H₂O₂assisted degradation of antibiotic norfloxacin over simulated solar light mediated Bi₂WO₆: Kinetics and reaction pathway

Highly efficient treatment technologies are urgently needed to remove antibiotics which are widely present in aquatic environment and can pose harmful effects on water quality and human health. In this study, we developed an efficient simulated-solar-light driven photocatalytic process by combining Bi2WO6and H2O2reagent (SSL/Bi2WO6/H2O2process) to degrade norfloxacin, an antibiotic agent widely used as a bactericide for the first time. It was found that the SSL/Bi2WO6/H2O2process can significantly accelerate norfloxacin degradation rate. Moreover, the effects of initial norfloxacin concentration (0.05-0.30 mM), Bi2WO6dosage (0.5-3.0 g/L), and hydrogen peroxide dosage (0.2-20.0 mM) were investigated and optimized. In most cases, the norfloxacin degradation followed two-stage pseudo first-order reaction kinetics: a fast first-stage (k1) followed by a slower second-stage (k2). The reaction kinetics was investigated in detail and the degradation models were built correspondingly in order to predict the decay of parent compound. The degradation pathway gave a clear illumination of norfloxacin's transformation and fate in our proposed process. It could be divided into two sub-pathways, and they were initiated by the attack ofOH on the benzene ring and piperazine ring, respectively. The high mineralization degree and absence of harmful intermediates suggested that the SSL/Bi2WO6/H2O2is a fast and safe process.