity environments, charge decays rapidly (efficiency decrease >40% in 24 hours), making it unable to stably capture nanoscale viral particles (such as H1N1 virus with a diameter of approximately 80-120 nm). Activated carbon filters are mainly used for VOCs adsorption; their microporous structure (<2 nm) easily encapsulates pathogens and disrupts their integrity, and they lack biocompatibility design. Moreover, existing filter membranes are prone to secondary escape under airflow impact, with an escape rate >15%. Summary of the Invention

[0003] In view of this, the present invention aims to provide a composite filter membrane for efficient collection of aerosol pathogens and its preparation method, so as to solve the above problems.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A composite filter membrane for efficient collection of aerosol pathogens is disclosed. The composite filter membrane comprises a coarse layer, an electrostatic layer, and an activated carbon enrichment layer arranged sequentially from top to bottom. The coarse layer is made of PP fiber membrane, the electrostatic layer is made of electret-treated PP fiber membrane with a surface potential >1.0kV, and the activated carbon enrichment layer uses activated carbon particles with a SiO2 film deposited on their surface. The activated carbon is passivated by SiO2 to reduce the chemical adsorption intensity.

[0006] Furthermore, the thickness of the coarse layer is 0.5 mm, the diameter of the PP fiber is 10 μm, and the porosity of the PP fiber membrane is 80-90%; the thickness of the electrostatic layer is 0.2 mm, the diameter of the PP fiber is 1-5 μm, and the porosity of the PP fiber membrane is ≥85%; the thickness of the activated carbon enrichment layer is 0.8 mm, the thickness of the SiO2 film is <5 nm, and the pore size of the activated carbon is 20-50 nm.

[0007] Furthermore, the pore size of activated carbon is adjusted through steam activation. The specific method is as follows:

[0008] (1) Crush the raw material to 2-4 mm, and in an inert atmosphere, heat it to 350-600℃ for low-temperature carbonization in a gradient heating manner for 60-120 minutes to remove volatile components and form an initial carbon skeleton and microporous structure.

[0009] (2) High-temperature activation at 800-850℃ for 60-90 minutes, with steam flow rate controlled at 3-4.5 L / min, achieves the transformation of micropores into mesopores. Studies have shown that at 850℃, water vapor reacts with carbon to generate CO and H2, expanding the pores and forming mesopores of 20-50 nm. Furthermore, secondary activation in a high-temperature inert atmosphere repairs surface defects and increases compressive strength by 40%.

[0010] Extending the activation time (60-90 minutes) can increase pore connectivity, but excessive heating should be avoided to prevent structural collapse.

[0011] The steam flow rate needs to be precisely controlled (e.g., 3-4.5 L / min). Too high a flow rate will reduce the surface temperature of the carbon and inhibit pore expansion; too low a flow rate will result in insufficient activation.

[0012] Preferably, step (1) adopts a gradient heating method: first, heat to 300℃ at 5℃ / min and keep warm for 20 minutes, then heat to the target temperature at 10℃ / min to improve the uniformity of pores.

[0013] Preferably, the time of step (1) needs to be dynamically adjusted according to the temperature gradient and optimized in combination with the characteristics of the raw materials and the equipment conditions to balance the volatile matter release rate and the stability of the carbon skeleton; specifically, the following heating methods are included:

[0014] A. React at 350-400℃ for 30-60 minutes, allowing volatilized components to escape at a low rate to avoid excessive shrinkage of the carbon skeleton. Appropriately extend the holding time to ensure uniform carbonization.

[0015] B. React at 400-500℃ for 15-30 minutes to rapidly decompose volatile components. Control the time to prevent excessive carbonization.

[0016] C. React at 500-600℃ for 15-30 minutes. High temperature increases the rate of volatile component release, while controlling the time to avoid raw material clumping.

[0017] Preferably, steps (1) and (2) are carried out under an inert atmosphere (N2 / Ar), which can shorten the carbonization time by 10%-15%.

[0018] Furthermore, activated carbon also includes the following processing steps:

[0019] Oxidation of the surface with dilute nitric acid or ozone introduces polar carboxyl and hydroxyl groups, enhancing the chemical adsorption of viral surface proteins.

[0020] And / or improve pore accessibility by using ultrasonic cavitation or interface oxidation techniques to prevent virus particles from clogging the pores;

[0021] And / or coating with biocompatible polymers (such as chitosan) to increase electrostatic attraction or specific binding to viruses.

[0022] Furthermore, the raw materials used in the steam activation method are woody or fruit shell materials, such as coconut shells and fruit tree branches, because they have high cellulose and lignin content and are more likely to form a well-developed mesoporous structure.

[0023] Furthermore, the PP fiber membrane used in the electrostatic layer is also grafted with ethylenediamine, with a grafting rate of 1.2%-2.0%. This range can balance surface activity and fiber mechanical properties, avoiding material embrittlement due to excessive grafting.

[0024] Experiments show that the electret electric field strength (1.2-1.8kV) and filtration efficiency (99.93%-99.97%) reach the optimal balance within this range.

[0025] Furthermore, the PP fiber membrane used in the electrostatic layer is prepared by the following method:

[0026] (1) PP fiber membrane was prepared by melt-blowing method;

[0027] (2) The prepared PP fiber membrane is cleaned to remove surface oil and processing aids;

[0028] (3) First, corona charge the PP fiber membrane: voltage 30-50kV, electret time 10-30 seconds, to give the fiber a lasting electrostatic charge; then perform hot pressing: temperature 120-140℃, pressure 0.1-0.3MPa, time 5-10 seconds, to enhance the bonding force of the fiber web and prevent pore collapse.

