Preparation method and application of zero-emission salt-resistant acid-resistant hydrogel antibacterial filtering membrane

Abstract

The invention discloses a preparation method and application of a zero-emission salt-resistant and acid-resistant hydrogel antibacterial filtering membrane. The method comprises the following steps: preparing a calcium alginate hydrogel membrane through calcium ion cross-linking, filtering a cross-linked cross-linking agent aqueous solution in which the concentration of calcium ions is reduced and sodium ions are introduced by using a nanofiltration membrane, supplementing soluble calcium salt into the ionic cross-linking agent aqueous solution in which the sodium ions are removed, and recovering the mass percent concentration of the calcium ions to be 2.5%, so that the regeneration of the ionic cross-linking agent solution is realized. And carrying out chemical crosslinking on the calcium alginate hydrogel membrane by adopting glutaraldehyde to obtain the zero-emission salt-resistant acid-resistant hydrogel antibacterial filtering membrane. Glutaraldehyde is added into the aqueous solution of glutaraldehyde after chemical crosslinking, and the mass percent concentration of glutaraldehyde is recovered to 3.0%, so that the regeneration of the chemical crosslinking agent solution is realized, and the zero emission requirement is met. The excellent antibacterial property of glutaraldehyde endows the film with obvious advantages in the aspects of storage and bacterial breeding inhibition. The hydrogel antibacterial filtering membrane can be applied to separation of dyes and inorganic salts under the conditions of high salt content and acidic pH.

Description

Technical Field

[0001] The invention discloses a preparation method and application of a zero-emission salt-resistant and acid-resistant hydrogel antibacterial filtration membrane, and belongs to the field of environmental functional materials, wastewater and sewage treatment. Background Art

[0002] With the rapid development of the printing and dyeing industry, the discharge of printing and dyeing wastewater containing multiple complex components has been increasing, which has become an environmental problem that needs to be solved urgently. This type of wastewater usually contains complex components such as high concentrations of salt, multiple organic pollutants, dyes and auxiliaries. It has high chemical oxygen demand, deep chromaticity, and poor biodegradability. Direct discharge will cause serious damage to the water ecology, affect the survival and reproduction of aquatic organisms, and threaten human health. The research and development of low-cost, high-efficiency, and resource-based printing and dyeing wastewater treatment technology has become a key issue for the sustainable development of the industry.

[0003] The most direct and effective way to treat this type of printing and dyeing wastewater is to efficiently separate the dye auxiliaries from the inorganic salts. Traditional methods for dye / salt separation have obvious limitations. For example, the salting-out method is used to add a large amount of inorganic salts to the solution to reduce the solubility of the dye and precipitate it. This method will reduce the purity of the dye and affect the quality of product recovery. The use of filter press method to separate the precipitated dye into solid and liquid will cause the loss of the main dye, and the separation efficiency is low. Membrane separation technology can achieve highly selective separation of different substances based on the physical and chemical properties of the substance such as molecular size, charge, solubility, etc. It can separate substances at a microscopic scale, and can accurately separate different ions, small molecular organic matter, etc. in the solution, with a separation accuracy much higher than traditional filtration, precipitation and other methods. The commercial nanofiltration membrane has a small pore size, resulting in low permeability and high retention rate of organic molecules. The low flux greatly affects the separation efficiency, and the anti-pollution performance is weak, which hinders its practical application. Hydrogels have attracted widespread attention due to their unique three-dimensional network structure, high hydrophilicity, biocompatibility and environmental friendliness [JJ Membr. Sci., 2023, 679: 11]. The use of hydrogels in membrane materials has significant advantages and provides new possibilities for the development of membrane separation technology.

[0004] Sodium alginate is a natural polysaccharide extracted from brown algae, with a stable chemical structure. It can be decomposed by microorganisms in the natural environment and ultimately degraded into carbon dioxide and water, without causing environmental pollution. It is a renewable resource with rich raw materials and low prices. Sodium alginate hydrogel films have cost advantages in large-scale production and practical applications, but there are also certain limitations. Traditional calcium alginate hydrogel films have relatively weak mechanical properties, are prone to rupture or deformation during use, and usually lack antibacterial properties. The properties of sodium alginate hydrogel films can be optimized and modified by various methods. For example, by adding nanomaterials (such as graphene oxide, nano-TiO2) or composite with other polymers, its mechanical properties and permeation flux can be significantly improved. In addition, through chemical cross-linking or physical modification, its anti-pollution properties and adsorption capacity can also be improved. By cross-linking with different metal ions, the structure and properties of sodium alginate gel films can be regulated, and the mechanical strength, thermal stability, and anti-swelling properties of the films can be improved. Using Ba 2+ , Cu 2+ etc. to cross-link with sodium alginate, the content of metal elements bound in the gel further increases, and the gel structure tends to be dense and the stability increases. Cu 2+ / La 3+ cross-linked sodium alginate membranes exhibit excellent mechanical properties in salt solutions. Due to the antibacterial properties of metal ions such as copper ions themselves, the prepared copper alginate hydrogel membranes have antibacterial properties.

