title: Molecular dynamics simulations of structural transformation of perfluorooctane sulfonate (PFOS) at water/rutile interfaces.
abstract: 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 (110) 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 CaCl2 to the system, the multi-layered structure changed to a monolayer again, indicating that the addition of CaCl2 enhanced the critical concentration value to yield PFOS multilayer assemblies. The divalent Ca(2+) 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.
authors.affiliation: Department of Environmental Nano-materials, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: gzhhe@rcees.ac.cn.
authors.forename: Guangzhi
authors.initials: G
authors.lastname: He
authors.affiliation: Department of Environmental Nano-materials, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: myzhang@rcees.ac.cn.
authors.forename: Meiyi
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Environmental Nano-materials, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: qinzhou@rcees.ac.cn.
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Department of Environmental Nano-materials, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: gpan@rcees.ac.cn.
authors.forename: Gang
authors.initials: G
authors.lastname: Pan
mesh_terms: D000327:Adsorption; D017738:Alkanesulfonic Acids / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D054712:Salinity; D014025:Titanium; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D017738:Alkanesulfonic Acids; D005466:Fluorocarbons; D014874:Water Pollutants, Chemical; D014867:Water; C009495:titanium dioxide; C076994:perfluorooctane sulfonic acid; D014025:Titanium
keywords: Assembling structure; Concentration effect; Environmental factors; Interfacial behavior; Perfluorinated compounds; Salinity effect