Preparation method of PS-b-PAA and modified aramid fiber porous membrane and antibacterial membrane thereof

Abstract

The invention discloses a PS-b-PAA preparation method and a modified aramid fiber porous membrane and an antibacterial membrane thereof.The preparation method comprises the steps that firstly, an amphiphilic block copolymer PS-b-PAA is successfully synthesized through a reversible addition fragmentation chain transfer (RAFT) method, the amphiphilic block copolymer PS-b-PAA serves as a modifying agent to be blended into a membrane casting solution, a PMIA porous ordered membrane is prepared through a non-solvent induced phase separation method, and then the PS-b-PAA porous ordered membrane is prepared. The permeability of the modified PS-b-PAA / PMIA membrane is greatly improved, and the modified PS-b-PAA / PMIA membrane is excellent in permeability and good in mechanical property. Furthermore, Ag NPs is loaded on the PS-b-PAA / PMIA membrane through dopamine to prepare the Ag NPs / PS-b-PAA / PMIA antibacterial membrane, the antibacterial rate of the Ag NPs / PS-b-PAA / PMIA antibacterial membrane on escherichia coli within a certain time reaches 98.17 + / -1.24%, and the membrane has a good antibacterial effect on escherichia coli, can prevent a biological membrane from being formed on the surface of the membrane, and avoids biological pollution.

Description

Technical Field

[0001] The present invention relates to a copolymer and a porous membrane modified based thereon, specifically to a preparation method of PS-b-PAA, and a PMIA porous membrane, an antibacterial membrane modified thereby, and their preparation methods; it belongs to the technical field of novel membrane materials. Background Art

[0002] PS-b-PAA (polystyrene-b-polyacrylic acid) is an amphiphilic block copolymer, which is formed by combining a hydrophobic polystyrene (PS) segment and a hydrophilic polyacrylic acid (PAA) segment through a block copolymerization technique. Its unique structure endows the material with multifunctional physical and chemical properties, and it is widely used in the fields of biomedicine and materials science. However, this material has not been domesticated yet, mostly relying on imports, with a very high cost. There are problems such as harsh reaction conditions and high difficulty in controlling the block ratio and structure, and it is difficult to achieve molecular weight uniformity at the laboratory level.

[0003] The PS-b-PAA / PMIA membrane is a highly ordered porous membrane, which combines the composite functions of the amphiphilic block copolymer PS-b-PAA and the high-performance polymer meta-aramid (PMIA), and can achieve performance complementarity and function integration. However, it is easily contaminated by organisms during actual use, so it is necessary to prepare a membrane with antibacterial properties. Although silver nanoparticles have good antibacterial properties, their compatibility with the PMIA membrane is poor during use, which will lead to uneven dispersion of silver nanoparticles on the membrane surface and easy loss from the membrane surface, thus causing the antibacterial membrane to lose its antibacterial properties. In a solution environment, the PAA end group of PS-b-PAA contains a carboxyl group, and the oxygen atom in the carboxyl group has a lone pair of electrons, which can form a stable coordination bond with Ag + to form a stable coordination bond (such as [Ag(COO - )] complex), reducing the reduction potential of Ag + so that it is more easily reduced to Ag 0 nanoparticles; especially under alkaline conditions, the carboxyl group is deprotonated to COO - , enhancing the coordination ability with Ag + and promoting the reduction of Ag + to Ag 0 nanoparticles; in addition, the selective adsorption of the carboxyl group on different crystal planes can regulate Ag 0The morphology of silver nanoparticles (AgNPs), so by using a PS-b-PAA block copolymer with good compatibility with PMIA as a bridge for constructing an antibacterial film, and relying on the carboxyl functional groups of PS-b-PAA, in a coordinated-reduction synergistic manner, the in-situ reduction efficiency, dispersibility, and size uniformity of silver nanoparticles can be significantly improved, thereby obtaining a high-performance antibacterial film. For the above reasons, it is necessary to further develop independent research and development of copolymers to optimize the performance of PMIA porous membranes and improve the stability and uniform dispersion of silver nanoparticles on the surface of the antibacterial film. Summary of the Invention

[0004] To solve the deficiencies of the prior art, one of the objectives of the present invention is to provide a synthesis method for an amphiphilic block copolymer PS-b-PAA; the second objective is to prepare a PS-b-PAA / PMIA porous membrane by the non-solvent induced phase separation method; the third objective is to prepare an Ag NPs / PS-b-PAA / PMIA antibacterial film.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] The present invention first discloses a preparation method for an amphiphilic block copolymer PS-b-PAA, including the following technological processes:

[0007] (1) Synthesis of the PS segment: Add 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid DDMAT to purified styrene (SM), stir until completely dissolved to form Solution 1; then dissolve azobisisobutyronitrile AIBN in tetrahydrofuran, and then add Solution 1 thereto, stir until evenly mixed to form Solution 2; use a pipette to transfer Solution 2 to a Schlenk flask, place the Schlenk flask in an oil bath, ensure that the mixture is completely immersed in the oil bath, react at 70 °C for 24 hours, then cool to normal temperature and pressure, and then wash with anhydrous methanol and tetrahydrofuran (THF), and dry in a vacuum drying oven to obtain a PS product;

[0008] (2) Synthesis of polystyrene-poly(tert-butyl acrylate) PS-PtBA: Add the dried PS product, AIBN, and purified tert-butyl acrylate (TBA) to THF and dissolve to a clear solution, transfer to a Schlenk flask, and place it in an oil bath at 65 °C for 24 hours. After the reaction is completed, wait for the Schlenk flask to cool to normal temperature and pressure, pour it into cold n-hexane, precipitate and filter; put the sample obtained from the reaction into a glass bottle, cover it with perforated tin foil, and dry it in an oven to obtain PS-PtBA;

[0009] (3) Hydrolysis of PS-PtBA: Dissolve PS-PtBA in THF, and then add HCl solution to the mixture; then carry out a reflux reaction by heating the mixture to 80 °C. After acid hydrolysis, precipitate PS-b-PAA in cold n-hexane and dry it in a vacuum oven to obtain the copolymer PS-b-PAA.

[0010] Preferably, the specific process of the foregoing purification operation is as follows: Block the glass dropper with absorbent cotton, fill the glass dropper with Al2O3 powder to a height of about 4 - 5 cm, then add the product to be purified into the filled column, and use an ear syringe to blow the product to be purified. The purification can be repeatedly performed multiple times.

[0011] More preferably, the Schlenk flask should be dehumidified and deoxygenated before operation. The specific operation process is as follows: Place the Schlenk flask in liquid nitrogen to freeze the mixture and solidify it, then use a vacuum pump to evacuate the air in the tube first, close the valve of the Schlenk flask, transfer it to thaw in normal temperature water, and then freeze it in liquid nitrogen again. After solidification, turn on the vacuum again. The above deoxygenation and dehumidification steps can be repeated multiple times.

[0012] Further preferably, the amphiphilic block copolymer PS-b-PAA prepared by the foregoing method has a molecular weight of 38702 Da and a polydispersity index of 1.26, and the relative molecular weight distribution of the PS-b-PAA polymer is relatively uniform.

[0013] The present invention also discloses a method for preparing the foregoing PS-b-PAA / PMIA porous membrane, including the following steps:

[0014] (1) Preparation of the casting solution: Dissolve a certain amount of LiCl in DMAc solvent, stir at high speed at room temperature until it is dissolved into a transparent solution, then add a certain amount of PS-b-PAA to the solution and continue to stir until it is dissolved into a homogeneous and stable solution. After adding PMIA, stir at high speed at 85 °C until it is dissolved into a homogeneous and stable casting solution, cool it to 25 °C, and let it stand for defoaming; the PS-b-PAA is prepared by the foregoing method;

[0015] (2) After complete defoaming, adopt the non-solvent induced phase separation method, use a glass rod to scrape on a smooth and flat glass plate, the thickness of the membrane is about 200 μm, the coagulation bath is deionized water, and the temperature is 25 °C. The prepared PMIA flat membrane is subjected to post-treatment operations such as soaking and cleaning, and stored in deionized water for standby.

