A gradient-pore activated carbon fiber composite filter screen and a preparation method thereof

Abstract

The present application relates to the technical field of composite filter screen, in particular to a gradient aperture activated carbon fiber composite filter screen and a preparation method thereof.The gradient aperture activated carbon fiber composite filter screen comprises an activated carbon fiber layer, a large aperture support transition layer, a functional intermediate layer and a surface protection enhancement layer; in the gradient aperture activated carbon fiber composite filter screen and the preparation method thereof, a five-stage gradient filtration system of "coarse filtration-adsorption-dynamic interception-precise purification-surface protection" is constructed, the hierarchical interception of pollutants is realized from the structural level, the problem of easy clogging of the traditional single aperture membrane is avoided, and the flux decline caused by membrane pollution is effectively alleviated; meanwhile, the interlayer bonding force is enhanced through chemical combination and physical winding between the materials of each layer, the problem of easy delamination of the existing gradient structure membrane is solved, frequent chemical cleaning is not required, the operation cost and the secondary pollution risk are reduced, and the effects of long-term anti-pollution and stable filtration are achieved.

Description

Technical Field

[0001] This invention relates to the field of composite filter technology, and more specifically, to a gradient pore size activated carbon fiber composite filter and its preparation method. Background Technology

[0002] In the field of water treatment, membrane separation technology is widely used due to its high filtration efficiency. However, membrane fouling can lead to a decrease in flux and affect the water treatment effect. Traditional membrane structures have a relatively uniform pore size distribution, making it easy for pollutants to accumulate on the membrane surface and in the pores. Frequent cleaning with acid and alkali agents not only accelerates membrane aging but also increases operating costs and introduces the risk of secondary pollution.

[0003] Currently, some existing technologies mitigate pollution by modifying membrane materials or optimizing pretreatment processes. However, modified materials are expensive and lack long-term stability, while pretreatment processes require additional energy-consuming equipment, making it difficult to achieve long-term anti-pollution from a structural perspective. For example, when treating complex water quality, large particulate pollutants easily clog the pores of activated carbon fiber membranes with a single pore size, leading to rapid flux decay. The layered structure of conventional composite filters also makes it difficult to achieve graded interception of pollutants.

[0004] In addition, existing gradient structure membranes mostly use a single material or simple stacking method, which makes it difficult to achieve precise graded filtration and efficient adsorption for complex and diverse pollutants. At the same time, this structure lacks flexibility in response to changes in water quality and cannot adaptively adjust the filtration effect according to the actual situation. Moreover, gradient structure membranes with single materials or simple stacking are prone to problems such as interlayer separation or structural damage during long-term use, affecting their overall performance and service life.

[0005] Therefore, there is an urgent need for a gradient pore size activated carbon fiber composite filter and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a gradient pore size activated carbon fiber composite filter and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, firstly, the present invention provides a gradient pore size activated carbon fiber composite filter, comprising an activated carbon fiber layer, a large pore size support transition layer, a functional intermediate layer, and a surface protection reinforcement layer;

[0008] The activated carbon fiber layer comprises at least 45-55 parts of coconut shell activated carbon fiber, 35-45 parts of viscose-based activated carbon fiber, and 8-12 parts of nano-sized activated carbon fiber. Modifiers include: coconut shell activated carbon fiber micropores with a pore size of less than 2 nm and a high specific surface area of ​​1500-2000 m² / g, providing adsorption sites for small molecules; and viscose-based activated carbon fiber mesopores with a pore size of 2-50 nm, serving as pre-adsorption channels for macromolecular pollutants and facilitating the hierarchical adsorption of organic matter and heavy metal ions in water. Simultaneously, it can form a multi-level porous network with coconut shell activated carbon fiber through physical entanglement; nano-... The modifier has a particle size of 5-10 nm. Its surface hydroxyl groups form hydrogen bonds with the carboxyl and phenolic hydroxyl oxygen-containing functional groups on the surface of coconut shell activated carbon fiber and viscose-based activated carbon fiber, which can build a hydrophilic nano-coating on the fiber surface. This coating can reduce the water contact angle, improve the hydrophilicity of the fiber surface, and accelerate the water molecule permeation rate. At the same time, it can reduce the direct contact between pollutants and fibers by utilizing the steric hindrance effect, thereby delaying the occurrence of membrane pore blockage.

[0009] The large-pore support transition layer comprises at least 25-35 parts of polyester (PET) nonwoven fabric, 6-10 parts of hydroxyapatite (HA) nanoparticles, and 4-6 parts of titanate coupling agent, wherein the hydroxyapatite (HA) nanoparticles have a particle size of 50-100 nm. The three-dimensional fiber network of polyester (PET) nonwoven fabric forms a framework structure with a pore size of 5-10 μm. Through the condensation reaction of the alkoxy groups of the titanate coupling agent with the ester groups on the PET molecular chain, hydroxyapatite (HA) nanoparticles are anchored on the fiber surface of the polyester (PET) nonwoven fabric. This allows the hydroxyapatite structure of the hydroxyapatite (HA) nanoparticles to form calcium and magnesium ion exchange sites in the water, thereby pre-removing calcium and magnesium ions in hard water to reduce the risk of scaling on the membrane surface. At the same time, the 5-10 μm framework structure and the mesopores of the viscose-based activated carbon fiber form a pore size gradient of "coarse filtration-pre-adsorption", which can preferentially intercept silt and algae suspended solids (particle size > 1 μm) in the water, reducing the load on the subsequent activated carbon fiber layer. Furthermore, the phosphate groups of the hydroxyapatite (HA) nanoparticles can form hydrogen bond bridges with the hydroxyl groups in the coconut shell activated carbon fiber and viscose-based activated carbon fiber, firmly binding the large-pore support transition layer with the activated carbon fiber layer, enhancing the interlayer bonding force, and preventing delamination during use.

