Transformation of 6:2 Fluorotelomer Sulfonate by Cobalt(II)-Activated Peroxymonosulfate
Yanyan Zhang, Jinxia Liu, Audrey Moores, Subhasis Ghoshal
Abstract
Peroxymonosulfate (PMS)-based advanced oxidation processes generate highly reactive SO4•– and are promising for water treatment. In this study, we investigated the reaction mechanism of 6:2 fluorotelomer sulfonate (6:2 FTS) with Co2+-activated PMS. 6:2 FTS was simultaneously transformed to perfluoroalkyl carboxylic acids (C2–C7 PFCAs) of different chain lengths, with perfluorohexanoic acid (C6) as the predominant one. The mass balance of the intermediates and products versus the initially added 6:2 FTS was close to 100% over the reaction period. Using chemical scavenging methods, we identified that •OH, instead of SO4•–, was the oxidant initiating the reaction of 6:2 FTS. •OH was mainly produced from SO4•– reacting with H2O. Thus, the reactivity of 6:2 FTS was controlled by the factors affecting the production and scavenging of both SO4•– and •OH. Density functional theory calculations showed that •OH oxidizes 6:2 FTS by H-abstraction from ethyl carbons. This is the first study that demonstrates that •OH in Co2+-activated PMS can play a significant role in contaminant transformations. The results indicate that great caution should be taken when PMS or other agents that generate •OH are used for the treatment of water containing 6:2 FTS or its structural analogs.