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. C60) in the aquatic environment. However, the mechanism for C60-DOM interactions and its environmental implications needs further investigations. In this study, the interaction of C60 with relevant reference compounds of DOM (DOMR) is computationally simulated by molecular mechanics and density functional theory (DFT). All the C60-DOMR complexes are firstly optimized by classical annealing, and then DFT using the Dmol3 code. The adsorption energies of C60 on DOMR were computed. The computed electrostatic potential indicates that DOMR are electron acceptors in the C60-DOMR complexes, and the thermodynamic calculations indicate that electrostatic interaction is the dominant driving force for the C60-gallic acid complexation process in water. The presence of DOMR increases the apparent water solubility of C60. It is also observed that the C60 apparent water solubility decrease with the increase of the energy gaps of frontier molecular orbitals (ELUMO–EHOMO) for each C60-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.

Research Highlights
► Molecular mechanics and DFT can be used to simulate C60-DOM interactions.
► DOMR are electron acceptors in C60-DOMR complexes.
► The dominant interaction between C60 and gallic acid is electrostatic in water.
► DOMR increases apparent water solubility of C60.