[0010] The functional intermediate layer comprises at least 50-65 parts of a polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite film solution, 10-15 parts of layered double metal hydroxide (LDH) nanosheets, and 6-9 parts of boric acid (…). Crosslinking agent, wherein: polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite film is crosslinked with boric acid (… Crosslinking agents crosslink to form a semi-interpenetrating network structure. Borate ions react with the hydroxyl groups on the PVA and CMC molecular chains to form reversible borate ester bonds, giving the network structure pH-responsive characteristics—the network expands to form larger pores under acidic conditions and contracts to form smaller pores under alkaline conditions, thus achieving dynamic regulation of water flow rate and ionic pollutant interception effect. Layered bimetallic hydroxide (LDH) nanosheets are uniformly dispersed in this network. The anion exchange sites in their layered structure can exchange and adsorb anionic pollutants in the water, while the interlayer... Ions form coordination bonds with carboxyl groups on the surface of activated carbon fibers, which can strengthen the bonding strength between the intermediate layer and the activated carbon fiber layer.

[0011] The surface protective reinforcement layer comprises at least 28-38 parts of polyvinyl chloride (PVC) nanomaterials. Composite film, 7-12 parts polytetrafluoroethylene (PTFE) micro powder and 3-5 parts chitosan quaternary ammonium salt (HTCC) modifier, wherein: polyvinyl chloride (PVC) - nano Composite membrane through Photocatalysis under ultraviolet light decomposes organic matter on the membrane surface. Ions inhibit microbial growth, achieving dual anti-pollution effects of "photocatalysis-antibacterial"; polytetrafluoroethylene (PTFE) micropowder fills the PVC matrix to form a rough micro-nano structure, reducing pollutant deposition through hydrodynamic effects and enhancing anti-pollution capabilities; the quaternary ammonium salt groups of chitosan quaternary ammonium salt (HTCC) modifier form electrostatic adsorption with the negative charge on the surface of activated carbon fiber, and the hydroxyl groups form hydrogen bonds with the oxygen-containing functional groups of the fiber, constructing a hydrophilic protective layer on the surface, blocking colloidal particles in the water from contacting the activated carbon fiber, while not affecting water flux.

[0012] Gradient pore size filtration logic: Water first passes through a large-pore support transition layer (5-10μm), preferentially intercepting suspended solids such as silt and algae with a particle size >1μm, reducing the subsequent filtration load; then it enters the mesopores (2-50nm) of viscose-based activated carbon fibers, adsorbing molecular pollutants in humic acid and oil with a diameter of 5-20nm, while hydroxyapatite nanoparticles pretreat hard water ions; next, it flows through a functional intermediate layer, whose pH-responsive semi-interpenetrating network expands to 50-100nm under acidic conditions to accelerate water flow, and shrinks to 20-50nm under alkaline conditions to enhance filtration. Ion interception: layered bimetallic hydroxide nanosheets simultaneously exchange and adsorb anionic pollutants; finally, formaldehyde and heavy metal ion small molecule pollutants are precisely adsorbed through the micropores (<2nm) of coconut shell activated carbon fiber. The surface protection reinforcement layer decomposes organic matter through photocatalysis, inhibits microorganisms with antibacterial agents, and reduces pollutant deposition through a rough structure, forming a five-stage gradient filtration system of "coarse filtration - pre-adsorption - dynamic interception - precise purification - surface protection". This achieves graded interception of pollutants according to particle size and dynamic anti-pollution, avoiding the pore blockage problem of single-pore membranes, and improving flux stability and long-term filtration efficiency.

[0013] Secondly, according to Figure 1 As shown, the present invention also provides a method for preparing a gradient pore size activated carbon fiber composite filter, comprising the following steps:

[0014] S1. Blending and Modification of Activated Carbon Fiber Layers: Coconut shell activated carbon fibers and viscose-based activated carbon fibers are added to a planetary mixer and dry-mixed at 200-300 rpm for 15-20 minutes to form a fiber-interwoven premix. Subsequently, nano-... The modifier was dispersed in deionized water to form a sol, which was then poured into the fiber-woven premix. A planetary mixer was used to heat the mixture to 60-70℃ and stirred at 150 rpm for 2 hours. The sol binds to oxygen-containing functional groups (carboxyl groups, phenolic hydroxyl groups) on the fiber surface via hydrogen bonds, forming a uniformly coated hydrophilic nanoparticle layer. The coated fiber mixture is then fed to a two-roll hot rolling mill and rolled at 120-130℃ and 0.5MPa pressure to form an activated carbon fiber layer with a thickness of 0.3-0.5mm. During this process, the micropores (<2nm) of coconut shell fiber and the mesopores (2-50nm) of viscose fiber interpenetrate each other to form a gradient pore network of "micropore-mesopore".

[0015] S2. Nanoparticle anchoring of the large-pore support transition layer: Polyester (PET) nonwoven fabric is laid flat on a coating machine, and hydroxyapatite (HA) nanoparticles and titanate coupling agent are mixed to form a solution. Then, the coating machine receives the solution through a trough and uniformly coats it onto the surface of the polyester (PET) nonwoven fabric with a 200-mesh anilox roller. The coating amount is 30-40 g / m². After coating, the nonwoven fabric is placed in an oven at 110-120℃ and dried for 1 hour. During this process, the alkoxy groups of the titanate coupling agent undergo a condensation reaction with the ester groups on the PET molecular chain, thereby firmly anchoring the hydroxyapatite (HA) nanoparticles onto the fiber surface of the polyester (PET) nonwoven fabric to form a three-dimensional skeleton structure with a pore size of 5-10 μm.