[0005] Glutaraldehyde is a highly effective and broad-spectrum disinfectant that can quickly kill microorganisms such as bacteria, viruses, spores, and fungi, and is widely used in the field of medical and health. At the same time, glutaraldehyde can undergo cross-linking reactions with biological macromolecules such as proteins and polysaccharides to form a stable network structure. It is used to prepare biofilms, cross-linked hydrogels, modified fibers, etc. Using glutaraldehyde can chemically cross-link hydrogel films, and the mechanical properties, chemical stability, anti-pollution properties, acid and salt resistance, and antibacterial properties of the films are significantly improved through cross-linking. Glutaraldehyde has strong bactericidal ability and can undergo cross-linking reactions with biological macromolecules such as proteins and enzymes in microbial cells, causing protein denaturation and inactivation, thereby destroying the cell structure and function of microorganisms and achieving antibacterial effects. By chemically modifying calcium alginate membranes with glutaraldehyde, its application prospects in the field of dye / salt separation are effectively expanded.

[0006] In view of the problems such as pollution caused by the emission of organic solvents in the preparation process of traditional filter membranes, low strength of calcium ion-crosslinked alginate filter membranes, easy bacterial growth on the membranes, poor salt and acid resistance, etc., the present invention reports a preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane. Glutaraldehyde is used for the secondary crosslinking of the calcium alginate hydrogel membrane. After chemical crosslinking, the carboxylic acid groups on the surface of the micro-nano organic particles self-assemble with the positively charged polyelectrolyte to form a denser protective and filtering layer on the membrane surface. The surface crosslinking degree and the membrane pore size can be controlled by crosslinking with different concentrations of glutaraldehyde. The inner layer is reinforced and pore-expanded by micron and nano inorganic particles, which improves the mechanical properties and flux. The outer membrane forms a dense layer through chemical bond crosslinking, which improves the anti-swelling property of the membrane. Glutaraldehyde molecules can penetrate the bacterial cell wall and enter the cytoplasm, and the aldehyde groups react with the intracellular components. This interaction inhibits DNA synthesis and ultimately leads to the death of bacterial cells. The excellent antibacterial property of glutaraldehyde endows the film with obvious advantages in storage and inhibiting bacterial growth. The crosslinked ionic crosslinker aqueous solution is filtered by a nanofiltration membrane. The nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, so as to recover the sodium ions in the permeate. Soluble calcium salt is added to the ionic crosslinker aqueous solution after removing sodium ions to restore the mass percentage concentration of calcium ions to 2.5%, thereby realizing the regeneration of the ionic crosslinker solution and avoiding the waste of soluble calcium salts. Glutaraldehyde is added to the aqueous solution of glutaraldehyde after chemical crosslinking to restore the mass percentage concentration of glutaraldehyde to 3.0%, thereby realizing the regeneration of the chemical crosslinker solution and meeting the zero-emission requirement. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is the problems such as pollution caused by the emission of organic solvents in the preparation process of traditional filter membranes, low strength of calcium ion-crosslinked alginate filter membranes, easy bacterial growth on the membranes, poor salt and acid resistance, etc. The technical solution of the present invention for the above-mentioned existing problems and deficiencies is to provide a preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane.

