Preparation method of layer-by-layer self-assembled enzyme catalysis nanofiltration membrane and application of layer-by-layer self-assembled enzyme catalysis nanofiltration membrane in removal of organic micropollutants

Abstract

The invention discloses a preparation method of a layer-by-layer self-assembled enzyme catalysis nanofiltration membrane and application of the layer-by-layer self-assembled enzyme catalysis nanofiltration membrane to removal of organic micropollutants. The preparation method comprises the following steps: manufacturing a hollow fiber ultrafiltration membrane assembly by using a polytetrafluoroethylene hard thick tube and polyether sulfone hollow fiber ultrafiltration membrane filaments; and alternately depositing polyelectrolyte and laccase in the hollow fiber membrane component to obtain the asymmetric polyelectrolyte gradient deposited layer-by-layer self-assembled enzyme catalysis nanofiltration membrane. When the layer-by-layer self-assembled enzyme catalysis nanofiltration membrane is applied to removal of organic micropollutants, due to the fact that the composite membrane has a relatively evacuated pore structure, and when the organic micropollutants are removed through rich hydrophilic functional groups of a modified layer of the membrane and the catalytic oxidation effect of laccase, high flux is achieved, and meanwhile the rejection rate is kept at a high level; the retention rate of organic micropollutant bisphenol A is 90% or above, and the retention rate of atrazine is 99% or above.

Description

Technical Field

[0001] The invention belongs to the field of organic micro-pollutant wastewater treatment, and particularly relates to a preparation method of a layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane and an application for removing organic micro-pollutants. Background Art

[0002] With the innovation and improvement of environmental analysis technologies, the detection frequency of organic micro-pollutants (OMPs) such as antibiotics and bisphenol A in environmental media has increased significantly. Although their concentrations are usually in the nanogram to microgram range, their bioaccumulation effects through the food chain can be amplified by tens of thousands of times, posing a potential threat to ecological balance and human health.

[0003] The separation performance of nanofiltration membranes mainly depends on their sieving effect, electrostatic effect, and adsorption effect. The pore size of nanofiltration membranes is about 1 nm, and the membrane surface and internal pores usually carry charges. Their retention molecular weight range for neutral molecules is 150 - 2000 Da, and they can effectively retain multivalent ions, but have a poor retention effect on monovalent ions. Nanofiltration technology can effectively remove organic substances with a relative molecular weight of 200 - 2000 daltons. Nanofiltration membranes show great potential in the removal of OMPs, and nanofiltration membrane technology is increasingly applied to the treatment of organic micro-pollutants. However, challenges such as low retention efficiency of small molecule pollutants by nanofiltration membranes, insufficient chemical resistance, easy degradation of some membrane materials under extreme conditions, high concentration of OMPs in the solution after retention and the need for further treatment, and high operating costs still need to be overcome, which pose new challenges to the currently commonly used treatment methods.

[0004] Compared with traditional nanofiltration membranes, asymmetric polyelectrolyte layer-by-layer self-assembled modified enzyme-catalyzed nanofiltration membranes have better removal performance and have become a research hotspot. Asymmetric polyelectrolyte layer-by-layer self-assembled enzyme-catalyzed nanofiltration membranes couple enzyme-catalyzed degradation and separation effects. However, traditional enzyme-catalyzed nanofiltration membranes are prone to disadvantages such as insufficient flux, poor pollutant retention, high concentration of OMPs in the solution after retention and the need for further treatment, and high operating costs. Therefore, the research on enzyme-catalyzed nanofiltration membranes is increasing. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0006] To achieve these objects and other advantages of the present invention, a preparation method of a layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane is provided, including the following steps:

[0007] Step 1: Fabricate a hollow fiber ultrafiltration membrane module using a polytetrafluoroethylene (PTFE) hard thick tube and a polyethersulfone (PES) hollow fiber ultrafiltration membrane filament soaked in absolute ethanol.

