Heterogeneous catalytic ozonation of ciprofloxacin in wastewater with red mud: Characterization and performance

As a kind of solid waste, red mud (RM) contains various metal oxides, which have been proven to be effective as catalysts in different reactions. This study investigates the impact of RM on the catalytic ozonation for degrading ciprofloxacin (CIP). Compared to the single O-3 system, the RM/O-3 system improved CIP and Total Organic Carbon (TOC) removal rates by 44.8 % and 21.6 %, respectively, under identical conditions, and exceeded catalytic ozonation by most oxides. The influence factors, CIP degradation products, and reaction mechanisms were discussed in detail. The redox pairs of Fe2+/Fe3+ promoted the formation of oxygen vacancies (O-vac), and the hydroxyl groups and Ovac on the surface of RM were the active sites, facilitating ozone decomposition to reactive oxygen species (ROS). The scavenging experiments confirmed the presence of hydroxyl radical (center dot OH), peroxyl radical(center dot O-2(-)), and singlet oxygen (O-1(2)) in the RM/O-3 system. Furthermore, toxicity assessment indicated reduced toxicity of intermediate products compared to the parent compound CIP. The catalytic performance of RM remained relatively stable after 5 cycles of experiments, with CIP removal remaining at 100 % and TOC removal decreasing by 5.3 %. This study offers a novel perspective on utilizing RM as an efficient catalyst in CIP ozonation, beneficial for both RM treatment and antibiotic pollution mitigation.