Preparation method and application of pH-responsive zwitterionic modified nylon membrane

Abstract

This invention discloses a method for preparing a pH-responsive zwitterionic modified nylon membrane and its applications. The preparation method involves: adding an organic acid solution, additives, and dissolving nylon particles in a reaction vessel to obtain a casting solution; casting the solution onto a glass plate and scraping it with a doctor blade until a film is formed; adding phosphate buffer, n-hexane, dioctyl succinate, and the zwitterionic polymer to be modified, along with a phenylacetaldehyde dimethyl acetal modifier, to the reaction vessel to obtain an acetal-modified zwitterionic polymer; and grafting the acetal-modified zwitterionic polymer onto the nylon surface using a crosslinking agent to obtain the pH-responsive zwitterionic modified nylon membrane. Through chemical polymerization and grafting modification onto the nylon surface, in a weakly acidic environment, the acetal groups react with the environment and hydrolyze into the corresponding aldehydes and alcohols, balancing the charge of the zwitterionic polymer. This allows for the acquisition of a highly efficient nylon membrane with low protein adsorption even in a weakly acidic environment.

Description

Technical Field

[0001] This invention relates to the field of microfiltration membrane separation, specifically to a method for preparing a pH-responsive zwitterionic modified nylon membrane and its application. Background Technology Nylon membranes are a commonly used polymer membrane. Compared with other traditional polymer membrane materials (such as polyvinylidene fluoride and polysulfone), they have better natural hydrophilicity and biocompatibility. Furthermore, due to their semi-crystalline structure, they also possess good mechanical, thermal stability, and chemical properties. However, when the surface of an unmodified nylon membrane comes into contact with the separation solution, the irregular network structure on the membrane surface can capture proteins from the bulk solution. This causes irreversible protein adsorption onto the membrane surface or within the pores, forming protein aggregates, leading to biofouling and reduced membrane separation performance. Surface modification of membranes is an effective way to reduce protein adsorption. Among many polymers, zwitterionic polymers have attracted much attention due to their unique properties. Zwitterionic polymer molecules contain both anions and cations; at specific pH values, they can form a hydrated layer on the material surface through electrostatic interactions, effectively reducing the adsorption of proteins, bacteria, and cells (PS Liu et al, Journal of Membrane Science, 2010, 350, 387-394). Samsung Electronics Co., Ltd. (EP 2544002 A1) used zwitterionic polymers to modify the surface of PVDF membranes, effectively reducing the non-specific adsorption of proteins. At pH 7.4, the non-specific adsorption of proteins decreased by up to 57.1%.

[0002] However, the charge of zwitterionic polymers easily changes with the pH of the solution. For example, in a neutral environment, zwitterions are electroneutrally neutral; in an acidic environment, the polymers exhibit a positive charge. Since proteins carry a negative charge, the adsorption of proteins inevitably increases under acidic conditions. To address this issue, phenylacetaldehyde dimethyl acetal, which has pH-responsive properties, is used. When zwitterionic polymers are grafted and modified, their ionization level changes with changes in environmental pH, leading to changes in their surface chemical state. This maintains the charge conservation of zwitterions and reduces the adsorption of proteins by the material. Therefore, using acetal-grafted zwitterionic polymers for surface modification of nylon membranes can produce a nylon membrane with pH-responsive characteristics and low protein adsorption. Summary of the Invention