[0016] S3, pH-responsive composite membrane with functional intermediate layer: After adding layered double metal hydroxide (LDH) nanosheets to the polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution, ultrasonic treatment was performed at 300-500W power for 1 hour to uniformly disperse the nanosheets in the solution, avoiding nanosheet aggregation and forming a stable nanocomposite sol. Subsequently, boric acid was added to the nanocomposite sol. Crosslinking agent, using a constant temperature magnetic stirrer, at a stirring speed of 200-300 rpm and 30℃ for 2 hours, crosslinking reaction is carried out. Polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) molecular chains are crosslinked through borate ester bonds to form an interpenetrating three-dimensional network structure.

[0017] S4. Antibacterial composite film for surface protective reinforcement layer: Polyvinyl chloride (PVC) - nano The composite membrane and polytetrafluoroethylene (PTFE) micropowder were added together to a hot press laminator and treated at 150°C and 0.3 MPa for 10 minutes. This allowed the PTFE micropowder to melt and embed into the surface of the polyvinyl chloride (PVC) matrix, forming a micro / nano structure with micron-level roughness (Ra=2.0μm). This micro / nano structure can reduce contaminant deposition through hydrodynamic effects. Subsequently, a chitosan quaternary ammonium salt (HTCC) modifier was dissolved in deionized water to prepare a solution. The solution was then uniformly coated onto the PVC-nano structure with the PTFE micropowder embedded in the micro / nano structure using a dip-coating machine at a linear speed of 2 m / min. The surface of the composite membrane is dried with hot air at 60°C for 30 minutes in a tunnel-type hot air dryer, so that the quaternary ammonium salt groups of chitosan quaternary ammonium salt (HTCC) form electrostatic adsorption with the negative charge on the surface of the subsequent activated carbon fiber. The hydroxyl groups are combined with the oxygen-containing functional groups of the fiber through hydrogen bonds to form a 0.5-1μm thick chitosan quaternary ammonium salt (HTCC) modified protective layer with both hydrophilicity and antibacterial properties.

[0018] S5. Gradient assembly and curing of multilayer composite membranes: The prepared activated carbon fiber layer, large-pore support transition layer, functional intermediate layer and surface protection reinforcement layer are stacked in sequence and placed in a hot press composite machine. The mixture is kept at 100-120℃ and 0.2-0.3MPa pressure for 15-20 minutes, so that the layers are tightly bonded through physical and chemical reactions to form a composite filter with gradient pore structure, high-efficiency filtration and anti-fouling performance.

[0019] Preferably, in step S1, the preparation of the sol includes the following steps:

[0020] nano The modifier is added to deionized water at a temperature of 50-60℃, among which, nano-... The solid-liquid mass ratio of the modifier to deionized water is 1:10. The dispersibility of the nanoparticles is enhanced by the thermal motion of water molecules in a warm water environment. Simultaneously, the nanoparticles are ultrasonically treated for 30-40 minutes using an ultrasonic processor with a power of 300-500W, breaking down the nanoparticles through the cavitation effect of ultrasound. The soft aggregation between particles allows them to be uniformly distributed in water in a monodisperse state, eventually forming a stable, transparent sol system without obvious sedimentation.

[0021] Preferably, in step S2, the preparation of the mixture includes the following steps:

[0022] First, hydroxyapatite (HA) nanoparticles (50-100 nm in diameter) are added to ethanol and stirred at 300-400 rpm for 15-20 min using a magnetic stirrer to initially disperse the nanoparticles. Then, titanate coupling agent is added and stirring is continued at 500-600 rpm for 30 min. At the same time, the mixture is subjected to ultrasonic-assisted treatment for 10-15 min using an ultrasonic processor with a power of 300-400W. The cavitation effect generated by high-frequency mechanical vibration breaks the agglomerates of hydroxyapatite (HA) nanoparticles and promotes the titanate coupling agent to be uniformly coated on the surface of hydroxyapatite (HA) nanoparticles, forming a stable dispersion system. Finally, a mixture with a solid-liquid ratio of 1:8 is obtained.

[0023] Preferably, in step S3, the preparation steps of the polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution are as follows:

[0024] First, add 35-45 parts of polyvinyl alcohol (PVA) with a degree of polymerization of 1750±50 to deionized water at 80℃. The solid-liquid ratio of PVA to water is 1:15. Stir continuously at 200-300 rpm for 4 hours until the PVA dissolves into a transparent colloid. Then, lower the temperature of the transparent colloid to 50℃ and add 15-20 parts of carboxymethyl cellulose (CMC) with a degree of substitution of 0.7-0.9. Continue stirring at 150-200 rpm for 2 hours to allow the CMC to swell and mix evenly with the PVA solution, finally obtaining a viscous and transparent PVA-CMC composite film solution.

[0025] Preferably, in S4, polyvinyl chloride (PVC)-nano The preparation and protection steps of the composite membrane are as follows:

[0026] Polyvinyl chloride (PVC) resin with 5-10% loading of nano The granules are fed into a twin-screw extruder, where... Particle size is 2-5 nm. With a particle size of 20-30 nm, the nanoparticles are melt-blended at a screw speed of 200-250 rpm under a gradient temperature system of 160℃ in the feeding section, 175℃ in the melting section, and 180℃ in the extrusion section, resulting in nanoparticles with a particle size of 20-30 nm. The particles are uniformly dispersed at the nanoscale in a polyvinyl chloride (PVC) matrix; the molten material is then cast through a T-die onto a cooling roller at 50°C, where it is solidified under a traction pressure of 1.0 MPa to produce PVC nanoparticles with a thickness of 50-80 μm. Composite membrane.

