Experimental and theoretical investigation on degradation of enoxacin in aqueous solution by UV-activated persulfate: Kinetics, influencing factors and degradation pathways

In this work, the degradation behavior of enoxacin (ENO) in aqueous solution by UV-activated persulfate (PS) was investigated, and the mechanism for aqueous ENO degradation initiated by sulfate (SO4 center dot-) and hydroxyl radicals ((OH)-O-center dot) was explored by performing density functional theory (DFT) calculation. Under the optimal condition ([ENO]0 = 0.0312 mM, [PS](0) = 1.560 mM, pH(0) = 7.0), nearly complete removal of ENO was achieved after 12 min of degradation. The degradation of ENO in the UV/PS system followed pseudo-first-order kinetic model, and the corresponding rate constants increased with increasing PS dosage and decreasing solution pH. The presence of CO32- or HCO3- had an obvious inhibitory effect on ENO degradation. (OH)-O-center dot contributed mainly to ENO degradation in the UV/PS system. The experimental results for intermediate identification suggested that ENO mainly undergo piperazine ring cleavage in the early stage of degradation, which can be well explained by the theoretical calculation. The computational results also indicated that the electron transfer reactions between ENO and SO4 center dot-; ((OH)-O-center dot) proceeded hardly both thermodynamically and kinetically. Furthermore, SO4 center dot- was found to be more reactive than (OH)-O-center dot in degrading ENO. The effective degradation of ENO by UV/PS process suggested that it can be used as an efficient technology to treat ENO-containing water and wastewater.