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

Cite this: Environ. Sci. Technol. 2020, 54, 7, 4631–4640
Publication Date (Web):February 16, 2020
Copyright © 2020 American Chemical Society
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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.

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  • Formula, molecular weight, and quantitative analytical methods of PFASs; semi-quantitative analytical methods for the intermediates; theoretical calculation methods; k1 of 6:2 FTS transformation and PMS decomposition; direct reaction of 6:2 FTS with PMS; chromatograms for the suspect intermediates in full-scan MS; time trend for the semi-quantified intermediates, 6:2 FTCA, and F; degradation of PFOA by Co2+/PMS; the estimated percentage (f, %) of SO4•– reacting with major species in Co2+/PMS; the k1 of NB and BA degradation by Co2+/PMS; equations for the decomposition of PMS and generation of SO4•–; effect of Co2+ and PMS amount on the decomposition of PMS; the aqueous concentration of cobalt and the percentage of HSO5 at different pH0; pKa of 6:2 FTS; and the results of PES scan (PDF)

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