A biodegradable polymeric flocculant and its application

Abstract

This invention discloses a biodegradable polymeric flocculant and its application, specifically comprising the following steps: dissolving sulfonated starch in deionized water, adding chitosan composite powder, heating and stirring until dissolved, ultrasonically dispersing, adding acrylamide, then adding N,N'-methylenebisacrylamide and potassium persulfate, stirring until a gel is formed, cutting the gel into small pieces and immersing them in distilled water for washing, drying, pulverizing and sieving the washed gel to obtain the biodegradable polymeric flocculant; this invention improves flocculation and biodegradability by combining synthetic organic polymers and natural polymeric materials, and enhances antibacterial ability and degradation performance by combining silver oxide, titanium oxide and graphene oxide, exhibiting good flocculation and sedimentation ability, excellent biodegradability, and good antibacterial ability.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a biodegradable polymeric flocculant and its application. Background Technology

[0002] With the continuous development of industrialization, water resource problems are becoming increasingly serious. Industrial wastewater and domestic sewage have become the main sources of water pollution. Polluted water sources need to be treated and recycled. At present, the most widely used and lowest-cost method is flocculation using flocculants. Flocculants include synthetic organic polymer flocculants and natural organic polymer flocculants. Synthetic organic polymer flocculants are expensive to produce and contain a certain amount of residual monomers, which inevitably brings toxicity to the environment. Furthermore, synthetic organic polymer flocculants are difficult to degrade, which will cause further pollution to the environment. On the other hand, natural organic polymer flocculants include derivatives of starch, chitosan, cellulose polysaccharides, and proteins, as well as modified products of plant gums. They are widely used because of their low cost, high performance, no secondary pollution, and recyclability. However, natural polymer flocculants have unstable performance and poor sedimentation performance.

[0003] Chinese invention patent application CN103183780A discloses a method for preparing a cellulose-based wastewater flocculant. The method involves graft polymerization of cellulose and acrylamide to prepare the cellulose-based wastewater flocculant. Pulp fiber serves as the basic molecular framework, partially replacing the original polymer materials, reducing the dependence of traditional polymeric wastewater flocculants on petroleum resources, and improving the biodegradability of the flocculant. However, when treating excessively eutrophic and high-bacterial domestic sewage, bacterial metabolites and large-molecule organic eutrophic substances may consume a large amount of flocculant, and the flocculation performance of the polymeric flocculant will be significantly reduced.

[0004] Chinese invention patent application CN118271522A discloses an antibacterial flocculant, its preparation method, and its application. It involves graft copolymerization of a carbon source, alkali solution, etherifying agent, initiator, and graft monomer to prepare an antibacterial flocculant with locally high charge concentration. However, the flocculant in this scheme is formed by the polymerization of organic matter, which is difficult to degrade in the environment and is detrimental to the ecological environment.

[0005] Therefore, there is a need for a polymeric flocculant with antibacterial properties that, while having good flocculation performance, is also biodegradable and has antibacterial capabilities. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of how to improve the degradability and antibacterial properties of flocculants, and to provide a degradable polymeric flocculant and its application.

[0007] This invention improves flocculation and degradation capabilities by combining synthetic organic polymers and natural polymer materials, and enhances antibacterial and degradation performance by combining silver oxide, titanium oxide and graphene oxide. It has good flocculation and sedimentation capabilities, excellent degradation performance, and good antibacterial ability.

[0008] The objective of this invention can be achieved through the following technical solution: a biodegradable polymeric flocculant, wherein the preparation method of the biodegradable polymeric flocculant includes the following steps:

[0009] Step 1: Prepare a graphene composite powder dispersion by ultrasonically dispersing graphene composite powder in deionized water. In a reaction vessel, mix 1-1.5 wt% of the graphene composite powder dispersion and 1-1.5 wt% of the chitosan acetate aqueous solution in equal volumes, heat to 85-95℃ and react for 5-6 hours. After cooling, add half the volume of the chitosan acetate aqueous solution and 70 wt% of the ethylamine solution, stir and react for 20-24 hours. After centrifugation, collect the precipitate, wash the precipitate, and freeze-dry to obtain chitosan composite powder.

