Preparation process of molecular screening nano filter membrane and plastic particle filter thereof

Abstract

The invention relates to the technical field of membrane separation, and discloses a preparation process of a molecular screening nano filter membrane and a plastic particle filter thereof.The preparation process comprises the steps that S1, a polymer-based material and an inorganic composite material are selected, the polymer-based material comprises polyethersulfone, polyvinylidene fluoride or polyimide, and the inorganic composite material is added into the polymer-based material; the inorganic composite material comprises a metal organic framework or graphene oxide; s2, an additive is prepared, and the additive comprises polyvinylpyrrolidone, nano titanium dioxide or silver nanoparticles; s3, the polymer-based material and the inorganic composite material are dissolved in a proper solvent, a polymer solution is obtained, and the solvent comprises NMP, DMF or THF; and S4, coating the polymer solution on the surface of the support body by adopting a phase inversion method. By optimizing the membrane layer structure, enhancing the mechanical strength, improving the anti-pollution capacity and improving the post-treatment process, the stability and durability of the nanofiltration membrane are improved, and the high-efficiency long-term separation requirement is met.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, in particular to a preparation process of a molecular screening nanofiltration membrane and a plastic particle filter thereof. Background Art

[0002] Nanofiltration membrane technology, as an important means in the field of separation and purification, has been widely used in many industries such as water treatment, food processing and medicine. Existing nanofiltration membranes use interfacial polymerization to prepare the separation layer to achieve effective screening of small molecular organic matter, heavy metal ions and nano-scale particles. Some studies have optimized the selective permeability of the membrane by means of chemical cross-linking, surface modification or layered composites to improve its stability in complex environments. However, in practical applications, traditional nanofiltration membranes still face problems such as difficult control of membrane thickness, insufficient mechanical strength, weak anti-pollution ability and poor long-term stability, which restricts its further promotion in the field of high-performance filtration.

[0003] The existing preparation methods of nanofiltration membranes mainly rely on interfacial polymerization to form a separation layer, but due to the non-uniformity of the reaction, the thickness of the membrane layer is difficult to accurately control, resulting in large fluctuations in screening capacity and affecting the stability of long-term operation. In addition, the degree of cross-linking of most nanofiltration membranes is limited, resulting in insufficient mechanical strength. They are prone to swelling or chemical degradation after long-term use, and are more likely to fail in high temperature, high pH or organic solvent environments. Furthermore, the problem of membrane surface contamination is serious, and the existing modification methods are not stable, resulting in easy accumulation of pollutants and reducing the service life of the membrane. At the same time, traditional post-treatment processes, such as natural air drying or high-temperature drying, cause uneven shrinkage of the membrane layer and even produce microcracks, affecting long-term storage and use. The above problems make it difficult for existing technologies to meet the needs of efficient and stable long-term filtration, and there is an urgent need to optimize the preparation process of the membrane to improve its screening performance, mechanical strength, anti-pollution ability and storage stability. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a preparation process for a molecular screening nanofiltration membrane and a plastic particle filter thereof, which solves the problems in the prior art of difficulty in accurately controlling the membrane thickness, insufficient long-term stability, easy adsorption of pollutants and performance degradation during storage.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: a preparation process of a molecular screening nanofiltration membrane and a plastic particle filter thereof, comprising: S1. Selecting a polymer-based material and an inorganic composite material, wherein the polymer-based material comprises polyethersulfone, polyvinylidene fluoride or polyimide, and the inorganic composite material comprises a metal organic framework or graphene oxide; S2, preparing additives, wherein the additives include polyvinyl pyrrolidone, nano titanium dioxide or silver nanoparticles; S3, dissolving the polymer-based material and the inorganic composite material in a suitable solvent to obtain a polymer solution, wherein the solvent comprises NMP, DMF or THF; S4, coating the polymer solution on the surface of the support by a phase inversion method, and immersing the coated membrane in a coagulation bath to form a membrane, wherein the phase inversion method includes controlling the solvent evaporation rate to 0.1-1.0 g / min and the coagulation time to 10-60 seconds to obtain a uniform pore size distribution; S5, using an interfacial polymerization method to alternately react an aqueous phase solution and an oil phase solution to form an ultra-thin film layer, wherein the aqueous phase solution includes piperazine and a surfactant, and the oil phase solution includes trimesoyl chloride dissolved in n-hexane; S6, using a layer-by-layer self-assembly method to form a multilayer membrane layer by alternately depositing cationic and anionic polymers, wherein the cationic polymer includes polyethyleneimine and the anionic polymer includes sodium polystyrene sulfonate; S7, post-treating the nanofiltration membrane, including washing with water and drying, to obtain a molecular sieving nanofiltration membrane.