[0008] Step 2: Prepare isopropanol solution, polystyrene sulfonate (PSS) solutions with gradient concentrations, poly(dimethyldiallylammonium chloride) (PDAD) solutions with gradient concentrations, laccase solution, and glutaraldehyde (GA) solution;

[0009] Step 3: Clean the hollow fiber ultrafiltration membrane module, and alternately deposit polyelectrolytes and laccase inside the hollow fiber membrane module using a syringe to construct a [PSS / laccase / PDAD / laccase]n membrane;

[0010] Step 4: After the deposition of the last layer of polyelectrolyte is completed and the cleaning is done, inject glutaraldehyde solution and laccase solution between the polyelectrolyte layers in sequence to obtain an asymmetric polyelectrolyte gradient-deposited layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane.

[0011] Preferably, Step 1 is specifically as follows: Use a polytetrafluoroethylene hard thick tube soaked in absolute ethanol and 10 polyethersulfone hollow fiber membrane filaments to make a membrane module. Thread the polyethersulfone hollow fiber membrane filaments into the polytetrafluoroethylene hard thick tube, arrange the 10 membrane filaments parallelly in the inner cavity of the polytetrafluoroethylene sleeve, and conduct end vacuum encapsulation using a two-component epoxy resin. After the epoxy resin glue air-dries and cures, use a knife to cut off the polyethersulfone hollow fiber nanofiltration membrane filaments and the gelled part at the tail end that are longer than the hard tube length, trim both ends flat, and leave it standing and drying for 24 h to be ready for normal use.

[0012] Preferably, it is characterized in that Step 2 is specifically as follows: Dilute isopropanol with deionized water to prepare a 25% isopropanol solution. Dissolve the polyelectrolyte PSS and sodium chloride in water, dilute with deionized water and stir evenly to obtain a PSS solution. Dissolve the polyelectrolyte PDAD and sodium chloride in water, dilute with deionized water and stir evenly to obtain a PDAD solution. Dissolve laccase powder in phosphate buffer solution, and dilute with phosphate buffer solution and stir evenly to obtain a laccase solution. Dilute the glutaraldehyde solution with deionized water to prepare a 0.5% glutaraldehyde solution.

[0013] Preferably, it is characterized in that Step 3 is specifically as follows:

[0014] S1. Clean the hollow fiber ultrafiltration membrane module with isopropanol solution using a syringe for 30 min, and then clean it with deionized water for 5 min;

[0015] S2. Inject the PSS solution into the inner cavity of the hollow fiber ultrafiltration membrane module using a syringe, let it stand for 5 min, then inject deionized water to clean the inner cavity of the membrane module for 5 min; then inject the laccase solution into the membrane module using a syringe, let it stand at 25 °C for 1 h, and then inject deionized water to rinse the inner cavity of the membrane module for 5 min to form a polyanionic polyelectrolyte PSS coating;

[0016] S3. Inject the PDAD solution into the inner cavity of the polyanion electrolyte PSS coating of the hollow fiber ultrafiltration membrane module through a syringe, let it stand for 5 min, and then inject deionized water to wash the inner cavity of the membrane module for 5 min. Then inject the laccase solution into the membrane module through a syringe. When the laccase solution enters the membrane module, let it stand at 25 °C for 1 h, and then inject deionized water to rinse the inner cavity of the membrane module for 5 min. A polycation electrolyte PDAD coating is formed on the polyanion electrolyte PSS coating to complete the first bilayer coating.

[0017] S4. Repeat S2 and S3. According to the required number of layers and the concentration of polyelectrolytes required for each layer, construct a [PSS / laccase / PDAD / laccase] n membrane.

[0018] Preferably, it is characterized in that the specific steps of step four are as follows: after the deposition and cleaning of the last layer of polyelectrolyte are completed, inject glutaraldehyde solution into the lumen of the membrane through a syringe. After contacting the surface of the lumen of the membrane for 5 min, remove the unreacted glutaraldehyde solution with deionized water, and then inject laccase solution. Let it stand at 25 °C for 1 h to immobilize the laccase. Finally, wash it with deionized water to obtain an asymmetric polyelectrolyte gradient-deposited layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane.

