Outer-sphere Pb(II) adsorbed at specific surface sites on single crystal alpha-alumina

Solvated Pb(II) ions were found to adsorb as structurally well-defined outer-sphere complexes at specific sites on the alpha-Al2O3 (0001) single crystal surface, as determined by grazing-incidence X-ray absorption fine structure (GI-XAFS) measurements. The XAFS results suggest that the distance between Pb(II) adions and the alumina surface is approximately 4.2 Angstrom. In contrast, Pb(II) adsorbs as more strongly bound inner-sphere complexes on alpha-Al2O3 (1 (1) over bar 02) The difference in reactivities of the two alumina surfaces has implications for modeling surface complexation reactions of contaminants in natural environments, catalysis, and compositional sector zoning of oxide crystals.