[0008] The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane of the present invention are characterized by including the following steps:

[0009] a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 2.0% - 3.0% as the casting solution, and set it aside after defoaming;

[0010] b) Prepare an aqueous solution of a soluble calcium salt with a calcium ion mass percentage concentration of 2.5% as the ionic crosslinker; prepare an aqueous glutaraldehyde solution with a mass percentage concentration of 3.0% as the chemical crosslinker;

[0011] c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, and use a film scraping rod to scrape out a uniform liquid film. Then, immerse the glass slide with the liquid film into the ionic crosslinking agent obtained in step b) and crosslink for 2 - 8 hours to obtain the first batch of ionically crosslinked calcium alginate hydrogel films. When performing the first batch of ionic crosslinking, the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution is 1:10, ensuring that sodium alginate is fully crosslinked by calcium ions. Although the calcium ion concentration in the aqueous ionic crosslinking agent solution will decrease after the first batch of crosslinking, it can still ensure the successful crosslinking of the second batch of casting solution when the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution is 1:10. The calcium alginate hydrogel film obtained after the second batch of crosslinking retains 90% - 95% of the mechanical properties and permeation flux of the first batch of ionically crosslinked calcium alginate hydrogel films. After the second batch of crosslinking, the calcium ion concentration in the aqueous ionic crosslinking agent solution further decreases, while the sodium ion concentration further increases. The calcium ion concentration is 0.8% - 1.4%. Crosslink for the third time according to the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution of 1:10, and the mechanical properties of the obtained calcium alginate film are only 40% - 60% of those of the first batch of ionically crosslinked calcium alginate hydrogel films.

[0012] d) Filter the aqueous ionic crosslinking agent solution after the second batch of crosslinking in step c) with a nanofiltration membrane. The nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Supplement soluble calcium salts to the aqueous ionic crosslinking agent solution after removing sodium ions to restore the mass percentage concentration of calcium ions to 2.5%, thus realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of soluble calcium salts, and meeting the zero - discharge requirement. The mechanical properties of the calcium alginate film crosslinked with the aqueous ionic crosslinking agent solution after supplementing soluble calcium salts are 95% - 100% of those of the first batch of ionically crosslinked calcium alginate films.

[0013] e) The first and second batches of ion-crosslinked calcium alginate hydrogel membranes obtained in step c) are washed with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, they are immersed in the chemical crosslinking agent aqueous solution obtained in step b) for crosslinking for 5 to 12 hours. The mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, obtaining the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes; no calcium ions were detected in the glutaraldehyde aqueous solution after the first batch of chemical crosslinking, but the concentration of glutaraldehyde decreased; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, the second batch of calcium alginate hydrogel membranes is chemically crosslinked with the glutaraldehyde aqueous solution after the first chemical crosslinking, obtaining the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes. The mechanical properties of the second batch of chemically crosslinked membranes are 92% - 96% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes is 90% - 97% of that of the first batch of chemically crosslinked membranes; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, the third batch of calcium alginate hydrogel membranes is chemically crosslinked with the glutaraldehyde aqueous solution after the second chemical crosslinking, obtaining the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes. The mechanical properties of the third batch of chemically crosslinked membranes are 40% - 70% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes is 60% - 80% of that of the first batch of chemically crosslinked membranes;

[0014] f) Glutaraldehyde is added to the glutaraldehyde aqueous solution after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, thereby realizing the regeneration of the chemical crosslinking agent and meeting the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane crosslinked by the chemical crosslinking agent obtained after supplementing glutaraldehyde are 95% - 100% of those of the first batch of chemically crosslinked membranes;

[0015] g) The obtained zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane is applied to the filtration of dyes with a molecular weight greater than 690 at a pH of 1 - 6 and an inorganic salt mass percentage concentration of 1% - 30%; the rejection rate of the filtration membrane for dyes with a molecular weight greater than 690 is 90% - 100%, and the rejection rate for inorganic salts is 5% - 16%, thereby achieving the purpose of dye desalination.

[0016] The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane described in the present invention against Staphylococcus aureus is 90% - 100%, and the antibacterial rate still reaches 80% - 98% after being placed in water for 2 months.

[0017] The soluble calcium salt described in the present invention is any one of calcium chloride, calcium nitrate, calcium gluconate, and calcium dihydrogen phosphate; the nanofiltration membrane is any one of polyamide nanofiltration membrane, sulfonated polysulfone nanofiltration membrane, and sulfonated polyethersulfone nanofiltration membrane; the inorganic salt is any one of sodium chloride, potassium chloride, sodium sulfate, and magnesium sulfate; the dye with a molecular weight greater than 690 is any one of Coomassie brilliant blue, direct black, congo red, and methyl blue.

