CN114904402B - A layer-by-layer self-assembled slow-release antibacterial polymer separation membrane and its preparation method and application - Google Patents

Abstract

The invention discloses a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane, and a preparation method and application thereof. The preparation method of the invention comprises the following steps: immersing a polymer separation membrane in a mixed solution of a polyphenol compound and polyethyleneimine to functionalize the surface of the polymer separation membrane; and then, the polysaccharide and the antibacterial peptide are loaded on the surface of the base film in a layer-by-layer self-assembly mode by utilizing the physical adsorption and electrostatic interaction between the polysaccharide with negative charges and the antibacterial peptide with positive charges, so that the polymer separation film with antibacterial and anti-biological pollution performance is obtained. The antibacterial capability and the anti-pollution capability of the modified polymer separation membrane are obviously improved, and the modified polymer separation membrane has obvious inhibition effect on the propagation of bacteria and microorganisms. The invention adopts the layer-by-layer self-assembly technology to perform antibacterial modification, has mild reaction and simple operation, and the prepared polymer separation membrane modified layer is adjustable and controllable, has good antibacterial and anti-pollution properties and has good application prospect in the field of water treatment.

Description

A layer-by-layer self-assembled slow-release antibacterial polymer separation membrane and its preparation method and application

Technical field

The invention relates to a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane and its preparation method and application, and belongs to the technical field of water treatment.

Background technique

Membrane separation technology has the characteristics of simple process, low energy consumption, green and high efficiency, and has been widely used in the field of water treatment. However, membrane pollution is still a major obstacle to the development of membrane separation technology, especially biological pollution caused by the adhesion and growth of bacteria in the separation liquid on the membrane surface, which seriously affects membrane separation efficiency and operating life. Therefore, finding a preparation method for a separation membrane with excellent performance, long-term antibacterial and anti-pollution properties has become a hot topic in the field of membrane preparation at this stage.

Layer-by-layer self-assembly uses the method of alternate deposition layer by layer, with the help of weak interactions between molecules (such as electrostatic attraction, hydrogen bonds, coordination bonds, etc.), to spontaneously combine between layers to form a complete structure, stable performance, The process of forming molecular aggregates or supramolecular structures with a specific function. The preparation method of layer-by-layer self-assembly is simple, and the preparation process does not require complicated equipment; the film-forming materials are rich, and the polyelectrolyte material can be either natural protein, cellulose, polysaccharide tissue, or artificially synthesized high molecular polymer. In addition, the conditions are controllable, the assembly process is not controlled by the size and material of the substrate, and the structure and properties of the assembly system can be controlled at the molecular level. For example, the invention patent publication CN 113731190 A uses nanocellulose as the membrane-making unit to construct a nanocellulose membrane material with a hydrophilic surface through a layer-by-layer self-assembly method; the invention patent publication CN114292428 A uses a layer-by-layer self-assembly method to construct a nanocellulose membrane material with a hydrophilic surface. The comb polymer quaternized cellulose nanocrystals loaded with hydrophobic antibacterial active substances are combined with the cellulose nanofiber-chitosan base layer to produce an antibacterial film with certain mechanical properties and barrier properties. However, the modification process of the above preparation method is complicated and the long-term stability is poor, which is not conducive to commercial production.

As an emerging class of antibacterial drugs, antimicrobial peptides have the advantages of high-efficiency, green, and broad-spectrum antibacterial properties, and can kill some viruses, bacteria, fungi, and protozoa. It is generally believed that most antimicrobial peptides are positively charged and act on anionic bacterial membranes to cause disruption of bacterial membrane potential, changes in membrane permeability and leakage of metabolites, ultimately leading to bacterial death. At present, there are few reports on the use of antimicrobial peptides to prepare antibacterial and antibiofouling membranes.

Contents of the invention

The purpose of the present invention is to provide a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane and a preparation method thereof. The modified polymer separation membrane has significantly improved antibacterial and anti-pollution capabilities, and has a significant effect on the reproduction of bacteria and microorganisms. The inhibitory effect; by regulating the reaction conditions and the number of self-assembly layers to control the loading and release of antimicrobial peptides, a certain sustained release effect can be achieved. The present invention uses layer-by-layer self-assembly technology for antibacterial modification, with mild reaction and simple operation. The prepared polymer separation membrane modified layer is controllable, has good antibacterial and anti-pollution properties, and has potential wide application value in the field of water treatment.