[0019] Preferably, it is characterized in that in step one, the length of the polytetrafluoroethylene hard thick tube is 25 - 30 cm, the length of the polyethersulfone hollow fiber membrane filament is 45 - 50 cm, its MWCO = 10 kDa, the inner diameter is 1.2 mm, the mixing ratio of the AB glue components of the two-component epoxy resin is 1:1, and the effective length of the membrane module after cutting is 25 cm.

[0020] Preferably, it is characterized in that in step two, the mass ratio of PSS to sodium chloride is 0.05 - 0.25:14.625. The PSS solution is made up to 500 mL, and the concentration of the obtained PSS solution is 0.1 wt% - 0.5 wt%. The mass ratio of PDAD to sodium chloride is 0.05 - 0.25:14.625. The PDAD solution is made up to 500 mL, and the concentration of the obtained PDAD solution is 0.1 wt% - 0.5 wt%. The stirring speed is 300 - 400 rpm, the stirring temperature is 25 °C, the stirring duration is 20 min, the dosage of laccase powder is 0.01 - 0.08 g, the concentration of the phosphate buffer solution is 0.1 M, the pH value is 5.3, the laccase solution is made up to 100 mL, the concentration of the glutaraldehyde solution is 50%, and the glutaraldehyde solution is made up to 100 mL.

[0021] Preferably, in the third step, five bilayer polyelectrolyte composite structures [PSS / laccase / PDAD / laccase]5 are constructed in the inner cavity of the hollow fiber ultrafiltration membrane module. The concentrations of the PSS solution in the first to fifth layers are 0.1 wt%, 0.2 wt%, 0.1 wt%, 0.5 wt%, and 0.1 wt% respectively, and the concentrations of the PDAD solution in the first to fifth layers are 0.1 wt%, 0.2 wt%, 0.1 wt%, 0.5 wt%, and 0.1 wt% respectively.

[0022] The present invention also provides an application of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane. The layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane is applied to the removal of organic micropollutants. The method is as follows: A layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane module composed of multiple hollow fiber nanofiltration membranes is connected to a small hollow fiber nanofiltration cross-flow filtration system through a peristaltic pump. The small hollow fiber nanofiltration cross-flow filtration device also includes a balance, and a magnetic stirrer is provided on the side of the organic micropollutant filtration feed liquid; the feed side of the membrane module is connected to the peristaltic pump, and the permeate side of the membrane module is externally connected to a permeate collection tank; a reflux pipe is provided at the output end of the membrane module and connected to the feed liquid.

[0023] Preferably, the types of organic micropollutants are bisphenol A (BPA), atrazine (ATZ), carbamazepine (CBZ), and ibuprofen (IBU), the concentration is 10 mg / L, the feed temperature is set at 25 °C, the feed flow rate is 1200 rpm, and the pressure is set at 0.2 Mpa; the preparation method of the organic micropollutants is as follows: Weigh 0.01 g of the organic micropollutants, dissolve them with methanol, stir evenly, the stirring speed is 300 - 400 rpm, the stirring temperature is 25 °C, the stirring duration is 20 min, and make up the volume to 1000 mL with deionized water.

[0024] The present invention has at least the following beneficial effects:

[0025] (1) The method provided by the present invention can effectively reduce the organic micropollutants in the effluent of urban sewage treatment plants, and solves the key problems of low efficiency and incomplete removal of organic micropollutants in traditional technologies from the technical perspective of nanofiltration membranes;

[0026] (2) By modifying the selective functional layer of the nanofiltration membrane with an asymmetric polyelectrolyte structure, the present invention can overcome problems such as low water flux and low removal rate of organic micropollutants of the nanofiltration membrane; Through the nanofiltration membrane technology of the asymmetric polyelectrolyte enzyme-catalyzed nanofiltration membrane material, the membrane flux can reach 17, the retention rate of organic micropollutants can reach 99%, and the degradation rate can reach 19%.