[0010] Step 2: Dissolve sulfonated starch in deionized water in a reaction vessel, add chitosan composite powder, heat to 60-70℃, stir until dissolved, ultrasonically disperse for 30-40 minutes, then add acrylamide, stir until dissolved, then add N,N'-methylenebisacrylamide and potassium persulfate, stir until a gel is formed, cut the gel into small pieces and immerse in distilled water to wash, dry at 60-70℃ for 20-24 hours after washing, pulverize and pass through a 200-mesh sieve to obtain a biodegradable polymeric flocculant.

[0011] Furthermore, in step two, the ratio of sulfonated starch, deionized water, chitosan composite powder, acrylamide, N,N'-methylenebisacrylamide, and potassium persulfate is 10-15g: 100-150mL: 3-6g: 30-50g: 0.4-0.5g: 0.8-1g.

[0012] Furthermore, the chitosan-acetic acid aqueous solution in step one is prepared by dissolving chitosan in a 0.1M acetic acid aqueous solution.

[0013] Furthermore, the graphene composite powder in step one is prepared by the following steps:

[0014] In a reaction vessel, zinc nitrate hexahydrate and 2-aminoterephthalic acid were dissolved in DMF and deionized water. Ti / graphene nanosheets were added and ultrasonically dispersed for 30-40 min. Under stirring, the temperature was raised to 90-100℃ and reacted for 20-24 h. After cooling, the precipitate was collected by centrifugation, washed, and vacuum dried for 10-12 h to obtain Ti / Zn composite graphene nanosheets. The Ti / Zn composite graphene nanosheets were placed in a muffle furnace and heated to 500-550℃ at a rate of 5℃ / min under an argon atmosphere for 4-5 h to obtain graphene composite powder.

[0015] Furthermore, the ratio of zinc nitrate hexahydrate, 2-aminoterephthalic acid, DMF, deionized water, and Ti / graphene nanosheets is 8-10g: 3-4g: 200-300mL: 200-300mL: 2-4g.

[0016] Furthermore, the Ti / graphene nanosheets are prepared by the following steps:

[0017] In a reaction vessel, 2-aminoterephthalic acid and tetrabutyl titanate were dissolved in a mixed solvent of DMF and methanol, and then graphene oxide nanosheets were added. The mixture was ultrasonically dispersed for 30-40 min, and then heated to 140-150℃ under stirring for 40-48 h. After cooling, the precipitate was collected by centrifugation, washed, and then vacuum dried to obtain Ti / graphene nanosheets.

[0018] Furthermore, the ratio of 2-aminoterephthalic acid, tetrabutyl titanate, DMF, methanol, and graphene oxide nanosheets is 5-6g: 3-4mL: 150-200mL: 20-30mL: 2-4g.

[0019] Furthermore, the sulfonated starch in step one is obtained by the following steps:

[0020] In a reaction vessel, aminosulfonic acid and urea are mixed, stirred and heated to 75-85℃ for 60-80 min. Starch is added and the temperature is raised to 90-95℃ for 5-6 h. After cooling, the precipitate is collected by filtration, washed and dried to obtain sulfonated starch.

[0021] Furthermore, the ratio of aminosulfonic acid, urea, and starch is 100-120g: 120-150g: 15-20g.

[0022] Starch can be any one of potato starch, corn starch, and tapioca starch.

[0023] Application of a biodegradable polymeric flocculant in the treatment of bacteria-containing wastewater.

[0024] The beneficial effects of this invention are:

[0025] (1) The biodegradable polymer flocculant prepared in this invention is obtained by combining synthetic organic polymers and natural polymer materials to improve flocculation and biodegradability. By combining silver oxide, titanium oxide and graphene oxide, the antibacterial ability and degradation performance of synthetic organic polymers are improved. The biodegradable polymer flocculant prepared has good flocculation and sedimentation ability, excellent degradation performance, and good antibacterial ability.

[0026] (2) In addition, the present invention will synthesize Ti-MOF and Zn-MOF containing amino groups as ligands. The amino groups form strong covalent bonds with graphene oxide nanosheets, so that Ti-MOF and Zn-MOF are grafted onto the surface of graphene oxide nanosheets one after another. Under high temperature carbonization, Ti-MOF and Zn-MOF are oxidized into nanoscale titanium oxide and zinc oxide. Under the carbonization of the ligands in the original Ti-MOF and Zn-MOF, titanium oxide and zinc oxide are firmly bonded to the surface of graphene oxide, increasing the surface area of ​​graphene oxide. The structure formed by carbonization continues the porous structure of Ti-MOF and Zn-MOF, which enhances the adsorption capacity of graphene oxide. Zinc oxide has antibacterial ability, so the graphene composite powder has antibacterial properties.