[0003] The purpose of this invention is to solve the above problems by proposing a method for preparing a pH-responsive zwitterionic modified nylon membrane and its application. To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a pH-responsive zwitterionic modified nylon membrane, characterized by comprising the following steps in sequence: S1 Preparation of Nylon Membrane: Add organic acid solution as solvent and additive as non-solvent to reaction vessel. Add nylon to the solution to dissolve. Stir at room temperature for 10-24 h to prepare casting solution. Let the casting solution stand for 12-24 h for degassing treatment. Prepare nylon membrane at a temperature of 20-30 ℃ and relative humidity of 40-60%. The specific steps are as follows: Use a 200-600 nm thick film scraper to uniformly coat the casting solution on the surface of a quartz plate. Immerse the quartz plate loaded with casting solution in a coagulation bath for 3 min to complete the phase inversion. Then put it into pure water to clean the residue on the membrane surface. S2 acetal-grafted modified zwitterionic polymer: with n-hexane as the continuous phase and dioctyl succinate as the surfactant; in an aqueous phase (5 mL, pH 8.4) of 100 mM phosphate buffer, the zwitterionic polymer to be modified and phenylacetaldehyde dimethyl acetal modifier are added, and the reaction is carried out at 90-120 °C for 6-10 h.

[0004] S3 Nylon Membrane Modification: The prepared nylon membrane was hydrolyzed in an acid solution for 2–6 h, the membrane surface was cleaned with water and ethanol, and dried; the hydrolyzed membrane was placed again in a solution containing a crosslinking agent, an appropriate amount of catalyst was added to promote crosslinking, and it was activated at 60–80 ℃ for 3–10 h, washed with hot water at 40–50 ℃, and dried; the activated membrane was then placed in a certain concentration of zwitterionic polymer and reacted at 60–80 ℃ for 1–3 h, washed and dried to prepare a zwitterionic modified nylon membrane.

[0005] Preferably, the organic acid solvent is one or a combination of formic acid and acetic acid; the organic acid mass fraction accounts for 60% to 80% of the mass fraction of the casting solution; the non-solvent additive is one or a combination of methanol, ethanol, n-propanol, and n-butanol; the additive mass fraction accounts for 0.01% to 10% of the mass fraction of the casting solution.

[0006] Preferably, the coagulation bath is a mixed solution of methanol and water; the mass ratio of methanol to water is in the range of 1:10 to 1:1.

[0007] Preferably, the acid solution is one or a combination of hydrochloric acid, sulfuric acid, and phosphoric acid; the concentration of the acid solution is 1 to 5 M.

[0008] Preferably, the crosslinking agent is one or a combination of formaldehyde, glutaraldehyde, epichlorohydrin, and sodium tripolyphosphate; the mass fraction is 0.5 to 2 wt%.

[0009] Preferably, the mass of n-hexane is 4–10 g; the mass of dioctyl succinate is 0.5–1.0 g; the mass of betaine is 1.0–5.0 g; and the mass of phenylacetaldehyde dimethyl acetal is 0.5–1.0 g.

[0010] Preferably, the catalyst is one of ZnO and CuO; the mass of the catalyst used is 0.1 to 1.0 g.

[0011] Preferably, the zwitterionic polymer is one of acetal-grafted modified hydroxysulfopropyl betaine, phosphate betaine, or carboxylic acid ester betaine; the mass fraction of the polymer solution ranges from 1 to 10 wt%.

[0012] Preferably, the pH control range is 5.0 to 7.4.

[0013] The use of a pH-responsive zwitterionic modified nylon membrane is characterized in that: the pH-responsive zwitterionic modified nylon membrane is used in the production of filter membranes and filter cartridges. The beneficial effects of this invention are as follows: By using zwitterionic polymerized acetal to graft and modify nylon membranes, on the one hand, zwitterionic polymers can reduce the adsorption of proteins by nylon membranes by balancing charges; on the other hand, the polymerization of acetals solves the problem that zwitterionic polymers cannot balance charges under acidic conditions. That is, under weakly acidic conditions, acetals generate negatively charged aldehyde groups and methanol through pH response, thereby balancing charges, thus obtaining nylon membranes with low protein adsorption under weakly acidic conditions.

[0014] By adding a catalyst, not only is the concentration of crosslinking agent reduced, but the modified surface also exhibits a more stable network structure, thereby enhancing the stability of membrane operation. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the pH response process of the zwitterionic modified nylon membrane of the present invention.

