Preparation method and application of sulfonated polyaniline-doped nanofiltration membrane

Abstract

The invention relates to a preparation method and application of a sulfonated polyaniline-doped nanofiltration membrane, and the preparation method comprises the following steps: firstly, pouring a surfactant solution on the surface of an ultrafiltration base membrane, standing, then removing redundant liquid, drying, then uniformly paving a sulfonated polyaniline-doped solution on the surface of the membrane, and finally, preparing the sulfonated polyaniline-doped nanofiltration membrane. Removing redundant liquid through a roller, then carrying out thermocuring treatment, and after thermocuring is finished, immersing into a citric acid aqueous solution to obtain the sulfonated polyaniline-doped nanofiltration membrane. The process is simple, the prepared nanofiltration membrane is high in interception performance, high in flux and excellent in solvent resistance, and the separation effect and long-term stability of the nanofiltration membrane on different antibiotics are improved.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane preparation technology, specifically relating to a method for preparing and applying a doped sulfonated polyaniline nanofiltration membrane. Background Technology

[0002] Currently used methods for treating antibiotic wastewater, such as oxidation and adsorption, all have certain limitations. Oxidation is complex, energy-intensive, and irreversibly damages the structure of antibiotics, rendering them unusable for recycling. While adsorption can partially remove pollutants, it is costly, difficult to regenerate the adsorbent, and poses a risk of secondary pollution. Among these technologies, commercially available polyamide nanofiltration membrane separation technology shows great potential for application in the field of antibiotic wastewater treatment due to its advantages such as simple operation, low energy consumption, and no need for solvents.

[0003] However, existing polyamide nanofiltration membranes still face two major technical bottlenecks: first, the high density of amide bonds in the separation layer makes them prone to swelling in polar organic solvent systems such as acetone and toluene, leading to damage to the pore structure of the separation layer and failure of its retention performance; second, nanofiltration membranes prepared based on layer-by-layer self-assembly technology generally suffer from low membrane flux, making it difficult to meet the technical requirements of long-term, efficient, and stable operation for large-scale antibiotic wastewater treatment. Therefore, developing a novel nanofiltration membrane that combines high retention performance, excellent solvent resistance, and high flux is of great significance for achieving deep purification and resource recovery of antibiotic wastewater. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art and provide a method for preparing and applying a doped sulfonated polyaniline nanofiltration membrane. The process is simple, and the prepared nanofiltration membrane has high retention performance, high flux and excellent solvent resistance, which improves the separation effect and long-term stability of the nanofiltration membrane for different antibiotics.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a doped sulfonated polyaniline nanofiltration membrane includes the following steps:

[0007] First, the surfactant solution is poured onto the surface of the ultrafiltration base membrane and allowed to stand. Then, excess liquid is removed and the membrane is dried. Next, the doped sulfonated polyaniline solution is evenly spread on the surface of the ultrafiltration base membrane, and excess liquid is removed by rollers. Then, the membrane is heat-cured. After heat curing, the membrane is immersed in a citric acid aqueous solution and then removed to obtain the doped sulfonated polyaniline nanofiltration membrane.

[0008] As a further technical solution, the mass concentration of the surfactant in the surfactant solution is 0.05-0.2%.

[0009] As a further technical solution, the solvent in the surfactant solution is an ethanol solution with a mass concentration of 50%.

[0010] As a further technical solution, the mass concentration of citric acid in the citric acid aqueous solution is 0.5-5%.

[0011] As a further technical solution, the surfactant is one or more of sodium dodecyl sulfonate, sodium dioctyl succinate sulfonate, sodium dodecyltrimethylammonium bromide, sodium dodecyl sulfate, or sodium dodecylbenzene sulfonate.

[0012] As a further technical solution, the doped sulfonated polyaniline solution comprises the following raw materials in the following mass percentages: anhydrous piperazine: 0.2-0.5%, sulfonated polyaniline: 0.01-0.2%, epoxy crosslinking agent: 0.2-0.6%, and deionized water: balance.

[0013] As a further technical solution, the preparation method of the doped sulfonated polyaniline solution includes: firstly, dissolving anhydrous piperazine in deionized water, stirring until dissolved, then adding sulfonated polyaniline, continuing to stir until a uniform dispersion is formed, then adding an epoxy crosslinking agent, stirring for 3-5 minutes until dissolved, to obtain the doped sulfonated polyaniline solution.