[0027] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will be understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0028] Figure 1 Structural formulas of the materials prepared in each step of the present invention;

[0029] Figure 2 Schematic diagram of the nanofiltration membrane filtration device in the application example of the present invention;

[0030] Figure 3 SEM image of the original polyethersulfone (PES) membrane in Example 1 of the present invention;

[0031] Figure 4 SEM image of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane prepared in Example 1 of the present invention;

[0032] Figure 5 Data graph of the treatment effect of removing organic micropollutants in the solution in Application Example 1 and Comparative Example 4 of the present invention;

[0033] Figure 6 Data graph of the treatment effect of removing organic micropollutants in the solution in Comparative Example 5 of the present invention. Detailed implementation manners

[0034] The following further elaborates on the present invention in conjunction with the accompanying drawings, so that those skilled in the art can implement it with reference to the text of the specification.

[0035] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0036] Example 1

[0037] A method for preparing a layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane, comprising the following steps:

[0038] Step 1: Use a 25-cm-long rigid polytetrafluoroethylene (PTFE) thick tube soaked in absolute ethanol and 10 45-cm-long polyethersulfone hollow fiber membrane filaments to make a membrane module. Thread the polyethersulfone hollow fiber membrane filaments into the PTFE rigid thick tube, arrange the 10 membrane filaments in parallel in the inner cavity of the PTFE sleeve, and perform end vacuum encapsulation using a two-component epoxy resin (AB components mixed in a ratio of 1:1). After the epoxy resin glue dries and cures, use a knife to cut off the polyethersulfone hollow fiber nanofiltration membrane filaments and the end gelled part that are longer than the length of the hard tube, trim both ends flat, with the effective length of the membrane filaments being 25 cm, and let it stand and dry for 24 h before it can be used normally;

[0039] Step 2: The specific operations in Step 2 are as follows: Prepare an isopropanol solution with a concentration of 25%. Dissolve 0.05 g, 0.1 g, and 0.25 g of polyelectrolyte PSS and 14.625 g of sodium chloride in water respectively, make up the volume to 500 mL with deionized water, and stir evenly to obtain PSS solutions with concentrations of 0.1 wt%, 0.2 wt%, and 0.5 wt%. Dissolve 0.05 g, 0.1 g, and 0.25 g of polyelectrolyte PDAD and sodium chloride in water respectively, make up the volume to 500 mL with deionized water, and stir evenly to obtain PDAD solutions with concentrations of 0.1 wt%, 0.2 wt%, and 0.5 wt%. Dissolve 0.01 g of laccase powder in 0.1 M phosphate buffer solution, make up the volume to 100 mL with phosphate buffer solution, and then stir evenly to obtain a laccase solution with a concentration of 0.1 g / L. During the stirring in the above steps, magnetic stirring is carried out at 200 r / min for 30 min at 25°C. Take 1 mL of 50% glutaraldehyde solution and make up the volume to 100 mL with deionized water to obtain a glutaraldehyde solution;

[0040] Step 3: Clean the hollow fiber ultrafiltration membrane module, and alternately deposit polyelectrolytes and laccase inside the hollow fiber membrane module by means of a syringe, specifically:

[0041] S1. Clean the hollow fiber ultrafiltration membrane module with the isopropanol solution through a syringe for 30 min, and then clean it with deionized water for 5 min;

[0042] S2. Inject the 0.1 wt% PSS solution into the inner cavity of the hollow fiber ultrafiltration membrane module through a syringe, let it stand for 5 min, and then inject deionized water to clean the inner cavity of the membrane module for 5 min; then inject the laccase solution into the membrane module through a syringe, let it stand at 25°C for 1 h, and then inject deionized water to rinse the inner cavity of the membrane module for 5 min to form a polyanionic electrolyte PSS coating;

[0043] S3. Inject the 0.1 wt% PDAD solution into the inner cavity of the polyanionic electrolyte PSS coating of the hollow fiber ultrafiltration membrane module through a syringe, let it stand for 5 min, and then inject deionized water to clean the inner cavity of the membrane module for 5 min; then inject the laccase solution into the membrane module through a syringe. Inject the laccase solution into the membrane module, let it stand at 25°C for 1 h, and then inject deionized water to rinse the inner cavity of the membrane module for 5 min; a polycationic electrolyte PDAD coating is formed on the polyanionic electrolyte PSS coating to complete the first double-layer coating, namely [PSS / laccase / PDAD / laccase]1;

