Spectroscopic evidence for Fe(II)-Fe(III) electron transfer at the iron oxide-water interface.
Using the isotope specificity of 57Fe Mössbauer spectroscopy, we report spectroscopic observations of Fe(II) reacted with oxide surfaces under conditions typical of natural environments (i.e., wet, anoxic, circumneutral pH, and about 1% Fe(II)). Mössbauer spectra of Fe(II) adsorbed to rutile (TiO2) and aluminum oxide (Al2O3) show only Fe(II) species, whereas spectra of Fe(II) reacted with goethite (alpha-FeOOH), hematite (alpha-Fe2O3), and ferrihydrite (Fe5HO8) demonstrate electron transfer between the adsorbed Fe(II) and the underlying iron(III) oxide. Electron-transfer induces growth of an Fe(III) layer on the oxide surface that is similar to the bulk oxide. The resulting oxide is capable of reducing nitrobenzene (as expected based on previous studies), but interestingly, the oxide is only reactive when aqueous Fe(II) is present. This finding suggests a novel pathway for the biogeochemical cycling of Fe and also raises important questions regarding the mechanism of contaminant reduction by Fe(II) in the presence of oxide surfaces.
Department of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, USA.
Aaron G B
AG
Williams
Michelle M
MM
Scherer
D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005293:Ferritins / Q000138:chemical synthesis / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry; D007503:Iron Isotopes / Q000737:chemistry; D008903:Minerals; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D005290:Ferric Compounds; D005296:Ferrous Compounds; D058085:Iron Compounds; D007503:Iron Isotopes; D008903:Minerals; D010087:Oxides; D014867:Water; C094886:goethite; C009495:titanium dioxide; C000499:ferric oxide; C092844:ferric oxyhydroxide; D005293:Ferritins; D014025:Titanium; C034236:ferrous oxide; D000537:Aluminum Oxide