[0016] Preferably, the mass percentage content of the foregoing PS-b-PAA does not exceed 0.5%.

[0017] The present invention also discloses a PS-b-PAA / PMIA porous membrane prepared by the foregoing method. The cross-section of the membrane includes a dense skin layer, a porous sublayer with a finger-like structure, and a macroporous support bottom layer. As the content of PS-b-PAA increases, the number of macropores in the membrane cross-section continuously increases, the connectivity between pores is stronger, and spherical substances gradually appear on the membrane surface, increasing the roughness.

[0018] The present invention also discloses a preparation method of an Ag NPs / PS-b-PAA / PMIA antibacterial membrane, comprising the following steps:

[0019] (1) Fix Ag NPs on the membrane surface by dip coating: Add silver nitrate solution into a container, immerse the PS-b-PAA / PMIA porous membrane prepared by the foregoing method into the silver nitrate solution, and oscillate it open in the air at room temperature to form a mixed solution;

[0020] (2) Drop dopamine aqueous solution into the foregoing mixed solution, then add NaOH solution thereto, wash the membrane with deionized water after a period of time, and dry it under room temperature environmental conditions to obtain an Ag NPs / PS-b-PAA / PMIA antibacterial membrane, which is stored in a dark room.

[0021] The method adopts an in-situ growth process, makes full use of the carboxyl groups that can be provided by the PAA end groups in the PS-b-PAA copolymer, and can better promote the uniform growth of silver nanoparticles, thereby obtaining an antibacterial membrane that is more prominent in terms of uniform antibacterial performance.

[0022] The present invention also requires the disclosure of an Ag NPs / PS-b-PAA / PMIA antibacterial membrane prepared by the foregoing method, characterized in that silver nanoparticles are loaded on the membrane surface, the hydrophilicity is better than that of the PS-b-PAA / PMIA porous membrane, and the antibacterial rate against Escherichia coli is as high as 98.17±1.24%.

[0023] The application of the PS-b-PAA / PMIA porous membrane as described in claim 6 in the field of high-temperature water treatment.

[0024] The advantages of the present invention are as follows:

[0025] (1) The present invention first successfully synthesizes an amphiphilic block copolymer PS-b-PAA by reversible addition-fragmentation chain transfer (RAFT) method. This copolymer basically relies on imports at present. The process of the present invention solves many defects in the prior art, such as harsh synthesis conditions, expensive raw materials and equipment, and high process costs, providing new ideas for material design and synthesis.

[0026] (2) The PS-b-PAA self-prepared in the present invention was used as a modifier and co-mixed into the casting solution. The non-solvent induced phase separation method was used to prepare the PMIA porous ordered membrane. The prepared PS-b-PAA / PMIA membrane was characterized by SEM and AFM. It was found that PS-b-PAA played a role in regulating the membrane pore structure. The prepared membrane had a highly ordered porous surface structure, and the cross-section of the membrane showed a typical asymmetric structure. The pore structure gradually evolved into a macroporous structure with the increase of the PS-b-PAA addition amount. Moreover, with the increase of the PS-b-PAA content, the surface roughness of the membrane increased.

[0027] (3) The permeation performance of the modified PS-b-PAA / PMIA porous membrane was greatly improved. And the examples showed that when the PS-b-PAA addition amount was 0.4 wt.%, it was the optimal example. The membrane had excellent permeation performance, good mechanical properties, and the rejection rate of 1000 mg / L BSA was above 95%, with good separation performance. However, due to membrane fouling and the poor hydrophilicity of the modified membrane, the FRR of the modified membrane was relatively low and the anti-fouling degree was poor. In addition, the PS-b-PAA / PMIA membrane prepared in the present invention also had excellent heat resistance and was applicable not only to general water treatment but also to the field of water treatment in high-temperature environments.

[0028] (4) Further, by providing an alkaline and redox reaction environment with dopamine solution, the catechol structure (two adjacent hydroxyl groups on the benzene ring) in dopamine molecules was oxidized to quinone under alkaline conditions (pH≥8), while releasing electrons (e - ) to reduce Ag + to Ag 0 nanoparticles. By using the carboxyl groups at the PAA end groups of PS-b-PAA in the solution environment, on the basis of improving the hydrophilicity of the membrane itself, it could also form stable coordination bonds with Ag + (such as [Ag(COO - )] complex), reducing the reduction potential of Ag + and making it easier to be reduced to Ag 0Nanoparticles (AgNPs), and the amino group (-NH2) and hydroxyl group (-OH) of dopamine can bind to the surface of AgNPs through coordination bonds or hydrogen bonds to form a stable organic-inorganic interfacial layer, preventing particle aggregation, coupling the pore-forming regulation of the copolymer with the uniform regulation of nanoparticle generation, and obtaining a more uniform and stable distribution of silver nanoparticles. The pure water flux and permeation performance of Ag NPs / M4 are slightly decreased compared with M0 without loaded Ag NPs, but it has better antibacterial performance. The antibacterial rate against Escherichia coli reaches 98.17±1.24% within a certain time, proving that the antibacterial membrane prepared by the present invention has a good antibacterial effect on Escherichia coli, can effectively inhibit the growth and reproduction of Escherichia coli, prevent the formation of biofilms on the membrane surface, and avoid biological contamination. Description of the Drawings

[0029] Figure 1 Synthesis route diagram of the block copolymer PS-b-PAA in Example 1;

[0030] Figure 2 1H NMR spectrum of the product in Example 1;

[0031] Figure 3 Infrared spectrum of the product in Example 1;

[0032] Figure 4 Gel permeation chromatography of the product in Example 1;

[0033] Figure 5 Surface SEM images of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0034] Figure 6 Cross-section SEM images of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0035] Figure 7 AFM three-dimensional images of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0036] Figure 8 Contact angle test result images of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0037] Figure 9 Test curves and pore size distribution diagrams of each PS-b-PAA / PMIA membrane in Examples 2 to 7 (MX - test curve, MX-1 - pore size distribution curve (X represents the membrane number));

[0038] Figure 10 Mechanical strength and tensile property diagrams of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0039] Figure 11 Thermogravimetric analysis curve diagrams of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0040] Figure 12 Diagrams of the pure water flux detection results of each PS-b-PAA / PMIA membrane in Examples 2 to 7;

[0041] Figure 13 Diagram of the pure water flux detection results of the PS-b-PAA / PMIA membrane M5 in Example 7 under different pressures;

[0042] Figure 14 Surface SEM images (magnification 1000) of the contaminated membranes M1 to M5;

[0043] Figure 15 Surface SEM images (magnification 10000) of the contaminated membranes M1 to M5;

[0044] Figure 16 Ultraviolet spectrum diagram of the AgNO3 / PDA / NaOH solution;

[0045] Figure 17 XPS spectrum diagrams, where (a) are the XPS spectrum diagrams of the membrane M4 and the Ag NPs / M4 membrane; (b) is the high-resolution XPS spectrum diagram of Ag;

[0046] Figure 18 Physical diagram, where (a) is the physical diagram of the membrane M4; (b) is the physical diagram of the Ag NPs / M4 membrane;

[0047] Figure 19 SEM images, where (a) is the SEM image of the membrane M4; (b) are the SEM images of the Ag NPs / M4 membrane at different magnifications (5000, 10000, 30000);

[0048] Figure 20 Test curves and pore size distribution diagrams of the membrane after loading silver nanoparticles (Ag NPs / MX - test curve, AgNPs / MX-1 - pore size distribution curve (X represents the membrane number));

[0049] Figure 21 A1 and A2 are the surface SEM images (magnifications are 5000 and 10000 respectively) of the M0 membrane loaded with Ag NPs, and B1 and B2 are the surface SEM images (magnifications are 5000 and 10000 respectively) of the M4 membrane loaded with Ag NPs;

[0050] Figure 22 For (a), it is the cross-section SEM image of the Ag NPs / M0 membrane, and for (b), it is the cross-section SEM image of the Ag NPs / M4 membrane;

[0051] Figure 23 The anti - Escherichia coli effect diagrams of membranes M0, M4 and Ag NPs / M4. Specific embodiments

[0052] The present invention will be specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

[0053] Unless otherwise specified in the present invention, all raw materials used are commercially available. Table 1 below shows the preferred material purchase channels.

