Study On The Activity And Application Of LED Photo-assisted The Activation Of PMS In The Degradation Of Levofloxacin In Water

Levofloxacin（LEV）is frequently detected in water environment due to its overuse and incomplete metabolism.Because of its biological characteristics,LEV is difficult to be eliminated in traditional wastewater treatment plants.Therefore,it is of great significance to study the degradation technology of LEV in water.The advanced oxidation technology based on persulfate activation can utilize sulfate radical（SO₄^-·）and hydroxyl radical（·OH）with high oxidation potential to oxidize and degrade antibiotics.ZnFe₂O₄ is a special semiconductor material,which exists in the form of spinel structure,has strong chemical stability,and can exist stably in aqueous solution.Its excellent visible light absorption and high catalytic activity make it widely used in photocatalytic and catalytic activated persulfate oxidation degradation of refractory organic pollutants.However,the high photogenerated electron hole recombination rate limits the application of ZnFe₂O₄.In this paper,a novel LED light assisted ZnFe₂O₄ activated PMS system with low energy efficiency is reported.The coupling effects of photo generated electrons assisted ZnFe₂O₄activated PMS and PMS inhibiting the recombination of electrons and holes on LEV degradation are studied;Further study on one-step synthesis of ZnFe₂O₄-ZnO,ZnO attached to the surface of ZnFe₂O₄ and form heterojunction,which can reduce the recombination of photogenerated electron hole pairs,improve its catalytic degradation activity of LEV.（1）The coupling effect of photogenerated electrons assisting ZnFe₂O₄ to activate PMS and PMS inhibiting the recombination of electrons and holes on LEV degradation was elucidated.Nano ZnFe₂O₄ materials with different calcination temperatures were synthesized by sol-gel calcination method.The effect of calcination temperature on the efficiency of PMS degradation by catalytic activation was further studied.When calcined at 500℃,ZnFe₂O₄ has higher catalytic activity for LEV degradation.ZFO-500/LED/PMS system can degrade 88.52%LEV in 180 min,and the defluorination efficiency is 28.93%,which is higher than other activated systems.In ZFO-500/LED/PMS system,photogenerated electrons participate in the activation of PMS to produce SO₄^-·and·OH,that is,PMS acts as the acceptor of photogenerated electrons,reducing the recombination of photogenerated electrons and holes,and then producing·O₂^-and¹O₂.The mechanism and process of LED assisted ZnFe₂O₄ activated PMS degradation of LEV were revealed.The stability of ZFO-500 material was clarified.After four cycles,the degradation efficiency of LEV only decreased by 12%,and 0.235%of Zn²⁺was dissolved.（2）Based on the synthesized ZFO-500,ZnFe₂O₄-ZnO composite was synthesized by adjusting the proportion of zinc and iron salts in the precursor.When Zn:Fe=3:2,the synthesized ZnFe₂O₄-ZnO composite was activated by PMS assisted by LED light,93.21%LEV could be oxidized and degraded in 90 min,and the defluorination rate reached 71.79%,which was much higher than that of pure ZnFe₂O₄.The results show that the degradation efficiency of the synthesized ZnFe₂O₄-ZnO composite is higher than that of the physical mixture of ZnFe₂O₄and ZnO;the photocurrent response of ZnFe₂O₄-ZnO composite is higher than that of ZnFe₂O₄;the photoluminescence spectrum of ZnFe₂O₄-ZnO composite is lower than that of ZnFe₂O₄,which fully proves that the heterojunction between ZnFe₂O₄ and ZnO is formed effectively and helps to enhance the separation of photogenerated electron hole pairs.The degradation mechanism and process of LED light assisted ZnFe₂O₄-ZnO activated PMS for LEV degradation were revealed.The stability of ZnFe₂O₄-ZnO composite was elucidated.After four cycles,the degradation efficiency of LEV only decreased by 7%and 1.285%of Zn²⁺was dissolved.In this study,we constructed a LED photo assisted degradation system of levofloxacin in water by activated PMS with spinel ZnFe₂O₄.Combined with a variety of in-situ/non in situ characterization methods,we revealed the relationship between the micro morphology,size,structural composition and catalytic degradation performance of the materials,as well as the synergistic mechanism of the coupling system.Furthermore,ZnFe₂O₄ was modified and ZnO was introduced to construct heterojunction to reduce the recombination of photogenerated electron hole pairs and improve its catalytic activity for the degradation of levofloxacin.This study provides new ideas and theoretical basis for solving the problem of antibiotic pollution,which will be a low energy consumption and environment-friendly research.