[0018] The preparation process of the present invention is simple. The cross-linking agent can be recycled, which saves costs and meets the zero-emission requirements. The obtained filtration membrane can be applied to the separation of dyes and inorganic salts under high salt content and acidic pH, and has practical application prospects. Detailed implementation manners

[0019] The following introduces the specific embodiments of the present invention, but the present invention is not limited by the embodiments.

[0020] Example 1.

[0021] a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 2.0% as the casting solution, and set it aside after defoaming;

[0022] b) Prepare an aqueous solution of calcium chloride with a mass percentage concentration of calcium ions of 2.5% as the ionic cross-linking agent; prepare an aqueous solution of glutaraldehyde with a mass percentage concentration of 3.0% as the chemical cross-linking agent;

[0023] c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, and scrape out a uniform liquid film with a scraping rod. Then, immerse it together with the glass slide into the ionic cross-linking agent obtained in step b) and cross-link for 2 hours to obtain the first batch of ion-crosslinked calcium alginate hydrogel membranes; when performing the first batch of ion cross-linking, the mass ratio of the casting solution to the aqueous ionic cross-linking agent solution is 1:10, ensuring that sodium alginate is fully cross-linked by calcium ions. The concentration of calcium ions in the aqueous ionic cross-linking agent solution will decrease after the first batch of cross-linking, but it can still ensure the successful cross-linking of the second batch of casting solution when the mass ratio of the casting solution to the aqueous ionic cross-linking agent solution is 1:10. The mechanical properties and permeation flux of the calcium alginate hydrogel membrane obtained after the second batch of cross-linking are 90% of those of the first batch of ion-crosslinked calcium alginate hydrogel membranes; the concentration of calcium ions in the aqueous ionic cross-linking agent solution further decreases after the second batch of cross-linking, while the concentration of sodium ions further increases. The concentration of calcium ions is 0.8%. Cross-link for the third time according to the mass ratio of the casting solution to the aqueous ionic cross-linking agent solution of 1:10, and the mechanical properties of the obtained calcium alginate membrane are only 40% of those of the first batch of ion-crosslinked calcium alginate hydrogel membranes;

[0024] d) Filter the second batch of crosslinked aqueous solution of the ionic crosslinking agent in step c) with a polyamide nanofiltration membrane. The polyamide nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Add calcium chloride to the second batch of crosslinked aqueous solution of the ionic crosslinking agent from which sodium ions have been removed to restore the mass percentage concentration of calcium ions to 2.5%, thus realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of calcium chloride, and meeting the zero-emission requirement; the mechanical properties of the calcium alginate membrane crosslinked by the ionic crosslinking agent aqueous solution obtained after adding calcium chloride are 95% of those of the first batch of ionically crosslinked calcium alginate membranes;

[0025] e) Wash the first and second batches of ionically crosslinked calcium alginate hydrogel membranes obtained in step c) with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, immerse it in the aqueous solution of the chemical crosslinking agent obtained in step b) for crosslinking for 5 hours. The mass ratio of the calcium alginate hydrogel membrane to the aqueous solution of the chemical crosslinking agent is 1:10 to obtain the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes; no calcium ions were detected in the aqueous solution of glutaraldehyde after the first batch of chemical crosslinking, but the concentration of glutaraldehyde decreased; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the aqueous solution of the chemical crosslinking agent is 1:10, use the aqueous solution of glutaraldehyde after the first chemical crosslinking to carry out the chemical crosslinking of the second batch of calcium alginate hydrogel membranes to obtain the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes. The mechanical properties of the second batch of chemically crosslinked membranes are 92% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes is 90% of that of the first batch of chemically crosslinked membranes; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the aqueous solution of the chemical crosslinking agent is 1:10, use the aqueous solution of glutaraldehyde after the second chemical crosslinking to carry out the chemical crosslinking of the third batch of calcium alginate hydrogel membranes to obtain the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes. The mechanical properties of the third batch of chemically crosslinked membranes are 40% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes is 60% of that of the first batch of chemically crosslinked membranes;

[0026] f) Add glutaraldehyde to the aqueous solution of glutaraldehyde after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, thus realizing the regeneration of the chemical crosslinking agent and meeting the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane crosslinked by the chemical crosslinking agent obtained after adding glutaraldehyde are 95% of those of the first batch of chemically crosslinked membranes;

[0027] g) Apply the zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane obtained in the above steps to filter Coomassie Brilliant Blue with a pH of 1 and a mass percentage concentration of sodium chloride of 1%. The rejection rate of the filter membrane for Coomassie Brilliant Blue is 90%, and the rejection rate for sodium chloride is 5%, thereby achieving the purpose of dye desalination.