[0029] (4) Active groups are generated by plasma treatment of PP fiber membrane, providing binding sites for grafting reaction;

[0030] (5) Under the protection of inert gas, the plasma-treated PP fiber membrane is immersed in ethylenediamine solution for reaction grafting;

[0031] (6) The reacted PP fiber membrane is cleaned to obtain the desired PP fiber membrane.

[0032] Furthermore, in step (4), the gas used for plasma treatment is argon or oxygen, and the vacuum degree is 10. -2 -10 - 3 Pa, power of 50-100W, processing time 2-5 minutes;

[0033] In step (5), the volume concentration of the ethylenediamine solution is 10%-20%, and it is immersed in the ethylenediamine solution and kept in a constant temperature water bath at 30-60°C for 1-3 hours of reaction time.

[0034] Furthermore, the activated carbon enrichment layer is formed into a "sandwich" structure by embedding activated carbon particles into a melt-blown fiber substrate through a hot pressing or needle punching process.

[0035] The fiber network can anchor the activated carbon particles, reducing the shedding caused by air flow scouring (the loss rate is reduced by more than 70%).

[0036] Furthermore, the activated carbon particles with a SiO2 thin film deposited on the surface are prepared by the following method:

[0037] (1) Pretreatment of activated carbon:

[0038] First, use plasma etching to clean the activated carbon, remove the surface organic residues and form a uniform nano-scale roughness of 1.1nm < Ra < 1.3nm to enhance the adhesion of the SiO2 thin film; then immerse the activated carbon in an amino silane coupling agent solution for reaction to introduce amino groups as anchoring sites to achieve the directional adsorption of the SiO2 precursor and inhibit the thickness unevenness caused by random nucleation;

[0039] (2) Atomic layer deposition of ultrathin SiO2 thin film:

[0040] Use the precursors bis(diethylamino)silane and ozone for deposition. After deposition, perform in-situ hydrogen plasma annealing to eliminate the dangling bonds inside the thin film and reduce the surface hydroxyl density to < 2 groups / nm 2 , reducing the chemisorption active sites;

[0041] (3) Surface terminal modification:

[0042] Vapor deposit 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTS). Utilize the residual hydroxyl groups on the SiO2 surface to react with 1H,1H,2H,2H-perfluorooctyltriethoxysilane to form a monolayer fluorinated terminal (contact angle > 110°), reducing the polar interaction between the virus / bacteria and the surface.

[0043] Furthermore, in step (1), the plasma etching cleaning uses an Ar / O2 mixed gas with a volume ratio of 4:1, a power of 300W, a treatment time of 5 min, and a vacuum degree of 10 -2 Pa;

[0044] The amino silane coupling agent solution is an ethanol solution of aminopropyltriethoxysilane (APTES) with a mass concentration of 1%, reacts at 60°C for 2 h, and is dried by nitrogen purging;

[0045] In step (2), the deposition parameters are: temperature 120℃, pulse time 0.1s, purge time 30s, and number of cycles 10-15. The gradient deposition method is adopted, with the first layer using a high purge ratio, i.e., the precursor:purge ratio is 1:5. Subsequently, the ratio is gradually reduced from 1:5 to 1:1, with each layer decreasing by 0.5, so as to achieve structural optimization while ensuring that the film is continuous and defect-free.

[0046] The purge ratio refers to the flow rate ratio of the reactant gas to the purge gas, used to control the thin film growth mode. A high purge ratio (e.g., 1:5) can suppress island growth, promote continuous film formation, and significantly improve film uniformity. Factors affecting film quality include purge ratio, precursor concentration, and temperature.

[0047] Achieve in-situ thickness monitoring: Integrate a quartz crystal microbalance (QCM) to provide real-time feedback on film thickness (single-cycle growth rate approximately 0.3 nm / cycle), and dynamically adjust the number of cycles to the target thickness (4.5 ± 0.5 nm).

[0048] The annealing conditions are: H2 flow rate 50 sccm, power 150 W, annealing time 10 min;

[0049] In step (3), the deposition conditions are 150℃ for 30 min.

[0050] This invention also provides a method for preparing a composite filter membrane for efficient collection of aerosol pathogens as described above, the method comprising the following steps:

[0051] (1) Preparation of coarse effective layer

[0052] PP fibers are prepared by melt-blowing. After melting PP resin, it is spun at high speed and stretched by airflow to form ultrafine fibers (10μm in diameter). The fibers are sprayed onto a receiving plate and solidified into a film, forming a fluffy and porous coarse layer.

[0053] (2) Preparation of electrostatic layer

[0054] Similarly, PP fiber (diameter 1-5μm) membranes are prepared by meltblowing. Then, the PP fiber membranes are first corona charged and then grafted with ethylenediamine to form the required electrostatic layer.

[0055] (3) Preparation of activated carbon enrichment layer

[0056] SiO2 thin films are deposited on activated carbon particles, and then a "sandwich" structure is formed by embedding the activated carbon particles into a meltblown fiber substrate through hot pressing or needle punching processes.

