Park, Hyunwoong and Vecitis, Chad D. and Cheng, Jie and Dalleska, Nathan F. and Mader, Brian T. and Hoffmann, Michael R. (2011) Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm. Photochemical and Photobiological Sciences, 10 (12). pp. 1945-1953. ISSN 1474-905X http://resolver.caltech.edu/CaltechAUTHORS:20111221-134214410
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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 [similar]25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.
|Additional Information:||© 2011 Royal Society of Chemistry. Received 25 Aug 2011, Accepted 29 Sep 2011. First published on the web 25 Oct 2011. We are grateful to 3M for financial support. Mr. Joowook Lee assisted with the electrochemical measurements and interpretation. In addition, portions of this research were also supported by Basic Science Research Program (No. 2009-0071350, 2009-0089904, 2010-0002674) and by the Korea Center for Artificial Photosynthesis (NRF-2009-C1AAA001-2009-0093879) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.|
|Official Citation:||Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm Hyunwoong Park, Chad D. Vecitis, Jie Cheng, Nathan F. Dalleska, Brian T. Mader and Michael R. Hoffmann Journal Article Photochem. Photobiol. Sci., 2011, 10, 1945-1953 DOI: 10.1039/C1PP05270E, Paper|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||22 Dec 2011 19:19|
|Last Modified:||26 Dec 2012 14:38|
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