Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 14, 2014 | Supplemental Material + Published
Journal Article Open

Fenton chemistry at aqueous interfaces


In a fundamental process throughout nature, reduced iron unleashes the oxidative power of hydrogen peroxide into reactive intermediates. However, notwithstanding much work, the mechanism by which Fe^(2+) catalyzes H_2O_2 oxidations and the identity of the participating intermediates remain controversial. Here we report the prompt formation of O=Fe^(IV)CI_3^− and chloride-bridged di-iron O=Fe^(IV)·CI·FeIICI_4^− and O=Fe^(IV)·CI·Fe^(III)CI_5^− ferryl species, in addition to Fe^(III)CI_4^−, on the surface of aqueous FeCI_2 microjets exposed to gaseous H_2O_2 or O_3 beams for <50 μs. The unambiguous identification of such species in situ via online electrospray mass spectrometry let us investigate their individual dependences on Fe^(2+), H_2O_2, O_3, and H^+ concentrations, and their responses to tert-butanol (an ·OH scavenger) and DMSO (an O-atom acceptor) cosolutes. We found that (i) mass spectra are not affected by excess tert-butanol, i.e., the detected species are primary products whose formation does not involve ·OH radicals, and (ii) the di-iron ferryls, but not O=Fe^(IV)CI_3^−, can be fully quenched by DMSO under present conditions. We infer that interfacial Fe(H_2O)_n^(2+) ions react with H_2O_2 and O_3 >10^3 times faster than Fe(H_2O)_6^(2+) in bulk water via a process that favors inner-sphere two-electron O-atom over outer-sphere one-electron transfers. The higher reactivity of di-iron ferryls vs. O=Fe^(IV)CI_3^− as O-atom donors implicates the electronic coupling of mixed-valence iron centers in the weakening of the Fe^(IV)–O bond in poly-iron ferryl species.

Additional Information

© 2014 National Academy of Sciences. Edited by Richard J. Saykally, University of California, Berkeley, CA, and approved December 9, 2013 (received for review August 6, 2013). We are grateful to Dr. Himanshu Mishra and Profs. Michael Hoffmann, William Goddard, and Harry Gray of the California Institute of Technology for valuable discussions. S.E. thanks the Japan Science and Technology Agency PRESTO program, Grant for Environmental Research Projects from The Sumitomo Foundation, and Steel Foundation for Environmental Protection Technology. Y.S. thanks the Grant-in-Aid for Japan Society for the Promotion of Science Fellows for financial support. Author contributions: S.E. designed research; S.E. and Y.S. performed research; S.E. contributed new reagents/analytic tools; S.E., Y.S., and A.J.C. analyzed data; and S.E. and A.J.C. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. Freely available online through the PNAS open access option.

Attached Files

Published - PNAS-2014-Enami-623-8.pdf

Supplemental Material - pnas.201314885SI.pdf


Files (1.3 MB)
Name Size Download all
917.4 kB Preview Download
389.0 kB Preview Download

Additional details

August 22, 2023
October 25, 2023