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Synergistic impact of humic acid on the photo-reductive decomposition of perfluorooctanoic acid

Guo, Chenxi and Zhang, Chaojie and Sun, Zhuyu and Zhao, Xiaoyun and Zhou, Qi and Hoffmann, Michael R. (2019) Synergistic impact of humic acid on the photo-reductive decomposition of perfluorooctanoic acid. Chemical Engineering Journal, 360 . pp. 1101-1110. ISSN 1385-8947 . http://resolver.caltech.edu/CaltechAUTHORS:20181029-094837733

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Abstract

Perfluorooctanoic acid (PFOA) is a stable perfluoro-surfactant due to the contribution of electronegative fluorine atoms and the high strength of C-F bonds (116 kcal/mol). However, UV irradiation of iodide at 254 nm produces hydrated electrons (e_(aq)^–) that react with PFOA to initiate its photo-reductive decomposition. In this study, we investigate the role of humic acid (HA) during the decomposition of PFOA at λ_(max) = 254 nm as mediated by the formation of e_(aq)^–. Results show that, in UV/iodide/HA system, the decomposition and defluorination ratios of PFOA at 1.5 h were increased to 67.5% and 23.5%, respectively, compared with iodide-photolysis alone results as 8.7% and 3.3%, respectively, at room temperature (25°C) and pH 10.0 under anaerobic conditions. Kinetic analysis indicated that the PFOA decomposition fit the first-order kinetics with a rate constant of 0.822 h^(–1). Reaction mechanism accounting for the effects of HA on the photo-reductive decomposition of PFOA is proposed that the aromatic rings of HA react with I_2 to form π-complexes, which effectively inhibits the reactive quenching of e_(aq)^– by I_2. After adduct formation and subsequent oxidation of phenolic hydroxy groups by I_2, I^– is regenerated, which allows for the continuous photo-production of e_(aq)^–. The quinone moieties in HA effectively act as electron shuttles leading to the reduction of I_2 back to 2 I^–. The reaction sequence involving HA provides a catalytic cycle that leads to the continuous production of e_(aq)^–, which in turn drives the decomposition and defluorination of PFOA.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.cej.2018.10.204DOIArticle
ORCID:
AuthorORCID
Zhang, Chaojie0000-0003-3108-8271
Hoffmann, Michael R.0000-0002-0432-6564
Additional Information:© 2018 Published by Elsevier. Received 13 August 2018, Revised 22 October 2018, Accepted 27 October 2018, Available online 28 October 2018. This study was supported by the National Natural Science Foundation of China (Project No. 21677109), and the Fundamental Research Funds for the Central Universities (Project No. 22120180118, 22120180247). Declarations of interest: None.
Funders:
Funding AgencyGrant Number
National Natural Science Foundation of China21677109
Fundamental Research Funds for the Central Universities22120180118
Fundamental Research Funds for the Central Universities22120180247
Subject Keywords:Perfluorooctanoic acid (PFOA); Photo-reductive defluorination; Hydrated electrons; UV/Iodide; Humic acid (HA)
Record Number:CaltechAUTHORS:20181029-094837733
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181029-094837733
Official Citation:Chenxi Guo, Chaojie Zhang, Zhuyu Sun, Xiaoyun Zhao, Qi Zhou, Michael R. Hoffmann, Synergistic impact of humic acid on the photo-reductive decomposition of perfluorooctanoic acid, Chemical Engineering Journal, Volume 360, 2019, Pages 1101-1110, ISSN 1385-8947, https://doi.org/10.1016/j.cej.2018.10.204. (http://www.sciencedirect.com/science/article/pii/S1385894718321636)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90448
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:29 Oct 2018 18:16
Last Modified:20 Feb 2019 22:02

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