[0027] Preferably, in step S4, the chitosan quaternary ammonium salt (HTCC) modifier is dissolved in a solution prepared by deionized water, comprising the following steps:

[0028] Add the chitosan quaternary ammonium salt (HTCC) modifier to deionized water at a mass ratio of 1:20. Stir the mixture at 150-200 rpm for 30-40 minutes at 25-30℃ until the chitosan quaternary ammonium salt (HTCC) dissolves, forming a transparent and homogeneous solution with a concentration of 5wt%.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. In this gradient pore size activated carbon fiber composite filter and its preparation method, a five-stage gradient filtration system of "coarse filtration-pre-adsorption-dynamic interception-precision purification-surface protection" is constructed. This achieves graded interception of pollutants at the structural level, avoiding the problem of easy clogging of traditional single-pore size membranes and effectively alleviating the flux reduction caused by membrane fouling. At the same time, the interlayer bonding force is enhanced through chemical bonding and physical entanglement between the materials of each layer, solving the problem of easy delamination of existing gradient structure membranes. Furthermore, frequent chemical cleaning is not required, reducing operating costs and the risk of secondary pollution, thereby achieving long-term anti-fouling and stable filtration effects.

[0031] 2. In this gradient pore size activated carbon fiber composite filter and its preparation method, the "micropore-mesopore" network of coconut shell and viscose-based activated carbon fiber achieves graded adsorption of pollutants, and the nanopores... Modified and hydrophilic coatings enhance antifouling performance; a large-pore support layer and hydroxyapatite (HA) particles pre-intercept suspended solids and reduce the risk of scaling; a pH-responsive network in the functional intermediate layer adaptively adjusts filtration precision; and a surface protective layer prevents membrane surface fouling through photocatalysis and antibacterial action. Each layer forms an integral structure through chemical cross-linking and interfacial interactions. This not only achieves graded interception of pollutants from a structural perspective, avoiding the clogging problem of traditional single-pore membranes and effectively alleviating flux reduction caused by membrane fouling, but also enhances interlayer bonding through chemical bonding and physical entanglement, solving the problem of easy delamination in existing gradient structure membranes. This improves the filter's antifouling ability and filtration efficiency, thereby increasing filter lifespan and reducing operating costs and the risk of secondary pollution. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the preparation method of the gradient pore size activated carbon fiber composite filter of the present invention. Detailed Implementation

[0033] The technical solutions in 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.

[0034] Example 1

[0035] Blending and modification of activated carbon fiber layers: 45 parts of coconut shell activated carbon fiber and 45 parts of viscose-based activated carbon fiber were added to a planetary mixer and dry-mixed at 200 rpm for 20 minutes to form a fiber interwoven premix; 10 parts of nano-modifier were dispersed in deionized water to make a sol, which was poured into the fiber interwoven premix. The planetary mixer was heated to 60°C and stirred at 150 rpm for 2 hours to form a fiber mixture with a uniform hydrophilic nano-coating on the surface. The mixture was then conveyed to a two-roll hot rolling mill and rolled at 120°C and 0.5 MPa to form a fiber felt with a thickness of 0.3 mm.

[0036] Nanoparticle anchoring of large-pore support transition layer: 30 parts of polyester (PET) nonwoven fabric are laid flat on a coating machine, 8 parts of hydroxyapatite (HA) nanoparticles and 5 parts of titanate coupling agent are mixed to form a mixture, and the coating machine is used to uniformly coat the nonwoven fabric surface with a 200-mesh anilox roller. The coating amount is 35g / m², and after coating, it is sent to a 110℃ oven to dry for 1 hour.

[0037] pH-responsive composite membrane with functional intermediate layer: 12 parts of layered double metal hydroxide (LDH) nanosheets were added to 40 parts of polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution, and ultrasonic treatment was performed at 400W power for 1 hour using an ultrasonic disperser. Then, 7 parts of boric acid crosslinking agent were added, and crosslinking reaction was carried out at 250rpm and 30℃ using a constant temperature magnetic stirrer for 2 hours.

[0038] Antibacterial composite film with surface protective reinforcement layer: 33 parts of polyvinyl chloride (PVC) nanocomposite film and 10 parts of polytetrafluoroethylene (PTFE) micro powder were added to a hot press composite machine and treated at 150℃ and 0.3MPa pressure for 10 min. Then, 4 parts of chitosan quaternary ammonium salt (HTCC) modifier were dissolved in deionized water to prepare a solution, which was coated on the surface of the composite film with a dip coating machine at a linear speed of 2m / min and dried with hot air at 60℃ for 30 min.

[0039] Gradient assembly and curing of multilayer composite membranes: Finally, the layers are stacked in sequence and placed in a hot press laminating machine, and kept at 100℃ and 0.2MPa pressure for 20 minutes to form a composite filter.

[0040] Example 2

[0041] Blending and modification of activated carbon fiber layers: 50 parts of coconut shell activated carbon fiber and 40 parts of viscose-based activated carbon fiber were placed in a planetary mixer and dry-mixed at 250 rpm for 18 min; 10 parts of nano-modifier were made into a sol and added to the fiber interwoven premix; the planetary mixer was heated to 65℃ and stirred at 150 rpm for 2 h; then it was rolled into a 0.4 mm thick fiber felt at 125℃ and 0.5 MPa pressure.