[0054]

[0055]

[0056] Table 1 Raw material models and sources

[0057] Example 1

[0058] PS - b - PAA, as a high - cost rare raw material, currently mostly relies on imports. We use the process route diagram as shown in Figure 1 to achieve self - preparation by the reversible addition - fragmentation chain transfer (RAFT) method. The specific process is as follows:

[0059] (1) Synthesis of the PS segment

[0060] First, purify styrene. The specific operation steps are as follows: Use absorbent cotton to block the glass dropper, fill the glass dropper with Al2O3 powder to a height of about 4 - 5 cm, then drop about 20 mL of styrene into the filled column, and use an ear - bulb to blow - purge the styrene to complete one purification operation. To improve the purity of styrene, this purification operation step can be repeated multiple times. Then, weigh 26.52 mg of DDMAT and add it to the above - mentioned styrene, and shake until completely dissolved.

[0061] Next, dissolve 119 mg of AIBN in 1 mL of tetrahydrofuran to form Solution 1. Use a micro - syringe to measure 10 μL of purified polystyrene and add it to the above - mentioned AIBN mixed solution (contained in a glass bottle), stir until evenly mixed to form Solution 2. Then, use a pipette to transfer Solution 2 to a Schlenk flask. To ensure that all reactions are carried out in an anhydrous and anaerobic environment, it is necessary to dehumidify and deoxygenate the reaction Schlenk flask. The specific operation is as follows: Place the Schlenk flask in liquid nitrogen for freezing to solidify the mixture. Then, use a vacuum pump to evacuate the air in the tube first, close the valve of the Schlenk flask, transfer it to warm water for thawing, and then put it in liquid nitrogen for freezing again. After solidification, turn on the vacuum again and repeat the above deoxygenation and dehumidification steps 3 times. After completing the dehumidification and deoxygenation operations, place the Schlenk flask in an oil bath to ensure that the mixture is completely immersed in the oil bath and react at 70 °C for 24 hours.

[0062] After the reaction is completed, cool the Schlenk flask to room temperature. After restoring normal pressure, open the lid and pour it into anhydrous methanol. The anhydrous methanol needs to be refrigerated in advance in the refrigerator and then used. Filter the precipitate in the methanol, then put it into a glass bottle, cover it with perforated tin foil, and dry it in a vacuum oven at 70 °C. For the dried powder, add tetrahydrofuran dropwise, shake while adding until the PS segment is dissolved, then pour it into cold anhydrous methanol again, precipitate again and dry in vacuum to obtain the PS product.

[0063] (2) Synthesis of Polystyrene-Poly(n-butyl acrylate) (PS-PtBA)

[0064] First, adopt the above purification method of styrene to perform two purification operations on 0.5 mL of TBA.

[0065] Then, weigh 0.3 g of the dried PS product, 1.23 mg of AIBN, and 0.5 mL of TBA, add them to 2.5 mL of THF and dissolve to a clear solution, transfer it to a Schlenk flask. The deoxygenation and dehumidification operations are the same as those in the PS synthesis step, repeat 3 times, and then place it in an oil bath at 65 °C and react for 24 hours. After the reaction is completed, wait for the Schlenk flask to cool to room temperature, pour it into cold n-hexane (refrigerated in the refrigerator before use), precipitate once, and filter with filter paper.

[0066] Put the sample obtained from the reaction into a glass bottle, cover it with perforated tin foil, and dry it in a vacuum oven at 65 °C to obtain PS-PtBA.

[0067] (3) Hydrolysis of PS-PtBA

[0068] Hydrolyze PS-PtBA in acid to obtain PS-b-PAA. The specific operation is as follows: dissolve 0.2 g of PS-PtBA in 20 - 30 mL of THF, then add about 15 mL of 1 mol / L HCl solution to the mixture; then reflux the reaction mixture at 80 °C for 24 hours. After acid hydrolysis, PS-b-PAA precipitates in cold n-hexane and is dried in a vacuum oven at 65 °C for use and characterization.

[0069] Examples 2 to 7

[0070] Prepare PS-b-PAA / PMIA porous membranes through Examples 2 to 7. The technological processes of each example are basically the same, and the main difference lies in the dosage of each raw material. The specific mass percentage of each raw material is shown in Table 2.

[0071] The specific process operation steps are as follows: Dissolve a certain amount of LiCl in DMAc solvent, stir at high speed at room temperature until it is dissolved into a transparent solution, then add a certain amount of PS-b-PAA into the solution and continue to stir until it is dissolved into a homogeneous and stable solution. After adding PMIA, stir at high speed at 85 °C to dissolve it into a homogeneous and stable casting solution, cool down to 25 °C, and let it stand for degassing. After complete degassing, adopt the non-solvent induced phase separation method, and use a glass rod to scrape on a smooth and flat glass plate. The thickness of the membrane is about 200 μm, and the coagulation bath is deionized water with a temperature of 25 °C. After post-treatment operations such as soaking and cleaning, the prepared PMIA flat membrane is stored in deionized water for standby.

[0072] Serial number Membrane number PMIA (wt%) LiCl (wt%) DMAc (wt%) PS-b-PAA (wt%) Example 2 M0 12 3.5 84.5 0 Example 3 M1 12 3.5 84.4 0.1 Example 4 M2 12 3.5 84.3 0.2 Example 5 M3 12 3.5 84.2 0.3 Example 6 M4 12 3.5 84.1 0.4 Example 7 M5 12 3.5 84.0 0.5

[0073] Table 2 Different compositions and names of casting solutions

[0074] ※ Note: Due to the large molecular weight of PS-b-PAA, when the addition amount reaches 0.6 wt.%, the viscosity of the casting solution is too high to be used for membrane preparation.

[0075] Examples 8 - 9

[0076] Using M0 and M4 as the bottom membranes respectively, the Ag NPs / PS-b-PAA / PMIA antibacterial membranes of Examples 8 and 9 were prepared by the following process.

[0077] The specific process operation steps are as follows:

[0078] (1) Fix Ag NPs on the membrane surface by dip coating method: Add 100 mL of 20 mM silver nitrate solution into a container, immerse the previously prepared PS-b-PAA / PMIA porous membrane (M0 or M4) into this solution, and open it in the air and shake at 60 rpm / min at room temperature for 10 min;

[0079] (2) Drop 2 mL of dopamine aqueous solution with a concentration of 0.1 g / mL into the above-mentioned mixed solution, then add 0.4 mL of NaOH solution with a concentration of 4 g / L, wash the membrane with deionized water after 2 h, and dry it under room temperature environmental conditions to obtain the Ag NPs / PS-b-PAA / PMIA antibacterial membrane, which is stored in a dark room for use.

[0080] Structure and property characterization

[0081] (1) Characterize the product of Example 1 to determine whether PS-b-PAA is successfully synthesized, and characterize its molecular weight and distribution.

[0082] (1) Use a nuclear magnetic resonance spectrometer (Bruker Ascend 400 MHz, Germany) to test the hydrogen spectrum of the product of Example 1.