In order to achieve the above objects, the present invention provides a method for preparing a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane, which includes the following steps:

Step 1: Use the polymer separation membrane as the base membrane, soak one side of the base membrane in a mixed solution of polyphenol compounds and polyethyleneimine for reaction to obtain a surface functionalized base membrane, wash it clean and set aside for use;

Step 2: Soak the surface functionalized base membrane obtained in Step 1 into a polysaccharide solution for reaction to obtain a polymer separation membrane with a polysaccharide coating on the surface, and wash it clean with water, wherein the polysaccharide solution contains negatively charged polysaccharides;

Step 3: React the antimicrobial peptide solution with the polymer separation membrane with a polysaccharide coating on the surface obtained in step 2 to form a polymer separation membrane with an antimicrobial peptide layer on the surface, and wash it clean with water, wherein the antimicrobial peptide solution contains Positively charged antimicrobial peptides;

Step 4: Repeat steps 2 and 3 for several cycles, and then repeat step 2 again to obtain a polysaccharide/antimicrobial peptide layer-by-layer self-assembled polymer separation membrane with a polysaccharide coating as the outermost layer;

Step 5: Soak the polymer separation membrane obtained in Step 4 in the cross-linking agent solution for reaction. After the reaction is completed, wash with water and dry to obtain a sustained-release antibacterial polymer separation membrane.

Preferably, the base film in step 1 is a PVDF film, PES film or PAN film.

Preferably, the mass concentration of polyphenolic compounds and polyethylenimine in the mixed solution of step 1 is 0.1 to 0.3%, the pH value of the mixed solution is 8 to 9, and the polyphenolic compounds are dopamine, At least one of catechol and tannic acid.

More preferably, the pH value of the mixed solution is adjusted using Tris-HCl buffer.

Preferably, the mass concentration of the polysaccharide solution in step 2 is 0.05% to 0.5%, and the polysaccharide contained in the polysaccharide solution is at least one of sodium alginate, chondroitin sulfate and dextran sulfate.

More preferably, the mass concentration of the polysaccharide solution is 0.05% to 0.1%.

Preferably, the concentration of the antimicrobial peptide solution in step 3 is 0.02-1.0g/L, the pH value of the antimicrobial peptide solution is 4.5-6, and the antimicrobial peptide contained in the antimicrobial peptide solution is selected from Ponericin G1, Magainin 2 and at least one of Cecropin B.

More preferably, the antimicrobial peptide solution is prepared using sodium acetate buffer.

Preferably, the mass concentration of the cross-linking agent solution in step 5 is 0.5 to 3%, and the cross-linking agent solution is at least one of CaCl ₂ solution and MgCl ₂ solution.

Preferably, the reaction conditions in step 1 are: reaction at 20-30°C for 3-5 hours; the reaction conditions in steps 2, 3 and 5 are: reaction at 20-30°C for 5-20 minutes.

Preferably, the number of cycles of step 2 and step 3 is 3 to 30 times.

The invention also provides a sustained-release antibacterial polymer separation membrane prepared by the above preparation method.

The present invention also provides the application of the above-mentioned sustained-release antibacterial polymer separation membrane in water treatment or water treatment devices.

The present invention also provides a water treatment device, which includes the above-mentioned sustained-release antibacterial polymer separation membrane.

Compared with the prior art, the beneficial effects of the present invention are:

(1) Antimicrobial peptides are cationic small molecule polypeptides with strong antibacterial effects. They inhibit bacteria through contact lethality and have broad-spectrum and efficient antibacterial effects. The separation membrane preparation method of the present invention innovatively uses antibacterial peptides as A green, pollution-free, broad-spectrum antibacterial agent that does not cause bacterial resistance. It uses a layer-by-layer self-assembly method to cyclically assemble antibacterial peptides and polysaccharides. It successfully introduces antibacterial functions into polymer separation membranes and improves the antibacterial resistance of the membrane. pollution performance;

(2) The present invention utilizes the negatively charged characteristics of polysaccharides and the positively charged characteristics of antimicrobial peptides to load antimicrobial peptides through physical adsorption and electrostatic interaction so that the polymer separation membrane obtains antimicrobial properties. The thickness of the formed antimicrobial layer is controllable and is not easy to fall off;

(3) The polymer separation membrane prepared by the present invention can regulate the release rate of antimicrobial peptides by changing the reaction conditions and the number of self-assembled layers to achieve the effects of delaying the release rate and prolonging the antibacterial time;

(4) The modified polymer separation membrane of the present invention has good antibacterial properties and has obvious inhibitory and killing effects on microorganisms such as Escherichia coli and Staphylococcus aureus;

(5) The membrane production process of the present invention is simple, easy to operate, low-cost equipment, good controllability, easy to implement industrially, and will not significantly change the water permeability of the separation membrane.

