Identification of Cr species at the aqueous solution-hematite interface after Cr(VI)-Cr(III) reduction using GI-XAFS and Cr L-edge NEXAFS.
Surface-mediated redox processes and sorption reactions occurring at the solid-liquid interface are of importance to a broad variety of environmental and industrial pollution or corrosion/passivation problems. A more fundamental understanding of the mechanisms of these reactions is required in order to increase our ability to predict interfacial phenomena. In this study, gazing-incidence XAFS (GI-XAFS) and near-edge XAFS (both Land K-edge NEXAFS) techniques were used to investigate the chemical and structural characteristics of interfacial Cr(III) and Cr(VI) species on a molecular level. In particular, products of postulated electron transfer reactions between Cr(VI) and Fe(II) at the oxide-solution interface were investigated. Both techniques confirmed the reduction of Cr(VI) to Cr(III) mediated by a partially reduced hematite (O001) surface. The observed local structure of the interracial chromium species emphasizes the need for an improved, molecular-level conceptualization of reactions occurring at the solid-solution interface.