Concerns over Sb contamination in soils and aquatic systems have received increasing attention recently. It is generally acknowledged that iron-(hydr)oxide substrates act as important scavengers for Sb in the environment through adsorption. However, studies probing Sb adsorption on iron oxide surfaces at a molecular scale are sparse.<br/>In the present study, the <i>in situ</i> adsorption of Sb(V) on a single crystal hematite (1-102) surface was explored using crystal truncation rod X-ray diffraction (CTR). The best fit model indicates that Sb(V) adsorbs via an inner-sphere mode, forming a tridentate binding geometry consisting of an edge-sharing and a corner-sharing binding configurations. It was found that the Sb octahedral local structure was distorted producing six Sb-O bonds with bond lengths ranging from 1.95 to 2.31 Å. The Sb-Fe distance (3.07 Å) derived from the present study is comparable to that published in previous XAFS studies. The chemical plausibility of the proposed structure was further verified by performing a bond valence analysis, which also deduced a protonation scheme. In addition, a simple but novel approach was developed to perform simulations to reveal the relationship between the site coverage and the inter-sorbate distance. The simulation results are compared to the CTR derived site coverage suggesting an inter-site distance of ~ 5.0 Å at apparent surface site saturation. The results of site simulation tests provided important insights into the steric and electrostatic effects, which are potential factors in controlling surface adsorption.

Structural study of Sb(V) adsorption on hematite(1-102) surface

249th National Meeting (2015)

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