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Photoreduction of Iron Oxyhydroxides and the Photooxidation of Halogenated Acetic Acids

Pehkonen, Simo O. and Siefert, Ronald L. and Hoffmann, Michael R. (1995) Photoreduction of Iron Oxyhydroxides and the Photooxidation of Halogenated Acetic Acids. Environmental Science and Technology, 29 (5). pp. 1215-1222. ISSN 0013-936X. doi:10.1021/es00005a012.

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The photolytic reduction of ferrihydrite (am-Fe_2O_3*3H_2O), lepidocrocite (γ-FeOOH), goethite (a-FeOOH), hematite (α-Fe_2O_3), maghemite (γ-Fe_2O_3) and iron-containing aerosol particles (Fe_(aerosol)) in the presence of a series of halogenated acetic acids has been investigated. The fastest rates of photoreduction of Fe(lll) to Fe(ll) were achieved with ferrihydrite as an electron acceptor and fluoroacetic acid as an electron donor. The relative rates of photooxidation of the monohalogenated acetic acids with ferrihydrite in order of decreasing reactivity were as follows: FCH_2CO_2H > CICH_2CO_2H > BrCH_2CO_2H > ICH_2CO_2H; for multiple substituents the relative order of reactivity was as follows: FCH_2CO_2H > F_2CHCO_2H > F_3CCO_2H. With respect to the iron oxide electron acceptors, the relative order of reactivity toward monohaloacetate oxidation was am-Fe_2O_3-3H_2O > γ-Fe_2O_3 > γ-FeOOH ≥ α-Fe_2O_3 ≥ Fe_(aerosol) > α-FeOOH. Strong kinetic isotope effects observed for the photooxidation of CICD_2CO_2H suggest that the oxidation of the mono- and disubstituted haloacetic acids proceeds via hydrogen-atom abstraction by surface-bound hydroxyl radicals to produce haloacetate radicals, which in turn yield the corresponding halide and glycolic acid. Fully halogenated haloacetic acids appear to be oxidized via a photo-Kolbe mechanism to yield the corresponding halo acids and CO_2.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1995 American Chemical Society. Received for review July 18, 1994. Revised manuscript received January 9, 1995. Accepted January 17, 1995. The authors wish to thank Prof. J. Morgan and Mr. Scot T. Martin for helpful discussions and Mr. Sam Webb for his help in the photoreduction experiments. Support for this research has been provided by a grant from the National Science Foundation, Division of Atmospheric Sciences, Atmospheric Chemistry Section (ATM 9015775).
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NSFATM 9015775
Issue or Number:5
Record Number:CaltechAUTHORS:20150810-083411943
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Official Citation:Photoreduction of Iron Oxyhydroxides and the Photooxidation of Halogenated Acetic Acids Simo O. Pehkonen, Ronald L. Siefert, and Michael R. Hoffmann Environmental Science & Technology 1995 29 (5), 1215-1222 DOI: 10.1021/es00005a012
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59334
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 18:59
Last Modified:10 Nov 2021 22:18

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