Description of the drawings

Figure 1 is a graph showing the calculated antibacterial efficiency of Escherichia coli after 12 hours of cultivation using the turbidity method to measure the polymer separation membrane prepared in Example 1 of the present invention after it was placed in a 24-well plate;

Figure 2 shows the release amount of antimicrobial peptides loaded in the PBS solution over time in the membrane samples of membranes M2, M3 and M4 in Example 1;

Figure 3 shows the changes in swelling degree and water permeability of the membrane as the number of LbL self-assembly cycles increases in Example 4;

Figure 4 is a graph showing the calculated antibacterial efficiency of E. coli after culturing for 12 hours after the polymer separation membrane prepared in Example 5 was placed in a 24-well plate;

Figure 5 shows the release amount of antimicrobial peptides loaded in the PBS solution over time in the membrane samples of membranes M5, M6, M7 and M8 in Example 5.

Figure 6 Changes in swelling degree and water permeability of the membrane with the mass concentration of sodium alginate.

Detailed ways

In order to make the present invention more obvious and understandable, preferred embodiments are described in detail below along with the accompanying drawings.

Example 1

Soak the PVDF separation membrane in clean water for 24 hours to remove impurities on the surface of the PVDF separation membrane (recorded as M0). Place the pretreated separation membrane in a polytetrafluoroethylene closed box (single-sided reaction box), add 1g/L dopamine and 1g/L polyethylenimine, and use Tris-HCl (50mM) to adjust pH = 8.5 Then, place it in a shaker and react for 4 hours at 120 rpm and 20°C until there is a yellow-brown PDA/PEI layer on the membrane. Afterwards, it was rinsed three times with deionized water and dried with _N2 to obtain a dopamine/polyethylenimine-coated PVDF separation membrane (marked as M1). Prepare 30mL of 0.1wt% sodium alginate solution, then prepare 0.05g/L Ponericin G1 in 0.1M sodium acetate buffer to obtain an antimicrobial peptide solution, and then place the obtained dopamine/polyethylenimine PVDF separation membrane alternately on the seaweed React in the sodium acid solution for 5 minutes and in the antimicrobial peptide solution for 10 minutes. After one reaction, rinse with deionized water for 1 minute. Repeat the assembly of sodium alginate and antimicrobial peptides for 10 cycles and then place the membrane in the sodium alginate solution for one more reaction. Then it was immersed in 15 mL of 2 wt% CaCl ₂ solution for cross-linking for 10 min. After washing with deionized water, an antimicrobial peptide/sodium alginate multilayer modified PVDF membrane (marked as M2) was obtained.

M3: After changing the reaction time between the above membrane and the antimicrobial peptide solution to 15 minutes, repeat the above process to obtain the antimicrobial peptide/sodium alginate multilayer modified PVDF membrane under different conditions (marked as M3).

M4: Keep the reaction time between the membrane and the antimicrobial peptide solution at 10 minutes, change the concentration of the above antimicrobial peptide solution to 0.1g/L, repeat the above process, and obtain the antimicrobial peptide/sodium alginate multilayer modified PVDF membrane under different conditions (note for M4).

Example 2

Antibacterial performance test: The turbidity method was used to determine the antibacterial performance of the membrane prepared in Example 1 against Escherichia coli. The operation was as follows. The model bacterial nutrient broth suspension was cultured at 37°C for 24 hours. The cultured bacterial liquid was diluted 10 ⁴ times with PBS to obtain a bacterial suspension (10 ⁵ cells/mL). Then the membrane sample was placed in a 24-well plate. For each group of membrane samples, 3 parallel samples were added, 1 mL of broth culture medium and 100 μL of bacterial liquid were added, and then placed in a shaker and cultured at 37°C and 100 rpm for 12 hours. Take out the culture medium, observe the bacterial density, use a microplate reader to compare the color of the culture medium at 600nm, and calculate its antibacterial efficiency.

The test results are shown in Figure 1. It can be seen that the membranes M0 and M1 obtained in Example 1 have no obvious inhibitory effect on E. coli. The membrane M2 obtained in Example 1 has no obvious inhibitory effect on E. coli. The membranes M3 and M4 obtained in Example 1 have no obvious inhibitory effect on E. coli. Escherichia coli has a significant inhibitory effect.

