Experimental Study On Degradation Of Cefalexin By Dielectric Barrier Discharge Plasma Coupled Composite Catalysts

In recent years,new pollutants such as drugs and personal care products（PPCPs）have been frequently detected in the water environment,and their treatment has become a research hotspot.As a kind of PPCPs,cephalosporin antibiotics have biological toxicity,pseudo-persistence and accumulation,and have certain antibacterial activity,which is difficult to biodegrade,which will seriously affect human health and ecological balance.In this study,cefalexin（CLX）was selected as the target pollutant,and DBD plasma technology was coupled with catalyst in order to study a more efficient treatment technology for cephalosporin antibiotic wastewater.In this paper,the factors affecting the removal of CLX by dielectric barrier discharge system are discussed,such as the number of dielectric holes,dielectric thickness and discharge voltage,discharge frequency,initial concentration of solution,air flow rate,initial pH value of solution,etc.,and the structure of DBD reactor is optimized to obtain the best discharge experimental parameters.The experimental results show that the more pores in the medium,the thinner the medium thickness,which is more conducive to the removal of CLX.The higher the voltage,the higher the removal rate of CLX;Discharge frequency and air flow rate have certain influence on the removal of CLX.When the initial concentration of solution increases,the removal rate of CLX decreases.Under acidic conditions,the removal effect of CLX is better.In the dielectric barrier discharge reaction system,when the number of holes is 15,the dielectric thickness is 1mm,the discharge voltage is 21 k V and the discharge frequency is 7500 Hz,the removal effect of CLX is the best,which is 88.6%.The removal effect of CLX in dielectric barrier discharge coupling catalyst system was further discussed.Pure bismuth tungstate catalyst and supported catalyst x%La-Mo/Bi₂WO₆ co-doped with La³⁺and Mo⁶⁺were prepared by hydrothermal method.The effects of precursor pH value and reaction temperature on the performance of the prepared catalyst were studied,and the effects of different La³⁺and Mo⁶⁺doping amounts and different catalyst dosage on the CLX removal efficiency were investigated.The samples were characterized and analyzed by SEM,XRD and BET.The results show that the precursor pH and reaction temperature have great influence on the photocatalytic performance of the pure Bi₂WO₆ catalyst.Compared with DBD system alone,the removal rate of CLX in DBD coupled Bi₂WO₆ system is obviously improved.A certain amount of ion doping can improve the photocatalytic performance.Under the best experimental conditions,adding 0.1g of 2%La-Mo/Bi₂WO₆ catalyst into the reaction system,the removal effect of CLX is the best,reaching 98.2%.The characterization results show that the catalyst structure becomes more fluffy and three-dimensional spherical particles with higher dispersion after 2%La³⁺and Mo⁶⁺are co-doped,and the crystallinity and specific surface area of Bi₂WO₆ are improved,so the prepared catalyst has higher stability.Finally,the degradation mechanism of cefalexin removal by dielectric barrier discharge was preliminarily explored.The results show that the mineralization rate of CLX wastewater increases with the discharge reaction,and the addition of catalyst can significantly improve the mineralization rate of wastewater.With the progress of the reaction,the solution in the reaction system is finally acidic;Free radical scavengers such as tert-butanol,p-benzoquinone and ammonium oxalate can effectively inhibit the removal of CLX.It is speculated that there may be five reaction pathways for the degradation of CLX,which are mainly manifested by the opening ofβ-lactam ring,further oxidation to small molecular acids,and final degradation to NH₄⁺,SO₄^2-,CO₂,H₂O,etc.