[0027] (3) The present invention also combines chitosan and graphene through an amide reaction to obtain chitosan-coated graphene composite powder. Chitosan improves antibacterial properties and is easily degraded, which is environmentally friendly. By grafting amino groups onto the surface of chitosan with ethylamine solution, starch sulfonation modification is easy to combine with chitosan composite powder containing amino groups. The combination strength is high and the dispersion is high, which improves the adsorption capacity of chitosan composite powder. Sulfonated starch has a strong adsorption capacity for cations in water. Sulfonated starch can also improve the water absorption capacity of flocculant, improve contact with the water to be treated, improve flocculation efficiency, and starch-based flocculant further improves the degradability of flocculant.

[0028] (4) In addition, the present invention also polymerizes acrylamide as a monomer on starch to form a polymeric flocculant polyacrylamide, thereby improving the flocculation ability of the flocculant. Free radicals are easily generated at the edge of graphene oxide in the graphene composite powder. Free radicals also have a destructive effect on bacteria. In synergy with zinc oxide and chitosan, the antibacterial ability of the biodegradable polymeric flocculant is improved. Titanium dioxide has a degradation-promoting effect on polyacrylamide, thereby increasing the degradation rate of the difficult-to-degrade organic polymeric flocculant polyacrylamide and improving the degradation performance of the biodegradable polymeric flocculant. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: A biodegradable polymeric flocculant, prepared by the following steps:

[0031] S1. In a reaction vessel, 5g of 2-aminoterephthalic acid and 3mL of tetrabutyl titanate were dissolved in a mixed solvent of 150mL DMF and 20mL methanol. Then, 2g of graphene oxide nanosheets were added, and the mixture was ultrasonically dispersed for 30min. Under stirring, the temperature was raised to 140℃ and reacted for 40h. After cooling, the precipitate was collected by centrifugation, washed with DMF and methanol, and dried under vacuum at 60℃ for 10h to obtain Ti / graphene nanosheets.

[0032] S2. In a reaction vessel, 8g of zinc nitrate hexahydrate and 3g of 2-aminoterephthalic acid were dissolved in 200mL of DMF and 200mL of deionized water. 2g of Ti / graphene nanosheets were added, and the mixture was ultrasonically dispersed for 30min. Under stirring, the temperature was raised to 90℃ and reacted for 20h. After cooling, the precipitate was collected by centrifugation, washed with DMF and deionized water, and vacuum dried at 60℃ for 10h to obtain Ti / Zn composite graphene nanosheets. The Ti / Zn composite graphene nanosheets were placed in a muffle furnace and heated to 500℃ at a rate of 5℃ / min under an argon atmosphere for 4h to obtain graphene composite powder.

[0033] S3. In a reaction vessel, graphene composite powder was ultrasonically dispersed in deionized water to prepare a 1 wt% graphene composite powder dispersion. Chitosan was dissolved in 0.1 M acetic acid aqueous solution to prepare a 1 wt% chitosan acetic acid aqueous solution. The graphene composite powder dispersion and chitosan acetic acid aqueous solution were mixed in equal volumes, heated to 85℃ and reacted for 5 h. After cooling, half the volume of chitosan acetic acid aqueous solution and 70 wt% ethylamine solution were added. The mixture was stirred and reacted for 20 h. After centrifugation, the precipitate was collected and washed with 0.1 M acetic acid aqueous solution and deionized water. The precipitate was then freeze-dried to obtain chitosan composite powder.

[0034] S4. Mix 100g of aminosulfonic acid and 120g of urea in a reaction vessel, stir and heat to 75℃ for 60min, add 15g of potato starch, heat to 90℃ for 5h, cool and filter to collect the precipitate, wash the precipitate with deionized water, and dry at 40℃ for 20h to obtain sulfonated starch.