Example 3

Release experiment of antimicrobial peptides in antibacterial modified membranes: Select membranes M2, M3 and M4 prepared in Example 1 and cut them into membrane samples with an area of ^0.5cm2 , add 1mL PBS solution to a 24-well plate, and cut the membrane samples Put it into the solution and place it on a constant temperature shaker at 37°C and 100rpm. Take out the membrane samples at 1h, 2h, 4h, 8h, and 12h respectively, detect the concentration of antimicrobial peptides in the PBS in the wells, and then put the taken out membrane samples into new 1mL PBS. Calculate the release amount of antimicrobial peptides loaded in the antimicrobial modified membrane over time based on the experimental results.

In the antimicrobial peptide release experiment, the antimicrobial peptides of the membranes M2, M3 and M4 prepared in Example 1 were rapidly released within 2 hours, and the release amount of M2 was smaller than that of M3 and M4; in the membrane M2 prepared in Example 1, The antimicrobial peptides were basically released within 4 hours, while the antimicrobial peptides in membranes M3 and M4 were continuously released within 12 hours. It can be seen that appropriately extending the reaction time between the membrane and the antimicrobial peptide solution or increasing the concentration of the antimicrobial peptide solution can increase the loading capacity of the antimicrobial peptide. The antimicrobial peptide release experiment corresponds to the antibacterial performance experiment results.

Example 4

Soak the PVDF separation membrane in clean water for 24 hours to remove impurities on the surface of the PVDF separation membrane (recorded as M0). Place the pretreated separation membrane in a polytetrafluoroethylene closed box (single-sided reaction box), add 1g/L dopamine and 1g/L polyethylenimine, and use Tris-HCl (50mM) to adjust pH = 8.5 Then, place it in a shaker and react for 4 hours at 120 rpm and 20°C until there is a yellow-brown PDA/PEI layer on the membrane. Then rinse it three times with deionized water and blow dry with _N2 to obtain a dopamine/polyethylenimine-coated PVDF separation membrane. Prepare 30mL of 0.05wt% sodium alginate solution, and then prepare 0.05g/LPonericin G1 in 0.1M sodium acetate buffer to obtain an antimicrobial peptide solution (pH = about 5.1), and then separate the obtained dopamine/polyethylenimine PVDF The membrane was alternately placed in the sodium alginate solution for 5 minutes and the antimicrobial peptide solution for 10 minutes. After one reaction, it was washed with deionized water for 1 minute. The assembly was repeated for 5, 10, 15, and 20 cycles before the membrane was placed in alginic acid. React once in sodium solution, and then immerse in 15 mL of 2wt% CaCl ₂ for cross-linking for 10 min. After cleaning, antibacterial peptide/sodium alginate multilayer modified PVDF membranes with self-assembly cycle numbers n=5, 10, 15, and 20 were obtained respectively ( n is the number of LbL self-assembly cycles).

Swelling degree test: At 25°C, dry a 2cm×3cm membrane sample at 40°C to a constant weight, record the mass W ₀ , then soak it in deionized water for 24 hours, take it out and use filter paper to absorb the moisture on the surface. , write down the mass W ₁ , and calculate the membrane swelling ratio (SR) as follows:

In the formula, W ₁ and W ₀ represent the mass of the film in the wet state and dry state respectively. The swelling of the membranes was analyzed and compared based on the calculated swelling ratio.

The results are shown in Figure 3. It can be seen from the test results that as the number of LbL self-assembly cycles increases, the swelling degree of the modified membrane gradually increases. This shows that as the self-assembly number of the antimicrobial peptide/sodium alginate multilayer modified membrane increases, the hydrogel layer on its surface will increase when in water, thereby strengthening the barrier performance of the membrane and improving the anti-pollution and anti-pollution properties of the membrane. Anti-adhesion.

Water permeability test: Use dead-end filtration to test the water permeability of the membrane. Place the membrane sample in the ultrafiltration cup, connect the pipe, pour in deionized water, adjust the nitrogen tank so that the membrane is prepressed with deionized water for about 30 minutes under a stable pressure of 20kPa, and then test the water that penetrates the membrane within a certain period of time. volume until the outlet water volume remains consistent, indicating that the water flux has stabilized. The water permeability is calculated according to J=V/Stp, where J is the water permeability of the membrane under a specific pressure (L/(m ² h·kPa)), V is the volume of water permeating the membrane within t time (L), S is the membrane area through which water passes (m ² ), t is the measurement time (h), and p is the stable pressure during testing (kPa).