[0044] S4. Repeat S2 and S3. According to the required number of layers and the polyelectrolyte concentration required for each layer, construct a [PSS / laccase / PDAD / laccase]5 membrane. Among them, the concentration of the PSS solution of [PSS / laccase / PDAD / laccase]2 is 0.2 wt%, and the concentration of the PDAD solution is 0.2 wt%; the concentration of the PSS solution of [PSS / laccase / PDAD / laccase]3 is 0.1 wt%, and the concentration of the PDAD solution is 0.1 wt%; the concentration of the PSS solution of [PSS / laccase / PDAD / laccase]4 is 0.5 wt%, and the concentration of the PDAD solution is 0.5 wt%; the concentration of the PSS solution of [PSS / laccase / PDAD / laccase]5 is 0.1 wt%, and the concentration of the PDAD solution is 0.1 wt%.

[0045] Step 4. After the deposition of the last layer of polyelectrolyte is completed and the membrane is washed, inject glutaraldehyde solution into the lumen of the membrane with a syringe. After contacting the surface of the lumen of the membrane for 5 min, remove the unreacted glutaraldehyde solution with deionized water, and then inject 0.8 g / L laccase solution (the preparation method is the same as the laccase solution in Step 2). Let it stand at 25 °C for 1 h to immobilize the laccase. Finally, wash it with deionized water to obtain an asymmetric polyelectrolyte gradient-deposited layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane. The prepared nanofiltration membrane is an enzyme-catalyzed nanofiltration (E-NF) membrane.

[0046] The structural formulas of the various materials used in this example are as Figure 1 shown. The SEM image of the PES membrane obtained in Step 1 is as Figure 3 shown. The original PES substrate surface shows a porous microstructure, which is characterized by a typical porous structure and a relatively smooth surface. These fibril voids act as transmembrane channels for water vapor to pass through, and the membrane pore diameter is in the range of 10 - 100 nm. The SEM image of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane with an asymmetric polyelectrolyte structure obtained in Step 3 is as Figure 4 shown. The surface roughness of the membrane increases significantly, and many laccase particulate substances adhere to the surface.

[0047] Comparative Example 1

[0048] Use the LBL-NF membrane without laccase deposition as Comparative Example 1. The operations in Step 1 and Step 2 of this comparative example are the same as those in Example 1. In Step 3, only PSS / PADA polyelectrolyte deposition is performed on the membrane module, without laccase deposition and the operations in Step 4.

[0049] Comparative Example 2

[0050] Use the E-NF1 membrane without laccase and glutaraldehyde capping as Comparative Example 2. The operations from Step 1 to Step 3 of this comparative example are the same as those in Example 1, and Step 4 is not performed to obtain the E-NF1 membrane.

[0051] Comparative Example 3

[0052] The E-NF2 membrane without gradient concentration polyelectrolyte deposition was used as Comparative Example 3. The first, second, and fourth steps of this comparative example were the same as those of Example 1. In the third step, the concentrations of the polyelectrolyte PSS solution and PDAD solution used were both 0.5 wt%, and the E-NF2 membrane was obtained.

[0053] Application Example 1

[0054] Using the E-NF membrane prepared in Example 1 as the membrane module to treat the organic micro-pollutant solution, the following steps are included:

[0055] Set up the nanofiltration membrane filtration device as shown in Figure 2 Connect multiple E-NF membranes to a small hollow fiber nanofiltration crossflow filtration system through a peristaltic pump. The small hollow fiber nanofiltration crossflow filtration system also includes a balance, and a magnetic stirrer is equipped on the side of the organic micro-pollutant filtration feed liquid; the feed side of the membrane module is connected to the peristaltic pump, and the permeate side of the membrane module is externally connected to a permeate collection tank; a reflux pipe is provided at the output end of the membrane module and connected to the feed liquid.