[0016] Figure 2 This is a scanning electron microscope image of the cross-section of the comparative sample 3 of this invention.

[0017] Figure 3 This is a scanning electron microscope image of the surface of comparative sample 3 of this invention.

[0018] Figure 4 This is a graph showing the effect of pH on membrane adsorption according to the present invention. Detailed Implementation

[0019] The following description, in conjunction with the accompanying drawings, further illustrates the preparation method and application of a pH-responsive zwitterionic modified nylon membrane according to the present invention. Example 1 S1 base film preparation: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution and dissolved. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing. The nylon membrane was prepared at 20 ℃ and 60% relative humidity. The specific steps were as follows: The casting solution was uniformly coated onto the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (water to methanol volume ratio of 7:3) for 3 min to complete the phase inversion. Then, the membrane surface was washed with pure water to remove any residue. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of hydroxysulfopropyl betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified hydroxysulfopropyl betaine.

[0020] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h. The membrane surface was cleaned with water and ethanol and dried. The hydrolyzed membrane was then placed in a solution containing 2 wt% glutaraldehyde, and 0.2 g of CuO catalyst was added to promote crosslinking. The membrane was activated at 60 °C for 3 h, washed with hot water at 40 °C, and dried. The activated membrane was then placed in 0.5 mM acetal-grafted modified hydroxysulfopropyl betaine zwitterionic polymer and reacted at 60 °C for 3 h. After washing and drying, the zwitterionic modified nylon membrane was prepared.

[0021] The modified nylon membrane had an average pore size of 0.21 μm, a porosity of 89.3%, and a flow rate of 11660 L·m⁻²·h⁻¹·bar⁻¹. The membrane's protein adsorption capacity was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 11.73 mg / g at pH 5.5, 10.25 mg / g at pH 6.0, 8.83 mg / g at pH 6.8, and 7.54 mg / g at pH 7.4. Example 2 Preparation of S1 base film: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution and dissolved. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon membrane was prepared at 20 ℃ and 60% relative humidity. The specific steps were as follows: the casting solution was uniformly coated onto the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (water to methanol volume ratio of 7:3) for 3 min to complete the phase inversion. Then, the membrane surface was washed with pure water to remove residues. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of phosphate betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified phosphate betaine.

[0022] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h. The membrane surface was cleaned with water and ethanol and dried. The hydrolyzed membrane was then placed in a solution containing 2 wt% glutaraldehyde, and 0.2 g of CuO catalyst was added to promote crosslinking. The membrane was activated at 60 ℃ for 3 h, washed with hot water at 40 ℃, and dried. The activated membrane was then placed in 0.5 mM acetal-grafted modified phosphate betaine zwitterionic polymer and reacted at 60 ℃ for 3 h. After washing and drying, the zwitterionic modified nylon membrane was prepared.

[0023] The modified nylon membrane had an average pore size of 0.2 μm, a porosity of 86.2%, and a flow rate of 10770 L·m⁻²·h⁻¹·bar⁻¹. The membrane's adsorption capacity for proteins was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 8.17 mg / g at pH 5.5, 7.82 mg / g at pH 6.0, 7.58 mg / g at pH 6.8, and 7.20 mg / g at pH 7.4. Example 3 S1 base film preparation: 77.5 g formic acid solution was added to the reaction vessel as a solvent, 7.5 g methanol was added as a non-solvent, 15 g nylon was added to the solution to dissolve, and the mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon film was prepared at a temperature of 20 ℃ and a relative humidity of 60%. The specific steps were as follows: the casting solution was uniformly coated on the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (the volume ratio of water to methanol was 7:3) for 3 min to complete the phase inversion. Then, the membrane surface residue was washed in pure water. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of carboxylic acid ester betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified carboxylic acid ester betaine.