[0083] Figure 2 Shown is the 1H NMR spectrum of the synthesized PS-b-PAA. According to the chemical shift values, it can be obtained that: the signal peak at 7.26 ppm is the signal of the solvent CDCl3, the signal peaks in the region of 1.2 - 2.3 ppm represent the signals of methylene (-CH2) and methine (-CH) on the main chain, the peaks in the region of 6.4 - 7.2 ppm represent the proton signals on the benzene ring, and the appearance of the signal peak at 1.5 ppm indicates the proton signal in tert-butyl (-C(CH3)3), indicating that the tBA segment is successfully connected to the end of the PS segment and hydrolyzed to PS-b-PAA. It can be seen that 1 The appearance of each characteristic peak in the 1H NMR spectrum proves that PS-b-PAA has been successfully prepared and can be used as an amphiphilic asymmetric block copolymer additive for subsequent membrane preparation.

[0084] (2) Analyze the chemical structure of the product of Example 1 by Fourier transform infrared spectrometer (FTIR) and characterize the characteristic peak positions.

[0085] As Figure 3 shown, the stretching vibration in the range of 3025 - 3085 cm -1 is the C-H bond on the benzene ring; the absorption peak caused by the skeletal vibration on the benzene ring is in the region of 1450 - 1600 cm -1 ; the wave numbers at 699 cm -1 and 759 cm -1 are the out-of-plane bending vibration absorption peaks of five hydrogen atoms on the benzene ring. The characteristic peaks in the infrared spectrum of PS-b-PAA are as follows: two characteristic absorption peaks of tert-butyl -C(CH3)3 appear near 1368 cm -1 and 1392 cm -1 ; the symmetric stretching vibration absorption peak of ester group C-O-C(O) appears near 1151 cm -1 and the absorption peak caused by the asymmetric stretching vibration is near 1256 cm -1 ; meanwhile, the stretching vibration absorption peak of carbonyl C=O appears at 1725 cm -1 . These characteristic peaks all belong to the characteristic absorption of tert-butyl acrylate in the block copolymer. The absorption peak of C=O ester bond becomes stronger at 1731 cm -1 , which is consistent with the C=O absorption peak in the carboxyl group; the broad absorption band in the region of 2650 - 3450 cm -1 is caused by the free hydroxyl group and associated hydroxyl group (by hydrogen bond interaction) in the carboxyl group -COOH.

[0086] From the above NMR and infrared results, it can be seen that PS-b-PAA asymmetric block polymer has been successfully synthesized in Example 1.

[0087] (3) Characterization of the molecular weight and distribution of PS-b-PAA

[0088] The relative molecular weight and distribution of the synthesized PS-b-PAA were characterized by gel permeation chromatography (GPC, Waters 1515, USA). The results are as Figure 4 shown. It can be seen from the figure that the gel permeation chromatography spectrum of the synthesized copolymer PS-b-PAA presents a narrow and symmetric single peak. The molecular weight of the synthesized polymer PS-b-PAA is 38702 Da, and the distribution index is 1.26, indicating that the relative molecular weight distribution of the synthesized PS-b-PAA polymer is relatively uniform.

[0089] When characterizing the molecular weight of a polymer, the following parameters are often involved: number-average molecular weight (M n n), weight-average molecular weight (M w w), molecular weight of the highest peak (M p p). In addition, higher average molecular weights are M z z+1, M z+1 z+2, which can be defined by the following equations. When n = 1, M = Mw; when n = 2, M = Mz; when n = 3, M = M z+1 z+3. For all synthesized polydisperse polymers: Mn < Mw < Mz < M z+1 z+4. The various parameters of the polymer molecular weight obtained are shown in Table 3 and satisfy the above relationship.

[0090]

[0091] Table 3 Parameter values of the molecular weight of PS-b-PAA prepared in Example 1

[0092] In summary, the PS-b-PAA synthesized in Example 1 has typical block copolymer characteristics and a relatively uniform relative molecular weight.

[0093] (2) Characterization and performance testing of the PS-b-PAA / PMIA porous membranes prepared in Examples 2 to 7

[0094] (1) Microstructural characterization of the PS-b-PAA / PMIA membrane

[0095] To investigate the effects of the blending of the asymmetric block copolymer PS-b-PAA on the surface structure, skin layer pore size, and cross-section of the PMIA membrane, the microstructures of the prepared PS-b-PAA / PMIA membranes were characterized using a field emission scanning electron microscope, as Figure 5As shown, the surfaces of all the membranes exhibit a smooth and uniform porous structure. And compared with the blank control PMIA membrane M0 (Example 2), a more uniform and ordered porous structure appears on the surface of the PS-b-PAA / PMIA membrane. The applicant analyzed the reason as follows: As an amphiphilic block copolymer, during the preparation of the PS-b-PAA / PMIA membrane by non-solvent induced phase separation, the phase separation caused by the self-assembly coupling of the asymmetric block copolymer and the segregation during the film-forming process of the block copolymer formed a highly porous structure of the selective layer.

[0096] It should be noted in particular that spherical structures also appear on the surfaces of membranes M4 and M5. The applicant speculates that this is because as the concentration of PS-b-PAA increases, the number and size of block copolymer micelles in the casting solution increase, which also leads to an increase in the viscosity of the casting solution. The above phenomena indicate that the blending modification of the PMIA polymer with PS-b-PAA does not significantly change its self-assembly characteristics, enabling a more ordered porous structure to appear on the membrane surface.

[0097] The cross-sectional structures of the blank control PMIA membrane M0 and the modified PS-b-PAA / PMIA membranes are as Figure 6 shown. It can be observed that the prepared blank membrane M0 and the PS-b-PAA / PMIA membranes after blending modification both have the asymmetric structure typical of NIPS-prepared membranes. The cross-section includes a dense skin layer, a porous sublayer with a finger-like structure, and a macroporous support bottom layer. And as the content of PS-b-PAA increases, the number of macropores in the membrane cross-section also continuously increases, and the connectivity between the pores is enhanced. This shows that the synthesis of PS-b-PAA blending has little effect on the good film-forming performance of the PMIA polymer material, but its addition will affect the formation of macropores in the membrane. Especially for M5 with an addition amount of 0.5 wt.%, the macropores have already connected to each other. This type of macroporous structure is likely to cause a decrease in the mechanical properties of the membrane, resulting in a "collapse" phenomenon during the application of the membrane. Subsequent detection of the membrane mechanical strength also confirmed this point.

[0098] (2) Surface topological structure of the PS-b-PAA / PMIA porous membrane

[0099] The three-dimensional maps of AFM were used to analyze the surface morphology of the prepared PS-b-PAA / PMIA modified membranes, and to explore the influence of the copolymer PS-b-PAA additive on the surface morphology and roughness of the membrane during the NIPS process. The scanning area was set to 5 μm × 5 μm, and the characterization results are as Figure 7 shown. It can be obtained from the figure that as the content of the amphiphilic block copolymer PS-b-PAA additive increases, the surface of the membrane gradually becomes rough, and many wavy peaks and deep groove protrusions gradually appear on the three-dimensional structure diagram.

[0100] The membrane surface roughness data are shown in Table 4. These parameters reflect the membrane surface morphology and roughness changes from different angles. It can be seen that the surface roughness of the membrane shows a gradually increasing trend with the increase in the addition amount of PS-b-PAA. The increase in roughness is attributed to the surface segregation of the amphiphilic block copolymer during the phase separation process, and the hydrophilic block PAA spontaneously segregates to the membrane surface. As a pore-forming modifier, PS-b-PAA increases the pores and porosity on the membrane surface. It can also be obtained from the SEM images of the aforementioned PS-b-PAA / PMIA membranes that spherical substances appear on the membrane surface due to the micelles formed by the self-assembly of the block copolymer, which will also increase the surface roughness of the membrane, further affecting the hydrophilicity of the membrane surface.