[0056] Conduct basic performance tests on the prepared nanofiltration membrane. Prepare solutions of magnesium sulfate, sodium sulfate, magnesium chloride, and sodium chloride at 1000 g / L respectively, and the volume of the salt solution feed liquid is 1.0 L for testing. This application is for intercepting and treating organic micro-pollutants in the effluent of the sewage treatment plant. Configure 10 mg / L of bisphenol A, atrazine, carbamazepine, and ibuprofen as the organic micro-pollutant feed liquid, and the volume of the organic micro-pollutant solution is 1.0 L; filter with the two feed liquids respectively, the peristaltic pump speed is 1200 rpm, pump the feed liquid into the lower end of the membrane module, the operating pressure is set at 0.2 MPa, the feed temperature is set at 25 °C, and the device operating time is 2 h. Take samples of the permeate every 30 min, and use high performance liquid chromatography to measure the change in the concentration of organic micro-pollutants in the effluent water quality. As shown in Figure 5 As shown, the membrane flux of the E-NF membrane prepared in Example 1 is 17 L / (m 2 ·h), the interception rates of organic micro-pollutants are 88% for bisphenol A, 99% for atrazine, 62% for ibuprofen, and 36% for carbamazepine, and the degradation rate of bisphenol A reaches 19%, proving that the membrane material achieves the purpose of removing organic micro-pollutants in the solution.

[0057] Comparative Example 4

[0058] Using the LBL-NF membrane prepared in Comparative Example 1 as the membrane module to treat the organic micro-pollutant solution, the method is the same as that of Application Example 1.

[0059] The results show that, as shown in Figure 5 As shown, the membrane flux of the LBL-NF membrane prepared in Comparative Example 1 is 19 L / (m 2·h), the interception rates of organic micro-pollutants are 65% for bisphenol A, 96% for atrazine, 56% for ibuprofen, and 27% for carbamazepine, and its degradation rate for bisphenol A is only 1%. It can be seen that the LBL-NF membrane prepared in Comparative Example 1 has a worse removal effect on organic micro-pollutants than the E-NF membrane prepared in Example 1.

[0060] Comparative Example 5

[0061] The E-NF1 membrane prepared in Comparative Example 2 and the E-NF2 membrane prepared in Comparative Example 3 were used as membrane modules to treat the organic micro-pollutant solution in Application Example 1, including the following steps:

[0062] On the premise of setting up the device, the two membranes were used for the organic micro-pollutant solution in Application Example 1, and experiments were carried out under the same process conditions. The results show that, as Figure 6 shown, the unsealed membrane flux of the E-NF1 membrane prepared in Comparative Example 2 was 17 L / (m 2 ·h), the interception rates of organic micro-pollutants are 77% for bisphenol A, 97% for atrazine, 50% for ibuprofen, and 17% for carbamazepine, and the degradation rate of bisphenol A reached 12%, showing a decrease in the removal effect of the E-NF membrane in Example 1 on organic micro-pollutants; the membrane flux of the E-NF2 membrane prepared in Comparative Example 3 was 10 L / (m 2 ·h), the membrane flux decreased significantly compared with the E-NF membrane in Example 1. The interception rates of organic micro-pollutants are 85% for bisphenol A, 98% for atrazine, 65% for ibuprofen, and 39% for carbamazepine, and the degradation rate of bisphenol A reached 16%. Its removal effect on organic micro-pollutants is similar to that of the E-NF membrane in Example 1, but the membrane flux is far lower than that of the E-NF membrane in Example 1.

[0063] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described here.

Claims

1. A preparation method of a layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane, characterized in that, It includes the following steps: Step 1: Fabricate a hollow fiber ultrafiltration membrane module using a polytetrafluoroethylene hard tube and polyethersulfone hollow fiber ultrafiltration membrane filaments. Step 2: Prepare isopropanol solution, polyelectrolyte solutions with gradient concentrations, laccase solution, and glutaraldehyde solution. Step 3: Clean the hollow fiber ultrafiltration membrane module, and alternately deposit polyelectrolytes and laccase inside the hollow fiber membrane module using a syringe. Step 4: After the deposition of the last layer of polyelectrolyte is completed and the cleaning is done, inject glutaraldehyde solution and laccase solution between the polyelectrolyte layers in sequence to obtain an asymmetric polyelectrolyte gradient-deposited layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane.

