In situ grazing-incidence extended X-ray absorption fine structure study of Pb(II) chemisorption on hematite (0001) and (1-102) surfaces

The dominant mode of binding of aqueous Pb(II) to single-crystal (0001) (C-cut) and (1-102) (R-cut) surfaces of alpha-Fe2O3 has been determined by grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy. Oligomeric Pb(II) complexes were found to bind in inner-sphere modes on both surfaces, which is in contrast with the binding of aqueous Pb(II) on alpha-Al2O3 (0001) surfaces, where Pb(II) was found in past GI-XAFS studies to bind in a dominantly outer-sphere mode, indicating a significant difference in reactivity of these two surfaces to Pb(II). This difference in reactivity to Pb(II) is explained on the basis of recent crystal truncation rod diffraction studies of the alpha-Fe2O3 and alpha-Al2O3 C-cut surfaces in contact with bulk water, which found major structural differences between the surfaces of these two metal oxides.