Enhancing photo-degradation of Ciprofloxacin using simultaneous usage of eaq− and OH over UV/ZnO /I- process: Efficiency, kinetics, pathways, and mechanisms

Abstract The aim of this study is to develop the process relies on the UV irradiation of ZnO and I − , i.e. UV/ZnO /I − (UZI), to create both oxidizer and reducer agents simultaneously for photo-degradation of the Ciprofloxacin (CIP). This paper shows that while applying UV irradiation, UV/ZnO and UV/I − for 20 min can lead to achieve 37.5%, 58.12%, and 61.4% photo-degradation of 100 mg L −1 CIP at pH 7, respectively. Moreover, the UZI treatment can provide 91.54% photo-degradation efficiency. The LC–MS analysis of the UZI effluent indicates that 10 min process was adequate to degrade CIP into simple ring-shaped metabolites while 15 min treatment, mostly of CIP intermediates were linear and biodegradable organic compounds. Furthermore, fourteen little fragments were identified in the CIP photo-degradation via UZI, during the photoreaction time of 2.5 to 20 min. Then, a pseudo first-order kinetics equation was utilized to model the observed photo-degradation process. Finally, the computational results show that the increased concentration of the CIP solution from 100 to 400 mg L −1 decreases the observed rate constant ( k obs ) from 0.4125 to 0.2189 min −1 while increases the photoreaction rate ( r obs ) from 41.25 to 87.56 mg L −1  min −1 .