2. The preparation method of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane according to claim 1, characterized in that, The specific operation of Step 1 is as follows: Arrange polyeethersulfone hollow fiber membrane filaments with a length of 45 - 50 cm parallelly in a polytetrafluoroethylene hard tube with a length of 25 - 30 cm soaked in absolute ethanol, and perform end vacuum encapsulation using a two-component epoxy resin. After curing, cut off the membrane filaments and the gelled part at the tail end that exceed the length of the hard tube, trim both ends flat. The effective length of the membrane module is 25 cm, and let it stand for drying for 24 h.

3. The preparation method of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane according to claim 1, characterized in that, The specific operation of Step 2 is as follows: Dilute isopropanol with deionized water to prepare a 25% isopropanol solution. Dissolve 0.05 - 0.25 g of polyelectrolyte sodium polystyrene sulfonate and 0.05 - 0.25 g of poly(dimethyldiallylammonium chloride) respectively with 14.625 g of sodium chloride in water, and dilute to 500 mL with deionized water and then stir to obtain sodium polystyrene sulfonate solution and poly(dimethyldiallylammonium chloride) solution. Dissolve 0.01 - 0.08 g of laccase powder in 0.1 M phosphate buffer solution with pH = 5.3 and dilute to 100 mL and then stir to obtain laccase solution. Dilute 50% glutaraldehyde solution with deionized water to prepare a 0.5% glutaraldehyde solution.

4. The preparation method of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane according to claim 1, characterized in that The specific operation of Step 3 is as follows: S1: Clean the hollow fiber ultrafiltration membrane module with isopropanol solution for 30 min, and then clean it with deionized water for 5 min. S2: Inject the sodium polystyrene sulfonate solution into the inner cavity of the hollow fiber ultrafiltration membrane module, let it stand for 5 min, and then clean the inner cavity of the membrane module with deionized water for 5 min. Then inject the laccase solution into the membrane module, let it stand at 25 °C for 1 h, and then rinse the inner cavity of the membrane module with deionized water for 5 min to form a polyanionic electrolyte sodium polystyrene sulfonate coating. S3: Inject the poly(dimethyldiallylammonium chloride) solution into the inner cavity of the polyanionic electrolyte sodium polystyrene sulfonate coating of the hollow fiber ultrafiltration membrane module, let it stand for 5 min, and then clean the inner cavity of the membrane module with deionized water for 5 min. Then inject the laccase solution into the membrane module, let it stand at 25 °C for 1 h, and then inject deionized water to rinse the inner cavity of the membrane module for 5 min. A polycationic electrolyte poly(dimethyldiallylammonium chloride) coating is formed on the polyanionic electrolyte sodium polystyrene sulfonate coating to complete the first double-layer coating. S4. Repeat S2 and S3 to construct a [sodium polystyrene sulfonate / laccase / poly(dimethyldiallylammonium chloride) / laccase] membrane according to the required number of layers and the polyelectrolyte concentration required for each layer. n membrane.

5. The preparation method of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane according to claim 1, wherein, Step 4 specifically includes: after the deposition of the last layer of polyelectrolyte is completed and the membrane is washed, glutaraldehyde solution is injected into the lumen of the membrane. After contacting the surface of the lumen of the membrane for 5 min, the unreacted glutaraldehyde solution is removed with deionized water. Then, laccase solution is injected and left standing at 25 °C for 1 h to immobilize the laccase. Finally, it is washed with deionized water to obtain an asymmetric polyelectrolyte gradient-deposited layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane.

6. Use of the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane prepared by the preparation method according to any one of claims 1-5 for removing organic micro-pollutants, characterized in that, The layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane is applied to the removal of organic micropollutants. Among them, the layer-by-layer self-assembled enzyme-catalyzed nanofiltration membrane module is connected to a small hollow fiber nanofiltration cross-flow filtration system through a peristaltic pump.

7. The application of the layer-by-layer self-assembled nanofiltration membrane for removing organic micro-pollutants according to claim 6, wherein, The types of organic micropollutants are bisphenol A, atrazine, carbamazepine, and ibuprofen.

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