[0014] As a further technical solution, the epoxy crosslinking agent is one or more of epichlorohydrin, tert-butyl glycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerol triglycidyl ether.

[0015] As a further technical solution, the preparation method of the sulfonated polyaniline includes the following steps:

[0016] In an ice-water bath at 0–5°C, polyaniline powder is stirred and dispersed evenly. Fuming sulfuric acid is then added dropwise to the polyaniline powder while stirring until a polyaniline suspension is formed. After the addition is complete, the mixture is heated to 40–60°C at a rate of 5–10°C / min and stirred at 300–500 r / min until evenly dispersed. The reaction is carried out for 1.5–3 hours to obtain a sulfonation reaction solution. After the reaction is completed, the sulfonation reaction solution is poured into an ice-water mixture and stirred to precipitate. The precipitate is then collected, washed, dried, and ball-milled to obtain sulfonated polyaniline.

[0017] As a further technical solution, the ratio of the polyaniline powder to fuming sulfuric acid (containing 20-40% SO3) is 5-20g: 100-200mL.

[0018] As a further technical solution, the fuming sulfuric acid is added dropwise within 30 to 60 minutes.

[0019] As a further technical solution, during washing, the precipitate is first repeatedly washed with deionized water until the filtrate is neutral to remove residual sulfuric acid, and then washed with anhydrous ethanol to remove organic impurities.

[0020] As a further technical solution, the drying is carried out by vacuum drying, and the temperature of the vacuum drying is 50-60℃.

[0021] As a further technical solution, the particle size of the ball-milled sulfonated polyaniline is 35-50 nm.

[0022] As a further technical solution, the ultrafiltration base membrane is any one of PES ultrafiltration base membrane, PSF ultrafiltration base membrane, PAN ultrafiltration base membrane, PVDF ultrafiltration base membrane or PTFE ultrafiltration base membrane.

[0023] As a further technical solution, the ultrafiltration membrane has an average pore size of 40-60 nm and a porosity of 50-70%.

[0024] As a further technical solution, the ultrafiltration membrane needs to be pretreated before use. The pretreatment method includes: soaking the ultrafiltration membrane in deionized water at 20-25°C for 4-6 hours, taking it out before use, blowing away residual moisture on the surface, and then setting it aside.

[0025] As a further technical solution, the surfactant solution is left to stand on the surface of the ultrafiltration membrane for 3 to 5 minutes.

[0026] As a further technical solution, the drying temperature is 30-40℃.

[0027] As a further technical solution, the residence time of the doped sulfonated polyaniline solution on the surface of the ultrafiltration membrane is 5 to 10 minutes.

[0028] As a further technical solution, the thermosetting temperature is 80-90℃ and the thermosetting time is 8-10 min.

[0029] As a further technical solution, the thermocured film is immersed in citric acid solution for 5 to 10 minutes.

[0030] The doped sulfonated polyaniline nanofiltration membrane prepared by the preparation method includes an ultrafiltration base membrane layer and a doped sulfonated polyaniline functional layer disposed on the ultrafiltration base membrane layer.

[0031] Application of the doped sulfonated polyaniline nanofiltration membrane prepared by the above preparation method in antibiotic wastewater treatment.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. This invention introduces sulfonated polyaniline (SPANI) nanoparticles (35-50 nm) into the separation layer of a nanofiltration membrane. These nanoparticles are uniformly dispersed in a piperazine-epoxy crosslinking system. By filling the separation layer with these particles, the pore size distribution range is reduced, achieving precise control of the pore size sieving effect. Simultaneously, the sulfonic acid groups (-SO3H) in the SPANI molecules provide stable negative charge sites for the separation layer, which can enhance the retention of different charged antibiotics through the Donnan effect. Ultimately, through the synergistic effect of the "pore size sieving effect and the Donnan effect," highly efficient retention of antibiotics is achieved. Elemental analysis shows that the degree of sulfonation of the sulfonated polyaniline is 0.8-1.2 mmol / g, ensuring that the number of sulfonic acid groups is sufficient to provide stable negative charge sites.