[0035] S5. Dissolve 10g of sulfonated starch in 100mL of deionized water in a reactor, add 3g of chitosan composite powder, heat to 60℃, stir until dissolved, ultrasonically disperse for 30min, then add 30g of acrylamide, stir until dissolved, add 0.4g of N,N'-methylenebisacrylamide and 0.8g of potassium persulfate to initiate polymerization, stir until a gel is formed, cut the gel into small pieces and immerse in distilled water to wash, dry at 60℃ for 20h after washing, pulverize and pass through a 200-mesh sieve to obtain a biodegradable polymeric flocculant.

[0036] Example 2: A biodegradable polymeric flocculant, prepared by the following steps:

[0037] S1. In a reaction vessel, 5.5 g of 2-aminoterephthalic acid and 3.5 mL of tetrabutyl titanate were dissolved in a mixed solvent of 175 mL DMF and 25 mL methanol. Then, 3 g of graphene oxide nanosheets were added, and the mixture was ultrasonically dispersed for 35 min. Under stirring, the temperature was raised to 145 °C and reacted for 44 h. After cooling, the precipitate was collected by centrifugation, washed with DMF and methanol, and dried under vacuum at 65 °C for 11 h to obtain Ti / graphene nanosheets.

[0038] S2. In a reaction vessel, 9g of zinc nitrate hexahydrate and 3.5g of 2-aminoterephthalic acid were dissolved in 250mL of DMF and 250mL of deionized water. 3g of Ti / graphene nanosheets were added, and the mixture was ultrasonically dispersed for 35min. Under stirring, the temperature was raised to 95℃ and reacted for 22h. After cooling, the precipitate was collected by centrifugation, washed with DMF and deionized water, and vacuum dried at 65℃ for 11h to obtain Ti / Zn composite graphene nanosheets. The Ti / Zn composite graphene nanosheets were placed in a muffle furnace and heated to 525℃ at a rate of 5℃ / min under an argon atmosphere for 4.5h to obtain graphene composite powder.

[0039] S3. In a reaction vessel, graphene composite powder was ultrasonically dispersed in deionized water to prepare a 1.25 wt% graphene composite powder dispersion. Chitosan was dissolved in 0.1 M acetic acid aqueous solution to prepare a 1.25 wt% chitosan acetic acid aqueous solution. The graphene composite powder dispersion and chitosan acetic acid aqueous solution were mixed in equal volumes, heated to 90℃ and reacted for 5.5 h. After cooling, half the volume of chitosan acetic acid aqueous solution and 70 wt% ethylamine solution were added. The mixture was stirred and reacted for 22 h. After centrifugation, the precipitate was collected and washed with 0.1 M acetic acid aqueous solution and deionized water. The precipitate was then freeze-dried to obtain chitosan composite powder.

[0040] S4. Mix 110g of aminosulfonic acid and 135g of urea in a reaction vessel, stir and heat to 80℃ for 70min, add 17.5g of corn starch, heat to 92.5℃ for 5.5h, cool and filter to collect the precipitate, wash the precipitate with deionized water, and dry at 45℃ for 22h to obtain sulfonated starch.

[0041] S5. Dissolve 12.5g of sulfonated starch in 125mL of deionized water in a reactor, add 4.5g of chitosan composite powder, heat to 65℃, stir until dissolved, ultrasonically disperse for 35min, then add 40g of acrylamide, stir until dissolved, add 0.45g of N,N'-methylenebisacrylamide and 0.9g of potassium persulfate to initiate polymerization, stir until a gel is formed, cut the gel into small pieces and immerse in distilled water to wash, dry the gel at 65℃ for 22h after washing, pulverize and pass through a 200-mesh sieve to obtain a biodegradable polymeric flocculant.

[0042] Example 3: A biodegradable polymeric flocculant, prepared by the following steps:

[0043] S1. In a reaction vessel, 6g of 2-aminoterephthalic acid and 4mL of tetrabutyl titanate were dissolved in a mixed solvent of 200mL DMF and 30mL methanol. Then, 4g of graphene oxide nanosheets were added, and the mixture was ultrasonically dispersed for 40min. Under stirring, the temperature was raised to 150℃ and reacted for 48h. After cooling, the precipitate was collected by centrifugation, washed with DMF and methanol, and dried under vacuum at 70℃ for 12h to obtain Ti / graphene nanosheets.