[0028] The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane described in this example against Staphylococcus aureus is 90%, and the antibacterial rate still reaches 80% after being placed in water for 2 months.

[0029] Example 2.

[0030] a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 3.0% as the casting solution, and set it aside after defoaming.

[0031] b) Prepare an aqueous calcium nitrate solution with a mass percentage concentration of calcium ions of 2.5% as the ionic crosslinking agent; prepare an aqueous glutaraldehyde solution with a mass percentage concentration of 3.0% as the chemical crosslinking agent.

[0032] c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, scrape out a uniform liquid film with a film scraping rod, and immerse it together with the glass slide into the ionic crosslinking agent obtained in step b) for crosslinking for 8 hours to obtain the first batch of ion-crosslinked calcium alginate hydrogel membranes; when the first batch of ion crosslinking occurs, the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution is 1:10, ensuring that sodium alginate is fully crosslinked by calcium ions. The concentration of calcium ions in the ionic crosslinking agent aqueous solution will decrease after the first batch of crosslinking, but it can still ensure the successful crosslinking of the second batch of casting solution when the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution is 1:10. The calcium alginate hydrogel membrane obtained after the second batch of crosslinking retains 95% of the mechanical properties and permeation flux of the first batch of ion-crosslinked calcium alginate hydrogel membranes; the concentration of calcium ions in the ionic crosslinking agent aqueous solution further decreases after the second batch of crosslinking, while the concentration of sodium ions further increases. The concentration of calcium ions is 1.4%. Crosslinking is carried out for the third time according to the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution of 1:10, and the mechanical properties of the obtained calcium alginate membrane are only 60% of those of the first batch of ion-crosslinked calcium alginate hydrogel membranes.

[0033] d) Filter the ionic crosslinking agent aqueous solution after the second batch of crosslinking in step c) with a sulfonated polysulfone nanofiltration membrane. The sulfonated polysulfone nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Calcium nitrate is added to the ionic crosslinking agent aqueous solution after removing sodium ions to restore the mass percentage concentration of calcium ions to 2.5%, thereby realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of calcium nitrate, and meeting the zero-emission requirements; the mechanical properties of the calcium alginate membrane crosslinked by the ionic crosslinking agent aqueous solution after adding calcium nitrate are 100% of those of the first batch of ion-crosslinked calcium alginate membranes.

[0034] e) The first and second batches of ion-crosslinked calcium alginate hydrogel membranes obtained in step c) were washed with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, they were immersed in the chemical crosslinking agent aqueous solution obtained in step b) for crosslinking for 12 hours. The mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, and the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained; no calcium ions were detected in the glutaraldehyde aqueous solution after the first batch of chemical crosslinking, but the concentration of glutaraldehyde decreased; the second batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the first chemical crosslinking under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, and the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the second batch of chemically crosslinked membranes were 96% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes was 97% of that of the first batch of chemically crosslinked membranes; the third batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the second chemical crosslinking under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, and the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the third batch of chemically crosslinked membranes were 70% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes was 80% of that of the first batch of chemically crosslinked membranes;

[0035] f) Glutaraldehyde was added to the glutaraldehyde aqueous solution after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, so as to realize the regeneration of the chemical crosslinking agent and meet the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane crosslinked with the chemical crosslinking agent after adding glutaraldehyde were 100% of those of the first batch of chemically crosslinked membranes;

[0036] g) The zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane obtained in the above steps was applied to the filtration of direct black with a pH of 6 and a mass percentage concentration of potassium chloride of 30%; the rejection rate of the filtration membrane for direct black was 100%, and the rejection rate for potassium chloride was 16%, so as to achieve the purpose of dye desalination.

[0037] The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane described in this example against Staphylococcus aureus was 100%, and the antibacterial rate still reached 98% after being placed in water for 2 months.

[0038] Example 3.