[0006] Preferably, the mass fractions of the polymer-based materials are: polyethersulfone 15%-20%, polyvinylidene fluoride 12%-18%, and polyimide 10%-15%.

[0007] Preferably, the mass fractions of the inorganic composite material are: 2%-10% of the metal organic framework and 3%-8% of the graphene oxide.

[0008] Preferably, the mass fractions of the additives are: 5%-20% polyvinyl pyrrolidone, 1%-5% nano titanium dioxide, and 0.5%-2% silver nanoparticles.

[0009] Preferably, the anti-pollution property of the membrane is improved by coating a composite coating of silver nanoparticles and nano-titanium dioxide on the membrane surface, and the mass ratio of the silver nanoparticles to the nano-titanium dioxide is 1:1 to 1:3.

[0010] A plastic particle filter, comprising: An upper container and a lower container, wherein the upper container is sealed and connected to the lower container to form a closed structure; A replaceable filter element assembly, the filter element assembly comprising a filter layer composed of a molecular sieving nanofiltration membrane; An ultrasonic cleaning module, used for regularly cleaning the filter element, wherein the ultrasonic cleaning module is integrated with a piezoelectric ceramic sheet; The intelligent monitoring system includes a nanoparticle sensor for real-time monitoring of the filter element usage status and connecting with external devices via wireless communication.

[0011] Preferably, the filter element assembly is manufactured using 3D printing technology to adapt to different types of particle filtration requirements, and the pore size of the molecular sieving nanofiltration membrane is 0.5 to 2 nanometers.

[0012] Preferably, the filter element assembly adopts a rotating snap-on design, and the filter element is integrated with an RFID chip for recording the filter element usage time and filtering performance, and providing replacement prompts to the user.

[0013] Preferably, the filter is capable of processing plastic particles with a diameter less than 100 nanometers and maintaining a stable flow rate during the filtration process.

[0014] The present invention provides a preparation process of a molecular screening nanofiltration membrane and a plastic particle filter thereof, which has the following beneficial effects: 1. The present invention adopts a composite membrane preparation process combining interfacial polymerization with layer-by-layer self-assembly to achieve the technical effect of accurately controlling the thickness of the membrane layer and improving the screening selectivity. Compared with the technical solution in the prior art that simply relies on interfacial polymerization to form the membrane layer, it solves the problems of difficult to accurately control the thickness of the membrane layer, insufficient selectivity and poor stability, so that the membrane maintains high-efficiency screening ability during long-term operation.

[0015] 2. The present invention achieves the technical effect of enhancing the mechanical strength and chemical resistance of the membrane by optimizing the monomer ratio of the water phase and the oil phase and combining the cross-linking and curing treatment. Compared with the traditional nanofiltration membrane without cross-linking treatment, the problems of membrane swelling, mechanical damage and insufficient solvent resistance during long-term use are solved, so that the membrane can still maintain stable separation performance in complex environments.

[0016] 3. The present invention adopts plasma surface modification combined with hydrophilic coating to achieve the technical effect of improving the anti-pollution ability of the membrane and reducing the adsorption of pollutants. Compared with the existing method of simply relying on physical flushing to remove pollutants, it solves the problems of easy contamination of the membrane surface, rapid decrease in water permeability, and shortened life due to frequent cleaning, so that the membrane has a longer service life in practical applications.

[0017] 4. The present invention combines ultraviolet light curing and vacuum drying processes in the post-processing process to achieve the technical effect of improving the stability of the membrane layer and reducing structural defects. Compared with the natural drying or high-temperature drying method used in the prior art, it solves the problems of uneven membrane shrinkage, cracks during the drying process, and rapid performance degradation, so that the membrane can still maintain good separation performance after long-term storage and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of the present invention; Figure 2 It is a schematic diagram of the structure of the plastic particle filter of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Please see attached Figure 1-Figure 2 The embodiment of the present invention provides a preparation process of a molecular screening nanofiltration membrane and a plastic particle filter thereof, comprising: Preparation technology of molecular sieving nanofiltration membrane Material selection The selection of substrates is crucial, as it determines the mechanical strength, chemical resistance and water treatment stability of the membrane. The present invention uses three types of polymer materials: Polyethersulfone (PES): Excellent antioxidant properties and tolerance to a wide pH range.

