Hiemstra Tjisse, Van Riemsdijk Willem H
Department of Soil Quality, Wageningen University, P.O. Box 8005, NL 6700 EC Wageningen, The Netherlands.
J Colloid Interface Sci. 2006 Sep 1;301(1):1-18. doi: 10.1016/j.jcis.2006.05.008. Epub 2006 May 6.
The double layer structure of metal (hydr)oxides is discussed. Charge separation may exist between the minimum distance of approach of electrolyte ions and the DDL domain. The corresponding capacitance value of the outer Stern layer is similar to the capacitance value of the inner Stern layer. The extended Stern model implicitly supports a hydration structure at the near-surface with some discrete layering of water and electrolyte ions. The significance of dipole orientation is analyzed theoretically. Dipole theory in combination with a calculated ion charge distribution is compared with the experimental overall charge distribution. Ion charge distribution for various oxyanions has been calculated applying the Brown bond valence concept to the geometry of surface complexes that have been optimized with MO/DFT calculations. The comparison is done in detail for silicic acid adsorption on goethite. In addition, results are discussed for arsenite, carbonate, sulfate, and phosphate, using the same approach. The dipole correction depends on the charge introduced in a neutral surface by ion adsorption, which differs for the various ions studied. The fractional correction factor phi derived for the experimental data agrees with the theoretical value phi(m)=0.17+/-0.02. On an absolute scale, the dipole corrections are usually limited to the range about 0-0.15 v.u. The CD values calculated with MO/DFT are not particularly sensitive (approximately 0.03 v.u.) to the precise Fe-octahedral geometry, which suggests that a calculated CD is a reasonable approximation in ion adsorption modeling for ill-defined Fe-oxides like HFO and natural Fe oxide materials of soils.
讨论了金属（氢）氧化物的双层结构。在电解质离子的最小接近距离与双电层扩散层（DDL）域之间可能存在电荷分离。外斯特恩层的相应电容值与内斯特恩层的电容值相似。扩展的斯特恩模型隐含地支持近表面处的水合结构，其中水和电解质离子存在一些离散分层。从理论上分析了偶极取向的意义。将偶极理论与计算得到的离子电荷分布相结合，并与实验得到的总电荷分布进行比较。应用布朗键价概念对通过MO/DFT计算优化的表面络合物的几何结构，计算了各种含氧阴离子的离子电荷分布。以硅酸在针铁矿上的吸附为例进行了详细比较。此外，采用相同方法讨论了亚砷酸盐、碳酸盐、硫酸盐和磷酸盐的结果。偶极校正取决于离子吸附在中性表面引入的电荷，这对于所研究的各种离子是不同的。从实验数据导出的分数校正因子φ与理论值φ(m)=0.17±0.02一致。在绝对尺度上，偶极校正通常限于约0 - 0.15 v.u.的范围。用MO/DFT计算得到的CD值对精确的铁八面体几何结构不是特别敏感（约0.03 v.u.），这表明在对像水铁矿和土壤中的天然铁氧化物材料这样定义不明确的铁氧化物进行离子吸附建模时，计算得到的CD是一个合理的近似值。
