In situ Structural Study of Sb(V) Adsorption on Hematite (1-102) Using X-ray Surface Scattering

The binding mechanism of Sb(V) on a single crystal hematite (1-102) surface was studied using crystal truncation rod X-ray diffraction (CTR) under in situ conditions. The best fit CTR model indicates Sb(V) adsorbs at the surface as an inner-sphere complex forming a binuclear tridentate binding geometry with the nearest Sb-Fe distance of 3.09(4) Å and an average Sb-O bond length of 2.08(5) Å. In this binding geometry Sb is bound at both edge-sharing and corner-sharing sites of the surface Fe-O octahedral units. The chemical plausibility of the proposed structure was further verified by bond valence analysis, which also deduced a protonation scheme for surface O groups. The stoichiometry of the surface reaction predicts the release of one OH- group at pH 5.5.