Study On The Performance And Mechanism Of Tetracycline Degradation By NZVI/g-C₃N₄ Photocatalytic Activation Of Persulfate

At present,people attach great importance to the environmental problems caused by the overuse of antibiotics,which pose a serious threat to the ecological environment and human health.Advanced oxidation technology based on persulfate（PS）activation has been widely used in the removal of refractory organic pollutants.Among them,nano-ferric zero-valent（nZVI）has the advantages of high reactivity and low manufacturing cost,but it is easy to agglutinate and surface is easy to be oxidized.These disadvantages significantly reduce the reactivity and stability of nano-ferric zero-valent（nZVI）to persulfate.It is an effective means to overcome the defects of nZVI by loading modification of graphite phase carbon nitride（g-C₃N₄）with multilayer sheet structure.Combined with the photocatalytic ability of g-C₃N₄,photocatalytic activation PS system of nZVI/g-C₃N₄ was constructed.In this study,tetracycline hydrochloride（TC）in tetracycline antibiotics was taken as the target pollutant to explore the performance and mechanism of removing TC from aqueous solution by photocatalytic activation PS system of nZVI/g-C₃N₄.Specific conclusions are as follows:（1）g-C₃N₄ was prepared by thermal condensation,and nZVI was successfully loaded on the surface of g-C₃N₄ by liquid phase reduction method.In order to improve the photoelectric chemical properties of composites,the optimal mass ratio of nZVI loaded with g-C₃N₄ was studied,and the mass ratio of nZVI to g-C₃N₄ was 1:1,1:2,1:3,2:1,respectively.The material was characterized and analyzed for its morphology,element type,crystal structure,element composition,optical properties,electrochemical properties,etc.SEM and EDS analysis results showed that the dispersion of nZVI particles on the surface of g-C₃N₄ was more uniform,which could effectively inhibit the agglomeration of nZVI.XRD and XPS analysis results show that the original crystal structure of g-C₃N₄ is not damaged by nZVI loading,and the nZVI/g-C₃N₄ contains Fe⁰ component,which proves the successful preparation of nZVI/g-C₃N₄.The analysis results of PL spectrum and UV-VIS diffuse reflection spectrum show that:Compared with g-C₃N₄,nZVI/g-C₃N₄ shows better optical characteristics.The load of nZVI can effectively promote the separation of photogenerated electron-hole and reduce the band gap energy of materials.nZVI/g-C₃N₄ has stronger visible light absorption and utilization ability than g-C₃N₄.The electrochemical analysis results show that the nZVI loading can reduce the charge transfer resistance and diffusion resistance of the material,and increase the charge transfer rate.In conclusion,compared with g-C₃N₄,nZVI/g-C₃N₄ has better photoelectric chemical properties.（2）Study the optimal process conditions of photocatalytic activation of PS by nZVI/g-C₃N₄ to remove TC,and investigate the effects of different reaction systems,catalyst dosage,PS concentration,initial pH value,light intensity,pollutant concentration and other factors on TC removal by the system.The results showed that under the optimal reaction conditions（catalyst concentration of 0.1 g/L,PS concentration of 3 mmol/L,initial pH value of 7,light intensity of 8000 LUX,pollutant concentration of 50 mg/L）,The photocatalytic activation of PS system by nZVI/g-C₃N₄（1:2）had the highest TC removal rate of 84.6%.The TOC mineralization rate of TC is 73.6%under the combined process condition.At the same time,the results of cycle experiment showed that nZVI/g-C₃N₄（1:2）had good reusability and stability.（3）By radical quenching experiment and electron spin resonance（EPR）analysis,sulfate free radical(SO₄^·-),hydroxyl free radical（·OH）,superoxide free radical（·O₂^-）,hole（h⁺）and other active substances were generated in the reaction process.The main active substances for TC removal by oxidation are(SO₄^·-)and（·OH）.Based on the analysis of intermediate products by means of liquid-mass spectrometry,two possible degradation pathways and degradation mechanisms of TC in this reaction system were proposed...