[0101] Membrane number <![CDATA[Average roughness (R a )]]> <![CDATA[Root mean square roughness (R q )]]> <![CDATA[Maximum roughness (R max )]]> M0 16.43±2.32 21.12±2.08 152.23±12.21 M1 22.77±3.96 28.7±3.21 201.00±16.86 M2 25.60±1.12 31.24±2.12 218.33±7.89 M3 28.60±1.84 36.03±2.25 233.33±15.69 M4 35.87±1.79 44.27±2.08 289.67±12.55 M5 37.10±1.70 48.50±2.57 327.33±23.90

[0102] Table 4 Surface roughness values of different PS-b-PAA / PMIA membranes

[0103] (3) Hydrophilic and hydrophobic characterization of PS-b-PAA / PMIA porous membranes

[0104] The hydrophilic property of the membrane surface has an important impact on the anti-fouling ability of the membrane. The hydrophilic property of the PS-b-PAA / PMIA membrane was characterized by measuring the contact angle of the membrane, and the results are as Figure 8 shown. The contact angles of all the prepared membranes are below 70°, indicating good hydrophilicity. The water contact angles of membranes M1 - M5 are all smaller than that of M0 (68.46 ± 1.21°). This is mainly due to the surface segregation effect of PS-b-PAA, and the hydrophilic block PAA segregates to the membrane surface and forms hydrogen bonds with water molecules, enhancing the hydrophilicity. However, since the maximum addition amount of PS-b-PAA is only 0.5 wt.%, the effect of hydrophilic modification is not obvious. Therefore, the membrane contact angles are all above 50°, and the anti-fouling performance is not as good as that of the subsequent antibacterial membranes.

[0105] (4) Characterization of pore structure parameters of PS-b-PAA / PMIA porous membranes

[0106] The pore structure parameters of the membrane are crucial for the separation performance of the membrane. In this invention, the bubble pressure method was used to test the pore size and pore size distribution curve of the membrane, and the results are as Figure 9 shown. The test curves of all PS-b-PAA / PMIA membranes conform to the standard flow-pressure curve, proving that the addition of PS-b-PAA does not affect the film-forming performance of PMIA, and the prepared membranes have no adverse defects.

[0107] According to the pore size and pore size distribution curve, the pore size distribution of all membranes is unimodal and narrow, indicating that the prepared membranes have uniform pore sizes. The average pore size and porosity of each membrane are shown in Table 5.

[0108] Membrane number Average pore size (nm) Porosity % M0 67.72±1.24 65.8±1.4 M1 70.01±0.31 78.6±5.3 M2 73.24±1.43 83.2±2.6 M3 79.53±2.26 80.2±1.8 M4 112.49±0.97 85.6±1.6 M5 115.41±1.56 84.3±2.3

[0109] Table 5: Pore diameter and porosity of membranes in Examples 2 to 7

[0110] As can be seen from Table 5, the average pore size of the membrane increases with the increase of PS-b-PAA concentration in the casting solution. This is because the number and size of block copolymer micelles in the casting solution increase after the PS-b-PAA concentration increases. When the larger block copolymer micelles are washed away during the preparation of the membrane by NIPS, larger pores in the selective layer are formed. Compared with the blank control membrane M0, the porosity of the membranes M1 to M5 modified by PS-b-PAA has been greatly improved, all above 70%, which is much larger than the porosity of M0, proving that PS-b-PAA can be introduced into the casting solution as a porogen to prepare ordered porous membranes.

[0111] (5) Mechanical properties characterization of PS-b-PAA / PMIA porous membrane

[0112] By performing tensile tests on PS-b-PAA / PMIA films, Figure 10 As shown, the mechanical strength and tensile properties of the membrane are relatively excellent, mainly because the structure of the membrane main material PMIA used belongs to the triclinic crystal system. There are hydrogen bonds arranged in a lattice on the two planes of the crystal in the PMIA structure, which provides a strong hydrogen bond interaction force, so that PMIA itself has good mechanical properties. These characteristics make the PMIA material still have excellent chemical stability and high mechanical strength after film formation.

[0113] However, it can be seen from the figure that with the increase of the blending content of the modifier PS-b-PAA, the mechanical strength and tensile properties of the membrane are reduced. The reasons are: on the one hand, from the SEM image of the aforementioned membrane, it can be seen that with the increase of the PS-b-PAA content, the number of macropores in the membrane increases and the porosity increases, especially M5 even has a membrane pore collapse phenomenon, which is not good for the mechanical properties; on the other hand, since PS-b-PAA is an additive with a large molecular weight, blending it into the casting liquid may cause the PMIA material to form weaknesses, increase the unevenness of stress distribution, destroy the rigidity of the PMIA chain, and lead to weakening of mechanical strength and tensile properties.

[0114] (6) Characterization of thermal stability of PS-b-PAA / PMIA porous membrane

[0115] The thermal stability of the PS-b-PAA / PMIA porous membrane was characterized by thermogravimetric analysis (TGA-60, SHIMADZU, Japan) at a heating rate of 10°C / min from 30°C to 500°C. Figure 11As shown. It can be seen that all PS-b-PAA / PMIA membranes start to decompose at around 420 °C, and with the increase in the addition amount of PS-b-PAA, the thermal decomposition temperature slightly decreases, but it is still above 400 °C, indicating that the prepared membranes have good heat resistance characteristics. The main reason is that the PMIA fiber, the main membrane material used in the present invention, is a new type of organic high-temperature resistant fiber with excellent heat resistance characteristics. The glass transition temperature of PMIA fiber is 270 °C, and there is no obvious melting point. Whether in nitrogen or air, the weight loss of the fiber is less than 10% at 400 °C, and rapid decomposition starts above 427 °C. After being exposed to high temperature, PMIA fiber can still maintain a certain strength, has excellent flame resistance, and will self-extinguish after leaving the flame. At a high temperature of 400 °C, the fiber will carbonize and become a heat insulation layer, playing an effective protective role. These characteristics make the membranes prepared from PMIA also have excellent heat resistance performance. Therefore, the PS-b-PAA / PMIA membranes prepared in the present invention are not only suitable for water treatment, but can also be extended to the field of water treatment in high-temperature environments, as well as water environment systems containing more microorganisms and bacteria.

[0116] (7) Permeation and separation performance of PS-b-PAA / PMIA porous membranes

[0117] The pure water flux of the membrane is an important parameter during membrane operation and can reflect the efficiency of membrane water treatment. Figure 12 It is the pure water flux change curve of membranes M0 to M5. As can be seen from the figure, with the increase in the content of PS-b-PAA, the pure water flux of the modified PS-b-PAA / PMIA membranes shows a trend of first increasing and then decreasing under a certain pressure. When the addition amount of PS-b-PAA is 0.4 wt.%, the pure water flux of membrane M4 reaches the maximum value of 981.86 ± 25.95 L·m -2 ·h -1 .

[0118] The applicant analyzed that the main reasons for the increase in the pure water flux with the increase in the addition amount of PS-b-PAA are: (1) As a pore-forming agent, with the increase in the addition amount, the pore size and porosity of the prepared membrane increase, the number of macropores in the membrane increases, and under a certain pressure, the resistance of pure water passing through the pores decreases, resulting in an increase in the flux; (2) With the increase in the content of the additive, the roughness of the membrane surface increases, and water is more easily adsorbed on the membrane surface; (3) PS-b-PAA is an amphiphilic block copolymer. During the process of preparing the membrane by NIPS, surface segregation occurs, and the hydrophilic PAA block migrates to the membrane surface, resulting in an increase in hydrophilicity and an increase in the pure water flux. However, when the addition amount of PS-b-PAA is 0.5 wt.%, the pure water flux of the membrane drops to 673.31 ± 15.05 L·m -2 ·h-1 , it is speculated that the high addition amount of PS-b-PAA may lead to an increase in pores and porosity, resulting in a decrease in the mechanical strength of the membrane. The pores of the membrane collapse under a pressure of 0.15 MPa, causing pore blockage and a decrease in the pure water flux.