[0021] Polyvinylidene fluoride (PVDF): highly hydrophobic, suitable for oil-water separation.

[0022] Polyimide (PI): Resistant to high temperature and high pressure, with excellent chemical stability.

[0023] Nanofillers improve separation efficiency: Metal-organic frameworks (MOFs), such as ZIF-8, have stable pore sizes and enhanced permselectivity.

[0024] Graphene oxide (GO) enhances the mechanical strength of the membrane and reduces the adhesion of pollutants.

[0025] Appropriate amount of additives improves the comprehensive performance of the membrane: Polyvinylpyrrolidone (PVP) regulates pore size and improves water flux.

[0026] Nano titanium dioxide (TiO2) reduces biological contamination and improves antibacterial properties.

[0027] Silver nanoparticles (Ag) inhibit microbial growth and prevent biofilm formation.

[0028] Preparation process steps S1. Preparation of membrane solution Select appropriate solvent (NMP, DMF) to dissolve the polymer substrate. Stir slowly to ensure uniform dissolution. Add MOFs and GO to improve structural stability. Add PVP to form a uniform solution. Stir for 5-12 hours to prevent local agglomeration.

[0029] In this embodiment, the membrane solution is prepared by using a combination of polymer-based materials, inorganic filler materials, solvents and functional additives to optimize the membrane forming conditions and the physical and chemical properties of the membrane.

[0030] Generally speaking, the selection of polymer-based materials has a decisive influence on the mechanical properties, chemical corrosion resistance and hydrophilicity of the membrane. In this embodiment, the following polymer materials are used as the substrate: Polyethersulfone (PES) has good chemical stability and high mechanical strength and is suitable for long-term water treatment environments.

[0031] Polyvinylidene fluoride (PVDF) has strong hydrophobicity and has good application prospects in the field of oil-water separation.

[0032] Polyimide (PI), resistant to high temperature and high pressure, suitable for filtration applications under high temperature operating conditions.

[0033] In some embodiments, PES and PVDF are selected for mixing to take into account both hydrophilicity and the mechanical strength of the membrane, and the ratio is generally controlled at about PES:PVDF=3:2.

[0034] As an option, inorganic nanofillers can be incorporated into the polymer matrix to improve the pore structure of the membrane, enhance water flux and anti-fouling ability. Specifically, the following nanofillers were added in this embodiment: Metal-organic frameworks (MOFs), such as ZIF-8, have regular pore structures that help to screen molecules of a certain size.

[0035] Graphene oxide (GO) improves the mechanical properties of the membrane and inhibits the adhesion of pollutants.

[0036] In one possible implementation, the amount of MOFs added is controlled within the range of 2%–10% by mass, while the amount of GO added is controlled within the range of 3%–8% by mass to ensure that the materials are evenly dispersed and do not affect the stability of the membrane solution.

[0037] The choice of solvent has a great influence on the solubility and film-forming properties of the polymer. Generally, a solvent with high polarity and good solubility should be selected. In this embodiment, the following common solvents are selected: N-Methylpyrrolidone (NMP) has strong solubility and is suitable for most polymer substrates.

[0038] Dimethylformamide (DMF) has a fast dissolution rate and is suitable for rapid film formation.

[0039] Tetrahydrofuran (THF) can be used to adjust the solvent evaporation rate to control the pore size.

[0040] In some embodiments, NMP and DMF are mixed in a mass ratio of 4:1 to improve the stability of the membrane solution while maintaining good solubility and avoid pore structure collapse during phase inversion.

[0041] In order to improve the anti-fouling property and pore size distribution of the membrane, it is usually necessary to introduce an appropriate amount of functional additives into the membrane solution. In this embodiment, the following additives are selected: Polyvinyl pyrrolidone (PVP), as a porogen, can effectively regulate the microporous structure of the membrane. The added amount is generally controlled in the range of 5%–20% by mass fraction.

[0042] Nano-titanium dioxide (TiO2) has photocatalytic properties and can degrade organic pollutants while enhancing the membrane’s anti-pollution ability. The added amount is controlled within the mass fraction range of 1%–5%.

[0043] Silver nanoparticles (Ag) have antibacterial properties and can effectively inhibit biological contamination. The addition amount is generally 0.5%–2% by mass.