[0024] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h. The membrane surface was cleaned with water and ethanol and dried. The hydrolyzed membrane was then placed in a solution containing 2 wt% glutaraldehyde, and 0.2 g of CuO catalyst was added to promote crosslinking. The membrane was activated at 60 °C for 3 h, washed with hot water at 40 °C, and dried. The activated membrane was then placed in 0.5 mM acetal-grafted modified phosphate betaine zwitterionic polymer and reacted at 60 °C for 3 h. After washing and drying, the zwitterionic modified nylon membrane was prepared.

[0025] The modified nylon membrane had an average pore size of 0.21 μm, a porosity of 87.3%, and a flow rate of 11200 L·m⁻²·h⁻¹·bar⁻¹. The membrane's adsorption capacity for proteins was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 10.32 mg / g at pH 5.5, 9.04 mg / g at pH 6.0, 8.56 mg / g at pH 6.8, and 7.41 mg / g at pH 7.4. Example 4 Preparation of S1 base film: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution to dissolve it, and the mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon film was prepared at 20 ℃ and 60% relative humidity. The specific steps were as follows: the casting solution was uniformly coated on the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (water to methanol volume ratio of 7:3) for 3 min to complete the phase inversion. Then, the membrane surface was washed with pure water to remove any residue. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of phosphate betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified phosphate betaine.

[0026] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h. The membrane surface was cleaned with water and ethanol and dried. The hydrolyzed membrane was then placed in a solution containing 2 wt% glutaraldehyde, and 0.2 g of ZnO catalyst was added to promote crosslinking. The membrane was activated at 60 ℃ for 3 h, washed with hot water at 40 ℃, and dried. The activated membrane was then placed in 0.5 mM acetal-grafted modified phosphate betaine zwitterionic polymer and reacted at 60 ℃ for 3 h. After washing and drying, the zwitterionic modified nylon membrane was prepared.

[0027] The modified nylon membrane had an average pore size of 0.2 μm, a porosity of 85.9%, and a flow rate of 10570 L·m⁻²·h⁻¹·bar⁻¹. The membrane's adsorption capacity for proteins was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 7.98 mg / g at pH 5.5, 7.53 mg / g at pH 6.0, 7.12 mg / g at pH 6.8, and 6.90 mg / g at pH 7.4. Example 5 S1 base film preparation: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution to dissolve it. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon film was prepared at a temperature of 20 ℃ and a relative humidity of 60%. The specific steps were as follows: the casting solution was uniformly coated on the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (the volume ratio of water to methanol was 7:3) for 3 min to complete the phase inversion. Then, the membrane surface residue was washed in pure water. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of phosphate betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified phosphate betaine.

[0028] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h. The membrane surface was cleaned with water and ethanol and dried. The hydrolyzed membrane was then placed in a solution containing 2 wt% formaldehyde, and 0.2 g of CuO catalyst was added to promote crosslinking. The membrane was activated at 60 ℃ for 3 h, washed with hot water at 40 ℃, and dried. The activated membrane was then placed in 0.5 mM acetal-grafted modified phosphate betaine zwitterionic polymer and reacted at 60 ℃ for 3 h. After washing and drying, the zwitterionic modified nylon membrane was prepared.

[0029] The modified nylon membrane had an average pore size of 0.21 μm and a porosity of 88.5%. The flow rate was 12030 L·m⁻²·h⁻¹·bar⁻¹. The membrane's adsorption capacity for proteins was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 12.57 mg / g at pH 5.5, 10.65 mg / g at pH 6.0, 9.38 mg / g at pH 6.8, and 8.91 mg / g at pH 7.4. Example 6 S1 base film preparation: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution to dissolve it. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon film was prepared at a temperature of 20 ℃ and a relative humidity of 60%. The specific steps were as follows: the casting solution was uniformly coated on the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (the volume ratio of water to methanol was 7:3) for 3 min to complete the phase inversion. Then, the membrane surface residue was washed in pure water. Preparation of S2 acetal-grafted modified zwitterionic polymer: Using 4 g of n-hexane as the continuous phase and 0.5 g of dioctyl succinate as the surfactant in an aqueous phase (5 mL, pH 8.4, 100 mM phosphate buffer), 1.0 g of phosphate betaine and 0.5 g of phenylacetaldehyde dimethyl acetal were added as modifiers. The reaction was carried out at 90 °C for 6 h to obtain acetal-grafted modified phosphate betaine.

