A molecular level understanding of antimony immobilization mechanism on goethite by the combination of X-ray absorption spectroscopy and density functional theory calculations

A molecular level understanding of antimony (Sb) immobilization mechanism on Fe oxides is required to clarify the fate of Sb in the soil. In this study, macroscopic sorption experiments, combined with extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT), were utilized to explore the interaction be-tween Sb and goethite. The ion strength has no effect on Sb sorption on goethite, indicating the inner-sphere complex Sb formed on goethite. Goethite has the higher sorption potential to Sb(III) than Sb(V), consistent with the higher ther-modynamic stability of the geometry for Sb(III) formed on goethite than Sb(V) revealed by DFT calculations. By com-paring the Sb-Fe distances obtained by EXAFS spectroscopy and DFT, eight kinds of Sb(III) surface complexes and nine kinds of Sb(V) surface complexes were considered to be the possible geometries Sb formed on different crystal planes of goethite, including monodentate mononuclear, bidentate mononuclear, bidentate binuclear, tridentate mononu-clear, tridentate binuclear, tridentate four-nuclear complexes. The structural and energetic details of these filtered ge-ometries provide comprehensive information on Sb immobilization mechanism on goethite, helpful in clarifying the fate of Sb in soils.

Automated summary

A combination of macroscopic sorption experiments, EXAFS spectroscopy, and DFT calculations was used to investigate the interaction between Sb and goethite. It was found that Sb forms inner-sphere complexes on goethite, and the thermodynamic stability of Sb(III) on goethite is higher than Sb(V). Different possible geometries of Sb(III) and Sb(V) surface complexes on goethite were identified. This study provides comprehensive information on the immobilization mechanism of Sb on goethite, contributing to a better understanding of Sb fate in soils.