[0034] 2. This invention employs a dual stabilization strategy of "primary crosslinking with epoxy crosslinking agent and secondary crosslinking with citric acid": the epoxy group can form ether and amine bonds with the hydroxyl group in the -SO3H group of SPANI and the amino group in piperazine to construct a preliminary crosslinking network; the carboxyl group of citric acid further undergoes esterification reaction with the hydroxyl group remaining after epoxy crosslinking to form a "covalent bond-hydrogen bond" interwoven network, which inhibits the swelling of the membrane in polar organic solvents such as acetone and toluene at the molecular level, and significantly improves the solvent resistance and long-term operational stability of the membrane.

[0035] 3. This invention optimizes the composition of the functional layers and the preparation process, ensuring high retention rates and solvent resistance while maintaining efficient water molecule transport channels. In antibiotic wastewater treatment, it achieves both deep purification of pollutants and recovery of high-value-added antibiotics from the wastewater, thus offering both environmental and economic benefits.

[0036] In summary, this invention uses sulfonated polyaniline as the main functional separation material of nanofiltration membrane, combined with a dual stabilization strategy of primary crosslinking with epoxy crosslinking agent and secondary crosslinking with citric acid, to form a flat, smooth and more dense functional separation layer on the base membrane surface. Its preparation process is simple and the components interact with each other, which not only improves the separation effect and long-term stability of nanofiltration membrane for different antibiotics, but also improves the solvent resistance of nanofiltration membrane. Attached Figure Description

[0037] Figure 1 Electron microscope scan of the base membrane or nanofiltration membrane;

[0038] exist Figure 1 In the figures, a: PAN ultrafiltration membrane, b: nanofiltration membrane of Example 2, and c: nanofiltration membrane of Comparative Example 1. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In this invention,

[0041] 1. Anhydrous piperazine, purity ≥99%, structural formula shown in Formula 1, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0042] Formula 1;

[0043] 2. Polyaniline, purity ≥98%, structural formula shown in Formula 2, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0044] Formula 2;

[0045] 3. Polyethylene glycol diglycidyl ether, epoxy equivalent: 125-145, structural formula as shown in Formula 3, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] Formula 3;

[0047] 4. Citric acid, purity ≥ 99.5%, structural formula shown in Formula 4, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0048] Equation 4;

[0049] 5. Tetracycline, Mw=444.4, purity ≥96%, electrically neutral, structural formula shown in Formula 5; purchased from Sinopharm Chemical Reagent Co., Ltd.

[0050] Formula 5;

[0051] 6. Tobramycin, Mw=465.5, purity ≥95%, positively charged, structural formula shown in Formula 6, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0052] Formula 6;

[0053] 7. Clindamycin phosphate, Mw=505.0, purity ≥96%, negatively charged, structural formula shown in Formula 7, purchased from Dalian Meilun Biotechnology Co., Ltd.

[0054] Formula 7;

[0055] 8. Amoxicillin, Mw=365.4, purity ≥95%, electrically neutral, structural formula shown in Formula 8, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0056] Formula 8;

[0057] 9. Sulfamethoxazole, Mw=253.28, purity ≥98%, electrically neutral, structural formula shown in Formula 9, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0058] Equation 9;

[0059] 10. Sulfonated polyaniline, prepared in-house, with a degree of sulfonation of 0.8–1.2 mmol / g determined by elemental analysis; structural formula shown in Formula 10.

[0060] Formula 10;

[0061] 11. The reaction formula for doped sulfonated polyaniline is as follows:

[0062]

[0063] 12. Unless otherwise specified, all raw materials used in this invention are commercially available.

[0064] Example 1

[0065] A nanofiltration membrane doped with sulfonated polyaniline is prepared by the following steps:

[0066] Step 1: Preparation of sulfonated polyaniline: Weigh 20.0 g of polyaniline powder and place it in a three-necked flask. Under the conditions of an ice-water bath at 0–5°C, slowly add 110 mL of fuming sulfuric acid (containing 20% ​​SO3) dropwise to the three-necked flask at a speed of 300 r / min while stirring. Control the dropping rate of the fuming sulfuric acid to ensure that the addition is completed within 45 min. During the dropping process, maintain the system temperature below 5°C. After the addition is complete, continue stirring and dispersing for 30 min to ensure that the polyaniline is fully dispersed and a uniform polyaniline suspension is obtained. Then, raise the temperature to 55°C at a rate of 5°C / min. The reaction was kept at a constant temperature and stirred for 2 hours to obtain a dark green sulfonated reaction solution. After the reaction was completed, the reaction solution was slowly poured into a 500 mL ice-water mixture and stirred to allow the reaction product to fully precipitate. The precipitate was collected by filtration, washed with deionized water until the filtrate was neutral, and then washed twice with anhydrous ethanol to remove residual acid and organic impurities. The precipitate was then placed in a vacuum drying oven and dried at 55 °C to constant weight. After drying, it was ball-milled to control the final particle size to 35–50 nm to obtain sulfonated polyaniline (the degree of sulfonation of the prepared sulfonated polyaniline was determined to be 1.0 mmol / g by elemental analysis).

[0067] Step 2, Solution preparation:

[0068] (1) Preparation of surfactant solution: Weigh 0.15g of sodium dodecyl sulfonate, dissolve it in 100mL of 50% ethanol solution, and sonicate it to completely dissolve it, so as to obtain a surfactant solution with a mass concentration of 0.15%.

[0069] (2) Preparation of solution for doped sulfonated polyaniline:

[0070] The doped sulfonated polyaniline solution comprises the following raw materials in the following mass concentrations: anhydrous piperazine: 0.3%, sulfonated polyaniline: 0.1%, epoxy crosslinking agent polyethylene glycol diglycidyl ether: 0.4%; deionized water balance;

[0071] Preparation method: Weigh 0.3g of anhydrous piperazine and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved. Add 0.1g of sulfonated polyaniline and stir continuously for 30 min to form a uniform dispersion. Then add 0.4g of polyethylene glycol diglycidyl ether and stir for another 5 min to obtain a doped sulfonated polyaniline solution.

[0072] (3) Preparation of citric acid aqueous solution: Weigh 1.0g of citric acid and dissolve it in 100mL of deionized water. Stir until completely dissolved to prepare a citric acid aqueous solution with a mass concentration of 1.0% for later use.

[0073] Step 3: Preparation of doped sulfonated polyaniline nanofiltration membrane:

[0074] The PAN ultrafiltration membrane was pretreated by soaking it in deionized water for 4 hours. After removal, it was fixed with resin clamps and the residual moisture on the membrane surface was blown away. Then, an appropriate amount of surfactant solution was poured onto the surface of the PAN ultrafiltration membrane to completely cover the membrane surface. After standing for 5 minutes, the excess liquid was poured off. The membrane was then placed in a 35°C oven to dry for 10 minutes. After removal, the doped sulfonated polyaniline solution was evenly spread on the membrane surface and retained for 5 minutes. Then, the excess liquid was removed by rolling with stainless steel rollers. Subsequently, the membrane was transferred to an 80°C oven for heat curing for 10 minutes. After removal and cooling, the membrane was immersed in a citric acid aqueous solution for 10 minutes to obtain the doped sulfonated polyaniline nanofiltration membrane.

[0075] Example 2

[0076] A nanofiltration membrane doped with sulfonated polyaniline is prepared by the following steps: Same as in Example 1, except that in step 1, fuming sulfuric acid containing 30% SO3 is used to prepare the sulfonated polyaniline, and the degree of sulfonation of the prepared sulfonated polyaniline is determined to be 1.05 mmol / g by elemental analysis.

[0077] Example 3

[0078] A nanofiltration membrane doped with sulfonated polyaniline is prepared by the following steps: Same as in Example 1, except that in step 1, fuming sulfuric acid containing 40% SO3 is used to prepare the sulfonated polyaniline, and the degree of sulfonation of the prepared sulfonated polyaniline is determined to be 1.11 mmol / g by elemental analysis.

[0079] Example 4

[0080] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: Same as Example 2, except that...

[0081] In step 2, the citric acid solution is prepared by dissolving 0.5g of citric acid in 100mL of deionized water to prepare a citric acid aqueous solution with a mass concentration of 0.5%.

[0082] Example 5

[0083] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: Same as Example 2, except that...

[0084] In step 2, the citric acid solution is prepared by dissolving 2.0g of citric acid in 100mL of deionized water to prepare a citric acid aqueous solution with a mass concentration of 2.0%.