[0057] (4) Composite 3-layer structure

[0058] The three layers of material are stacked and pressed together by hot rollers at a temperature of 60-160℃ and a pressure of 0.1-1MPa for 30-60 seconds per layer, ensuring that heat penetrates the three-layer structure.

[0059] Preferably, using an infrared heating roller can improve the uniformity of temperature change by more than 20%, achieving reliable bonding at the interface.

[0060] The temperature of the hot roller needs to be dynamically adjusted according to the processing stage (preheating / bonding / shaping) and material characteristics.

[0061] Preheating stage: 60-80℃, material activation before composite film lamination, gradually softening the material, reducing melt viscosity, and avoiding local overheating that could lead to material degradation.

[0062] Adhesion stage: 120-140℃, hot pressing of three-layer composite film, it is necessary to balance the adhesion strength and the temperature resistance of the material to ensure that the coarse layer and the electrostatic layer are fully melted and bonded, while not affecting the stability of the fiber skeleton structure and avoiding the escape of volatile components from the activated carbon enrichment layer.

[0063] The solidification stage: 90-110℃, to achieve the effect of solidifying the composite structure, eliminating internal stress, and improving mechanical strength.

[0064] Compared with existing technologies, the composite filter membrane for efficient collection of aerosol pathogens and its preparation method described in this invention have the following advantages:

[0065] (1) A silica (SiO2) film is deposited on the surface of activated carbon as an inert barrier with a thickness of <5 nm. By controlling the thickness and passivating the surface, a low chemical adsorption strength and biocompatibility protection function are achieved, blocking the oxidative damage of free radicals on the activated carbon surface to the viral capsid and avoiding damage to the viral capsid or bacterial cell membrane. This method breaks through the bottleneck of biological damage caused by the strong adsorption of traditional activated carbon and provides an innovative solution for the development of biosafety-grade filter materials.

[0066] (2) A silica (SiO2) film is deposited on the surface of activated carbon to inhibit adsorption through a dual mechanism: (i) chemical passivation: hydrogen annealing reduces the hydroxyl density and reduces hydrogen / ionic bonding; (ii) physical shielding: fluorinated terminals weaken van der Waals forces to achieve “soft contact” adsorption.

[0067] (3) Activated carbon has a pore size of 20-50 nm, which can effectively trap virus particles (such as the SARS-CoV-2 virus with a diameter of 80-120 nm) and achieve physical adsorption through steric hindrance. Activated carbon has high temperature resistance. Activated carbon activated by water vapor is structurally stable at high temperatures (<600℃) and is suitable for air purification equipment. It also has regeneration capabilities. Adsorbed viruses can be removed by thermal desorption or chemical cleaning (such as alkaline solution) to restore its activity. Through process control, activated carbon can be adapted to virus adsorption requirements, combining high efficiency, selectivity and environmental friendliness, providing new material support for infectious disease prevention and control.

[0068] (4) Grafting PP fibers to introduce amino groups significantly improves their biocompatibility while taking into account the mechanical properties and chemical stability of the material.

[0069] (5) The composite filter membrane has a hierarchical pore structure: micropores-mesopores-macropores, which accelerates the diffusion of viruses to adsorption sites; the multi-layer gradient filtration method allows the coarse layer to intercept particles >10μm (such as dust and pollen), reducing biolayer contamination and reducing the airflow impact on the downstream activated carbon enrichment layer (flow velocity controlled at 0.1-0.3m / s); the electrostatic layer can capture 0.5-10μm aerosols (such as virus-containing droplet nuclei); and the activated carbon enrichment layer has a specific surface area of ​​800-1000m². 2 / g, adsorbs nanoscale particles (such as free viruses) and buffers airflow impact. Attached Figure Description

[0070] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0071] Figure 1 This is a schematic diagram of the composite filter membrane for efficient collection of aerosol pathogens according to an embodiment of the present invention;

[0072] Figure 2 These are photographs of the composite filter membrane for efficient collection of aerosol pathogens as described in the embodiments of the present invention. (a) is the front of the filter membrane, and (b) is the back of the filter membrane.

[0073] Figure 3 This is a comparison chart of the capture rates of Escherichia coli by the filter membrane of this invention, a traditional nylon filter membrane, and a PTFE filter membrane;

[0074] Figure 4 This is a comparison chart of the survival rates of Escherichia coli against the filter membrane of this invention, a traditional nylon filter membrane, and a PTFE filter membrane;

[0075] Figure 5 The graph shows the experimental results of the survival rate of Escherichia coli against the filter membrane of this invention, the traditional nylon filter membrane, and the PTFE filter membrane.

[0076] Figure 6 The PCR detection rates of Escherichia coli by the filter membrane of this invention, traditional nylon filter membrane, and PTFE filter membrane;

[0077] Figure 7 A comparison chart of the capture rates of viable E. coli using five different membranes;

[0078] Figure 8 A comparison of fungal spore germination rates for five different membranes;

[0079] Figure 9 A comparison chart of DNA extraction yield from five different membranes;

[0080] Figure 10 A comparison chart of Ct values ​​for five different membranes.

