New Insights into the Mechanism of the UV/Sulfite Process: Formation of SO<sub>2</sub><sup>•–</sup> Radicals and Their Derivatives under Acidic Conditions
Linghao Kong, Zhe Jin, Feng Zhu, Mengchang He, Feng Qian, Xianjia Peng
Abstract
The UV/sulfite process shows great potential for reductively degrading or eliminating pollutants. While its mechanism in neutral and alkaline environments has been well-elucidated, the reaction pathway under acidic conditions remains unclear. Herein, we report the novel findings of the formation of reductive SO 2 •– radicals and their derivatives in the UV/sulfite process at pH levels below 4. Mechanistic investigation revealed that H• radicals and SO 3 •– radicals formed by the photolysis of sulfite under acidic conditions, with the H• radicals being scavenged by sulfite to produce SO 2 •– radicals. Subsequently, these SO 2 •– radicals are transformed into dithionite, thiosulfate, hydrogen sulfide, and elemental sulfur through a series of intricate reactions. This study is expected to expand the potential application of the UV/sulfite process under acid conditions.