[0085] Example 6

[0086] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: Same as Example 2, except that...

[0087] In step 2, the preparation of the doped sulfonated polyaniline solution is as follows: 0.5 g of polyethylene glycol diglycidyl ether is added; the mass concentration of polyethylene glycol diglycidyl ether, an epoxy crosslinking agent, in the doped sulfonated polyaniline solution is 0.5%.

[0088] Example 7

[0089] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: Same as Example 2, except that...

[0090] In step 2, the preparation of the doped sulfonated polyaniline solution is as follows: 0.6 g of polyethylene glycol diglycidyl ether is added; the mass concentration of polyethylene glycol diglycidyl ether, an epoxy crosslinking agent, in the doped sulfonated polyaniline solution is 0.6%.

[0091] Comparative Example 1

[0092] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: the same as in Example 2, except that deionized water is used instead of the citric acid aqueous solution in the example.

[0093] Comparative Example 2

[0094] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: the same as in Example 2, except that 0.4g of glutaraldehyde, a crosslinking agent without epoxy groups, is used to replace the polyethylene glycol diglycidyl ether in Example 2, and the mass concentration of glutaraldehyde is 0.4%.

[0095] Comparative Example 3

[0096] A doped sulfonated polyaniline nanofiltration membrane is prepared by the following steps: Similar to Example 2, except that 0.4g of glutaraldehyde (a crosslinking agent without epoxy groups) is used instead of polyethylene glycol diglycidyl ether in Example 2, and deionized water is used instead of the citric acid aqueous solution in Example 2. Glutaraldehyde is an aldehyde crosslinking agent, lacking epoxy groups, and cannot form ether bonds with the sulfonic acid groups of SPANI. It can only undergo a Schiff base reaction between the aldehyde group and the amino group, resulting in lower crosslinking efficiency and poorer stability of the formed crosslinked network compared to Example 2.

[0097] Comparative Example 4

[0098] A nanofiltration membrane doped with sulfonated polyaniline is prepared by the following steps: the same as in Example 2, except that piperazine is not added to the solution of doped sulfonated polyaniline.

[0099] Comparative Example 5

[0100] A polyaniline-doped nanofiltration membrane is prepared by means of the following steps: the same as in Example 2, except that a polyaniline solution is used instead of the doped sulfonated polyaniline solution in Example 2. The preparation method of the polyaniline solution is the same as that of the doped sulfonated polyaniline solution in Example 2, except that polyaniline is used instead of sulfonated polyaniline.

[0101] Comparative Example 6

[0102] A polyaniline-free nanofiltration membrane is prepared by the following steps: Same as in Example 2, except that sulfonated polyaniline is not added in step 4, and a separation layer solution containing only anhydrous piperazine and polyethylene glycol diglycidyl ether is prepared.

[0103] Comparative Example 7

[0104] A pure polyaniline nanofiltration membrane is prepared by the following steps:

[0105] Step 1, Solution preparation:

[0106] (1) Preparation of surfactant solution: Same as in Example 2;

[0107] (2) Preparation of polyaniline solution: 0.1 g of polyaniline powder was ball-milled to 40 nm and dispersed in 100 mL of deionized water to obtain a polyaniline solution (the mass concentration of polyaniline was 0.1%).

[0108] Step 2, Preparation of polyaniline nanofiltration membrane:

[0109] First, the PAN ultrafiltration membrane was pretreated by soaking it in deionized water for 4 hours. After removal, it was fixed with resin clamps and the residual moisture on the membrane surface was blown away. Then, an appropriate amount of surfactant solution was poured onto the surface of the PAN ultrafiltration membrane to completely cover the membrane surface. After standing for 5 minutes, the excess liquid was poured off. Then, the membrane was placed in a 35°C oven to dry for 10 minutes. After removal, the polyaniline solution was directly applied to the membrane surface and heat-cured at 80°C for 10 minutes to obtain the polyaniline nanofiltration membrane.

[0110] Comparative Example 8:

[0111] Commercially available polyamide nanofiltration membranes (Veolia DK series, molecular weight cutoff between 150 and 300 Da).

