Molecular dynamics simulation study of benzene adsorption to montmorillonite: Influence of the hydration status
Molecular dynamics simulation study of benzene adsorption to montmorillonite: Influence of the hydration status
复制标题
蒙脱石吸附苯的分子动力学模拟研究：水化状态的影响
DOI：
10.1016/j.colsurfa.2013.05.056
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发表时间：
2013-10-05
影响因子：
5.2
通讯作者：
Liu, Yun
中科院分区：
文献类型：
--
作者：
Liu, Xingwang;Zhu, Runliang;Liu, Yun
粘土矿物广泛存在于土壤和沉积物中，是重要的有机污染物吸附剂。然而，粘土矿物的吸附能力很大程度上取决于其水化状态。采用经典分子动力学（MD）模拟方法，研究了苯在一组含有不同抗衡离子（Na+、K+、Cs+）和含水量的水合蒙脱石上的吸附特性。苯在未水化蒙脱石外表面的吸附能为：Na型蒙脱石（-0.46 eV）> K型蒙脱石（-0.39 eV）> Cs型蒙脱石（-0.36 eV）。水合后的苯分子会被水分子逐渐从硅氧烷表面驱逐出去，并被吸附在水-真空界面上。在未水化的蒙脱石层间空间内，苯分子只能平放在硅氧烷表面，由于层间膨胀需要消耗能量，因此获得较大的正吸附能。水化作用使蒙脱石层间膨胀，有利于苯在蒙脱石层间的吸附。结果表明，随着含水量的增加，吸附能逐渐由大的正值变为负值，之后吸附能保持负值。水合作用也显著影响抗衡离子与苯分子之间的相互作用，水化能力较弱的苯可以更靠近抗衡阳离子。与水合抗衡离子相比，水合硅氧烷表面更容易成为苯分子的吸附位点。以上结果表明，蒙脱石的水化作用对有机污染物的吸附具有多方面的影响。(C)2013爱思唯尔有限公司版权所有。
Clay minerals are ubiquitous in soil and sediments and they have been considered as important geosorbents for organic contaminants. However, the adsorption capacity of clay minerals strongly depends on their hydration status. In this work, the adsorptive characteristics of benzene on a set of hydrated montmorillonites which contain different counterions (Na+, K+, Cs+) and water content were studied using classical molecular dynamics (MD) simulations. On the outer surface of unhydrated montmorillonites the adsorption energy of benzene decreases in the order: Na-montmorillonite (-0.46 eV) > K-montmorillonite (-0.39 eV) > Cs-montmorillonite (-0.36 eV). After hydration benzene molecule will be gradually expelled away from the siloxane surface by water molecules and be adsorbed at the water-vacuum interface. Within the interlayer space of unhydrated montmorillonite benzene molecule can only lay flat on the siloxane surface, and a large positive adsorption energy is obtained due to the energy consumption which is needed to expand the interlayers. Hydration causes the expansion of montmorillonite interlayers, which then can help the adsorption of benzene to the interlayer spaces. As a result, the adsorption energy gradually evolves from large positive to negative as the water content increases to monolayer arrangement, and after that the adsorption energy remains negative. Hydration also significantly influences the interaction between counterions and benzene molecule, and benzene can bind closer to the counterbalance cation with weaker hydration capacity. Compared to the hydrated counterions, the hydrated siloxane surface is more likely to be the adsorption sites for benzene molecule. The above findings indicate that the hydration of montmorillonite has versatile effects on the adsorption of organic contaminants. (C) 2013 Elsevier B.V. All rights reserved.