Molecular dynamics simulations of structural transformation of perfluorooctane sulfonate (PFOS) at water/rutile interfaces.
Molecular dynamics simulations of structural transformation of perfluorooctane sulfonate (PFOS) at water/rutile interfaces.
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DOI：
10.1016/j.chemosphere.2015.04.056
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发表时间：
2015-09
期刊：
影响因子：
8.8
通讯作者：
G. He;Meiyi Zhang;Qin Zhou;G. Pan
中科院分区：
文献类型：
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作者：
G. He;Meiyi Zhang;Qin Zhou;G. Pan
浓度和盐度条件是影响全氟化合物（PFCs）在各种固体基质（悬浮颗粒、沉积物和天然矿物）表面行为的主要环境因素。然而，该机制尚未在分子尺度上进行研究。本文采用分子动力学模拟方法，研究了全氟辛烷磺酸（PFOS）浓度水平和盐条件变化引起的PFOS在水/金红石界面上的结构转变。在低浓度和中等浓度下，所有全氟辛烷磺酸分子主要通过磺酸头基通过静电吸引与金红石（1 1 0）表面直接相互作用，产生典型的单层结构。随着PFOS浓度的增加，PFOS分子聚集成复杂的多层结构，全氟烷基链之间通过货车范德华相互作用以不规则的组装构型吸附在单层结构上。当向体系中加入CaCl 2时，多层结构再次转变为单层结构，表明CaCl 2的加入提高了PFOS多层组装的临界浓度值.二价Ca ~（2+）取代一价K ~+作为PFOS吸附的桥连抗衡离子。分子动力学模拟在全氟化合物（PFCs）的原子/分子尺度研究中具有广泛的应用前景。
Concentration and salinity conditions are the dominant environmental factors affecting the behavior of perfluorinated compounds (PFCs) on the surfaces of a variety of solid matrices (suspended particles, sediments, and natural minerals). However, the mechanism has not yet been examined at molecular scales. Here, the structural transformation of perfluorooctane sulfonate (PFOS) at water/rutile interfaces induced by changes of the concentration level of PFOS and salt condition was investigated using molecular dynamics (MD) simulations. At low and intermediate concentrations all PFOS molecules directly interacted with the rutile (1 1 0) surface mainly by the sulfonate headgroups through electrostatic attraction, yielding a typical monolayer structure. As the concentration of PFOS increased, the molecules aggregated in a complex multi-layered structure, where an irregular assembling configuration was adsorbed on the monolayer structure by the van der Waals interactions between the perfluoroalkyl chains. When adding CaCl2to the system, the multi-layered structure changed to a monolayer again, indicating that the addition of CaCl2enhanced the critical concentration value to yield PFOS multilayer assemblies. The divalent Ca2+substituted for monovalent K+as the bridging counterion in PFOS adsorption. MD simulation may trigger wide applications in study of perfluorinated compounds (PFCs) from atomic/molecular scale.