[0042] Nanoparticle anchoring of large-pore support transition layer: Take 32 parts of polyester (PET) nonwoven fabric, mix 7 parts of hydroxyapatite (HA) nanoparticles with 5 parts of titanate coupling agent to form a mixture and coat it on the nonwoven fabric. The coating amount is 38g / m², and it is dried in an oven at 115℃ for 1h.

[0043] pH-responsive composite membrane with functional intermediate layer: 13 parts of layered double metal hydroxide (LDH) nanosheets were added to 38 parts of polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution, and ultrasonic treatment was performed at 450W power for 1 hour using an ultrasonic disperser. Then, 8 parts of boric acid crosslinking agent were added, and crosslinking reaction was carried out at 280rpm and 30℃ for 2 hours.

[0044] Antibacterial composite film for surface protective reinforcement layer: 35 parts of polyvinyl chloride (PVC) nanocomposite film and 9 parts of polytetrafluoroethylene (PTFE) micro powder were hot-pressed together, and then coated with 4 parts of chitosan quaternary ammonium salt (HTCC) modifier solution. The drying conditions were the same as in Example 1.

[0045] Gradient assembly and curing of multilayer composite membranes: Finally, the layers are stacked in sequence and hot-pressed at 110℃ and 0.25MPa pressure for 18 minutes to obtain a composite filter.

[0046] Example 3

[0047] Blending and modification of activated carbon fiber layer: 55 parts of coconut shell activated carbon fiber and 35 parts of viscose-based activated carbon fiber were added to a planetary mixer and dry-mixed at 300 rpm for 15 min; 8 parts of nano-modifier were made into a sol and added to it; the planetary mixer was heated to 70℃ and stirred at 150 rpm for 2 h; and then rolled into a 0.5 mm thick fiber felt at 130℃ and 0.5 MPa pressure.

[0048] Nanoparticle anchoring of large-pore support transition layer: 35 parts polyester (PET) nonwoven fabric, 10 parts hydroxyapatite (HA) nanoparticles and 4 parts titanate coupling agent are mixed and coated, coating amount 40g / m², and dried in oven at 120℃ for 1h.

[0049] pH-responsive composite membrane with functional intermediate layer: 15 parts of layered double metal hydroxide (LDH) nanosheets were added to 35 parts of polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution, and ultrasonic treatment was performed at 500W power for 1 hour using an ultrasonic disperser. 6 parts of boric acid crosslinking agent were added, and crosslinking reaction was carried out at 300rpm and 30℃ for 2 hours.

[0050] Antibacterial composite film for surface protective reinforcement layer: 38 parts of polyvinyl chloride (PVC) nanocomposite film and 7 parts of polytetrafluoroethylene (PTFE) micro powder are hot-pressed together and coated with 3 parts of chitosan quaternary ammonium salt (HTCC) modifier solution;

[0051] Gradient assembly and curing of multilayer composite membranes: Finally, the layers are stacked in sequence and hot-pressed at 120℃ and 0.3MPa pressure for 15 minutes to obtain composite filter.

[0052] Example 4

[0053] Blending and modification of activated carbon fiber layers: Weigh 48 parts of coconut shell activated carbon fiber and 42 parts of viscose-based activated carbon fiber, add them to a planetary mixer and dry mix at 220 rpm for 16 min; disperse 12 parts of nano-modifier into a sol and add it to the fiber premix; heat the planetary mixer to 62℃ and stir at 150 rpm for 2 h; then roll it into a fiber felt with a thickness of 0.35 mm at 122℃ and 0.5 MPa pressure.

[0054] Nanoparticle anchoring of large-pore support transition layer: Take 28 parts of polyester (PET) nonwoven fabric, mix 6 parts of hydroxyapatite (HA) nanoparticles with 6 parts of titanate coupling agent to form a mixture and coat it, with a coating amount of 32g / m², and dry it in an oven at 112℃ for 1h.

[0055] pH-responsive composite membrane with functional intermediate layer: 10 parts of layered double metal hydroxide (LDH) nanosheets were added to 42 parts of polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution, and ultrasonic treatment was performed at 300W power for 1 h using an ultrasonic disperser. Then, 9 parts of boric acid crosslinking agent were added, and crosslinking reaction was carried out at 200 rpm and 30℃ for 2 h.

[0056] Antibacterial composite film for surface protective reinforcement layer: 30 parts of polyvinyl chloride (PVC) nanocomposite film and 12 parts of polytetrafluoroethylene (PTFE) micro powder are added to a hot press composite machine for processing, and coated with 5 parts of chitosan quaternary ammonium salt (HTCC) modifier solution;

[0057] Gradient assembly and curing of multilayer composite membranes: Finally, the layers are stacked in sequence and hot-pressed at 105℃ and 0.22MPa pressure for 16 minutes to prepare a composite filter.

[0058] Table 1. Amounts of each raw material used in Examples 1-4

[0059]

[0060] To verify that the composite filter prepared in the embodiments of the present invention has good anti-fouling properties and filtration efficiency, the following experimental examples are used to illustrate the activated carbon fiber composite filter provided in the embodiments of the present invention.

[0061] Test case

[0062] The purpose of this experimental group is to investigate the effect of different component ratios on composite filters and to test the antifouling properties, filtration efficiency, and flux stability of the composite filter of this invention.

[0063] Experimental Objective: Experimental groups A, B, C, and D used the component ratios of the composite filters provided in Examples 1-4, respectively; the control group consisted of control groups A, B, C, D, E, and F, wherein:

[0064] Control group A

[0065] Take 100 parts of coconut shell activated carbon fiber, add it to a planetary mixer, and dry mix it at 200 rpm for 15 minutes; then convey it to a two-roll hot rolling mill and roll it at 120℃ and 0.5MPa pressure to make a fiber felt with a thickness of 0.3mm, which serves as a single-pore activated carbon fiber membrane with a micropore size of less than 2nm.