[0044] In a possible implementation, the mass fraction of PVP is 15%, the mass fraction of TiO2 is 3%, and the mass fraction of Ag is 1%. Under this combination, the formed nanofiltration membrane has good water flux and pollution inhibition ability.

[0045] In this embodiment, to ensure the uniformity of the film liquid, all materials need to be fully stirred after adding the solvent. The stirring method is usually magnetic stirring or mechanical stirring, and the stirring is continued for 5-12 hours at a temperature of 40-60°C until a uniform and transparent film liquid is formed. In some embodiments, ultrasonic dispersion (20-40kHz) can also be used for 30-60 minutes to further promote the uniform dispersion of the filler.

[0046] In order to facilitate the subsequent phase inversion treatment, the membrane liquid needs to be degassed before use to remove bubbles that may affect the film quality. In this embodiment, a vacuum degassing method is used to place the membrane liquid in a -0.08MPa vacuum environment for 30-60 minutes to ensure that the membrane liquid is uniform and free of bubbles, thereby improving the porosity and uniformity of the final membrane.

[0047] In some embodiments, in order to further optimize the film-forming performance, the viscosity of the membrane solution can be adjusted to be controlled within the range of 1000-3000 mPa·s. The viscosity is usually adjusted by adjusting the mass fraction of the polymer matrix. For example, when the mass fraction of PES is increased to 18%, the viscosity of the membrane solution can reach 2500 mPa·s, which helps to improve the film-forming quality and control the pore size distribution.

[0048] In summary, this step prepares a uniform and stable membrane liquid by optimizing the ratio of substrate, filler, solvent and additive, and combining stirring, ultrasonic dispersion, vacuum degassing and other treatment methods, which provides a good foundation for the subsequent phase transformation membrane formation.

[0049] S2. Phase transformation film formation The membrane liquid is evenly coated on the stainless steel mesh support. The membrane thickness is controlled at 50-200 microns. It is then immersed in a coagulation bath (25-50°C) to induce phase separation and form a microporous structure. The solvent diffusion rate is strictly controlled to avoid membrane collapse.

[0050] In this embodiment, the membrane substrate preferably uses a polyethersulfone (PES) ultrafiltration membrane or a polyvinylidene fluoride (PVDF) support membrane, and its pore size range is generally controlled to be 5-50nm to ensure a suitable support structure during subsequent interfacial polymerization. Generally, the base membrane needs to be pre-wetted before use to remove impurities that may affect subsequent reactions and adjust the surface tension of the membrane to adapt it to the subsequent solution immersion process. Specifically, deionized water (DIW) can be used for soaking for 30-120 minutes, or in some embodiments, an ethanol / water (volume ratio 1:1) mixture can be used for wetting to increase the hydrophilicity of the membrane surface.

[0051] As an option, in some cases, the surface of the substrate membrane may be highly hydrophobic, affecting the uniform distribution of the aqueous phase monomer, and therefore requires plasma modification or chemical oxidation treatment. In one possible implementation, O2 plasma (power 50–300W, time 30–180s) can be used to introduce surface active groups and enhance interfacial affinity. In addition, in another embodiment, 0.01–0.5mol / LNaOH solution can be used to slightly hydrolyze the membrane surface, improve its wettability to the aqueous phase solution, and optimize the subsequent polymerization uniformity.

[0052] In this embodiment, the surface roughness of the membrane substrate has a significant impact on the quality of the subsequent separation layer, so it is necessary to use swelling-drying control technology to optimize its surface morphology. In general, the residual solvent can be gradually removed by solvent evaporation treatment (temperature 40-60°C, time 2-6h) to stabilize the microporous structure of the substrate membrane. In some embodiments, a low surface tension solvent (such as isopropanol) can be used for rapid evaporation to reduce pore size shrinkage and improve the uniformity of the substrate membrane. In addition, if the basement membrane has large pore size distribution fluctuations, it can be adjusted by wet phase inversion method, such as by alternating NMP (N-methylpyrrolidone)-water treatment to make the internal structure of the membrane more uniform.

[0053] After wetting and surface adjustment of the substrate membrane, solvent replacement and drying are required to improve the mechanical strength of the membrane and optimize the surface pore size distribution. In this embodiment, the membrane substrate is successively immersed in deionized water, ethanol and acetone solutions (30 minutes per step) to gradually reduce the internal stress of the membrane and remove residual solvent. As an option, freeze drying (-50–0°C, 24h) can be used in specific application environments to prevent shrinkage and deformation of the membrane and maintain good support.

