Effective degradation of quinoline by catalytic ozonation with MnCexOy 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, MnCe_xO_y was consciously synthesized by α-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 MnCe_xO_y, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCe_xO_y catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCe_xO_y, α-MnO₂ and single ozonation systems, respectively. The radical scavenging tests demonstrated that ^•OH and ^•O₂^- were the dominant reactive oxygen species in the MnCe_xO_y ozonation system. Meanwhile, the contribution levels of ^•OH and ^•O₂^- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCe_xO_y catalyst were two important factors for decomposing molecular O₃ into more ^•OH and ^•O₂^-. This study could provide scientific support for the application of the MnCe_xO_y/O₃ system in degrading quinoline in bio-treated coking wastewater.