[0119] To verify the above speculation, the pure water fluxes of membrane M5 under different pressures were tested, and the results are as Figure 13 shown. The pure water flux of the membrane decreases with the increase of pressure. When the pressure is 0.10 MPa, the pure water flux reaches the maximum value. It can be concluded that the decrease in the flux of M5 membrane is due to the decrease in the mechanical strength of the PS-b-PAA / PMIA membrane. M5 membrane has a large number of macropores. During the 30-min pre-pressurization process at a test pressure of 0.15 MPa, the pores of the membrane collapse, resulting in a decrease in the water flux. In addition, as the mass fraction of PS-b-PAA in the casting solution system increases, the viscosity of the casting solution system increases as a whole, and the solvent precipitation rate becomes slower during the phase inversion film formation process, making the membrane skin layer denser, which also leads to a decrease in the water flux of the membrane.

[0120] Based on this, when preparing the antibacterial membrane subsequently, we will select M4 with an addition amount of 0.4 wt.% as the antibacterial membrane substrate.

[0121] The rejection rate of the membrane to protein molecules can reflect the separation performance of the membrane. The higher the rejection rate, the better the separation performance of the ultrafiltration membrane. In the present invention, 1000 mg / L of bovine serum albumin (BSA) was used as a simulated pollutant to test the rejection performance of the membrane. The results are shown in Table 6. It can be seen that the rejection rate of ultrafiltration membrane M0 is 98.92 ± 0.59%, and the rejection rates of the other membranes are all less than that of M0, but they can all be maintained above 95%, indicating that the separation performance of the membranes is relatively good. This is mainly because as the content of PS-b-PAA increases, the membrane surface becomes rougher, the specific surface area increases continuously, and it is easier to adsorb some BSA molecules, forming a filter cake layer during filtration. And as the content of PS-b-PAA additive in the casting solution system increases, a thicker surface skin layer is formed. Under the combined action of the above various factors, it is more difficult for BSA molecules to pass through the membrane pores, thereby improving the separation performance of the membrane.

[0122]

[0123]

[0124] Table 6 Rejection rates of different PS-b-PAA / PMIA membranes

[0125] (8) Study on the anti-fouling performance of PS-b-PAA / PMIA porous membranes

[0126] Table 7 shows the flux recovery rates (FRR) of different PS-b-PAA / PMIA membranes (indicating the fouling resistance of the membranes). It can be seen that the FRR of the membranes are all less than 90%, indicating that the anti-fouling ability of the membranes is average. When the membranes initially filter pure water, the permeation flux maintains at a relatively high level. However, when filtering the BSA solution, the flux rapidly drops to a relatively low level. This is because BSA molecules are easily adsorbed on the membrane surface, causing the surface membrane pores to be blocked and resulting in a rapid decline in the BSA filtration flux of the membrane. After the filtration is completed, a cake layer forms on the membrane surface. Due to the effect of concentration polarization, protein molecules are not easily removed by rinsing with pure water. This also explains why the rejection rates of the modified membranes are all above 95%. In addition, the static water contact angles of the modified membranes are all above 50°, without good hydrophilicity and with low anti-fouling performance.

[0127] Membrane number Flux recovery rate FRR (%) M0 80.95±3.57 M1 72.97±1.42 M2 78.13±2.53 M3 53.85±1.29 M4 46.51±1.97 M5 73.08±2.86

[0128] Table 7 Flux recovery rates of different PS-b-PAA / PMIA membranes

[0129] To verify whether a cake layer was formed, SEM tests were performed on the fouled membranes after the BSA filtration experiment. Figure 14 、 Figure 15 Figures 14 and 15 are SEM images of the fouled PS-b-PAA / PMIA membranes with a magnification of 1000 times and 10000 times respectively, after being rinsed with pure water. The results show that a thick layer of contaminants appears on the surface of the fouled PS-b-PAA / PMIA membranes, forming a relatively thick cake layer that covers the original porous structure on the membrane surface, resulting in a small FRR and poor anti-fouling performance. In addition, it can be seen that cracks appear on the surface of membrane M5 after filtration, which also confirms that the pure water flux of membrane M5 decreases due to the decline in mechanical strength.

[0130] (3) Characterization and performance testing of the Ag NPs / PS-b-PAA / PMIA antibacterial membranes prepared in Examples 8 - 9

[0131] (1) Chemical structure characterization of the Ag NPs / PS-b-PAA / PMIA antibacterial membranes

[0132] From Figure 16 the results of ultraviolet-visible spectrophotometric analysis, the prepared AgNO3 / DOPA / NaOH liquid phase system has a strong absorption peak near 420 nm, while the ultraviolet absorption peak of silver nanoparticles is between 390 - 440 nm. Therefore, it can be inferred that a chemical reaction occurred in the AgNO3 / DOPA / NaOH liquid phase system, and DOPA reduced AgNO3 to form silver nanoparticles.

[0133] Select the M4 membrane as the bottom membrane to prepare the antibacterial membrane. XPS was used to characterize the elemental changes of the PS-b-PAA / PMIA blank membrane and the Ag NPs / PS-b-PAA / PMIA modified membrane to confirm the successful adhesion of silver nanoparticles on the membrane surface.

[0134] Figure 17 Figure (a) is the XPS spectra of the PS-b-PAA / PMIA and Ag NPs / PS-b-PAA / PMIA membranes, and figure (b) is the enlarged view of the Ag characteristic peak. Figure 17 As can be seen from (a), compared with the PS-b-PAA / PMIA blank membrane, the characteristic peak of Ag appears significantly on the Ag NPs / PS-b-PAA / PMIA modified membrane, proving that dopamine successfully reduced the silver nanoparticles in silver nitrate and adhered to the membrane surface; in figure (b), two absorption peaks of Ag NPs appear at 368 eV and 374 eV, corresponding to Ag 0 3d 5 / 2 and Ag 0 3d 3 / 2 respectively, indicating that silver elements exist on the surface of the PS-b-PAA / PMIA membrane in the form of a single substance.

[0135] Furthermore, combined with the atomic content composition on the membrane surface in Table 8, it can be seen that the content of Ag element on the surface of the Ag NPs / PS-b-PAA / PMIA membrane is 1.06 at.%. In addition, from Figure 18 the physical pictures of the blank membrane and the modified membrane, it can be seen that the physical picture of the PS-b-PAA / PMIA membrane is white, and the physical picture of the Ag NPs / PS-b-PAA / PMIA modified membrane presents brown. This is mainly because dopamine hydrochloride is an acidic substance with two free phenolic hydroxyl groups in its molecular structure, which is easily oxidized into quinones in the air to form black polymers, especially more obvious under the condition of alkaline NaOH solution. All these confirm that silver nanoparticles are successfully loaded on the membrane surface.