[0044] S2. In a reaction vessel, 10g of zinc nitrate hexahydrate and 4g of 2-aminoterephthalic acid were dissolved in 300mL of DMF and 300mL of deionized water. 4g of Ti / graphene nanosheets were added, and the mixture was ultrasonically dispersed for 40min. Under stirring, the temperature was raised to 100℃ and reacted for 24h. After cooling, the precipitate was collected by centrifugation, washed with DMF and deionized water, and vacuum dried at 70℃ for 12h to obtain Ti / Zn composite graphene nanosheets. The Ti / Zn composite graphene nanosheets were placed in a muffle furnace and heated to 550℃ at a rate of 5℃ / min under an argon atmosphere for 5h to obtain graphene composite powder.

[0045] By synthesizing Ti-MOF and Zn-MOF ligands containing amino groups, and utilizing the strong covalent bonds formed between the amino groups and graphene oxide nanosheets, Ti-MOF and Zn-MOF are successively grafted onto the surface of graphene oxide nanosheets. Under high-temperature carbonization, Ti-MOF and Zn-MOF are oxidized into nanoscale titanium oxide and zinc oxide. Under the carbonization effect of the ligands in the original Ti-MOF and Zn-MOF, titanium oxide and zinc oxide are firmly bonded to the surface of graphene oxide, increasing the surface area of ​​graphene oxide. Furthermore, the structure formed by carbonization continues the porous structure of Ti-MOF and Zn-MOF, enhancing the adsorption capacity of graphene oxide. Zinc oxide has antibacterial properties, giving the graphene composite powder certain antibacterial performance.

[0046] S3. In a reaction vessel, graphene composite powder was ultrasonically dispersed in deionized water to prepare a 1.5 wt% graphene composite powder dispersion. Chitosan was dissolved in 0.1 M acetic acid aqueous solution to prepare a 1.5 wt% chitosan acetic acid aqueous solution. The graphene composite powder dispersion and chitosan acetic acid aqueous solution were mixed in equal volumes, heated to 95℃ and reacted for 6 h. After cooling, half the volume of chitosan acetic acid aqueous solution and 70 wt% ethylamine solution were added. The mixture was stirred and reacted for 24 h. After centrifugation, the precipitate was collected and washed with 0.1 M acetic acid aqueous solution and deionized water. The precipitate was then freeze-dried to obtain chitosan composite powder.

[0047] Chitosan and graphene were combined using an amide reaction to obtain chitosan-coated graphene composite powder. Chitosan improved the antibacterial properties and is easily degraded, making it environmentally friendly. Amino groups were grafted onto the surface of chitosan using an ethylamine solution.

[0048] S4. Mix 120g of aminosulfonic acid and 150g of urea in a reaction vessel, stir and heat to 85℃ for 80min, add 20g of cassava starch, heat to 95℃ for 6h, cool and filter to collect the precipitate, wash the precipitate with deionized water, and dry at 50℃ for 24h to obtain sulfonated starch.

[0049] After sulfonation modification, starch is easily combined with chitosan composite powder containing amino groups, resulting in high bonding strength and high dispersibility, which enhances the adsorption capacity of chitosan composite powder. Sulfonated starch has a strong adsorption capacity for cations in water. Sulfonated starch can also enhance the water absorption capacity of flocculants, improve contact with the water to be treated, and improve flocculation efficiency. Furthermore, starch-based flocculants further enhance the biodegradability of flocculants.

[0050] S5. Dissolve 15g of sulfonated starch in 150mL of deionized water in a reactor, add 6g of chitosan composite powder, heat to 70℃, stir until dissolved, ultrasonically disperse for 40min, then add 50g of acrylamide, stir until dissolved, add 0.5g of N,N'-methylenebisacrylamide and 1g of potassium persulfate to initiate polymerization, stir until a gel is formed, cut the gel into small pieces and soak them in distilled water to wash, dry the gel at 70℃ for 24h after washing, pulverize and pass through a 200-mesh sieve to obtain a biodegradable polymeric flocculant.