[0112] Example 1: Electron microscope scanning

[0113] Surface scanning electron microscopy (SEM) was performed on the PAN ultrafiltration membrane and the nanofiltration membranes prepared in Example 2 and Comparative Example 1. The results are shown in the figure. Figure 1 ;

[0114] from Figure 1 The results show that:

[0115] 1) The PAN ultrafiltration membrane has many defects and an irregular pore structure (see...). Figure 1 (a)

[0116] 2) In Example 2, under the dual crosslinking effect of piperazine-doped SPANI with epoxy crosslinking agents and citric acid, a smooth, denser surface layer was formed on the membrane surface. The SPANI nanoparticles were uniformly dispersed without agglomeration, and the pore structure was effectively filled (see...). Figure 1 (b)

[0117] 3) Comparative Example 1, which underwent crosslinking modification with anhydrous piperazine and polyethylene glycol diglycidyl ether and was filled with sulfonated polyaniline but did not undergo secondary crosslinking modification with citric acid, still exhibited a significant membrane pore structure on its membrane surface, resulting in insufficient compactness (see Comparative Example 1). Figure 1 (c in the text)

[0118] Example 2: Solvent Resistance Test

[0119] 1. Solvent resistance of the nanofiltration membrane in Example 2 to different solvents

[0120] The nanofiltration membrane prepared by the method in Example 2 was dried and ground, and then pressed into tablets with a diameter of 10 mm and a thickness of 1 mm using a tablet press. The tablets were accurately weighed (m0) and immersed in different solvents. After 48 hours, the tablets were removed, the residual solvent on the surface was absorbed with filter paper, and the tablets were accurately weighed (m1). The morphological changes were observed, and the solvent adsorption rate was calculated (adsorption rate = (m1-m0) / m0×100%). The results are shown in Table 1.

[0121] Table 1

[0122]

[0123] For solvents like ethanol, which have properties similar to water, nanofiltration membrane materials are formed solely through physical processes during tableting, failing to effectively maintain their cross-linked structure. Furthermore, the presence of hydrophilic components in the nanofiltration membrane material facilitates the binding of hydroxyl groups, leading to ethanol molecules intruding into the sheet structure and gradually dispersing without dissolving. In practical applications, when antibiotic wastewater contains hydrophilic solvents such as ethanol, stability can be improved through membrane module encapsulation optimization.

[0124] Nanofiltration membrane materials maintain their morphological stability in common organic solvents such as acetone, DMF, and toluene, without significant dissolution or structural damage. The adsorption rates of nanofiltration membrane materials in different solvents are in the following order: DMF > toluene > acetone > ethyl acetate.

[0125] 2. Solvent resistance of nanofiltration membranes in acetone for each embodiment and comparative example: The solvent adsorption rate of the membranes was determined using acetone as the solvent according to the method in Part 1 above; the results are shown in Table 2.

[0126] Table 2

[0127]

[0128] From the data in Table 2, we can see that:

[0129] 1) As can be seen from the comparison between Examples 1-7 and Comparative Examples 1-9, the introduction of sulfonated polyaniline in this invention, as well as the dual crosslinking stabilization scheme of "initial crosslinking with epoxy crosslinking agent and secondary crosslinking with citric acid", enables the present invention to form a flat, smooth and more dense functional separation layer, thereby inhibiting the swelling of nanofiltration membrane in polar organic solvents such as acetone and toluene. Compared with traditional polyamide nanofiltration membranes, it significantly improves the solvent resistance and long-term operational stability of the membrane.

[0130] 2) The acetone adsorption rate of Example 2 was the lowest because its fuming sulfuric acid sulfonation degree was appropriate and the network was dense under double cross-linking. Compared with Example 2, Example 5 had a slightly higher adsorption rate because the citric acid concentration was higher and some cross-linking sites reacted excessively, resulting in an increase in porosity. Compared with Example 2, Example 6 and Example 7 had an increased epoxy cross-linking agent, and the excessive cross-linking in the membrane caused micropores, increasing the adsorption rate to about 30%.

[0131] In summary, the introduction of sulfonic acid groups on polyaniline, the selection of epoxy crosslinking agents, the participation of piperazine and citric acid, and the dosage of each reagent in this invention form an organic whole, and their interaction has a crucial impact on the solvent resistance of nanofiltration membranes.