[0039] a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 2.5% as the casting solution, and set it aside after defoaming;

[0040] b) Prepare an aqueous solution of calcium gluconate with a mass percentage concentration of calcium ions of 2.5% as the ionic crosslinking agent; prepare an aqueous solution of glutaraldehyde with a mass percentage concentration of 3.0% as the chemical crosslinking agent;

[0041] c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, scrape out a uniform liquid film with a film scraping rod, and immerse it together with the glass slide into the ionic crosslinking agent obtained in step b) for crosslinking for 5 hours to obtain the first batch of ionically crosslinked calcium alginate hydrogel films; the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution during the first batch of ionic crosslinking is 1:10 to ensure that sodium alginate is fully crosslinked by calcium ions. The concentration of calcium ions in the ionic crosslinking agent aqueous solution will decrease after the first batch of crosslinking, but it can still ensure the successful crosslinking of the second batch of casting solution when the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution is 1:10. The calcium alginate hydrogel film obtained after the second batch of crosslinking retains 92% of the mechanical properties and permeation flux of the first batch of ionically crosslinked calcium alginate hydrogel films; the concentration of calcium ions in the ionic crosslinking agent aqueous solution further decreases after the second batch of crosslinking, while the concentration of sodium ions further increases. The concentration of calcium ions is 1.0%. Crosslinking is carried out for the third time according to the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution of 1:10, and the mechanical properties of the obtained calcium alginate film are only 50% of those of the first batch of ionically crosslinked calcium alginate hydrogel films;

[0042] d) Filter the ionic crosslinking agent aqueous solution after the second batch of crosslinking in step c) with a sulfonated polyethersulfone nanofiltration membrane. The sulfonated polyethersulfone nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Calcium gluconate is added to the ionic crosslinking agent aqueous solution after removing sodium ions to restore the mass percentage concentration of calcium ions to 2.5%, thereby realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of calcium gluconate, and meeting the zero-emission requirement; the mechanical properties of the calcium alginate film crosslinked by the ionic crosslinking agent aqueous solution after adding calcium gluconate are 96% of those of the first batch of ionically crosslinked calcium alginate films;

[0043] e) The first and second batches of ion-crosslinked calcium alginate hydrogel membranes obtained in step c) were washed with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, they were immersed in the chemical crosslinking agent aqueous solution obtained in step b) for crosslinking for 8 hours. The mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, and the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes were obtained; no calcium ions were detected in the glutaraldehyde aqueous solution after the first batch of chemical crosslinking, but the glutaraldehyde concentration decreased; in the case where the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, the second batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the first chemical crosslinking, and the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the second batch of chemically crosslinked membranes were 94% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes was 95% of that of the first batch of chemically crosslinked membranes; in the case where the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, the third batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the second chemical crosslinking, and the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the third batch of chemically crosslinked membranes were 60% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes was 70% of that of the first batch of chemically crosslinked membranes;

[0044] f) Glutaraldehyde was added to the glutaraldehyde aqueous solution after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, so as to realize the regeneration of the chemical crosslinking agent and meet the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane crosslinked with the chemical crosslinking agent after adding glutaraldehyde were 98% of those of the first batch of chemically crosslinked membranes;

[0045] g) One kind of zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane obtained in the above steps was applied to the filtration of congo red with a pH of 2 and a mass percentage concentration of sodium sulfate of 5%; the rejection rate of the filtration membrane for congo red was 99%, and the rejection rate for sodium sulfate was 6%, so as to achieve the purpose of dye desalination.

[0046] The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane described in this example against Staphylococcus aureus was 96%, and the antibacterial rate still reached 95% after being placed in water for 2 months.

[0047] Example 4.

[0048] a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 2.8% as the casting solution, and reserve it after defoaming;

[0049] b) Prepare an aqueous solution of calcium dihydrogen phosphate with a mass percentage concentration of calcium ions of 2.5% as the ionic crosslinking agent; prepare an aqueous solution of glutaraldehyde with a mass percentage concentration of 3.0% as the chemical crosslinking agent;

[0050] c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, scrape out a uniform liquid film with a film scraping rod, and soak it together with the glass slide into the ionic crosslinking agent obtained in step b) for 7 hours to obtain the first batch of ionically crosslinked calcium alginate hydrogel films; the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution during the first batch of ionic crosslinking is 1:10 to ensure that sodium alginate is fully crosslinked by calcium ions. The concentration of calcium ions in the ionic crosslinking agent aqueous solution will decrease after the first batch of crosslinking, but it can still ensure the successful crosslinking of the second batch of casting solution when the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution is 1:10. The calcium alginate hydrogel film obtained after the second batch of crosslinking retains 94% of the mechanical properties and permeation flux of the first batch of ionically crosslinked calcium alginate hydrogel films; the concentration of calcium ions in the ionic crosslinking agent aqueous solution further decreases after the second batch of crosslinking, while the concentration of sodium ions further increases. The concentration of calcium ions is 1.3%. Crosslink for the third time according to the mass ratio of the casting solution to the ionic crosslinking agent aqueous solution of 1:10, and the mechanical properties of the obtained calcium alginate film are only 57% of those of the first batch of ionically crosslinked calcium alginate hydrogel films;