[0051] Polyacrylamide, a high-molecular-weight flocculant, is formed by polymerizing acrylamide on starch-based substrates, thereby enhancing its flocculation ability. Free radicals are easily generated at the edges of graphene oxide in graphene composite powder, and these free radicals also have a destructive effect on bacteria. In synergy with zinc oxide and chitosan, the antibacterial ability of the biodegradable high-molecular-weight flocculant is enhanced. Titanium dioxide promotes the degradation of polyacrylamide, thereby increasing the degradation rate of the difficult-to-degrade organic high-molecular-weight flocculant polyacrylamide and improving the degradation performance of the biodegradable high-molecular-weight flocculant.

[0052] Chitosan is a high molecular weight chitosan, 310,000-375,000 Da, with a degree of deacetylation >75%.

[0053] Comparative Example 1: The difference from Example 1 is that in S2, graphene nanosheets were used to replace Ti / graphene nanosheets to prepare a biodegradable polymeric flocculant.

[0054] Comparative Example 2: The difference from Example 1 is that in S5, sulfonated starch was replaced with starch to obtain a biodegradable polymeric flocculant.

[0055] Comparative Example 3: The difference from Example 1 is that in S3, ethylamine solution is not added to obtain chitosan composite powder, and a biodegradable polymeric flocculant is prepared.

[0056] The performance of the biodegradable polymeric flocculants prepared in Examples 1-3 and Comparative Examples 1-3 was tested.

[0057] 1L of 1wt% kaolin suspension was used to simulate wastewater. The mixture was stirred at 25rpm for 30min at room temperature and allowed to stand for 30min. The turbidity of the supernatant was measured using a WGZ-200 photoelectric turbidimeter, and the turbidity removal rate was calculated.

[0058] Escherichia coli (ATCC25922) was inoculated into solid LB medium for activation culture, and then expanded into liquid medium to obtain a cell density of 1×10⁻⁶. 8 For a CFU / mL E. coli suspension, add 1g of biodegradable polymeric flocculant to 1L of E. coli suspension, stir at 25rpm for 30min, let stand for 30min, take 1mL of floc and disperse it in physiological saline, then dilute the test sample tenfold stepwise, take 0.1mL of the diluted solution and add it dropwise to solid LB medium for activation culture, and expand the culture in liquid medium using the same method. Calculate the number of floc colonies, and calculate the antibacterial efficiency by comparing the number of floc colonies with the number of E. coli colonies in the E. coli suspension. The calculation formula is as follows:

[0059] Antibacterial rate % = (1 - number of flocculent colonies / 1 × 10) 8 (CFU / mL) × 100%.

[0060] Add 300g of fresh soil to 1L of deionized water and stir vigorously for 20min. Then centrifuge at 6000rpm for 15min, collect the supernatant, filter out particles and impurities, add 1g of biodegradable polymeric flocculant to the supernatant, and treat under constant temperature and light conditions of 37℃ for 30 days and 90 days. Take out the biodegradable polymeric flocculant, dry and weigh it, calculate the weight loss, and obtain the degradation rate. The results are shown in Table 1.

[0061] Table 1: Performance Test Table of Biodegradable Polymer Flocculants

[0062] As shown in Table 1, the biodegradable polymeric flocculant prepared by this invention has a high turbidity removal rate, indicating that the flocculation performance of this invention is good. The antibacterial efficiency reaches more than 83%, indicating that the invention has good antibacterial ability. The degradation rate reaches more than 50% after 30 days and more than 77% after 90 days, indicating that the biodegradable polymeric flocculant prepared by this invention has good biodegradability and is environmentally friendly.

[0063] Comparative Example 1, due to the absence of Ti-MOF to form titanium dioxide, had a poor effect on promoting the degradation of the synthesized organic polymer polyacrylamide, resulting in a low degradation rate.

[0064] In Comparative Example 2, since the starch was not sulfonated, the composite strength of the starch and chitosan powder was low, the flocculation effect was slightly lower, and the antibacterial efficiency was also reduced. It is speculated that the sulfonic acid groups also have a certain antibacterial effect on bacteria.

