Effective degradation of quinoline by catalytic ozonation with MnCe_xO_y catalysts: performance and mechanism

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by alpha-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, alpha-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that (OH)-O-center dot and O-center dot(2)- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of (OH)-O-center dot and O-center dot(2)- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O-3 into more (OH)-O-center dot and O-center dot(2)-. This study could provide scientific support for the application of the MnCexOy/O-3 system in degrading quinoline in bio-treated coking wastewater. HIGHLIGHTS center dot MnCexOyCe3+, (MnCexOyOH)-O-center dot and O-center dot(2)- MnCexOy were successfully synthesized by alpha-MnO2 doped with Ce3+. center dot The by abundant oxygen vacancies and surface hydroxyl groups of the MnCexOy catalyst enhanced its catalytic activity. center dot (OH)-O-center dot and O-center dot(2)- formation contributed to quinoline degradation in the MnCexOy ozonation system.