Bargar JR, Towle SN, Brown GE, Parks GA
Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305-2115
J Colloid Interface Sci. 1997 Jan 15;185(2):473-92. doi: 10.1006/jcis.1996.4574.
The structures and compositions of Pb(II) adsorption complexes and surface binding sites on alpha-Al2O3 (0001) and (1&1macr;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-Al2O3 (1&1macr;02) but as outer-sphere complexes on alpha-Al2O3 (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 [AlAlAl-->O-1/2--> and [Al-OH+1/22] surface functional groups. In contrast, [AlAl > 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.
利用掠入射X射线吸收精细结构（GI-XAFS）光谱，研究了在有水存在的情况下，α-Al2O3（0001）和（11̅02）表面上Pb（II）吸附络合物和表面结合位点的结构与组成。发现Pb（II）离子以内层球模式吸附在α-Al2O3（11̅02）上，但以外层球络合物形式吸附在α-Al2O3（0001）上。外层球络合物与表面之间的距离对水的双层性质施加了有用的限制。描述了一种键价模型，该模型将表面官能团和吸附络合物的反应性与其分子结构和组成相关联，并对包括质子释放在内的吸附反应的化学计量施加限制。扩展X射线吸收精细结构（EXAFS）和建模结果表明，Pb（II）和Co（II）离子与[AlAlAl→O-1/2→和[Al-OH+1/22]表面官能团结合。相比之下，[AlAl>OH]基团络合Co（II）但不络合Pb（II）。结果表明使用结构明确的表面位点来描述氧化物-水界面反应的重要性。
