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

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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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 [similar]25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1039/c1pp05270eDOIArticle
http://pubs.rsc.org/en/Content/ArticleLanding/2011/PP/c1pp05270ePublisherArticle
ORCID:
AuthorORCID
Dalleska, Nathan F.0000-0002-2059-1587
Hoffmann, Michael R.0000-0002-0432-6564
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.
Funders:
Funding AgencyGrant Number
3MUNSPECIFIED
Basic Science Research Program2009-0071350
Basic Science Research Program2009-0089904
Basic Science Research Program2010-0002674
National Research Foundation of KoreaNRF-2009-C1AAA001-2009-0093879
Ministry of Education, Science and Technology (Korea)UNSPECIFIED
Record Number:CaltechAUTHORS:20111221-134214410
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20111221-134214410
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 Photochem. Photobiol. Sci., 2011, 10, 1945-1953 DOI: 10.1039/C1PP05270E
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28551
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:22 Dec 2011 19:19
Last Modified:11 Apr 2017 16:17

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