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Issue 12, 2011
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Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm

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Abstract

The perfluoroalkyl compounds (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examination of the UV-254 nm production of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compounds (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidation and −1.0 V is required to induce PFC reduction indicating that PFC reduction is the thermodynamically preferred process. However, PFCs are observed to degrade faster during UV(254 nm)/persulfate (S2O82) photolysis yielding sulfate radicals (E° = +2.4 V) as compared to UV(254 nm)/iodide (I) photolysis yielding aquated electrons (E° = −2.9 V). Aquated electron scavenging by photoproduced triiodide (I3), which achieved a steady-state concentration proportional to [PFOS]0, reduces the efficacy of the UV/iodide system towards PFC degradation. PFC photoreduction kinetics are observed to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concentration, and iodide concentration. From 2 to 12, pH had no observable effect on PFC photoreduction kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large number of gaseous fluorocarbon intermediates were semi-quantitatively identified and determined to account for ∼25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.

Graphical abstract: Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm

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Publication details

The article was received on 25 Aug 2011, accepted on 29 Sep 2011 and first published on 25 Oct 2011


Article type: Paper
DOI: 10.1039/C1PP05270E
Citation: Photochem. Photobiol. Sci., 2011,10, 1945-1953
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    Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm

    H. Park, C. D. Vecitis, J. Cheng, N. F. Dalleska, B. T. Mader and M. R. Hoffmann, Photochem. Photobiol. Sci., 2011, 10, 1945
    DOI: 10.1039/C1PP05270E

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