[0081] Explanation of reference numerals in the attached figures:

[0082] 1. Coarse layer; 2. Electrostatic layer; 3. Activated carbon enrichment layer. Detailed Implementation

[0083] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0084] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0085] Example 1: Composite Filter Membrane for High-Efficiency Collection of Aerosol Pathogens

[0086] The composite filter membrane includes a coarse layer 1, an electrostatic layer 2, and an activated carbon enrichment layer 3 arranged from top to bottom;

[0087] Coarse layer 1:

[0088] With a thickness of 0.5 mm, a PP fiber diameter of 10 μm, and a PP fiber membrane porosity of 90%, it intercepts particles larger than 10 μm (such as dust and pollen), reducing biolayer contamination.

[0089] Electrostatic layer 2:

[0090] The fiber has a thickness of 0.2 mm, an ethylenediamine grafting rate of 2.0%, a surface potential of 1.5 kV, a fiber diameter of 4 μm, and a porosity of ≥85%.

[0091] Activated carbon enrichment layer 3:

[0092] The activated carbon particles are 0.8 mm thick, passivated by SiO2, with a silicon dioxide film thickness of 4 nm and an activated carbon pore size of 40 nm.

[0093] I. Preparation of activated carbon particles with SiO2 thin film deposited on the surface

[0094] I. Activated Carbon Pore Size Control

[0095] The pore size of activated carbon can be adjusted to 20-50 nm by steam activation (to match the size of viruses, such as the SARS-CoV-2 virus, which has a diameter of about 80-120 nm) to improve selective adsorption.

[0096] 1. Raw material selection and pretreatment

[0097] Raw material type: Prioritize woody or fruit shell materials, such as coconut shells and fruit tree branches, because they have high cellulose and lignin content and are more likely to form a well-developed mesoporous structure.

[0098] Particle size control: Crush the raw material to 2-4mm. If it is too small, it will easily cause pore collapse; if it is too large, the activation will be uneven.

[0099] Carbonization pretreatment: In an inert atmosphere (N2 / Ar), carbonization is carried out at 350-600℃ using a gradient heating method to remove volatile components and form an initial carbon skeleton and microporous structure. Specifically, the temperature is first increased to 300℃ at a rate of 5℃ / min and held for 20 minutes, then increased to the target temperature at a rate of 10℃ / min to improve pore uniformity. The time needs to be dynamically adjusted according to the temperature gradient (60-120 minutes) and optimized in combination with raw material characteristics and equipment conditions to balance the volatile matter escape rate and the stability of the carbon skeleton.

[0100] Specifically, the heating methods include the following:

[0101] A. React at 350-400℃ for 30-60 minutes, allowing volatilized components to escape at a low rate to avoid excessive shrinkage of the carbon skeleton. Appropriately extend the holding time to ensure uniform carbonization.

[0102] B. React at 400-500℃ for 15-30 minutes to rapidly decompose volatile components. Control the time to prevent excessive carbonization.

[0103] C. React at 500-600℃ for 15-30 minutes. High temperature increases the rate of volatile component release, while controlling the time to avoid raw material clumping.

[0104] 2. Activation by water vapor

[0105] Activation temperature: High temperature range (800-850℃) promotes mesopore formation. In this embodiment, 850℃ was selected for activation. Experiments show that at 850℃, water vapor reacts with carbon to generate CO and H2, expanding the pores and forming mesopores of 20-50 nm. Furthermore, secondary activation in a high-temperature inert atmosphere repairs surface defects and increases compressive strength by 40%.

[0106] Activation time: Extending the activation time (60-90 minutes) can increase pore connectivity, but excessive heating should be avoided to prevent structural collapse.

[0107] Steam flow rate: The steam flow rate should be precisely controlled within the range of 3-4.5 L / min. Too high a flow rate will reduce the surface temperature of the carbon and inhibit pore expansion; too low a flow rate will result in insufficient activation.

[0108] 3. Post-treatment optimizes adsorption selectivity

[0109] Acid washing / oxidation treatment: The surface is oxidized with dilute nitric acid or ozone to introduce polar groups such as carboxyl and hydroxyl groups, thereby enhancing the chemical adsorption of viral surface proteins. In this embodiment, ozone oxidation is used after activation.

[0110] II. Deposition of SiO2 thin film

[0111] 1. Activated carbon pretreatment (to improve surface uniformity)

[0112] 1-1. Plasma etching and cleaning

[0113] Process parameters: Ar / O2 mixed gas (ratio 4:1), power 300W, processing time 5min, vacuum degree 10 -2 Pa.

[0114] Removes surface organic residues and forms a uniform nanoscale roughness (Ra≈1.2nm), enhancing the adhesion of SiO2 thin films.

[0115] 1-2. Self-assembly of aminosilane coupling agents

[0116] Activated carbon was immersed in a 1% APTES (aminopropyltriethoxysilane) ethanol solution and reacted at 60°C for 2 hours, then dried by nitrogen purging.

[0117] Introducing amino groups (-NH2) as anchoring sites enables directional adsorption of SiO2 precursors and suppresses uneven thickness caused by random nucleation.

[0118] 2. Atomic Layer Deposition (ALD) for Ultrathin SiO2 Films

[0119] 2-1. Precise deposition of low-temperature ALD

[0120] Precursor: Bis(diethylamino)silane (BDEAS) and ozone (O3);

[0121] Deposition parameters: temperature 120℃, pulse time 0.1s, purging time 30s, number of cycles 10-15.

[0122] In-situ thickness monitoring: Integrated quartz crystal microbalance (QCM) provides real-time feedback on film thickness (single cycle growth rate approximately 0.3 nm / cycle), dynamically adjusting the number of cycles to the target thickness (4.5 ± 0.5 nm).

