C60-DOM interactions and effects on C60 apparent solubility: A molecular mechanics and density functional theory study

Dissolved organic matter (DOM) plays a critical role in the transport of carbon nano-particles (e.g. C-60) in the aquatic environment. However, the mechanism for C-60-DOM interactions and its environmental implications needs further investigations. In this study, the interaction of C-60 with relevant reference compounds of DOM (DOMR) is computationally simulated by molecular mechanics and density functional theory (DFT). All the C-60-DOMR complexes are firstly optimized by classical annealing, and then DFT using the Dmol(3) code. The adsorption energies of C-60 on DOMR were computed. The computed electrostatic potential indicates that DOMR are electron acceptors in the C-60-DOMR complexes, and the thermodynamic calculations indicate that electrostatic interaction is the dominant driving force for the C-60-gallic acid complexation process in water. The presence of DOMR increases the apparent water solubility of C-60. It is also observed that the C-60 apparent water solubility decrease with the increase of the energy gaps of frontier molecular orbitals (E-LUMO-E-LUMO) for each C-60-DOMR complex. These findings indicate that computational simulation is an important tool for predicting the behavior and fate of carbon nano-particles in the aquatic environment. (C) 2011 Elsevier Ltd. All rights reserved.