XAFS and bond-valence determination of the structures and compositions of surface functional groups and Pb(II) and Co(II) sorption products on single-crystal {alpha}-Al{sub 2}O{sub 3}
- Stanford Univ., CA (United States)
- Stanford Synchrotron Radiation Lab., CA (United States)
The structures and compositions of Pb(II) adsorption complexes and surface binding sites on {alpha}-Al{sub 2}O{sub 3} (0001) and (1{bar 1}02) surfaces were investigated in the presence of water using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy. Pb(II) ions were found to adsorb in an inner-sphere mode on {alpha}-Al{sub 2}O{sub 3} (1{bar 1}02) but as outer-sphere complexes on {alpha}-Al{sub 2}O{sub 3} (0001). The distance between the outer-sphere complexes and the surface places useful constraints on double-layer properties of water. A bond-valence model is described that relates the reactivities of surface functional groups and adsorption complexes to their molecular structures and compositions, and places constraints on the stoichiometries of adsorption reactions, including proton release. The EXAFS and modeling results suggest that Pb(II) and Co(II) ions bond to [3Al--O{sup {minus}1/2}] and [Al--OH{sub 2}{sup +1/2}] surface functional groups. In contrast, [2Al--OH] groups complex Co(II) but not Pb(II). The results indicate the importance of using structurally defined surface sites to describe reactions at oxide-water interfaces.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-93ER14347
- OSTI ID:
- 438897
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 185, Issue 2; Other Information: PBD: 15 Jan 1997
- Country of Publication:
- United States
- Language:
- English
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