Molecular Simulation Study on the Interaction of Nanoparticles with Clay Minerals: C60 on Surfaces of Pyrophyllite and Kaolinite

Abstract

AbstractBuckminsterfullerene (C60) is one of the most important carbon-based nanoparticles (CNPs). Industrial-scale production of C60 has reached the level of tons; release to the environment has been confirmed (Tremblay, 2002; Qiao et al., 2007). The present study was devoted to study of the effect of clay minerals on the migration process of C60. Molecular dynamics (MD) simulations were used to study the interaction of CNPS with clay minerals through study of the adsorption of C60 on various surfaces of kaolinite and pyrophyllite in vacuum and aqueous environments. Two kinds of surfaces, hydrophobic siloxane surfaces and hydrophilic hydroxyl surfaces, were investigated. C60 is mainly adsorbed onto the vacancy of the six-membered ring, composed of SiO4 tetrahedra or AlO6 octahedra, on clay-mineral surfaces. A single adsorption layer consisting of C60 molecules with an ordered hexagonal arrangement is presented for all surfaces in vacuum. In aqueous environments, however, the monolayer appears on the siloxane surfaces only, while a cluster of C60 molecules is formed on the hydroxyl surfaces. Free energies prove that the attachment of two C60 molecules is stronger than the adsorption of C60 onto the hydroxyl surface in water, which is the reason for unfavorable formation of C60 monolayer. On the other hand, the adsorption free energy is more negative on the hydrophobic siloxane surface, explaining the monolayer formation. The existence of water, which forms hydration layers on the surfaces of clay minerals, produces energy barriers, and reduces the adsorption affinity to some extent. Because clay minerals act as geosorbents in the environment, the present study is significant in terms of understanding the migration and fate of CNPS in nature.