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

Solvated Pb(II) ions were found to adsorb as structurally well-defined outer-sphere complexes at specific sites on the α-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 Å. In contrast, Pb(II) adsorbs as more strongly bound inner-sphere complexes on α-Al₂O₃ (102). 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.