Insights into Generation Mechanisms of Halogen Radicals from Excited Triplet State of Dissolved Organic Matter

Triplet states of dissolved organic matter ( 3 DOM*) can sensitize the generation of halogen radicals in marine water. The generation pathways of halogen radicals from 3 DOM* is still not fully understood. In this study, the generation of halogen radicals from DOM was investigated with Suwanee River fulvic acid (SRFA) as a representative and detailed generation pathways were further revealed with anthraquinone-2-sodium sulfonate (AQ2S) as a triplet sensitizer. The results showed that in SRFA solutions with halogen ions, various halogen radicals can be generated. Among which, Br • is formed by the reaction of Br − with 3 AQ2S*, and Cl • is produced by the reaction of Cl − with AQ2S •+ that generated in the presence of dissolved oxygen (DO). Cl 2 •− and Br 2 •− were generated via the subsequent combination of Cl • /Br • with another Cl − /Br − . In solutions without DO, BrCl •− is mainly generated through the combination of Br • with Cl − , and BrCl •− could also be generated through the combination of Cl • with Br − in solutions with DO. This study provides deep insights into the generation mechanisms of different halogen radicals from 3 DOM* and is helpful for understanding the photochemical processes of halogen radicals in marine waters