[0054] In summary, step S2 ensures the surface uniformity and chemical activity of the substrate membrane through a series of wetting, modification and drying treatments, so that it can stably support the interfacial polymerization process and improve the separation performance and mechanical strength of the final membrane layer.

[0055] S3. Interface polymerization Apply a water phase solution (piperazine) on the surface of the base membrane and let it stand for 30 seconds. Then immerse it in an oil phase solution (TMC / n-hexane) to allow interfacial polymerization to occur. This step determines the thickness of the membrane's selective layer, which is usually controlled at 10-50 nanometers.

[0056] In this embodiment, the interfacial polymerization reaction adopts the method of alternating reaction of water phase and oil phase solution, so that the active monomer forms an ultra-thin polymer layer on the membrane surface, thereby obtaining the desired screening function.

[0057] Generally, the aqueous phase solution contains monomers containing amino groups or alcoholic hydroxyl groups to ensure that an effective polymerization reaction can occur in the oil phase solution. In this embodiment, piperazine (PIP) is selected as the main aqueous phase monomer. The compound has a stable structure and is easy to form a cross-linked network, thereby improving the stability of the membrane layer. In some embodiments, ethylenediamine (EDA) or triethylenetetramine (TETA) can also be added to adjust the hydrophilicity and mechanical strength of the membrane. The concentration of the aqueous phase solution is usually controlled between 0.1-2.0wt% to ensure uniform reaction and no excessively thick polymerization layer.

[0058] As an option, a surfactant can be added to the aqueous solution to optimize the uniformity of interfacial polymerization. Specifically, sodium dodecyl sulfate (SDS) or polyethylene glycol (PEG) is used in this embodiment to reduce interfacial tension and improve the density of the film layer. The concentration of SDS is generally controlled at 0.05-0.5wt%, and the molecular weight of PEG can range from 600-2000Da.

[0059] The oil phase solution usually uses monomers containing acyl chloride groups to ensure polymerization reaction with amino monomers in the aqueous phase solution. In this embodiment, trimesoyl chloride (TMC) is used as the main oil phase monomer, which can form a cross-linked structure during the reaction and provide excellent molecular sieving performance. In some embodiments, isophthaloyl chloride (IPC) or terephthaloyl chloride (TPC) can also be added to adjust the mechanical properties of the membrane layer. The concentration of the oil phase solution is generally controlled at 0.05-1.0wt% to ensure uniform formation of the membrane layer.

[0060] In one possible implementation, the pH value of the aqueous solution is controlled between 7.5 and 9.0 to ensure the activity of the amine monomer, while the solvent of the oil phase solution is selected to be n-hexane or isooctane to improve the uniformity of the reaction and avoid the swelling effect of the solvent on the base membrane.

[0061] In order to ensure uniform thickness of the film layer, the contact time of interfacial polymerization is one of the key parameters. In this embodiment, the aqueous solution is first coated on the surface of the support layer on which the film is initially formed, and is left to stand for 30-120 seconds to ensure sufficient monomer adsorption. Subsequently, the oil phase solution is slowly poured in, and the reaction time is generally controlled to be 30-180 seconds to form a uniform polymer layer.

[0062] In some embodiments, the reaction rate can be increased by external heating, for example, the membrane is kept in an environment of 25-50°C for reaction to promote the cross-linking reaction of the monomers and improve the mechanical strength of the membrane layer. In addition, after the reaction is completed, it is usually necessary to rinse the membrane surface with n-hexane or isopropanol to remove unreacted monomers and solvent residues to ensure the integrity of the membrane layer.

[0063] The control of the membrane thickness is crucial to the final filtration performance. In this embodiment, the final membrane thickness is controlled within the range of 10–50 nm by adjusting the oil phase monomer concentration and the reaction time to obtain the desired screening performance. In some embodiments, the membrane layer can also be characterized using Fourier transform infrared spectroscopy (FTIR) or scanning electron microscopy (SEM) to ensure that its structure is uniform and there are no obvious defects.

[0064] After the reaction is completed, the film needs to be dried. In this embodiment, a gentle drying method of 30-60°C is adopted to avoid high temperature damage to the film structure. Generally, the drying time is controlled within 2-12 hours to ensure that the film is stably cured and maintains its initial performance.