[0136] Membrane C (at.%) N (at.%) O (at.%) Ag (at.%) Ag NPs / PS-b-PAA / PMIA 73.04 10.25 15.65 1.06 PS-b-PAA / PMIA 74.49 8.53 16.98 0

[0137] Table 8 Atomic composition on the surface of different PS-b-PAA / PMIA membranes

[0138] (2) Microstructure of the surface of the Ag NPs / PS-b-PAA / PMIA antibacterial membrane

[0139] Figure 19SEM images of PS-b-PAA / PMIA membrane M4 and Ag NPs / PS-b-PAA / PMIA at different magnifications. As can be seen from the figure, the surface of the PS-b-PAA / PMIA membrane M4 presents a uniform and ordered porous structure. Compared with the blank membrane, after the reduction of silver nitrate by polydopamine, the surface morphology of the membrane becomes dense. This may be due to the formation of a PDA layer on the membrane surface, and the reduced Ag NPs layer covers the membrane surface. The number of silver nanoparticles is large and evenly distributed. This benefits from the alkaline and redox reaction environment provided by the dopamine solution. With the help of the catechol structure (two adjacent hydroxyl groups on the benzene ring) in the dopamine molecule being oxidized to quinone under alkaline conditions (pH≥8), electrons (e - ) are released to reduce Ag + to form Ag 0 nanoparticles. Using the carboxyl groups at the PAA end groups of PS-b-PAA in the solution environment, stable coordination bonds can be formed with Ag + (such as [Ag(COO - )] complex), reducing the reduction potential of Ag + , making it easier to be reduced to Ag 0 nanoparticles (AgNPs). In addition, the amino group (-NH2) and hydroxyl group (-OH) of dopamine can bind to the surface of AgNPs through coordination bonds or hydrogen bonds to form a stable organic-inorganic interface layer, preventing particle aggregation and obtaining a more uniform and stable distribution of silver nanoparticles. In addition, the selective adsorption of carboxyl groups on different crystal planes can regulate the morphology of AgNPs (such as spherical, flaky or rod-shaped). The morphology of the AgNPs generated in the present invention is mainly spherical particles. This proves that the silver nanoparticles prepared by reducing silver nitrate solution with dopamine under alkaline conditions and adhering to the membrane surface can be uniformly deposited on the membrane surface.

[0140] (3) Pore structure parameters of Ag NPs / PS-b-PAA / PMIA antibacterial membrane

[0141] The pore size distribution and test curves of the Ag NPs / PS-b-PAA / PMIA antibacterial membrane are as Figure 20 shown. The specific values of the pore size change are shown in Table 9. It can be seen that after adding silver nanoparticles, the pore sizes of membranes M0 and M4 both decrease, from 67.72±1.21 nm and 112.49±0.97 nm to 64.73±2.84 nm and 91.59±2.51 nm respectively. It can be seen that compared with M0, after adding silver nanoparticles to M4, the average pore size decreases to a greater extent. The main reason is that after adding silver nanoparticles, a layer of dopamine and silver nanoparticles covers the membrane surface, resulting in the blockage of the membrane surface pore size and the reduction of the membrane average pore size.

[0142] In addition, for the membrane M4 with PS-b-PAA added, due to the presence of carboxyl groups, there is a strong coordination bond between Ag NPs and carboxyl groups, which can reduce the excessive leaching of Ag NPs, increase the stability of Ag NPs, load more silver nanoparticles, and the pore-blocking effect is more obvious.

[0143] Membrane number Average pore size (nm) M0 67.72±1.21 M4 112.49±0.97 Ag NPs / M0 64.73±2.84 Ag NPs / M4 91.59±2.51

[0144] Table 9 Comparison of average pore sizes of different membranes before and after loading silver nanoparticles

[0145] (4) Hydrophilicity of Ag NPs / PS-b-PAA / PMIA antibacterial membrane

[0146] Table 10 shows the comparison of contact angles of different membranes before and after loading silver nanoparticles. The contact angle values represent the hydrophilicity and hydrophobicity of the membranes. It can be seen that the initial contact angles of membranes M0 and M4 are 68.46±1.21° and 56.26±3.08° respectively. After adding silver nanoparticles, the contact angles both decrease, dropping to 39.24±3.21° and 38.17±2.40° respectively. Membranes M0 and M4 are both hydrophilic membranes. Thanks to the fact that the main membrane material PMIA itself is a hydrophilic material, after poly-dopamine reduces silver nitrate and is modified and loaded on the membrane surface, the hydrophilicity of the membrane is further improved. The reasons are as follows: (1) The presence of amino and hydroxyl groups in PDA makes it easier to form hydrogen bonds with water molecules, greatly improving the hydrophilicity of the membrane; (2) After silver nanoparticles are loaded on the membrane surface, the roughness of the membrane does not increase accordingly, and water molecules can spread better on the membrane surface, improving the hydrophilicity; (3) Silver nanoparticles also have a certain hydrophilicity, promoting the penetration of water molecules into the membrane pores, and the hydrophilicity is improved.

[0147] Membrane number Contact angle (°) M0 68.46±1.21 M4 56.26±3.08 Ag NPs / M0 39.24±3.21 Ag NPs / M4 38.17±2.40

[0148] Table 10 Comparison of contact angles of different membranes before and after loading silver nanoparticles

[0149] (5) Permeation performance of Ag NPs / PS-b-PAA / PMIA antibacterial membrane

[0150] Table 11 shows the pure water fluxes of different membranes. It can be seen that after antibacterial modification, the pure water flux of membrane M0 decreases from 446.30±11.37 L·m -2 ·h -1 to 413.24±17.19 L·m -2 ·h -1 , and the pure water flux of membrane M4 decreases from 981.86±25.95 L·m -2 ·h -1 to 666.64±19.25 L·m -2 ·h -1, the pure water fluxes of Ag NPs / M0 and Ag NPs / M4 both decreased compared with the initial membranes M0 and M4, and the decrease in the pure water flux of membrane M4 was more obvious.

[0151] Membrane number <![CDATA[Flux (L·m -2 ·h -1 )]]> M0 446.30±11.37 M4 981.86±25.95 Ag NPs / M0 413.24±17.19 Ag NPs / M4 666.64±19.25

[0152] Table 11 Comparison of pure water fluxes of different Ag NPs / PS-b-PAA / PMIA membranes

[0153] The applicant analyzed that there may be the following reasons: (1) By observing Figure 21 the loading situation of silver nanoparticles on the membrane surface, it can be obtained that there are uniformly loaded Ag NPs and polydopamine layers on the surfaces of both Ag NPs / M0 and Ag NPs / M4 membranes. The existence of silver nanoparticles and polydopamine layers causes the pores on the membrane surface to be blocked, increasing the resistance when water permeates through the membrane, resulting in a decrease in the pure water flux. Moreover, compared with Ag NPs / M0, Ag NPs / M4 has more silver nanoparticles loaded on the surface due to the coordination effect between carboxyl groups and silver nanoparticles, and the blockage is more serious. Therefore, the pure water flux of Ag NPs / M4 decreases more significantly; (2) Combining the comparison of the average pore diameters of different membranes before and after loading silver nanoparticles in Table 9, after Ag NPs / M0 and Ag NPs / M4 are loaded with silver nanoparticles, the average pore diameters of the membranes both decrease, and the pure water flux of the membranes decreases. Moreover, the more obvious decrease in the average pore diameter of Ag NPs / M4 leads to a more significant decrease in the pure water flux.

[0154] In addition, Figure 22 Figure is the cross-sectional SEM image of Ag NPs / M0 and Ag NPs / M4. It can be seen that the silver nanoparticles did not penetrate into the pores but were only loaded on the membrane surface, so they would not block the internal pores of the membrane.

[0155] (6) Antibacterial property of Ag NPs / PS-b-PAA / PMIA antibacterial membrane

[0156] To test the antibacterial properties of the Ag NPs-modified membranes, the ratio of the number of colonies of the blank membrane M0 and the Ag NPs / PS-b-PAA / PMIA membrane modified with silver nanoparticles after contacting and culturing Escherichia coli for a certain time was used as the sterilization efficiency R. The antibacterial properties of the membranes were quantitatively characterized by the sterilization efficiency R, and the obtained antibacterial effects are as Figure 23 shown.

[0157] For Ag NPs / M4, through the plate counting method, the antibacterial rate of the Ag NPs / M4 membrane was calculated to be about 98.17 ± 1.24%.

