摘要
Sulfate radicals (SO4˙−) have been extensively used in the advanced oxidation process (AOP) upon ultraviolet exposure of peroxydisulfate (S2O82−) solution, namely UV/S2O82−. Conventionally, SO4˙− was regarded as the reactive species under acidic conditions, but hydroxyl radicals (OH˙) under alkaline conditions. However, a significant concentration of dissolved oxygen in aqueous solution, ca. 0.26 mM, was not considered in most of the studies reported in the literature. In this work, the transient species and the reaction mechanisms upon photolysis of Na2S2O8 solution under non-deoxygenated and alkaline conditions were investigated using the steady-state and time-resolved IR and UV-vis spectroscopic approaches. As the pH increased, the concentration of the stable end product, SO42−, in the infrared absorption spectra was greatly increased, and the decay of SO4˙− was accelerated in the time-evolved absorption at 455 nm due to the reaction SO4˙− + OH− → SO42− + OH˙. At a later stage, slow kinetics also observed at 455 nm was attributed to the generation of O3˙−via the reactions OH˙ + OH− → H2O + O˙− and O˙− + O2 → O3˙−. This mechanism has been further verified by the accelerated generation and increased concentration of O3˙−via increasing the pH and introducing more O2. From the use of UV/S2O82− AOP, the roles of dissolved oxygen and O3˙− should be reconsidered under non-deoxygenated and alkaline conditions.