[0065] In summary, this step optimizes the ratio of aqueous and oil phase monomers, controls reaction conditions and membrane thickness, so that the final ultra-thin polymer layer has uniform sieving ability, providing a stable substrate for the subsequent layer-by-layer self-assembly step (S4). S4. Layer-by-layer self-assembly (LbL) PEI and PSS are deposited alternately to form a stable structure through electrostatic adsorption. Each layer is 10-50 nanometers thick and 5-20 layers are deposited. This method enhances mechanical strength while precisely regulating the separation ability of the membrane.

[0066] In this embodiment, the layer-by-layer self-assembly method utilizes the alternating deposition of cationic and anionic polymers to form a uniform and stable separation layer.

[0067] In general, cationic polymers can provide positive charges, improve the hydrophilicity of the membrane surface, and regulate the molecular sieving performance. In this embodiment, polyethyleneimine (PEI) is selected as the main cationic polymer. This material has a high charge density and can enhance the electrostatic sieving effect of the membrane. In some embodiments, quaternized chitosan (QCS) or polydiallyl dimethyl ammonium chloride (PDADMAC) can also be used to further optimize the surface properties of the membrane.

[0068] As an option, the concentration of the cationic solution is usually controlled at 0.05-2.0wt%, and the solvent can be deionized water (DIW) or a mixed solution containing a small amount of ethanol (EtOH, mass fraction ≤5%) to improve the dispersion of the polymer and promote uniform deposition. In a possible implementation, the pH value of the PEI solution can be adjusted to 6.5-8.0 to optimize the electrostatic adsorption capacity of the membrane layer and reduce the self-agglomeration effect of the solution.

[0069] Anionic polymers are mainly used to regulate the anti-pollution ability of the membrane and provide a stable interlayer structure. In this embodiment, sodium polystyrene sulfonate (PSS) is used as the main anionic polymer. This material has a strong anionic charge and can effectively reduce the adsorption of pollutants on the membrane surface. In some embodiments, carboxymethyl cellulose (CMC) or sodium alginate (Alginate) can also be added to adjust the flexibility and durability of the membrane.

[0070] Specifically, the concentration of the anionic solution is usually controlled at 0.1–1.5 wt % and the pH value is in the range of 6.0–7.5 to ensure its interlayer interaction with the cationic polymer. In one possible implementation, the molecular weight of PSS is selected in the range of 70 kDa–500 kDa to optimize the density and permeability of the membrane layer.

[0071] During the layer-by-layer self-assembly process, the thickness of each layer needs to be precisely controlled to ensure the structural stability and screening ability of the final membrane layer. In this embodiment, the deposition thickness of the single layer of polymer is usually 5-30nm, and the final membrane layer thickness is controlled in the range of 50-300nm to balance the screening accuracy and water flux.

[0072] In general, the film deposition process includes the following steps: First, the interfacially polymerized membrane was immersed in a cationic polymer solution, and the adsorption time was controlled at 5–20 min to ensure that the polymer evenly covered the membrane surface.

[0073] Then, deionized water (DIW) was used to rinse the membrane surface to remove unbound cationic polymers and avoid interference between subsequent layers.

[0074] Subsequently, the membrane was immersed in anionic polymer solution, and the adsorption time was also controlled within 5–20 min to ensure sufficient deposition of the polymer.

[0075] Through alternating washing and deposition operations, a multi-layer stable structure is finally formed.

[0076] In some embodiments, the quality of the film layer can be further optimized by changing the deposition time or controlling the solution temperature. For example, controlling the deposition temperature at 25–45°C can improve the solubility of the polymer and make the film layer more uniform. In another possible implementation, electrostatic spraying technology can be used to form an ultra-thin and uniform layered structure on the membrane surface to improve the screening performance of the membrane.

[0077] In addition, in order to improve the long-term stability of the membrane, a cross-linking treatment can be used in this embodiment to enhance the mechanical strength of the self-assembled membrane layer by layer. For example, after the final deposition is completed, chemical cross-linking can be performed by glutaraldehyde (GA) or epichlorohydrin (EPC), and the reaction time is usually controlled within 30-120 minutes to optimize the stability and anti-swelling ability of the membrane layer.

[0078] In some embodiments, ultraviolet (UV) or heat treatment can also be used to further solidify the film structure. For example, irradiation with UV at a wavelength of 254nm for 10-30min can effectively enhance the cross-linking degree of the film and reduce the risk of dissolution between layers. In addition, the heat treatment temperature is usually controlled at 60-90°C for 2-6h to ensure the structural stability of the film.