[0123] Gradient deposition: The first layer uses a high purge ratio (precursor:purge = 1:5) to suppress island growth. The ratio is then gradually reduced in each subsequent layer, from 1:5 to 1:1, with a decrease of 0.5 per layer. This achieves structural optimization while ensuring a continuous and defect-free film.

[0124] 2-2 In-situ hydrogen plasma annealing

[0125] Process parameters: H2 flow rate 50 sccm, power 150 W, annealing time 10 min.

[0126] Eliminating dangling bonds within the thin film reduces the surface hydroxyl density to <2 groups / nm. 2 This reduces the number of active sites for chemisorption.

[0127] In this embodiment, chitosan is coated onto the surface of activated carbon after SiO2 deposition to increase electrostatic attraction or specific binding to viruses.

[0128] 3. Surface terminal modification (suppressing non-specific adsorption) - fluorosilane hydrophobication treatment

[0129] 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTS) was vapor-deposited at 150 °C for 30 min.

[0130] Selective modification: Residual hydroxyl groups on the SiO2 surface react with FOTS to form a monolayer fluorinated terminal (contact angle > 110°), reducing the polar interaction between viruses / bacteria and the surface.

[0131] III. Preparation of Activated Carbon Enrichment Layer

[0132] The prepared activated carbon particles are embedded in a meltblown fiber substrate, and a "sandwich" structure of activated carbon enrichment layer is formed by hot pressing or needle punching. The fiber network can anchor the activated carbon particles and reduce shedding caused by airflow erosion (loss rate reduced by more than 70%).

[0133] Ultrasonic sealing: High-frequency welding is used to seal the edges of the filter element to prevent particles from leaking from the side.

[0134] II. Preparation of electrostatic layer materials

[0135] I. Preparation of PP fibers

[0136] 1. Material preparation and pretreatment

[0137] Objective: To ensure the purity and melting properties of raw materials, laying the foundation for uniform fiber forming.

[0138] Raw material selection:

[0139] Polypropylene (PP) resin: Melt index (MFI) ≥ 800 g / 10 min (high fluidity).

[0140] Optional addition of electret masterbatch, such as SiO2 / PP composite masterbatch, can improve electrostatic adsorption and retention efficiency.

[0141] Preprocessing:

[0142] The resin particles are dried in an 80°C vacuum oven for 4 hours to prevent moisture evaporation during the melting process from causing fiber breakage.

[0143] 2. Meltblown process parameter settings

[0144] Objective: To achieve a fiber diameter of 1-5 μm and a high porosity structure by adjusting the parameters of the meltblown equipment.

[0145] Melting and Extrusion:

[0146] Melt temperature: 220-250℃ (too high a temperature can easily lead to degradation, while too low a temperature will result in insufficient fluidity).

[0147] Die head temperature: 250-280℃, spinneret diameter: 0.3-0.5mm.

[0148] High-speed hot air stretching:

[0149] Hot air temperature: 250-300℃, air pressure: 0.3-0.6MPa.

[0150] Airflow velocity: 500-800m / s, stretch the fiber to the target diameter (1-5μm).

[0151] Fiber receiving and web forming:

[0152] Receiver distance (DCD): 10-30cm (the closer the distance, the denser the fiber packing and the lower the porosity).

[0153] Air permeability of receiving mesh curtain: ≥200L / (m 2 •s)@100Pa, ensuring that the fibers are randomly distributed to form a porous structure.

[0154] Receiving speed: 5-20m / min (too fast a speed will result in a thinner fiber web, increased porosity but decreased mechanical strength).

[0155] Fiber diameter control: As hot air pressure increases, fiber tensile strength improves, and the diameter decreases, with a target of 1-5 μm. Increased melt temperature leads to decreased melt viscosity, making it easier to refine the fibers.

[0156] Porosity Improvement: Increased receiving distance improves fiber dispersion and porosity, with a target of ≥85%. This can reduce receiving speed or increase the air permeability of the mesh curtain, thereby reducing fiber bulk density.

[0157] Reducing fiber diameter (1-3 μm) can improve retention, but may increase pressure drop; the increased pressure drop can be compensated by increasing porosity (≥85%).

[0158] 3. Post-processing of fiber membrane structures

[0159] Objective: To optimize pore distribution and stability, and to balance retention rate and pressure drop.

[0160] Electret treatment:

[0161] Corona charging: voltage 30-50kV, electret time 10-30 seconds, imparts a lasting electrostatic charge to the fiber, improving particle retention rate (especially for submicron particles).

[0162] Hot pressing (light pressing):

[0163] Temperature: 120-140℃, pressure: 0.1-0.3MPa, time: 5-10 seconds, to enhance the bonding force of the fiber web and prevent pore collapse.

[0164] Hot pressing requires strict pressure control to avoid a significant decrease in porosity.

[0165] The ambient humidity for electret treatment needs to be less than 30% to prevent charge decay.

[0166] Through the above process, the fiber diameter of 1-5μm can be precisely controlled under high porosity (≥85%), and the particle retention rate and airflow resistance (pressure drop <100Pa@10L / min, 25±2℃) can be balanced to meet the requirements of high-performance filter materials.

