Synergetic effect of vacuum ultraviolet photolysis and ozone catalytic oxidation for toluene degradation over MnO2-rGO composite catalyst

Abstract

Advanced oxidation processes (AOPs) are regarded as one of the most promising technologies for VOC degradation. In this study, MnO2-rGO composite samples were prepared and applied in a system consisting of VUV photolysis and ozone catalytic oxidation for the degradation of toluene. Extensive characterizations, including BET, SEM, TEM, HRTEM, Raman, XRD, FTIR and XPS, were conducted to analyze the features of the composite MnO2-rGO samples. Results of toluene removal, mineralization and ozone decomposition showed that the MnO2-rGO composite sample with Mn loading of 25 wt% exhibited the best performance in this study due to its superior adsorption activity and moderated MnO2 loading. The intermediates of the degradation process were analyzed showing more by-products with shorter chains in the presence of the MnO2-rGO catalysts compared to VUV photolysis alone, indicating more complete reactions occurred. Generation of hydroxyl radicals (•OH) and superoxide radicals (•O2–) were confirmed to contribute in the toluene degradation. Two reaction pathways (i.e. •O2– and OH• based) and mechanism of toluene degradation were proposed.