Department of Earth and Environmental Sciences, Rutgers University, Newark, NJ 07102, USA.
J Colloid Interface Sci. 2009 Dec 15;340(2):153-9. doi: 10.1016/j.jcis.2009.08.033. Epub 2009 Aug 24.
The interaction of selenate, selenite, and chromate with the hydrated surface of gamma-Al(2)O(3) was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4-9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of gamma-Al(2)O(3) upon adsorption; however, only selenite decreased the pH(PZC) of the gamma-Al(2)O(3) sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO(6) octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated gamma-Al(2)O(3). The results point to substantial differences between these anions as to the mode of adsorption at the hydrated gamma-Al(2)O(3) surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration.
使用宏观 pH 边缘数据、电泳迁移率测量和 X 射线吸收光谱分析相结合的方法研究了硒酸盐、亚硒酸盐和铬酸盐与γ-Al(2)O(3)水合表面的相互作用。pH 边缘数据表明，随着 pH 的降低，含氧阴离子的吸附通常会增加，并表明在 4-9 pH 范围内，铬酸盐和硒酸盐的吸附与离子强度无关，而在该 pH 范围内，亚硒酸盐的吸附与离子强度无关。铬酸盐的吸附在 pH 5.0 时达到峰值，而对于硒酸盐和亚硒酸盐，没有观察到 pH 吸附最大值。电泳迁移率测量表明，所有三种含氧阴离子在吸附时都会降低γ-Al(2)O(3)的 ζ 电位；然而，只有亚硒酸盐降低了γ-Al(2)O(3)吸附剂的 pH(PZC)。EXAFS 数据表明，亚硒酸盐离子以桥联双齿配位方式与表面 AlO(6)八面体配位，而吸附的硒酸盐离子没有观察到第二个近邻 Al 散射。综合来看，这里提出的结果表明，pH 是决定硒酸盐、亚硒酸盐和铬酸盐在水合γ-Al(2)O(3)上吸附程度的主要因素。结果表明，这些阴离子在水合γ-Al(2)O(3)表面的吸附方式存在显著差异，硒酸盐作为非质子化的外层络合物吸附，铬酸盐形成单质子化和非质子化的外层络合物吸附混合物，而亚硒酸盐以桥接配位的内络合表面络合物形式配位。