[0167] II. Grafting Modification

[0168] Aminolation modification: Plasma grafting of ethylenediamine is used to make the surface of the fiber membrane positively charged (Zeta potential +15mV at pH=7), which enhances the electrostatic adsorption with negatively charged pathogens (such as viral surface potential -20mV).

[0169] 1. Material pretreatment

[0170] Objective: To remove impurities from the surface of fiber membranes and improve the effect of subsequent modification.

[0171] Cleaning: Immerse the polypropylene fiber membrane in anhydrous ethanol or acetone and ultrasonically clean for 20-30 minutes to remove surface oil and processing aids. Ethanol is economical and practical, while acetone has a stronger cleaning ability.

[0172] Specifically, in this embodiment, anhydrous ethanol was used for ultrasonic cleaning for 30 minutes at an ultrasonic frequency of 40kHz and a power of 200W.

[0173] Drying: Dry in a vacuum oven at 60℃ for 2 hours to ensure the fiber membrane is completely dehydrated.

[0174] 2. Plasma surface activation

[0175] Objective: To generate active groups through plasma treatment, providing binding sites for grafting reactions.

[0176] The plasma treatment uses either argon or oxygen, and the vacuum level is 10. -2 -10 -3 Pa, power of 50-100W, processing time of 2-5 minutes; lay the fiber membrane flat in the reaction chamber, start the plasma, and generate free radicals and oxygen-containing groups (such as -OH, -COOH) on the fiber surface.

[0177] Argon plasma focuses on physical etching to increase surface roughness; oxygen plasma introduces oxygen-containing polar groups to enhance hydrophilicity.

[0178] At the same time, avoid processing for too long, which could cause heat damage to the fibers.

[0179] 3. Ethylenediamine grafting reaction

[0180] Objective: To graft ethylenediamine (EDA) onto the surface of activated fiber membranes to introduce amino groups (-NH2).

[0181] Solution preparation:

[0182] Dissolve ethylenediamine in deionized water or ethanol at a concentration of 10%-20% (v / v).

[0183] Add 0.5%-1% of the crosslinking agent glutaraldehyde to improve grafting stability (optional).

[0184] Specifically, in this embodiment, ethylenediamine is dissolved in deionized water to form a concentration of 10% (v / v), and glutaraldehyde with a volume fraction of 1% (v / v) is added.

[0185] Grafting reaction:

[0186] The plasma-treated fiber membrane was immersed in an ethylenediamine solution and kept in a constant temperature water bath at 50°C for 1.5 hours. An inert gas (N2 in this example) was used for protection to prevent oxidation side reactions.

[0187] The grafting reaction reduces side reactions at lower temperatures (30℃) and accelerates the reaction rate at higher temperatures (60℃). Excessive reaction time may lead to over-crosslinking.

[0188] 4. Post-treatment and cleaning

[0189] Objective: To remove unreacted ethylenediamine and byproducts, and to stabilize the modified surface.

[0190] Cleaning: Sonicate with deionized water and ethanol for 10 minutes each time, repeating 3 times. Note that water should be used first to remove water-soluble impurities, and then ethanol should be used to remove organic residues.

[0191] Drying: Vacuum dry at 40℃ for 4 hours.

[0192] This process allows for the efficient introduction of amino groups onto the surface of polypropylene fiber membranes, significantly enhancing their biocompatibility while maintaining the material's mechanical properties and chemical stability.

[0193] III. Preparation of Composite Filter Membranes

[0194] Includes the following steps:

[0195] (1) Preparation of coarse effective layer

[0196] PP fibers are prepared by melt-blowing. After melting PP resin, it is spun at high speed and stretched by airflow to form ultrafine fibers (10μm in diameter). The fibers are sprayed onto a receiving plate and solidified into a film, forming a fluffy and porous coarse layer.

[0197] (2) Preparation of electrostatic layer

[0198] Similarly, PP fiber membranes are prepared by meltblowing, and then the PP fiber membranes are first subjected to corona charging, and then ethylenediamine is grafted onto the PP fiber membranes to obtain the desired electrostatic layer.

[0199] (3) Preparation of activated carbon enrichment layer

[0200] SiO2 thin films are deposited on activated carbon particles, and then a "sandwich" structure is formed by embedding the activated carbon particles into a meltblown fiber substrate through hot pressing or needle punching processes.

[0201] (4) Composite 3-layer structure

[0202] Three layers of material are stacked and pressed together using a heated roller at a temperature of 60-160℃ and a pressure of 0.1-1MPa for 30-60 seconds per layer, ensuring heat penetration through the three-layer structure. Using an infrared heating roller can improve temperature uniformity by more than 20%, achieving reliable interfacial bonding.

[0203] Specifically, the temperature of the hot roller needs to be dynamically adjusted according to the processing stage (preheating / bonding / setting) and material properties, including the following processes:

[0204] Preheating stage: 60-80℃, material activation before composite film lamination, gradually softening the material, reducing melt viscosity, and avoiding local overheating that could lead to material degradation.

[0205] Adhesion stage: 120-140℃, hot pressing of three-layer composite film, it is necessary to balance the adhesion strength and the temperature resistance of the material to ensure that the coarse layer and the electrostatic layer are fully melted and bonded, while not affecting the stability of the fiber skeleton structure and avoiding the escape of volatile components from the activated carbon enrichment layer.

[0206] The solidification stage: 90-110℃, to achieve the effect of solidifying the composite structure, eliminating internal stress, and improving mechanical strength.

