Ruan Xiuxiu, Zhu Lizhong, Chen Baoliang
Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310028, China.
Environ Sci Technol. 2008 Nov 1;42(21):7911-7. doi: 10.1021/es801034h.
To elucidate interactions of neutral organic contaminants (NOCs) with siloxane surfaces (often referred to hydrophobic nanosites)found between cations in 2:1 phyllosilicates, adsorption of aliphatic and aromatic compounds onto both internal and external siloxane surfaces oftetramethylammonium-intercalated bentonite with a cation exchange capacity (CEC) of 108 cmol/kg (108TMA) and its reduced-charge bentonite (CEC = 65 cmol/ kg, 65TMA) were investigated. Reduction of the layer charge and saturation of bentonite interlayers with TMA+ modify the interlayer microenvironments, which dramatically promote adsorption of NOCs. Specific mechanisms (i.e., steric restriction and phenyl-effect) control the adsorption of NOCs onto internal siloxane surfaces of TMA+ -bentonites from water. The adsorption sites of 108TMA can not provide sufficient space to accommodate NOCs, hence hindering adsorption. Adsorption mechanism on 65TMA varies with solute-loadings, from polarity-selective at low loadings to aromaticity-preferable at high loadings. Significant contribution of phenyl-effect between adsorbed-solutes to aromatics adsorption on 65TMA is found. Solvent polarity effect on the aggregation of TMA+ -bentonites and aniline adsorption demonstrated that the contribution of external siloxane surfaces to favor adsorption in n-hexane are actually exploited but generally omitted. These observations provide significant insights into distinguishing different uptake mechanisms as well as the potential means for the rational design of better organic sorbents.
为阐明中性有机污染物（NOCs）与2:1型层状硅酸盐中阳离子间存在的硅氧烷表面（通常称为疏水纳米位点）的相互作用，研究了脂肪族和芳香族化合物在阳离子交换容量（CEC）为108 cmol/kg的四甲基铵插层膨润土（108TMA）及其低电荷膨润土（CEC = 65 cmol/kg，65TMA）的内、外硅氧烷表面上的吸附情况。膨润土层电荷的降低以及TMA+对膨润土夹层的饱和作用改变了层间微环境，极大地促进了NOCs的吸附。特定机制（即空间位阻和苯基效应）控制着NOCs从水中吸附到TMA+膨润土的内硅氧烷表面上。108TMA的吸附位点无法提供足够空间容纳NOCs，因此阻碍了吸附。65TMA上的吸附机制随溶质负载量而变化，从低负载时的极性选择性吸附到高负载时的芳香性优先吸附。发现吸附溶质之间的苯基效应对65TMA上芳香族化合物的吸附有显著贡献。溶剂极性对TMA+膨润土团聚和苯胺吸附的影响表明，外硅氧烷表面在正己烷中有利于吸附的作用实际上已被利用，但通常被忽略。这些观察结果为区分不同的吸附机制以及合理设计更好的有机吸附剂的潜在方法提供了重要见解。