The test results are shown in Figure 3. It can be seen from the figure that when the number of LbL self-assembly cycles is less than 10, the water permeability of the antimicrobial peptide/sodium alginate multilayer modified membrane is basically consistent with that of the base film; conversely, its water permeability begins decreasing gradually. Although the water permeability of the antimicrobial peptide/sodium alginate multilayer modified membrane will be affected by the number of assembly layers, even when the number of LbL self-assembly cycles is 20, it can still maintain 74.1% of the water permeability of the base membrane, still Has good water permeability. This shows that the antimicrobial peptide/sodium alginate modified layer will not significantly affect the basic performance of the membrane. On the contrary, by regulating the number of LbL self-assembly cycles, antimicrobial peptides/alginic acid can be simultaneously endowed without affecting the basic performance of the membrane. Sodium multilayer modified membrane has excellent anti-biofouling properties.

Example 5

Soak the PVDF separation membrane in clean water for 24 hours to remove impurities on the surface of the PVDF separation membrane (recorded as M0). Place the pretreated separation membrane in a polytetrafluoroethylene closed box (single-sided reaction box), add 1g/L dopamine and 1g/L polyethylenimine, and use Tris-HCl (50mM) to adjust pH = 8.5 Then, place it in a shaker and react for 4 hours at 120 rpm and 20°C until there is a yellow-brown PDA/PEI layer on the membrane. Then rinse it three times with deionized water and blow dry with _N2 to obtain a dopamine/polyethylenimine-coated PVDF separation membrane. Prepare 30 mL of 0.05wt% sodium alginate solution respectively, and then prepare 0.05g/L Ponericin G1 in 0.1M sodium acetate buffer to obtain an antimicrobial peptide solution, and then place the obtained dopamine/polyethylenimine PVDF separation membranes alternately. React in sodium alginate solution for 5 minutes and antimicrobial peptide solution for 10 minutes. After one reaction, rinse with deionized water for 1 minute. Repeat assembly for 5 or 15 cycles respectively, then place the membrane in sodium alginate solution for one reaction, and then Immerse in 15 mL of 2wt% CaCl ₂ for cross-linking for 10 min. After cleaning, self-assembly cycle number n=5 and 15 antimicrobial peptide/sodium alginate multilayer modified PVDF membranes (marked as M5 and M6) were obtained.

Change the mass concentration of the above sodium alginate solution to 0.1wt%, repeat the above process, and obtain antimicrobial peptide/sodium alginate multilayer modified PVDF membranes under different conditions. The number of self-assembly cycles obtained under these conditions is n=5, 15 The antimicrobial peptide/sodium alginate multilayer modified PVDF membranes are marked as M7 and M8 respectively.

The antibacterial performance of the membrane was tested with reference to Example 2. The results are shown in Figure 4. The prepared membranes M5 and M7 had no obvious inhibitory effect on E. coli, while the membranes M6 and M8 had obvious inhibitory effect on E. coli. It can be explained that when the number of self-assembled layers is large, the modified membrane can ensure a good antibacterial effect.

A release experiment of antimicrobial peptides was performed with reference to Example 5. The results are shown in Figure 5. It can be clearly seen that more self-assembly layers result in a greater total amount of antimicrobial peptides loaded on the modified membrane. The antimicrobial peptide release experiment corresponds to the antibacterial performance experiment results.

Example 6

Soak the PVDF separation membrane in clean water for 24 hours to remove impurities on the surface of the PVDF separation membrane (recorded as M0). Place the pretreated separation membrane in a polytetrafluoroethylene closed box (single-sided reaction box), add 1g/L dopamine and 1g/L polyethylenimine, and use Tris-HCl (50mM) to adjust pH = 8.5 Then, place it in a shaker and react for 4 hours at 120 rpm and 20°C until there is a yellow-brown PDA/PEI layer on the membrane. Then rinse it three times with deionized water and blow dry with _N2 to obtain a dopamine/polyethylenimine-coated PVDF separation membrane. Prepare 30mL of 0.5wt% sodium alginate solution, and then prepare 0.05g/L Ponericin G1 in 0.1M sodium acetate buffer to obtain an antimicrobial peptide solution, and then place the obtained dopamine/polyethylenimine PVDF separation membrane alternately React in sodium alginate solution for 5 minutes and antimicrobial peptide solution for 10 minutes. After one reaction, rinse with deionized water for 1 minute. Repeat assembly for 5 cycles, then place the membrane in sodium alginate solution for one reaction, and then immerse in 15 mL of _Cross- linked with 2wt% CaCl for 10 minutes, and after cleaning, an antimicrobial peptide/sodium alginate multilayer modified PVDF membrane with a self-assembly cycle number n=5 at a concentration of 0.5wt% sodium alginate was obtained.