[0158] Experiments show that the blank membrane M0 has no bactericidal effect on Escherichia coli. Due to the addition of the additive PS-b-PAA containing -COOH in the M4 membrane, the living environment of Escherichia coli on the surface of the M4 membrane has changed compared with the blank membrane M0, and dead Escherichia coli appear. Therefore, the M4 membrane without the addition of Ag NPs can also cause a decrease in the number of bacteria, showing certain antibacterial properties.

[0159] Analysis of the reasons: (1) The introduction of PDA can enhance the hydrophilicity of the membrane surface and introduce protonated amino groups. Amino groups are required for the synthesis of bacterial proteins. The introduction of protonated amino groups can slightly inhibit the synthesis of bacterial own proteins and has extremely weak bactericidal properties; (2) The coordination of carboxyl groups in PS-b-PAA with silver nanoparticles and the adhesion of dopamine make the surface of Ag NPs / M4 have uniformly loaded silver nanoparticles. On the one hand, when bacteria come into contact with the surface of the membrane loaded with Ag NPs, Ag NPs can adhere to the surface of the bacteria and enter the bacterial cells, causing the loss of intracellular cytoplasm and inactivating the bacteria; on the other hand, Ag NPs can slowly release Ag + ,Ag + can act on the thiol groups on the bacterial cell membrane, block the electron transfer, dimerize DNA, and ultimately cause the contraction of the bacterial cytoplasm and the shedding of the cell membrane, resulting in an increase in the bactericidal rate of the modified membrane Ag NPs / M4.

[0160] In summary, in the present invention, first, the amphiphilic block copolymer PS-b-PAA was successfully synthesized by the reversible addition-fragmentation chain transfer (RAFT) method, and it was used as a modifier and co-mixed into the casting solution. The non-solvent induced phase separation method was used to prepare the PMIA porous ordered membrane. The permeability of the modified PS-b-PAA / PMIA membrane has been greatly improved, with excellent permeability and good mechanical properties. Further, Ag NPs were loaded on the PS-b-PAA / PMIA membrane through dopamine to form the AgNPs / PS-b-PAA / PMIA antibacterial membrane. The antibacterial rate against Escherichia coli reached 98.17 ± 1.24% within a certain time, proving that the membrane has good antibacterial effects on Escherichia coli, can prevent the formation of biofilms on the membrane surface, and avoid biological contamination.

[0161] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A preparation method of an amphiphilic block copolymer PS-b-PAA, characterized in that, It includes the following technological processes: (1) Synthesize the PS segment: Add 2-(dodecylthio thiocarbonylthio)-2-methylpropionic acid DDMAT to the purified styrene (SM), stir until completely dissolved to form Solution 1; then dissolve azobisisobutyronitrile AIBN in tetrahydrofuran, and then add Solution 1 thereto, stir until evenly mixed to form Solution 2; use a pipette to transfer Solution 2 to a Schlenk flask, place the Schlenk flask in an oil bath, ensure that the mixture is completely immersed in the oil bath, react at 70 °C for 24 hours, then cool to normal temperature and pressure, and then wash with anhydrous methanol and tetrahydrofuran (THF), and dry in a vacuum drying oven to obtain the PS product; (2) Synthesize polystyrene-poly(tert-butyl acrylate) PS-PtBA: Add the dried PS product, AIBN, and purified tert-butyl acrylate (TBA) to THF and dissolve to a clear solution, transfer to a Schlenk flask, and place it in an oil bath at 65 °C for 24 hours. After the reaction is completed, wait for the Schlenk flask to cool to normal temperature and pressure, pour it into cold n-hexane, precipitate and filter; put the sample obtained from the reaction into a glass bottle, cover it with perforated tin foil, and dry it in an oven to obtain PS-PtBA; (3) Hydrolyze PS-PtBA: Dissolve PS-PtBA in THF, and then add the HCl solution to the mixture; then carry out a reflux reaction with heating to 80 °C. After acid hydrolysis, precipitate PS-b-PAA in cold n-hexane and dry it in a vacuum oven to obtain the copolymer PS-b-PAA.

2. The preparation method of an amphiphilic block copolymer PS-b-PAA according to claim 1, characterized in that, The specific process of the purification operation is as follows: Block the glass dropper with absorbent cotton, fill the glass dropper with Al2O3 powder to a height of about 4-5 cm, then add the product to be purified into the filled column, and use an ear bulb to blow the product to be purified. The purification can be repeatedly performed multiple times.

3. The preparation method of an amphiphilic block copolymer PS-b-PAA according to claim 1, characterized in that, The Schlenk flask should be dehumidified and deoxygenated before operation. The specific operation process is as follows: Place the Schlenk flask in liquid nitrogen to freeze, so that the mixture solidifies, then use a vacuum pump to evacuate the air in the tube first, close the valve of the Schlenk flask, transfer it to warm water to thaw, and then put it in liquid nitrogen to freeze again. After solidification, turn on the vacuum again. The above deoxygenation and dehumidification steps can be repeated multiple times.

4. The amphiphilic block copolymer PS-b-PAA prepared by the method according to any one of claims 1 to 3, characterized in that, Its molecular weight is 38702 Da, the distribution index is 1.26, and the relative molecular weight distribution of the PS-b-PAA polymer is relatively uniform.

5. A preparation method of a PS-b-PAA / PMIA porous membrane, characterized in that, It includes the following steps: (1) Prepare the casting solution: Dissolve a certain amount of LiCl in the DMAc solvent, stir at high speed at room temperature until dissolved into a transparent solution, then add a certain amount of PS-b-PAA to the solution and continue to stir until dissolved into a homogeneous and stable solution. After adding PMIA, stir at high speed at 85 °C until dissolved into a homogeneous and stable casting solution, cool to 25 °C, and let it stand for defoaming; the PS-b-PAA is prepared according to the foregoing claim 4; (2) After complete degassing, the non-solvent induced phase separation method is adopted, and a glass rod is used to scrape on a smooth and flat glass plate. The thickness of the membrane is about 200 μm, the coagulation bath is deionized water, and the temperature is 25 °C. The prepared PMIA flat membrane is subjected to post-treatment operations such as soaking and cleaning, and then stored in deionized water for standby.

6. The preparation method of a PS-b-PAA / PMIA porous membrane according to claim 5, wherein, The mass percentage content of the PS-b-PAA does not exceed 0.5%.

7. The PS-b-PAA / PMIA porous membrane prepared by the method of claim 6, characterized in that, The cross-section of the membrane includes a dense skin layer, a porous sublayer with a finger-like structure, and a macroporous support bottom layer; as the content of PS-b-PAA increases, the number of macropores in the membrane cross-section continuously increases, the connectivity between pores is stronger, and spherical substances gradually appear on the membrane surface, increasing the roughness.

8. A preparation method of an Ag NPs / PS-b-PAA / PMIA antibacterial film, characterized in that, It includes the following steps: (1) Fix Ag NPs on the membrane surface by dip coating: Add silver nitrate solution into a container, immerse the PS-b-PAA / PMIA porous membrane obtained in the previous claim 7 into the silver nitrate solution, and oscillate it in the air at room temperature to form a mixed solution; (2) Drop the dopamine aqueous solution into the aforementioned mixed solution, then add NaOH solution to it. After a period of time, wash the membrane with deionized water and dry it under room temperature environmental conditions to obtain the Ag NPs / PS-b-PAA / PMIA antibacterial membrane, which is stored in a dark room.

9. An Ag NPs / PS-b-PAA / PMIA antibacterial film prepared by the method of claim 8, characterized in that, The surface of this membrane is loaded with silver nanoparticles, and its hydrophilicity is better than that of the PS-b-PAA / PMIA porous membrane. The antibacterial rate against Escherichia coli is as high as 98.17 ± 1.24%.

10. The application of the PS-b-PAA / PMIA porous membrane as described in claim 6 in the field of high-temperature water treatment.

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