Transformation of 6:2 Fluorotelomer Sulfonate by Cobalt(II)-Activated Peroxymonosulfate

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.