[0132] Example of effect 3:

[0133] The nanofiltration membranes prepared in each example and comparative example were placed in a test apparatus. Under the test conditions of 25°C, 70 psi pressure, and feed solutions of 500 ppm NaCl, 1000 ppm NaSO4, 1000 ppm tetracycline, 1000 ppm amoxicillin, 1000 ppm tobramycin, 1000 ppm clindamycin phosphate, and 100 ppm sulfamethoxazole aqueous solution, after the membranes had been running stably for 30 min, their pure water flux and rejection rate were measured. Salt concentration was measured using a conductivity meter (DDSJ-308A, Shanghai Instrument & Electronics Scientific Instruments Co., Ltd.), and antibiotic concentration was measured using a total organic carbon analyzer (TOC, Shimadzu, TOC-LCPH, Japan). The results are shown in Tables 3-4.

[0134] Table 3

[0135]

[0136] Table 4

[0137]

[0138] From the data in Tables 3 and 4, we can see that:

[0139] 1) The doped sulfonated polyaniline nanofiltration membranes prepared in Examples 1-7 of this invention exhibit excellent separation selectivity and mass transfer efficiency through the synergistic effect of "pore size sieving effect and Donnan effect". 35–50 nm SPANI nanoparticles are uniformly dispersed in a piperazine-epoxy crosslinking system. The pore size of the separation layer is precisely controlled through the particle filling effect. The sulfonic acid groups contained in its molecular structure provide stable negative surface charge sites for the separation layer, enhancing the retention of substances with different charges and neutrality. Membrane performance test results show that the nanofiltration membrane achieves a retention rate of 97.36%–98.62% for divalent salt Na2SO4, a retention rate of 97.38%–99.18% for target antibiotics such as clindamycin phosphate and tetracycline, and a retention rate of 40.10%–60.93% for monovalent salt NaCl, demonstrating good ion selectivity. Meanwhile, the "primary crosslinking with epoxy crosslinking agent and secondary crosslinking with citric acid" constructs a dense and stable crosslinking network, which effectively preserves efficient water molecule transport channels while ensuring high retention performance. The pure water flux can reach 22.00-39.87 LMH, which is superior to the commercially available Veolia DK series nanofiltration membrane (31.64 LMH). It successfully achieves synergistic optimization of separation selectivity and water permeability, meeting the needs of deep purification and resource recovery of antibiotic wastewater.

[0140] 2) In Comparative Example 1, no secondary crosslinking with citric acid was performed; in Comparative Example 2, the epoxy crosslinking agent was replaced; in Comparative Example 3, the epoxy crosslinking and citric acid crosslinking were cancelled; and in Comparative Example 4, piperazine was not added and the piperazine-epoxy crosslinking network could not be formed. All these operations resulted in the nanofiltration membrane failing to form a stable and dense membrane structure, which led to an abnormally high water flux and a significant decrease in the rejection rate of salt and antibiotics.

[0141] In contrast, when polyaniline was replaced with sulfonated polyaniline in Comparative Example 5, the Donnan effect was lost due to the lack of sulfonic acid groups, resulting in a significant decrease in its antibiotic retention rate.

[0142] In contrast, without the addition of sulfonated polyaniline, the separation layer pore size control was missing in Comparative Example 6, confirming that the pore size sieving effect of sulfonated polyaniline is the key to achieving precise pore size sieving, which led to a significant decrease in both water flux and antibiotic rejection rate.

[0143] Comparative Example 7 used only traditional polyaniline without sulfonation modification and multiple crosslinking treatment, resulting in a membrane structure lacking effective separation function. This further verifies the innovation and necessity of the sulfonation modification and dual crosslinking process of this invention.

[0144] Comparative Example 8 showed an antibiotic rejection rate close to that of some examples, but lacked sulfonated polyaniline doping and a double cross-linked structure, resulting in poor solvent resistance. It was prone to failure due to swelling during long-term operation, and its pure water flux (31.64 LMH) was lower than that of most examples.

[0145] Therefore, the data above shows that the introduction of sulfonated polyaniline and its sulfonic acid groups, the selection of epoxy crosslinking agents, the participation of piperazine and citric acid, and the amount of each reagent form an organic whole. Their interaction has a crucial impact on the salt rejection performance, antibiotic rejection performance, and water flux of nanofiltration membranes.