[0051] d) Filter the ionic crosslinking agent aqueous solution after the second batch of crosslinking in step c) with a polyamide nanofiltration membrane. The polyamide nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Add calcium dihydrogen phosphate to the ionic crosslinking agent aqueous solution after removing sodium ions to restore the mass percentage concentration of calcium ions to 2.5%, thereby realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of calcium dihydrogen phosphate, and meeting the zero-emission requirement; the mechanical properties of the calcium alginate film crosslinked by the ionic crosslinking agent aqueous solution after adding calcium dihydrogen phosphate are 98% of those of the first batch of ionically crosslinked calcium alginate films;

[0052] e) The first and second batches of ion-crosslinked calcium alginate hydrogel membranes obtained in step c) were washed with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, they were soaked in the chemical crosslinking agent aqueous solution obtained in step b) for crosslinking for 8 hours. The mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, and the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained; no calcium ions were detected in the glutaraldehyde aqueous solution after the first batch of chemical crosslinking, but the concentration of glutaraldehyde decreased; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, the second batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the first chemical crosslinking, and the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the second batch of chemically crosslinked membranes were 95% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes was 96% of that of the first batch of chemically crosslinked membranes; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution was 1:10, the third batch of calcium alginate hydrogel membranes was chemically crosslinked with the glutaraldehyde aqueous solution after the second chemical crosslinking, and the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filtration membranes was obtained. The mechanical properties of the third batch of chemically crosslinked membranes were 68% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes was 79% of that of the first batch of chemically crosslinked membranes;

[0053] f) Glutaraldehyde was added to the glutaraldehyde aqueous solution after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, so as to realize the regeneration of the chemical crosslinking agent and meet the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane crosslinked by the chemical crosslinking agent after adding glutaraldehyde were 96% of those of the first batch of chemically crosslinked membranes;

[0054] g) The zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane obtained in the above steps was applied to the filtration of methylene blue with a pH of 3 and a mass percentage concentration of magnesium sulfate of 3%; the rejection rate of the filtration membrane for methylene blue was 99%, and the rejection rate for magnesium sulfate was 6%, so as to achieve the purpose of dye desalination.

[0055] The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane described in this example against Staphylococcus aureus was 91%, and the antibacterial rate still reached 97% after being placed in water for 2 months.

Claims

1. A preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane, characterized in that The steps include: a) Prepare an aqueous sodium alginate solution with a mass percentage concentration of 2.0% - 3.0% as the casting solution, and reserve it after defoaming; b) Prepare an aqueous solution of a soluble calcium salt with a calcium ion mass percentage concentration of 2.5% as the ionic crosslinking agent; prepare an aqueous glutaraldehyde solution with a mass percentage concentration of 3.0% as the chemical crosslinking agent; c) Pour the casting solution obtained in step a) onto a dry and clean glass slide, scrape out a uniform liquid film with a film scraping rod, and soak it together with the glass slide into the ionic crosslinking agent obtained in step b) for crosslinking for 2 - 8 hours to obtain the first batch of calcium alginate hydrogel films crosslinked ionically; when crosslinking ionically for the first batch, the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution is 1:10 to ensure that sodium alginate is fully crosslinked by calcium ions. The concentration of calcium ions in the aqueous ionic crosslinking agent solution after the first batch of crosslinking will decrease, but it can still ensure the successful crosslinking of the second batch of casting solution when the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution is 1:

