Kinetics, structural effects and transformation pathways for norfloxacin oxidation using the UV/chlorine process

Abstract

The UV/chlorine process is a novel light-driven oxidation technique. In this study, norfloxacin (NOR), a typical quinolone contaminant, was degraded by using the UV/chlorine process. The effects of the process parameters were also investigated. The UV/chlorine process was observed to be capable of fully removing NOR in 360 s with a high degradation rate constant of 0.0196 s−1. NOR degradation was found to be positively correlated with chlorine dose and UV intensity but negatively correlated with ammonia. FMO, MSPA, and CDFT quantum chemical structure analyses reveal the most reactive sites for electrophilic or radical attack are the N6 or N5 atoms in the piperazine ring of the NOR molecule, which are also potential starting reaction sites for the degradation process. Thirteen degradation intermediates were detected and identified by UPLC/Q-TOF HRMS. Three sub-pathways are present during the degradation process, including cleavage and removal of the piperazine ring, transformation and cleavage of the quinolone structure, and chlorination reaction with chlorine active matter (RCS). The full elimination of NOR does not ensure a decrease in acute toxicity. Environmental risks associated with the UV/chlorine process need to be assessed further.