[0207] The structure of the filter membrane prepared by the above method is as follows: Figure 1 As shown, Figure 2 This is a photograph of the actual filter membrane.

[0208] The obtained filter membrane was subjected to the following experiments:

[0209] 1. Mechanical performance parameters:

[0210] 1) Tensile strength:

[0211] Tested according to ASTM D882 standard, the coarse layer has a pressure of ≥15MPa, the electrostatic layer has a pressure of ≥8MPa, the activated carbon enrichment layer has a pressure of ≥5MPa, and the composite filter membrane of this invention has a pressure of ≥20MPa.

[0212] 2) Elongation at break:

[0213] The coarse layer is ≥200%, the electrostatic layer is ≥10%, the activated carbon enrichment layer is ≤5% (to ensure structural stability), and the composite filter membrane of this invention is ≤5%.

[0214] 3) Compressive strength:

[0215] Through simulated airflow impact testing, the filter membrane showed a pressure drop of ≤200Pa at a flow rate of 30L / min, with no delamination or damage.

[0216] Using a traditional nylon filter membrane as a comparative example:

[0217] Tensile strength 12MPa, elongation at break 5%, pressure drop >300Pa (prone to clogging at high flow rates).

[0218] Comparison using polytetrafluoroethylene (PTFE) filter membranes:

[0219] It has high compressive strength but weak surface electrostatic adsorption, and its capture rate for 0.1-10μm particles is only 60%.

[0220] 2. Pathogen capture rate and survival rate experiment

[0221] Experimental design: Using Escherichia coli (ATCC8739) as a model, the survival rate after capture by different filter membranes was compared.

[0222] Table 1 Survival rate of bacteria captured by each filter membrane

[0223]

[0224] Survival rate was determined by staining the bacteria with STYO9 and PI dyes. If the bacteria were alive, STYO9 dye would penetrate them, turning them green; PI dye would passively penetrate dead bacteria, turning them red. Live bacteria would not absorb PI dye. The results were as follows: Figure 5 As shown.

[0225] The comparison results are shown in Table 1 and Figure 3-6 As shown, the capture rate, survival rate, and PCR detection rate of this invention are the highest.

[0226] Traditional filter membrane defects: physical interception leads to the rupture of pathogen membranes (e.g., nylon filter membranes result in a survival rate of <55% for E. coli).

[0227] Advantages of this invention: gradient adsorption + biocompatible modification, which balances high capture rate (>95%) and high survival rate (>80%), and reduces pressure drop by 40%.

[0228] 3. The effect of grafting rate on electrostatic layer performance

[0229] Table 2 Comparison of different grafting rates

[0230]

[0231] 4. Focusing on the bioactivity retention performance in aerosol pathogen collection scenarios, a comparative experimental scheme was designed for activated carbon (AC) with a silica (SiO2) film covering the surface, and compared with untreated activated carbon and mainstream filter membranes on the market.

[0232] I. Experimental Design

[0233] 1) Sample grouping

[0234] Table 3. Design of Different Schemes

[0235]

[0236] 2) Testing for pathogens

[0237] Bacterial model: Escherichia coli (E. coli ATCC25922);

[0238] Viral model: MS2 bacteriophage (non-enveloped RNA virus);

[0239] Fungal spores: Aspergillus niger.

[0240] 3) Simulated aerosol collection conditions

[0241] Flow rate: 10 L / min, sampling time: 30 minutes;

[0242] Environment: Temperature 25℃, Humidity 60%RH;

[0243] Aerosol concentration: 10 4 CFU / m 3 (bacteria), 10 3 PFU / m 3 (Virus)

[0244] II. Key Performance Comparison Data

[0245] 1) Bioactivity retention capacity

[0246] Table 4. Bioactivity retention capacity of different membranes

[0247]

[0248] From Table 4 and Figure 7-8 It can be seen that the live bacteria recovery rate is the highest when SiO2 passivates activated carbon. The PES membrane has a high retention rate but leads to microbial inactivation (surface hydrophobic stress). Fungal spores are completely intercepted by the PES membrane but cannot be cultured and revived.

[0249] 2) qPCR detection compatibility

[0250] Table 5. qPCR detection compatibility of different membranes

[0251]

[0252] According to Table 5 and Figure 9-10 As shown, it can be concluded that SiO2 film can reduce oxidative stress on activated carbon surface, reduce lipid peroxidation of microbial membranes, and block the inhibition of DNA polymerase by polyphenols (such as quinones) dissolved from activated carbon.

[0253] Furthermore, the use of SiO2 film in Example 1 significantly improves the biocompatibility of activated carbon, with minimal impact on the bioactivity of bacteria, viruses, and fungi, and no inhibitors interfere with qPCR. Additionally, whether or not surface terminal modification is performed also affects bioactivity.

