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 so lid-liquid interface are of importance to a broad variety of environmental and industrial pollution or corrosion/passivation problems. A more fundamen tal understanding of the mechanisms of these reactions is required in order to increase our ability to predict interfacial phenomena. In this study, g azing-incidence XAFS (GI-XAFS) and near-edge XAFS (both L- and K-edge NEXAF S) techniques were used to investigate the chemical and structural characte ristics of interfacial Cr(III) and Cr(VI) species on a molecular level. In particular, products of postulated electron transfer reactions between Cr(V I) and Fe(II) at the oxide-solution interface were investigated. Both techn iques confirmed the reduction of Cr(VI) to Cr(III) mediated by a partially reduced hematite (0001) surface. The observed local structure of the interf acial chromium species emphasizes the need for an improved, molecular-level conceptualization of reactions occurring at the solid-solution interface.