Arai Yuji, Elzinga Evert J., Sparks Donald L.
Department of Plant and Soil Sciences, University of Delaware, Newark Delaware, 19717-1303
J Colloid Interface Sci. 2001 Mar 1;235(1):80-88. doi: 10.1006/jcis.2000.7249.
We investigated the As(III) and As(V) adsorption complexes forming at the gamma-Al(2)O(3)/water interface as a function of pH and ionic strength (I), using a combination of adsorption envelopes, electrophoretic mobility (EM) measurements, and X-ray absorption spectroscopy (XAS). The As adsorption envelopes show that (1) As(III) adsorption increases with increasing pH and is insensitive to I changes (0.01 and 0.8 M NaNO(3)) at pH 3-4.5, while adsorption decreases with increasing I between pH 4.5 and 9.0, and (2) As(V) adsorption decreases with increasing pH and is insensitive to I changes at pH 3.5-10. The EM measurements show that As(III) adsorption does not significantly change the EM values of gamma-Al(2)O(3) suspension in 0.1 M NaNO(3) at pH 4-8, whereas As(V) adsorption lowered the EM values at pH 4-10. The EXAFS data indicate that both As(III) and As(V) form inner-sphere complexes with a bidentate binuclear configuration, as evidenced by a As(III)-Al bond distance of congruent with3.22 Å and a As(V)-Al bond distance of congruent with3.11 Å. The As(III) XANES spectra, however, show that outer-sphere complexes are formed in addition to inner-sphere complexes and that the importance of outer-sphere As(III) complexes increases with increasing pH (5.5 to 8) and with decreasing I. In short, the data indicate for As(III) that inner- and outer-sphere adsorption coexist whereas for As(V) inner-sphere complexes are predominant under our experimental conditions. Copyright 2001 Academic Press.
我们使用吸附包络线、电泳迁移率（EM）测量和X射线吸收光谱（XAS）相结合的方法，研究了在γ-Al₂O₃/水界面形成的As(III)和As(V)吸附络合物随pH值和离子强度（I）的变化情况。砷的吸附包络线表明：（1）As(III)的吸附量随pH值升高而增加，在pH 3 - 4.5时对I的变化（0.01和0.8 M NaNO₃）不敏感，而在pH 4.5至9.0之间吸附量随I的增加而降低；（2）As(V)的吸附量随pH值升高而降低，在pH 3.5 - 10时对I的变化不敏感。EM测量表明，在pH 4 - 8的0.1 M NaNO₃溶液中，As(III)的吸附对γ-Al₂O₃悬浮液的EM值没有显著影响，而As(V)的吸附在pH 4 - 10时降低了EM值。扩展X射线吸收精细结构（EXAFS）数据表明，As(III)和As(V)均形成具有双齿双核构型的内球络合物，As(III)-Al键距约为3.22 Å，As(V)-Al键距约为3.11 Å，这证明了上述结论。然而，As(III)的X射线吸收近边结构（XANES）光谱表明，除了内球络合物外还形成了外球络合物，并且外球As(III)络合物的重要性随pH值升高（5.5至8）和I降低而增加。简而言之，数据表明对于As(III)，内球和外球吸附共存，而对于As(V)，在我们的实验条件下内球络合物占主导地位。版权所有2001年学术出版社。