[0254] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite filter membrane for efficient collection of aerosol pathogens, characterized in that: The composite filter membrane includes a coarse layer, an electrostatic layer, and an activated carbon enrichment layer arranged from top to bottom. The coarse layer is made of PP fiber membrane, the electrostatic layer is made of electret-treated PP fiber membrane with a surface potential >1.0kV, and the activated carbon enrichment layer uses activated carbon particles with SiO2 film deposited on the surface. The activated carbon is passivated by SiO2 to reduce the chemical adsorption intensity. The thickness of the coarse layer is 0.5 mm, the diameter of the PP fiber is 10 μm, and the porosity of the PP fiber membrane is 80-90%; the thickness of the electrostatic layer is 0.2 mm, the diameter of the PP fiber is 1-5 μm, and the porosity of the PP fiber membrane is ≥85%; the thickness of the activated carbon enrichment layer is 0.8 mm, the thickness of the SiO2 film is <5 nm, and the pore size of the activated carbon is 20-50 nm. The PP fiber membrane used in the electrostatic layer is also grafted with ethylenediamine, with a grafting rate of 1.2%-2.0%. This range can balance surface activity and fiber mechanical properties, and avoid material embrittlement caused by excessive grafting.

2. The composite filter membrane for efficient collection of aerosol pathogens according to claim 1, characterized in that: The pore size of activated carbon can be adjusted by steam activation. The specific method is as follows: (1) Crush the raw material to 2-4 mm, and in an inert atmosphere, heat it to 350-600℃ for low-temperature carbonization in a gradient heating manner for 60-120 minutes to remove volatile components and form an initial carbon skeleton and microporous structure. (2) Activate at high temperature of 800-850℃ for 60-90 minutes, and control the steam flow rate at 3-4.5L / min to realize the transformation of micropores into mesopores.

3. The composite filter membrane for efficient collection of aerosol pathogens according to claim 1, characterized in that: The PP fiber membrane used in the electrostatic layer is prepared by the following method: (1) PP fiber membrane was prepared by melt-blowing method; (2) The prepared PP fiber membrane is cleaned to remove surface oil and processing aids; (3) First, corona charge the PP fiber membrane: voltage 30-50 kV, electret time 10-30 seconds, to give the fiber a lasting electrostatic charge; then perform hot pressing and shaping: temperature 120-140℃, pressure 0.1-0.3MPa, time 5-10 seconds, to enhance the bonding force of the fiber web and prevent pore collapse. (4) Active groups are generated by plasma treatment of PP fiber membrane, providing binding sites for grafting reaction; (5) Under the protection of inert gas, the plasma-treated PP fiber membrane is immersed in ethylenediamine solution for reaction grafting; (6) The reacted PP fiber membrane is cleaned to obtain the desired PP fiber membrane.

4. The composite filter membrane for efficient collection of aerosol pathogens according to claim 3, characterized in that: In step (4), the gas used for plasma treatment is argon or oxygen, and the vacuum degree is 10. -2 -10 -3 Pa, power of 50-100W, processing time 2-5 minutes; In step (5), the volume concentration of the ethylenediamine solution is 10%-20%, and the solution is immersed in the ethylenediamine solution and kept in a constant temperature water bath at 30-60℃ for 1-3 hours.

5. The composite filter membrane for efficient collection of aerosol pathogens according to claim 1, characterized in that: The activated carbon enrichment layer is formed by embedding activated carbon particles into a meltblown fiber substrate and then forming a "sandwich" structure through hot pressing or needle punching processes.

6. The composite filter membrane for efficient collection of aerosol pathogens according to claim 1, characterized in that: Activated carbon particles with a SiO2 thin film deposited on their surface were prepared by the following method: (1) Activated carbon pretreatment: First, use plasma etching to clean the activated carbon, removing surface organic residues and forming a uniform nanoscale roughness of 1.1 nm < Ra < 1.3 nm; then immerse the activated carbon in an amino silane coupling agent solution for reaction, introducing amino groups as anchoring sites to achieve the directional adsorption of SiO2 precursors and inhibit the thickness non-uniformity caused by random nucleation. (2) Atomic layer deposition of ultrathin SiO2 film: Deposition was performed using bis(diethylamino)silane precursors and ozone. Following deposition, in-situ hydrogen plasma annealing was performed to eliminate dangling bonds within the film, reducing the surface hydroxyl density to <2 groups / nm. 2 This reduces the number of active sites for chemical adsorption. (3) Surface terminal modification Vapor deposition of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, reacting the residual hydroxyl groups on the SiO2 surface with 1H,1H,2H,2H-perfluorooctyltriethoxysilane to form a monolayer fluorinated terminal, reducing the polar interaction between viruses / bacteria and the surface.

7. A method for preparing a composite filter membrane for efficient collection of aerosol pathogens as described in any one of claims 1-6, characterized in that: This method includes the following steps: (1) Preparation of the primary filter layer Prepare PP fibers by melt blowing. After melting the PP resin, extrude the filaments at high speed and form ultrafine fibers by air stretching. The fibers are sprayed onto the receiving plate and solidify into a film, forming a fluffy and porous primary filter layer. (2) Preparation of the electrostatic layer Similarly, prepare a PP fiber membrane by melt blowing. Then, first corona charge the PP fiber membrane and then graft ethylenediamine onto the PP fiber membrane to form the required electrostatic layer. (3) Preparation of the activated carbon enrichment layer Deposit a SiO2 film on the surface of activated carbon particles, and then embed the activated carbon particles into the melt-blown fiber substrate to form a "sandwich" structure by hot pressing or needle punching processes. (4) Composite three-layer structure Stack the three layers of materials and press them tightly by a hot roller for composite. The temperature is 60 - 160 °C, the pressure is 0.1 - 1 MPa, and the time is 30 - 60 seconds per layer to ensure that the heat penetrates through the three-layer structure.

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