[0079] In summary, this step achieves precise control of the membrane structure through the alternating deposition of cationic and anionic polymers. At the same time, the mechanical strength and durability of the membrane are enhanced by cross-linking or heat treatment, providing the final nanofiltration membrane with stable molecular sieving performance, enabling it to meet the needs of complex water treatment and separation applications.

[0080] S5. Post-processing Wash away the unreacted products and use gentle drying (<50°C) to prevent structural damage. Some membranes can be treated with UV light to improve anti-pollution capabilities. The final membrane pore size can be controlled at 0.5-2 nanometers, which is suitable for plastic particle separation.

[0081] In this embodiment, the post-treatment first adopts a water washing step to remove the unreacted monomers, low molecular weight polymers and solvents remaining on the surface and inside of the membrane.

[0082] In general, the water washing process needs to select appropriate solvents and temperatures to ensure effective removal of residues while avoiding damage to the membrane structure. Specifically, in this embodiment, deionized water (DIW) is used for preliminary cleaning, and the water temperature is controlled at 25-50°C to improve the dissolution efficiency. In some embodiments, an ethanol / water mixture (volume ratio 1:1) can be used to improve the removal ability of oil phase residues. In addition, in order to enhance the cleaning effect, ultrasonic assisted cleaning (20-40kHz) can be used, and the time is controlled at 5-30min to reduce the adhesion of surface pollutants.

[0083] As an option, the water washing environment can be adjusted by acid-base solution to remove specific residues. For example, in one possible implementation, a 0.1-0.5wt% NaOH solution can be used to remove possible residual carboxylic acid or acyl chloride groups, followed by DIW washing to restore the stability of the membrane. In another embodiment, a 0.05-0.3wt% HCl solution can be used to neutralize possible amine residues to ensure the chemical stability of the membrane surface.

[0084] After washing, the membrane needs to be cross-linked and cured to enhance the durability and anti-swelling ability of the membrane layer. In this embodiment, a combination of chemical cross-linking and thermal cross-linking is used to improve the stability of the membrane.

[0085] Generally, chemical crosslinking can be carried out by treating with glutaraldehyde (GA) or epichlorohydrin (EPC) to form a stable covalent crosslinking network. In this embodiment, a 1–5wt% GA solution is used to carry out the crosslinking reaction at pH 7.0–9.0 for 30–120 min to optimize the crosslinking degree of the membrane. In some embodiments, a 1–3wt% paraformaldehyde (PF) solution can be used to further improve the chemical resistance and mechanical strength of the membrane layer.

[0086] As an option, ultraviolet (UV) cross-linking can be used to enhance the durability of the film layer. In this embodiment, a UV light source with a wavelength of 254nm is used, and the irradiation time is controlled to be 10-30min to promote the cross-linking reaction of the film layer. In another possible implementation, heat treatment (60-100°C) can be used, and the time is controlled to be 2-6h to improve the thermal stability of the film and reduce the residue of the cross-linking agent.

[0087] After the cross-linking treatment is completed, a drying treatment is required to remove moisture and solvent residues and maintain the integrity of the film layer. In this embodiment, room temperature air drying or low temperature drying (30-60°C) is used, and the time is controlled within 12-48 hours to ensure that the film structure does not shrink or deform. In some embodiments, vacuum drying (-0.05 to -0.1MPa) can be used to increase the drying rate and reduce the surface tension change of the film.

[0088] In addition, in order to improve the anti-pollution ability of the membrane, the membrane surface can be modified to be hydrophobic or hydrophilic. Specifically, in this embodiment, plasma treatment (Plasma Treatment) is used to change the surface energy of the membrane and improve its anti-pollution ability. For example, using oxygen plasma (O2 Plasma, 100-300W) for 30-120s can improve the hydrophilicity of the membrane and reduce the adsorption of organic pollutants. In another possible implementation, fluorine-containing compound modification can be used, such as perfluorooctyl triethoxysilane (PFOTS), to enhance the hydrophobicity of the membrane and improve its anti-oil ability.

[0089] In some embodiments, polyethylene glycol (PEG) coating can also be used to further optimize the anti-fouling performance of the membrane. For example, the membrane is immersed in a 0.5-5wt% PEG solution and allowed to stand for 30-180 minutes to form an anti-fouling protective layer. In addition, polydopamine (PDA) deposition can also be used to improve the stability of the membrane and enhance its ability to resist protein pollution.

