Inhibition of bromate formation in plasmon-enhanced catalytic ozonation over silver-doped spinel ferrite

High energy consumption and formation of harmful byproducts are two challenges faced by advanced oxidation processes (AOPs). While much research efforts have been devoted to improving the treatment efficiency, byproduct formation and control calls for more attention. In this study, the underlying mechanism of bromate formation inhibition during a novel plasmon-enhanced catalytic ozonation process with silver-doped spinel ferrite (0.5wt%Ag/MnFe₂O₄) as the catalysts was investigated. By scrutinizing the effects of each factor (i.e. irradiation, catalyst, ozone) as well as the combinations of different factors on major Br species involved in bromate formation, examining the distribution of Br species, and probing the reactive oxygen species partaking in the reactions, it was found that accelerated ozone decomposition which inhibited two main bromate formation pathways and surface reduction of Br species (e.g. HOBr/OBr^- and BrO₃^-) contributed to the inhibition of bromate formation, both of which can be enhanced by the plasmonic effects of Ag and the good affinity between Ag and Br. A kinetic model was developed by simultaneously solving 95 reactions to predict the aqueous concentrations of Br species during different ozonation processes. The good agreement between the model prediction and experimental data further corroborated the hypothesized reaction mechanism.