[0030] Preparation of S3 pH-responsive modified nylon membrane: The prepared nylon membrane was hydrolyzed in C hydrochloric acid solution for 6 h, the membrane surface was cleaned with water and ethanol, and dried; the hydrolyzed membrane was placed again in a solution containing 2 wt% epichlorohydrin, 0.2 g CuO catalyst was added to promote crosslinking, activated at 60 ℃ for 3 h, washed with hot water at 40 ℃, and dried; the activated membrane was then placed in 0.5 mM acetal-grafted modified phosphate betaine zwitterionic polymer, reacted at 60 ℃ for 3 h, washed and dried to prepare zwitterionic modified nylon membrane.

[0031] The modified nylon membrane had an average pore size of 0.2 μm, a porosity of 86.4%, and a flow rate of 10320 L·m⁻²·h⁻¹·bar⁻¹. The membrane's adsorption capacity for proteins was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 8.50 mg / g at pH 5.5, 8.14 mg / g at pH 6.0, 7.78 mg / g at pH 6.8, and 7.37 mg / g at pH 7.4. Comparative Example 1 Base membrane preparation: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution and dissolved. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing. Nylon membranes were prepared at 20 ℃ and 60% relative humidity. The specific steps were as follows: the casting solution was uniformly coated onto the surface of a quartz plate using a scraper with a thickness of 100–500 nm. The quartz plate loaded with the casting solution was immersed in a coagulation bath (water to methanol volume ratio of 7:3) for 3 min to complete the phase inversion. Then, the membrane surface was washed with pure water to remove residues. The parameters of the original membrane sample are shown in Table 1 below. Table 1

[0032] The data in the table clearly shows that, with the membrane solution ratio and coagulation bath composition remaining constant, the thickness of the scraper has little effect on the porosity of the formed membrane, but a great effect on the membrane thickness. Moreover, the amount of protein adsorbed increases with the increase of membrane thickness. Comparative Example 2 S1 base film preparation: 77.5 g of formic acid solution was added to the reaction vessel as a solvent, and 7.5 g of methanol was added as a non-solvent. 15 g of nylon was added to the solution to dissolve it. The mixture was stirred at room temperature for 24 h to prepare the casting solution. The casting solution was allowed to stand for 24 h for degassing treatment. Nylon film was prepared at a temperature of 20 ℃ and a relative humidity of 60%. The specific steps were as follows: the casting solution was uniformly coated on the surface of a quartz plate using a 300 nm thick film scraper. The quartz plate loaded with the casting solution was immersed in a coagulation bath (the volume ratio of water to methanol was 7:3) for 3 min to complete the phase inversion. Then, the membrane surface residue was washed in pure water.

[0033] Preparation of S2 zwitterionic polymer-modified nylon membrane: The prepared nylon membrane was hydrolyzed in 100 mL of 2 M hydrochloric acid solution for 6 h, the membrane surface was washed with water and ethanol, and dried; the hydrolyzed membrane was placed again in a solution containing 2 wt% glutaraldehyde and activated at 60 ℃ for 3 h, washed with hot water at 40 ℃, and dried; the activated membrane was then placed in 0.5 mM hydroxysulfopropyl betaine zwitterionic polymer and reacted at 60 ℃ for 3 h, washed and dried to prepare the zwitterionic modified nylon membrane.