Refer to the test method of Example 4 to test the swelling degree and water permeability of the membrane. The test results are shown in Figure 6. It can be seen from the figure that the swelling degree and water permeability of the antimicrobial peptide/sodium alginate multilayer modified membrane are affected by the mass concentration of sodium alginate. When the mass concentration of sodium alginate is 0.05wt%, the modified membrane The water permeability of the base film has little impact; when the concentration is 0.5wt%, its water permeability is reduced to one-third of that of the base film, which greatly affects the basic performance of the membrane. Therefore, the mass concentration of the sodium alginate solution is preferably 0.05wt% to 0.1wt%.

The above embodiments are only preferred embodiments of the present invention, and do not limit the present invention in any form or substance. It should be pointed out that those of ordinary skill in the art can also make other modifications without departing from the present invention. There are several improvements and supplements, which should also be considered as the protection scope of the present invention.

Claims (7)

1. A method for preparing a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane, characterized in that the method includes the following steps: Step 1: Use the polymer separation membrane as the base membrane, and soak one side of the base membrane in React in a mixed solution of polyphenols and polyethyleneimine to obtain a surface functionalized base film, which is washed and ready for use; Step 2: Soak the surface functionalized base membrane obtained in Step 1 into a polysaccharide solution for reaction to obtain a polymer separation membrane with a polysaccharide coating on the surface, and wash it clean with water, wherein the polysaccharide solution contains negatively charged polysaccharides; Step 3: React the antimicrobial peptide solution with the polymer separation membrane with a polysaccharide coating on the surface obtained in step 2 to form a polymer separation membrane with an antimicrobial peptide layer on the surface, and wash it clean with water, wherein the antimicrobial peptide solution contains Positively charged antimicrobial peptides; Step 4: Repeat steps 2 and 3 for several cycles, and then repeat step 2 again to obtain a polysaccharide/antimicrobial peptide layer-by-layer self-assembled polymer separation membrane with a polysaccharide coating as the outermost layer; Step 5: Soak the polymer separation membrane obtained in Step 4 in the cross-linking agent solution for reaction. After the reaction is completed, wash with water and dry to obtain a sustained-release antibacterial polymer separation membrane; Wherein, the mass concentration of polyphenolic compounds and polyethylenimine in the mixed solution of step 1 is 0.1 to 0.3%, the pH value of the mixed solution is 8 to 9, and the polyphenolic compounds are dopamine, At least one of tea phenol and tannic acid; The mass concentration of the polysaccharide solution in step 2 is 0.05% to 0.5%, and the polysaccharide contained in the polysaccharide solution is at least one of sodium alginate, chondroitin sulfate and dextran sulfate; The concentration of the antimicrobial peptide solution in step 3 is 0.02-1.0g/L, the pH value of the antimicrobial peptide solution is 4.5-6, and the antimicrobial peptides contained in the antimicrobial peptide solution are selected from Ponericin G1, Magainin 2 and Cecropin At least one of B. 2. The method for preparing a layer-by-layer self-assembled slow-release antibacterial polymer separation membrane according to claim 1, characterized in that the base film in step 1 is a PVDF film, a PES film or a PAN film. 3. The preparation method of a layer-by-layer self-assembled sustained-release antibacterial polymer separation membrane according to claim 1, characterized in that the mass concentration of the cross-linking agent solution in step 5 is 0.5-3%, and the cross-linking agent solution is 0.5-3%. The joint agent solution is at least one of CaCl ₂ solution and MgCl ₂ solution. 4. The preparation method of layer-by-layer self-assembled slow-release antibacterial polymer separation membrane according to claim 1, characterized in that the reaction conditions in step 1 are: reaction at 20-30°C for 3-5 hours; The reaction conditions in steps 2, 3 and 5 are: react at 20-30°C for 5-20 minutes. 5. The sustained-release antibacterial polymer separation membrane prepared by the preparation method according to any one of claims 1 to 4. 6. Application of the slow-release antibacterial polymer separation membrane according to claim 5 in water treatment or water treatment equipment. 7. A water treatment device, characterized by comprising the sustained-release antibacterial polymer separation membrane according to claim 5.