Degradation Of Levofloxacin In Aqueous Solution By Water Falling Film Dielectric Barrier Discharge Plasma Combined With Ag₃PO₄/activated Carbon Fibers

Levofloxacin(LFX)is a common fluoroquinolone antibiotic,which is widely used in clinical medicine and aquaculture due to its excellent antibacterial properties.With the extensive use of LFX,it has been found that LFX can neither be fully metabolized by humans or animals,nor can it be completely removed by conventional treatment methods when discharged into sewage treatment plants.At present,low-temperature plasma technology has attracted more and more attention because of its high oxidation and low selectivity.It is very promising to regard it as an efficient advanced oxidation technology in the field of environmental pollution control.In this study,water falling film dielectric barrier discharge plasma was used in conjunction with Ag3PO4/ACFs composite catalyst to treat LFX in water.In this study,the activated carbon fibers-loaded silver phosphate(Ag3PO4/ACFs)composites were prepared by surface precipitation method.A series of material characterization methods including XRD,SEM,BET and XPS was applied to analyze the morphology,composition and characterization features of the prepared Ag3PO4/ACFs.The results show that the Ag3PO4/ACFs materials has good catalytic performance and stability.Subsequently,the degradation of LFX in water by water falling film dielectric barrier discharge plasma combined with Ag3PO4/ACFs was studied.The effect of some operating parameters on the degradation efficiency of LFX and the energy efficiency during the reaction were explored,such as discharge voltage,initial solution concentration,initial pH value of the solution,liquid circulation flow rate,catalyst addition amount and catalyst cycle number.The results showed that the addition of Ag3PO4/ACFs can improve the degradation efficiency of LFX.In addition,increasing discharge voltage is conducive to the degradation of LFX,but the larger discharge voltage can lead to the waste of energy and decrease energy yield.A larger initial concentration of the solution,liquid circulation flow rate and more catalyst addition amount are all beneficial to the improvement of the degradation efficiency and the energy efficiency of LFX in the system.Acidic conditions were more favorable for the removal of LFX,but the initial pH value of the solution increased from 9.79 to 11.06,which promoted the decomposition of O3 to produce·OH and improved the removal efficiency of LFX.The catalytic performance of Ag3PO4/ACFs composite material were still effective after several repeated use,indicating that the synthesized Ag3PO4/ACFs has good stability.Finally,the mechanism and possible degradation pathway as well as the degradation products of the degradation of LFX by water falling film dielectric barrier discharge plasma combined with Ag3PO4/ACFs composite material were investigate.The concentration of H2O2 and O3 accumulated in the reaction solution when the reaction solution was LFX solution and ultrapure water respectively was measured.The results showed that H2O2 and O3 were consumed during the degradation of LFX in the combined system.Free radical capture experiments showed that both·OH,hole and·H were involved in the removal process of LFX.The effect of the addition of catalyst on the TOC value of the reaction solution was also determined.The results showed that the addition of catalyst could effectively improve the TOC removal rate of the reaction solution.Based on the results of quantum chemical calculation and the detection results of liquid chromatography-mass spectrometry(LC-MS),the possible degradation pathways and degradation products of LFX in the composite system were proposed.