[0066] Control group B

[0067] Preparation of activated carbon fiber layer: 50 parts of coconut shell activated carbon fiber and 50 parts of viscose-based activated carbon fiber were added to a planetary mixer and dry-mixed at 200 rpm for 15 min. Then, the mixture was rolled into a 0.3 mm thick fiber felt at 120℃ and 0.5 MPa pressure.

[0068] Preparation of large-pore support transition layer: 30 parts of polyester (PET) nonwoven fabric were laid flat on a coating machine, and 8 parts of hydroxyapatite (HA) nanoparticles and 5 parts of titanate coupling agent were mixed to form a mixture. The coating machine was used to uniformly coat the nonwoven fabric surface with a 200-mesh anilox roller. The coating amount was 35 g / m². After coating, the fabric was sent to a 110℃ oven to dry for 1 hour.

[0069] The two layers are simply stacked and placed in a hot press composite machine, and kept at 100℃ and 0.2MPa pressure for 15 minutes to form a conventional composite filter screen.

[0070] Control group C

[0071] Take 100 parts of polyvinyl chloride (PVC) material and use a special stretching process to form a structure with a gradient pore size, ranging from 5 to 50 nm. During the preparation process, no other nanoparticles or modifiers are added, and the gradient pore size is achieved solely by the structural changes of polyvinyl chloride (PVC) itself.

[0072] Control group D

[0073] Preparation of the first layer: Take 50 parts of polypropylene (PP) material and make it into a non-woven fabric with a pore size of 5-10μm through melt-blowing process, as a large pore layer;

[0074] Preparation of the second layer: Take 30 parts of polyvinylidene fluoride (PVDF) material and prepare a membrane with a pore size of 2-50 nm by phase inversion method as a mesopore layer;

[0075] Preparation of the third layer: Take 20 parts of polytetrafluoroethylene (PTFE) material and sinter it to form a membrane with a pore size of less than 2nm as a small pore layer.

[0076] The three layers are simply stacked together in the order of large pore size layer, medium pore size layer, and small pore size layer.

[0077] Control group E

[0078] The method for preparing the activated carbon fiber layer, the large-pore support transition layer, and the surface protective reinforcement layer is the same as in Example 1;

[0079] Preparation of the intermediate layer: 12 parts of layered double metal hydroxide (LDH) nanosheets were added to 40 parts of polyvinyl alcohol (PVA)-carboxymethyl cellulose (CMC) composite membrane solution and ultrasonically treated with an ultrasonic disperser at 400W power for 1 hour to form a nanocomposite sol, but boric acid crosslinking agent was not added to avoid forming a pH-responsive semi-interpenetrating network structure.

[0080] The layers are stacked sequentially and placed in a hot press composite machine. They are kept at 100℃ and 0.2MPa pressure for 20 minutes to form a composite filter screen.

[0081] control group F

[0082] The method for preparing the activated carbon fiber layer, the large-pore support transition layer, and the functional intermediate layer is the same as in Example 1;

[0083] The prepared activated carbon fiber layer, large-pore support transition layer, and functional intermediate layer are stacked in sequence and placed in a hot press composite machine. They are kept at 100℃ and 0.2MPa pressure for 20 minutes to form a composite filter without a surface protective reinforcement layer.

[0084] Test methods: Based on the present invention, tests were conducted on the antifouling resistance, filtration efficiency, and flux stability of the composite filter. Specific test methods are as follows:

[0085] Pollution resistance: Employs a cross-flow filtration mode with a concentration of 100 mg / L humic acid (simulating organic pollutants) and 50 mg / L... A mixed solution of colloids (simulating inorganic pollutants) was used as the test solution. The system was continuously operated for 12 hours at 25℃, 0.1 MPa operating pressure, and a cross-flow velocity of 1.5 m / s. Before the experiment, the filter screen was soaked in deionized water for 24 hours to remove surface impurities and pre-pressurized with 0.1 MPa pure water for 30 minutes until the flux stabilized. The membrane flux (J) was recorded every 30 minutes and calculated using the formula for flux decay rate: ,in For initial flux, The flux at time t was used. After the operation was completed, the deposition of pollutants on the membrane surface was observed by scanning electron microscopy (SEM), and the surface elemental composition was analyzed by X-ray photoelectron spectroscopy (XPS).

[0086] Table 2 Anti-pollution test indicators

[0087]

[0088] As shown in Table 2, the 12-hour flux decay rate of the experimental group of this invention was less than 10%, and the contaminant coverage on the membrane surface was low. In contrast, the flux decay rate of the control group was higher than 15%, and the contaminant coverage on the membrane surface was higher. This indicates that by constructing a five-stage gradient filtration system of "coarse filtration-pre-adsorption-dynamic interception-precision purification-surface protection", this invention achieves graded interception of contaminants at the structural level, avoiding the problem of easy clogging of traditional single-pore membranes, effectively alleviating the flux decline caused by membrane fouling. Furthermore, the interlayer bonding force is enhanced through chemical bonding and physical entanglement between the materials of each layer, solving the problem of easy delamination of existing gradient structure membranes, and the antifouling performance is better than that of the control group.