[0090] In summary, this step ensures the stability, durability and anti-pollution ability of the membrane layer by optimizing the water washing, cross-linking curing, drying and surface modification processes, providing excellent performance for the final molecular sieving nanofiltration membrane.

[0091] Design of plastic particle filters Structural composition The filter of the present invention comprises the following core components: Upper container - water inlet area, where plastic particles are evenly distributed after entering.

[0092] Lower container - collects pure water and discharges it through pipes.

[0093] Filter element assembly - the core part, containing the molecular sieving nanofiltration membrane.

[0094] Ultrasonic cleaning module - vibrates regularly to prevent clogging by contamination.

[0095] Intelligent monitoring system - real-time feedback of filtering status and connection to external terminals.

[0096] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a molecular screening nanofiltration membrane, characterized in that: include: S1. Selecting a polymer-based material and an inorganic composite material, wherein the polymer-based material comprises polyethersulfone, polyvinylidene fluoride or polyimide, and the inorganic composite material comprises a metal organic framework or graphene oxide; S2, preparing additives, wherein the additives include polyvinyl pyrrolidone, nano titanium dioxide or silver nanoparticles; S3, dissolving the polymer-based material and the inorganic composite material in a suitable solvent to obtain a polymer solution, wherein the solvent comprises NMP, DMF or THF; S4, coating the polymer solution on the surface of the support by a phase inversion method, and immersing the coated membrane in a coagulation bath, wherein the phase inversion method includes controlling the solvent evaporation rate to 0.1-1.0 g / min and the coagulation time to 10-60 seconds to obtain a uniform pore size distribution; S5, using an interfacial polymerization method to alternately react an aqueous phase solution and an oil phase solution to form an ultra-thin film layer, wherein the aqueous phase solution includes piperazine and a surfactant, and the oil phase solution includes trimesoyl chloride dissolved in n-hexane; S6, using a layer-by-layer self-assembly method to form a multilayer membrane layer by alternately depositing cationic and anionic polymers, wherein the cationic polymer includes polyethyleneimine and the anionic polymer includes sodium polystyrene sulfonate; S7, post-treating the nanofiltration membrane, including washing with water and drying, to obtain a molecular sieving nanofiltration membrane.

2. The preparation process of the molecular screening nanofiltration membrane according to claim 1, characterized in that: The mass fractions of the polymer-based material are: polyethersulfone 15%-20%, polyvinylidene fluoride 12%-18%, and polyimide 10%-15%.

3. The preparation process of the molecular screening nanofiltration membrane according to claim 1, characterized in that: The mass fractions of the inorganic composite material are: 2%-10% of the metal organic framework and 3%-8% of the graphene oxide.

4. The process for preparing the molecular screening nanofiltration membrane according to claim 3, characterized in that: The mass fractions of the additives are: 5%-20% polyvinyl pyrrolidone, 1%-5% nano titanium dioxide, and 0.5%-2% silver nanoparticles.

5. The process for preparing the molecular screening nanofiltration membrane according to claim 1, characterized in that: The anti-pollution property of the membrane is improved by coating a composite coating of silver nanoparticles and nano-titanium dioxide on the membrane surface, wherein the mass ratio of the silver nanoparticles to the nano-titanium dioxide is 1:1 to 1:

3.

6. A plastic particle filter, used in the process for preparing the molecular screening nanofiltration membrane according to any one of claims 1 to 5, characterized in that: include: An upper container and a lower container, wherein the upper container is sealed and connected to the lower container to form a closed structure; A replaceable filter element assembly, the filter element assembly comprising a filter layer composed of a molecular sieving nanofiltration membrane; An ultrasonic cleaning module, used for regularly cleaning the filter element, wherein the ultrasonic cleaning module is integrated with a piezoelectric ceramic sheet; The intelligent monitoring system includes a nanoparticle sensor for real-time monitoring of the filter element usage status and connecting with external devices via wireless communication.

7. A plastic particle filter according to claim 6, characterized in that: The filter element component is manufactured using 3D printing technology to meet the needs of different types of particle filtration, and the pore size of the molecular sieving nanofiltration membrane is 0.5 to 2 nanometers.

8. A plastic particle filter according to claim 6, characterized in that: The filter element assembly adopts a rotating snap-on design, and the filter element is integrated with an RFID chip for recording the filter element usage time and filtering performance, and providing replacement prompts to the user.

9. A plastic particle filter according to claim 6, characterized in that: The filter is capable of processing plastic particles with a diameter of less than 100 nanometers and maintains a stable flow rate during the filtration process.

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