[0034] The modified nylon membrane had an average pore size of 0.22 μm, a porosity of 90.1%, and a flow rate of 14025 L·m⁻²·h⁻¹·bar⁻¹. The membrane's protein adsorption capacity was measured using a 1.0 mg / L BSA solution. The adsorption capacity for BSA was 46.34 mg / g at pH 5.5, 28.56 mg / g at pH 6.0, 20.37 mg / g at pH 6.8, and 12.80 mg / g at pH 7.4.

[0035] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a pH-responsive zwitterionic modified nylon membrane, characterized in that: This includes performing the following steps in sequence: S1 Preparation of Nylon Membrane: Add organic acid solution as solvent and additive as non-solvent to reaction vessel. Add nylon to the solution to dissolve. Stir at room temperature for 10-24 h to prepare casting solution. Let the casting solution stand for 12-24 h for degassing treatment. Prepare nylon membrane at a temperature of 20-30 ℃ and relative humidity of 40-60%. The specific steps are as follows: Use a 200-600 nm thick film scraper to uniformly coat the casting solution on the surface of a quartz plate. Immerse the quartz plate loaded with casting solution in a coagulation bath for 3 min to complete the phase inversion. Then put it into pure water to clean the residue on the membrane surface. S2 acetal-grafted modified zwitterionic polymer: using n-hexane as the continuous phase and dioctyl succinate as the surfactant; in an aqueous phase (5 mL, pH 8.4) of 100 mM phosphate buffer, the zwitterionic polymer to be modified and phenylacetaldehyde dimethyl acetal modifier are added, and the reaction is carried out at 90–120 °C for 6–10 h; the zwitterionic polymer is one of acetal-grafted modified hydroxysulfopropyl betaine, phosphate betaine, and carboxylic acid ester betaine; the mass of n-hexane is 4–10 g; the mass of dioctyl succinate is 0.5–1.0 g; the mass of betaine is 1.0–5.0 g; and the mass of phenylacetaldehyde dimethyl acetal is 0.5–1.0 g. S3 Nylon Membrane Modification: The prepared nylon membrane is hydrolyzed in an acid solution for 2–6 h, the membrane surface is cleaned with water and ethanol, and then dried. The hydrolyzed membrane is then placed in a solution containing a crosslinking agent, and an appropriate amount of catalyst is added to promote crosslinking. The membrane is activated at 60–80 °C for 3–10 h, washed with hot water at 40–50 °C, and dried. The activated membrane is then immersed in a zwitterionic polymer of a certain concentration and reacted at 60–80 °C for 1–3 h. After washing and drying, a zwitterionic modified nylon membrane is prepared. The catalyst is one of ZnO and CuO.

2. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The organic acid solvent is one or a combination of formic acid and acetic acid; the organic acid mass fraction accounts for 60% to 80% of the mass fraction of the casting solution; the non-solvent additive is one or a combination of methanol, ethanol, n-propanol, and n-butanol; the additive mass fraction accounts for 0.01% to 10% of the mass fraction of the casting solution.

3. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The coagulation bath is a mixed solution of methanol and water; the mass ratio of methanol to water is in the range of 1:10 to 1:

1.

4. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The acid solution is one or a combination of hydrochloric acid, sulfuric acid, and phosphoric acid; the concentration of the acid solution is 1–5 M.

5. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The crosslinking agent is one or a combination of formaldehyde, glutaraldehyde, epichlorohydrin, and sodium tripolyphosphate; the mass fraction is 0.5 to 2 wt%.

6. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The mass of the catalyst used is 0.1 to 1.0 g.

7. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The polymer solution has a mass fraction ranging from 1 to 10 wt%.

8. The method for preparing a pH-responsive zwitterionic modified nylon membrane according to claim 1, characterized in that: The pH control range is 5.0 to 7.

4.

9. The use of a pH-responsive zwitterionic modified nylon membrane according to any one of claims 1-8, characterized in that: pH-responsive zwitterionic modified nylon membranes are used in the production of filter membranes and filter cartridges.

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