[0065] In Comparative Example 3, since the chitosan was not amination modified, the chitosan composite powder had low composite strength with starch, low dispersion of chitosan composite powder in starch solution, and decreased antibacterial efficiency and degradation performance.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biodegradable polymeric flocculant, characterized in that, The preparation method of the biodegradable polymeric flocculant includes the following steps: Step 1: Prepare a graphene composite powder dispersion by ultrasonically dispersing graphene composite powder in deionized water. In a reaction vessel, mix 1-1.5 wt% of the graphene composite powder dispersion and 1-1.5 wt% of the chitosan acetate aqueous solution in equal volumes, heat to 85-95℃ and react for 5-6 hours. After cooling, add half the volume of the chitosan acetate aqueous solution and 70 wt% of the ethylamine solution. Stir and react for 20-24 hours. After centrifugation to collect the precipitate, wash the precipitate and freeze-dry to obtain chitosan composite powder. Step 2: Dissolve sulfonated starch in deionized water in a reaction vessel, add chitosan composite powder, heat to 60-70℃, stir until dissolved, ultrasonically disperse for 30-40 minutes, then add acrylamide, stir until dissolved, then add N,N'-methylenebisacrylamide and potassium persulfate, stir until a gel is formed, cut the gel into small pieces and wash in distilled water, dry at 60-70℃ for 20-24 hours after washing, pulverize and pass through a 200-mesh sieve to obtain a biodegradable polymeric flocculant; The graphene composite powder mentioned in step one is prepared by the following steps: In a reaction vessel, zinc nitrate hexahydrate and 2-aminoterephthalic acid were dissolved in DMF and deionized water. Ti / graphene nanosheets were added and ultrasonically dispersed for 30-40 min. Under stirring, the temperature was raised to 90-100℃ and reacted for 20-24 h. After cooling, the precipitate was collected by centrifugation, washed, and vacuum dried for 10-12 h to obtain Ti / Zn composite graphene nanosheets. The Ti / Zn composite graphene nanosheets were placed in a muffle furnace and heated to 500-550℃ at a rate of 5℃ / min under an argon atmosphere for 4-5 h to obtain graphene composite powder.

2. The biodegradable polymeric flocculant according to claim 1, characterized in that, In step two, the ratio of sulfonated starch, deionized water, chitosan composite powder, acrylamide, N,N'-methylenebisacrylamide, and potassium persulfate is 10-15g: 100-150mL: 3-6g: 30-50g: 0.4-0.5g: 0.8-1g.

3. The biodegradable polymeric flocculant according to claim 1, characterized in that, The chitosan-acetic acid aqueous solution mentioned in step one is prepared by dissolving chitosan in a 0.1M acetic acid aqueous solution.

4. The biodegradable polymeric flocculant according to claim 1, characterized in that, The ratio of zinc nitrate hexahydrate, 2-aminoterephthalic acid, DMF, deionized water, and Ti / graphene nanosheets is 8-10g:3-4g:200-300mL:200-300mL:2-4g.

5. The biodegradable polymeric flocculant according to claim 4, characterized in that, The Ti / graphene nanosheets were prepared by the following steps: In a reaction vessel, 2-aminoterephthalic acid and tetrabutyl titanate were dissolved in a mixed solvent of DMF and methanol, and then graphene oxide nanosheets were added. The mixture was ultrasonically dispersed for 30-40 min, and then heated to 140-150℃ under stirring for 40-48 h. After cooling, the precipitate was collected by centrifugation, washed, and then vacuum dried to obtain Ti / graphene nanosheets.

6. The biodegradable polymeric flocculant according to claim 5, characterized in that, The ratio of 2-aminoterephthalic acid, tetrabutyl titanate, DMF, methanol and graphene oxide nanosheets is 5-6g: 3-4mL: 150-200mL: 20-30mL: 2-4g.

7. The biodegradable polymeric flocculant according to claim 2, characterized in that, The sulfonated starch mentioned in step one is obtained by the following steps: In a reaction vessel, aminosulfonic acid and urea are mixed, stirred and heated to 75-85℃ for 60-80 min. Starch is added and the temperature is raised to 90-95℃ for 5-6 h. After cooling, the precipitate is collected by filtration, washed and dried to obtain sulfonated starch.

8. The biodegradable polymeric flocculant according to claim 7, characterized in that, The ratio of aminosulfonic acid, urea and starch is 100-120g: 120-150g: 15-20g.

9. The application of a biodegradable polymeric flocculant according to any one of claims 1-8 in the treatment of bacteria-containing wastewater.

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