[0146] The embodiments described above are merely preferred embodiments of the present invention, and not an exhaustive list of all possible implementations of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a doped sulfonated polyaniline nanofiltration membrane, characterized in that, Includes the following steps: First, the surfactant solution is poured onto the surface of the ultrafiltration base membrane and allowed to stand. Then, excess liquid is removed and the membrane is dried. Next, the doped sulfonated polyaniline solution is evenly spread on the membrane surface and excess liquid is removed by rollers. Then, the membrane is heat-cured. After the heat curing is completed, the membrane is immersed in a citric acid aqueous solution and then removed to obtain the doped sulfonated polyaniline nanofiltration membrane. The doped sulfonated polyaniline solution comprises the following raw materials in the following mass percentages: anhydrous piperazine: 0.2-0.5%, sulfonated polyaniline: 0.01-0.2%, epoxy crosslinking agent: 0.2-0.6%, and deionized water: balance; The citric acid aqueous solution has a citric acid concentration of 0.5-5% by mass.

2. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 1, characterized in that, The surfactant in the surfactant solution has a mass concentration of 0.05-0.2%, and the solvent used in the surfactant solution is an ethanol solution with a mass concentration of 50%.

3. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 2, characterized in that, The surfactant is one or more of sodium dodecyl sulfonate, sodium dioctyl succinate sulfonate, sodium dodecyltrimethylammonium bromide, sodium dodecyl sulfate, or sodium dodecylbenzene sulfonate.

4. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 1, characterized in that, The method for preparing the doped sulfonated polyaniline solution includes: firstly, dissolving anhydrous piperazine in deionized water, stirring until dissolved, then adding sulfonated polyaniline, continuing to stir until a uniform dispersion is formed, then adding an epoxy crosslinking agent, stirring for 3-5 minutes until dissolved, to obtain the doped sulfonated polyaniline solution.

5. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 1, characterized in that, The epoxy crosslinking agent is one or more of epichlorohydrin, tert-butyl glycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerol triglycidyl ether.

6. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 4, characterized in that, The preparation method of the sulfonated polyaniline includes the following steps: In an ice-water bath at 0–5°C, polyaniline powder is stirred and dispersed evenly. Fuming sulfuric acid is then added dropwise to the polyaniline powder while stirring until a polyaniline suspension is formed. After the addition is complete, the mixture is heated to 40–60°C at a rate of 5–10°C / min and stirred at 300–500 r / min until evenly dispersed. The reaction is carried out for 1.5–3 hours to obtain a sulfonation reaction solution. After the reaction is completed, the sulfonation reaction solution is poured into an ice-water mixture and stirred to precipitate. The precipitate is then collected, washed, dried, and ball-milled to obtain sulfonated polyaniline.

7. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 6, characterized in that, The ratio of polyaniline powder to fuming sulfuric acid is 5-20g: 100-200mL; The fuming sulfuric acid should be added dropwise over a period of 30–60 minutes. During washing, the precipitate is first washed repeatedly with deionized water until the filtrate is neutral, and then washed with anhydrous ethanol. The drying process employs vacuum drying, and the temperature of the vacuum drying is 50–60°C. The particle size of the ball-milled sulfonated polyaniline is 35–50 nm.

8. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 6, characterized in that, The ultrafiltration membrane is any one of PES ultrafiltration membrane, PSF ultrafiltration membrane, PAN ultrafiltration membrane, PVDF ultrafiltration membrane or PTFE ultrafiltration membrane; The ultrafiltration membrane needs to be pretreated before use. The pretreatment method includes: soaking the ultrafiltration membrane in deionized water at 20-25°C for 4-6 hours, taking it out before use, blowing away residual moisture on the surface, and then setting it aside.

9. The method for preparing a doped sulfonated polyaniline nanofiltration membrane according to claim 1, characterized in that, The surfactant solution is allowed to stand on the surface of the ultrafiltration membrane for 3 to 5 minutes. The drying temperature is 30–40°C; The residence time of the doped sulfonated polyaniline solution on the surface of the ultrafiltration membrane is 5 to 10 minutes; The thermosetting temperature is 80-90℃, and the thermosetting time is 8-10 min; The thermocured film is immersed in citric acid solution for 5 to 10 minutes.

10. The application of the doped sulfonated polyaniline nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 9 in the treatment of antibiotic wastewater.

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