Catalytic ozonation of norfloxacin using Co₃O₄/C composite derived from ZIF-67 as catalyst

In this study, Co₃O₄-carbon composite was synthesized by calcined metal organic framework (MOF) ZIF-67 and used as efficient catalysts for ozonation of norfloxacin (NOF). The MOF-derived Co₃O₄-C composite remained similar polyhedrons structure of ZIF-67, suggesting that Co₃O₄ was well-dispersed in Co₃O₄-C composite. Furthermore, a larger amount of surface carbon-oxygen functional groups were distributed on Co₃O₄-C composite, which resulted in the diversification of active sites for catalytic ozonation reaction. NOF degradation and mineralization could be effectively enhanced in Co₃O₄-C/O₃ process. Moreover, NOF mineralization by catalytic ozonation strongly depended on the solution pH, while other operational conditions, such as O₃ concentration and catalyst dosage had not obvious influence on it. Co₃O₄-C composite could significantly accelerate O₃ decomposition to produce active free radicals (such as •OH), which enhanced the mineralization of NOF. The possible catalytic mechanism of Co₃O₄-C composite was proposed. Additionally, after five consecutive use of Co₃O₄-C composite in catalytic ozonation process, there was no obvious decrease in TOC removal efficiency, indicating a stable performance of Co₃O₄-C composite, which was suitable for the catalytic ozonation for wastewater treatment.