10. The calcium alginate hydrogel film obtained after the second batch of crosslinking retains 90% - 95% of the mechanical properties and permeation flux of the first batch of calcium alginate hydrogel films crosslinked ionically; the concentration of calcium ions in the aqueous ionic crosslinking agent solution further decreases after the second batch of crosslinking, while the concentration of sodium ions further increases. The concentration of calcium ions is 0.8% - 1.4%. Crosslink for the third time according to the mass ratio of the casting solution to the aqueous ionic crosslinking agent solution of 1:10, and the mechanical properties of the obtained calcium alginate film are only 40% - 60% of those of the first batch of calcium alginate hydrogel films crosslinked ionically; d) Filter the aqueous ionic crosslinking agent solution after the second batch of crosslinking in step c) with a nanofiltration membrane. The nanofiltration membrane can retain calcium ions and allow sodium ions to pass through, thereby recovering the sodium ions in the permeate. Supplement the soluble calcium salt to the aqueous ionic crosslinking agent solution after removing sodium ions in the second batch of crosslinking to restore the calcium ion mass percentage concentration to 2.5%, thereby realizing the regeneration of the ionic crosslinking agent solution, avoiding the waste of soluble calcium salt, and meeting the zero - discharge requirement; the mechanical properties of the calcium alginate film crosslinked by the aqueous ionic crosslinking agent solution obtained after supplementing the soluble calcium salt are 95% - 100% of those of the first batch of calcium alginate films crosslinked ionically; e) The first and second batches of ion-crosslinked calcium alginate hydrogel membranes obtained in step c) are washed with deionized water to remove the residual calcium ions on the surface. After drying the water on the membrane surface, they are immersed in the chemical crosslinking agent aqueous solution obtained in step b) for crosslinking for 5 to 12 hours. The mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, and the first batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes are obtained; no calcium ions are detected in the glutaraldehyde aqueous solution after the first batch of chemical crosslinking, but the glutaraldehyde concentration decreases; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, the second batch of calcium alginate hydrogel membranes are chemically crosslinked with the glutaraldehyde aqueous solution after the first chemical crosslinking, and the second batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes are obtained. The mechanical properties of the second batch of chemically crosslinked membranes are 92% - 96% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the second batch of chemically crosslinked membranes is 90% - 97% of that of the first batch of chemically crosslinked membranes; under the condition that the mass ratio of the calcium alginate hydrogel membrane to the chemical crosslinking agent aqueous solution is 1:10, the third batch of calcium alginate hydrogel membranes are chemically crosslinked with the glutaraldehyde aqueous solution after the second chemical crosslinking, and the third batch of chemically crosslinked zero-emission salt- and acid-resistant hydrogel antibacterial filter membranes are obtained. The mechanical properties of the third batch of chemically crosslinked membranes are 40% - 70% of those of the first batch of chemically crosslinked membranes, and the antibacterial rate of the third batch of chemically crosslinked membranes is 60% - 80% of that of the first batch of chemically crosslinked membranes; f) Glutaraldehyde is added to the glutaraldehyde aqueous solution after the second batch of chemical crosslinking in step e) to make the mass percentage concentration of glutaraldehyde 3.0%, so as to realize the regeneration of the chemical crosslinking agent and meet the zero-emission requirement; the mechanical properties of the zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane crosslinked by the chemical crosslinking agent after adding glutaraldehyde are 95% - 100% of those of the first batch of chemically crosslinked membranes; g) The obtained zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane in the above steps is applied to the filtration of dyes with a molecular weight greater than 690 and an inorganic salt mass percentage concentration of 1% - 30% at a pH of 1 - 6; the rejection rate of the filter membrane for dyes with a molecular weight greater than 690 is 90% - 100%, and the rejection rate for inorganic salts is 5% - 16%, so as to achieve the purpose of dye desalination.

2. The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane according to claim 1, characterized in that The antibacterial rate of the zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane against Staphylococcus aureus is 90% - 100%, and the antibacterial rate still reaches 80% - 98% after being placed in water for 2 months.

3. The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filtration membrane according to claim 1, characterized in that The soluble calcium salt is any one of calcium chloride, calcium nitrate, calcium gluconate, and calcium dihydrogen phosphate.

4. The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane according to claim 1, characterized in that The nanofiltration membrane is any one of polyamide nanofiltration membrane, sulfonated polysulfone nanofiltration membrane, and sulfonated polyethersulfone nanofiltration membrane.

5. The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane according to claim 1, characterized in that The inorganic salt is any one of sodium chloride, potassium chloride, sodium sulfate, and magnesium sulfate.

6. The preparation method and application of a zero-emission salt- and acid-resistant hydrogel antibacterial filter membrane according to claim 1, characterized in that The dye with a molecular weight greater than 690 is any one of Coomassie Brilliant Blue, Direct Black, Congo Red, and Methyl Blue.