Preparation Of Polyimide Composite Materials And Study On Photocatalytic Degradation Of Tetracycline In Wastewater

With the rapid development of economy,the pollution of water resources is becoming increasingly serious.Among them,the pollution of medicine and personal care products（PPCPs）to water resources cannot be ignored.Antibiotics are one of the typical categories of PPCPs.Tetracycline（TC）is a typical broad-spectrum antibiotic produced by actinomycetes.In addition to polluting water,TC residues in the environment can also induce microorganisms to produce drug resistance,leading to the enrichment of drug-resistant bacteria and the production of drug-resistant genes.Therefore,it is of great significance to find a clean and effective method to reduce TC in the environment.Among them,photocatalytic technology stands out because of its unique advantages.Its operation process is simple,efficient and clean.It is an excellent antibiotic wastewater treatment technology.However,one of the biggest challenges in the practical application of photocatalytic technology is the need to develop an efficient,low-cost and harmless photocatalyst.Polyimide（PI）,as an organic polymer material with the best comprehensive performance,has the characteristics of appropriate bandwidth（～2.8 e V）,strong chemical inertia,stable aromatic heterocyclic structural units and rich sources of raw materials.However,the short carrier lifetime and small specific surface area of PI limit its application and development.Optimizing the energy band structure of PI and improving the specific surface area and carrier life through appropriate modification methods will make PI have higher photocatalytic activity and adsorption performance,so as to realize the efficient degradation of organic wastewater,which has great research value.In this paper,through the modification of PI,combined with a series of characterization methods,the structure and properties of the material are deeply analyzed,and it is used for the efficient degradation of tetracycline wastewater.Explore the energy band structure of different polyimide composites and the mechanism of improving carrier life,and the degradation mechanism of efficient treatment of tetracycline wastewater.It mainly includes the following aspects:Firstly,PI was prepared by solid-state polymerization.Secondly,Zn S/PI composite photocatalyst was successfully synthesized by solvothermal method with prepared PI,zinc acetate and thiourea,and its degradation performance to TC was investigated under visible light irradiation.The structure and properties of the composite catalyst were analyzed by XRD,FT-IR,XPS,UV-vis DRS,XPS and PL.The results showed that under visible light irradiation for240 min,45Zn S/PI（the ratio of the mass of Zn S to the sum of the mass of Zn S and PI was 45%,labeled 45Zn S/PI）had the highest degradation efficiency of TC,and the best degradation efficiency was 84%,which was 11 times and 8 times higher than that of pure PI and Zn S,respectively.After four cycles of degradation experiments,the degradation efficiency of the composite was 59%.The photocatalytic properties of the composites prepared by different hydrothermal temperature,hydrothermal time and solvent were studied.The optimum preparation conditions were obtained:hydrothermal temperature 160℃,hydrothermal time 16h and solvent deionized water.At the same time,the effects of catalyst dosage,initial concentration and initial p H on the photocatalytic performance of the catalyst were explored,and the best degradation conditions were found:p H=7,the initial concentration of TC was 20mg/L,and the dosage of catalyst was 25 mg.The formation of Z-scheme heterostructure leads to the improvement of charge separation efficiency and the prolongation of electron hole pair life,which makes the composites have excellent photocatalytic activity.This was confirmed by HRTEM,XPS analysis,free radical capture experiment and ESR analysis.Compared with pure PI and Zn S,the composite photocatalyst can produce more active species·O₂^-and h⁺,and has high mineralization ability,good stability and recoverability.In addition,the possible photocatalytic degradation pathway of TC on Zn S/PI materials was studied based on HPLC-MS analysis.Finally,Zn@Sn O₂/PI composite photocatalyst was successfully synthesized by solvothermal method with PI,tin chloride pentahydrate and zinc nitrate hexahydrate,and its degradation efficiency of TC was discussed under visible irradiation.A series of characterization methods are used to explore the structure and characteristics of materials.BET results show that the specific surface area of 35Zn@Sn O₂/PI composite（the ratio of Zn@Sn O₂mass to total mass is 35%,marked as 35Zn@Sn O₂/PI）is 31 times,6 times and 4 times that of PI,Sn O₂ and 15%Zn@Sn O₂（the ratio of doping amount of zinc to total mass is 15%,marked as 15%Zn@Sn O₂）.The larger specific surface area makes the composite have more active sites.PL and i-t photocurrent test results show that the carrier life of the composite is longer than that of the monomer material.Hence,under the synergistic action of adsorption and photocatalytic degradation,TC was removed efficiently.The test results showed that after 35Zn@Sn O₂/PI treated TC for 60 min through the synergistic effect of adsorption and photocatalysis,the removal efficiency of TC by the composite was as high as 86%.The removal efficiency is 35times,7 times and 2 times that of PI,Sn O₂ and Zn@Sn O₂ respectively.Meanwhile,the effect of coexisting ions on the photocatalytic properties of the composites was investigated.The experimental results show that the inhibitory effect of different cations on the photocatalytic activity of the materials is from weak to strong are as follows:Na⁺+2+2+;The inhibition effect of different anions on the photocatalytic performance of the composites from strong to weak are as follows:CO₃^2->HCO₃^->SO₄^2->Cl^-.At the same time,the effects of catalyst dosage,initial concentration and p H on the photocatalytic performance of the catalyst were investigated,and the best degradation conditions were obtained:the dosage of material was 25 mg,the initial concentration of TC was 20 mg/L,and the initial p H=5.The intermediate products of photodegradation of TC were dynamically detected by HPLC-MS,and it was speculated that TC was finally transformed into small molecules.