[0089] Filtration efficiency: Tested in dead-end filtration mode at 25℃ and 0.1MPa. Test solutions included 10mg / L formaldehyde (small molecule organic matter), 50mg / L Cr(VI) (heavy metal ions), and 100NTU turbidity water (containing sediment particles). Escherichia coli suspension (microorganism); during the experiment, 1000 mL of the test solution was passed through a filter, and the filtrate was collected. Formaldehyde concentration was determined by high-performance liquid chromatography (HPLC), Cr(VI) concentration by atomic absorption spectrometry (AAS), turbidity of the filtrate was measured by a turbidimeter, and the number of E. coli was determined by plate counting. Each experiment was repeated three times, and the average value was taken. The removal rate was calculated using the formula: ;in, The concentration of pollutants in the raw water. The concentration of contaminants in the filtrate;

[0090] Table 3 Filtration efficiency test indicators

[0091]

[0092] As shown in Table 3, the experimental group of this invention achieved removal rates of over 95% for formaldehyde, Cr(VI), turbidity, and Escherichia coli. The highest removal rates were 99.2% for formaldehyde, 97.3% for Cr(VI), 99.9% for turbidity, and over 99.98% for Escherichia coli. In contrast, the removal rates of the control groups were relatively low, especially in control groups C and D, where the removal rates for each pollutant were all below 90%. This indicates that the "microporous-mesoporous" network of coconut shell and viscose-based activated carbon fiber in this invention achieves graded adsorption of pollutants; nano-modification and hydrophilic coating enhance antifouling performance; the large-pore support layer and hydroxyapatite particles pre-intercept suspended solids and reduce the risk of scaling; the pH-responsive network of the functional intermediate layer adaptively adjusts the filtration precision; and the surface protective layer prevents membrane surface fouling through photocatalysis and antibacterial properties, resulting in excellent filtration efficiency and the ability to efficiently remove various pollutants from water.

[0093] Flux stability: Using a circulating filtration mode, actual domestic sewage with a COD of 300 mg / L and a turbidity of 50 NTU was used as the test solution. The system was continuously operated for 72 hours at 25℃, 0.15 MPa operating pressure, and a cross-flow velocity of 2.0 m / s. Every 12 hours, the system was alternately washed with 2% citric acid solution and 1% NaOH solution for 30 minutes each time. The initial flux was recorded during the experiment. ) and recovery flux after each wash ( ), calculate flux recovery rate ( ),formula: Meanwhile, dynamic light scattering (DLS) was used to monitor changes in the particle size distribution of pollutants in the filtrate.

[0094] Table 4 Flux Stability Testing Indicators

[0095]

[0096] As shown in Table 4, the flux recovery rate of the experimental group of this invention reached over 89% after 72 hours of continuous operation, with a cleaning cycle of 12 hours. In contrast, the flux recovery rate of the control group was below 80%, and the cleaning cycle was shorter. This indicates that the composite filter of this invention, through the synergistic effect of each layer, not only effectively alleviates membrane fouling but also recovers flux well after fouling through cleaning. It exhibits strong flux stability and can operate stably for a long time, reducing the cleaning frequency and operating costs. In contrast, the control group, due to its poor anti-fouling performance and rapid flux decay, requires more frequent cleaning, resulting in higher operating costs.

[0097] In summary, this invention achieves highly efficient anti-pollution and precise filtration through a five-stage gradient filtration system and the synergistic effect of each layer of materials. Tests show that its 12-hour flux decay rate is less than 10%, superior to the control group; the removal rate of formaldehyde and Cr(VI) pollutants exceeds 95%, and the removal rate of E. coli reaches over 99.98%; the 72-hour flux recovery rate exceeds 89%, the cleaning cycle reaches 12 hours, and it exhibits high long-term stability. This filter structurally solves the problems of easy clogging and delamination common in traditional membranes, eliminating the need for frequent chemical cleaning, reducing operating costs and the risk of secondary pollution, thereby extending its service life.

[0098] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a gradient pore size activated carbon fiber composite filter, characterized in that, Includes the following steps: S1. Dry-mix coconut shell activated carbon fiber and viscose-based activated carbon fiber in a planetary mixer to form a fiber-interwoven premix, then add nano-sized... The modifier is dispersed in deionized water to form a sol, which is then poured into the fiber interwoven premix and stirred continuously to form a fiber mixture. This mixture is then conveyed to a two-roll hot rolling mill for roll forming to produce an activated carbon fiber layer. S2. Lay the polyester nonwoven fabric flat on the coating machine, then prepare a mixture of hydroxyapatite nanoparticles and titanate coupling agent, coat the surface of the polyester nonwoven fabric with a 200-mesh anilox roller, and then put the nonwoven fabric into an oven at 110-120℃ to dry for 1 hour to form a large-pore support transition layer with a pore size of 5-10μm. S3. After adding layered bimetallic hydroxide nanosheets to the polyvinyl alcohol-carboxymethyl cellulose composite membrane solution, ultrasonically disperse the solution to form a nanocomposite sol. Then, add boric acid crosslinking agent and stir with a constant temperature magnetic stirrer to form a functional intermediate layer. S4, Polyvinyl Chloride-Nano The composite membrane and polytetrafluoroethylene micro powder are added together to a hot press composite machine to form a micro-nano structure. Then, chitosan quaternary ammonium salt modifier is dissolved in deionized water to make a solution. The solution is coated onto the surface of the composite membrane using a dip-coating machine and dried by a hot air dryer to form a surface protective reinforcement layer. S5. Stack the prepared activated carbon fiber layer, large-pore support transition layer, functional intermediate layer and surface protection reinforcement layer in sequence, put them into a hot press composite machine, and keep them at 100-120℃ and 0.2-0.3MPa pressure for 15-20 minutes to form a composite filter.

2. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S1, the preparation of the sol includes the following steps: nano The modifier is added to deionized water at a temperature of 50-60℃, among which, nano-... The solid-liquid mass ratio of the modifier to deionized water is 1:

10. The dispersibility of nanoparticles is enhanced by the thermal motion of water molecules in a warm water environment. At the same time, an ultrasonic processor with a power of 300-500W is used to ultrasonically treat the nanoparticles for 30-40 minutes to form a stable, transparent sol system without obvious precipitation.

3. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S1, a planetary mixer is used to dry mix coconut shell activated carbon fiber and viscose-based activated carbon fiber at a speed of 200-300 rpm for 15-20 minutes; the planetary mixer is then heated to 60-70℃ and stirred at a speed of 150 rpm for 2 hours to mix the sol and fiber interwoven premix; and a two-roll hot rolling mill is used to roll and form the material at a temperature of 120-130℃ and a pressure of 0.5 MPa.

4. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S2, the preparation of the mixture includes the following steps: First, hydroxyapatite nanoparticles are added to ethanol and stirred at 300-400 rpm for 15-20 minutes using a magnetic stirrer to initially disperse the nanoparticles. Then, titanate coupling agent is added and stirred at 500-600 rpm for 30 minutes. At the same time, the mixture is subjected to ultrasonic-assisted treatment for 10-15 minutes using an ultrasonic processor with a power of 300-400W to obtain a mixture with a solid-liquid ratio of 1:

8.

5. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S3, the preparation steps of the polyvinyl alcohol-carboxymethyl cellulose composite membrane solution are as follows: First, add 35-45 parts of polyvinyl alcohol with a degree of polymerization of 1750±50 to deionized water at 80℃. The solid-liquid ratio of polyvinyl alcohol to water is 1:

15. Stir continuously at 200-300 rpm for 4 hours until the polyvinyl alcohol dissolves into a transparent colloid. Then, lower the temperature of the transparent colloid to 50℃ and add 15-20 parts of carboxymethyl cellulose with a degree of substitution of 0.7-0.

9. Continue stirring at 150-200 rpm for 2 hours to obtain a viscous and transparent polyvinyl alcohol-carboxymethyl cellulose composite film solution.

6. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S3, the ultrasonic disperser performs ultrasonic treatment at a power of 300-500W for 1 hour; and the constant temperature magnetic stirrer performs crosslinking reaction at a speed of 200-300rpm and a temperature of 30℃ for 2 hours.

7. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In S4, polyvinyl chloride-nano The preparation and protection steps of the composite membrane are as follows: Polyvinyl chloride resin with 5-10% loaded nano The granules are fed into a twin-screw extruder, where... Particle size is 2-5 nm. With a particle size of 20-30 nm, the material is melt-blended under a gradient temperature system of 160℃ in the feeding section, 175℃ in the melting section, and 180℃ in the extrusion section, at a screw speed of 200-250 rpm. The molten material is then cast through a T-die onto a cooling roller at 50℃ and solidified under a traction pressure of 1.0 MPa to obtain PVC-nanopolymer composites with a thickness of 50-80 μm. Composite membrane.

8. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S4, the chitosan quaternary ammonium salt modifier is dissolved in a solution prepared by deionized water, comprising the following steps: Add the chitosan quaternary ammonium salt modifier to deionized water at a mass ratio of 1:

20. Stir the mixture at 150-200 rpm for 30-40 minutes at 25-30℃ until the chitosan quaternary ammonium salt dissolves, forming a transparent and homogeneous solution with a concentration of 5wt%.

9. The method for preparing the gradient pore size activated carbon fiber composite filter according to claim 1, characterized in that, In step S4, the hot-press laminating machine processes the material at 150°C and 0.3 MPa for 10 minutes; the dip-coating machine uniformly coats the solution onto the polyvinyl chloride-nano structure with embedded polytetrafluoroethylene micropowder at a linear speed of 2 m / min. The surface of the composite film was dried in a hot air dryer at 60°C for 30 minutes.

10. A gradient pore size activated carbon fiber composite filter prepared by the method for preparing a gradient pore size activated carbon fiber composite filter according to any one of claims 1-9, characterized in that, It includes an activated carbon fiber layer, a large-pore support transition layer, a functional intermediate layer, and a surface protection reinforcement layer; The activated carbon fiber layer comprises at least 45-55 parts of coconut shell activated carbon fiber, 35-45 parts of viscose-based activated carbon fiber, and 8-12 parts of nano-sized activated carbon fiber. Modifiers, including: coconut shell activated carbon fiber micropores with a pore size of less than 2nm, and coconut shell fiber with a high specific surface area of ​​1500-2000m² / g; viscose-based activated carbon fiber mesopores with a pore size of 2-50nm; nano-... The particle size of the modifier is 5-10 nm; The large-pore support transition layer comprises at least 25-35 parts of polyester nonwoven fabric, 6-10 parts of hydroxyapatite nanoparticles and 4-6 parts of titanate coupling agent, wherein: the particle size of the hydroxyapatite nanoparticles is 50-100 nm, and the three-dimensional fiber network of the polyester nonwoven fabric forms a skeleton structure with a pore size of 5-10 μm. The functional intermediate layer comprises at least 50-65 parts of a polyvinyl alcohol-carboxymethyl cellulose composite film solution, 10-15 parts of layered bimetallic hydroxide nanosheets, and 6-9 parts of boric acid crosslinking agent, wherein the polyvinyl alcohol-carboxymethyl cellulose composite film is crosslinked by boric acid crosslinking agent to form a semi-interpenetrating network structure. The surface protective reinforcement layer comprises at least 28-38 parts of polyvinyl chloride-nanopolymer. Composite membrane, 7-12 parts polytetrafluoroethylene micro powder and 3-5 parts chitosan quaternary ammonium salt modifier.

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