Insights into the surface oxidation modification mechanism of nano-diamond: An atomistic understanding from ReaxFF simulations

Nano-diamond is widely utilized in various fields due to its excellent properties. However, in comparison with micron-sized materials, the higher surface energy of nano-diamond can make it easy to agglomerate, which seriously impedes its application. Heat treatment is an effective method to reduce agglomeration and improve dispersion. Therefore, it is important to elucidate the micro-surface modification mechanism of nano-diamond during heat treatment. In this work, ReaxFF molecular dynamics simulations are applied to study the dissociation and adsorption processes of H2O and O-2 on the diamond surface as well as the forms of mass loss and surface terminal groups under different crystal plane orientations during heat treatment. The simulation results show that the adsorption of H2O is dominant in (100) surface and forms C-H and C-OH as well as C-OH and H3O+. The adsorption of O-2 forms C-O and C-O-C on the (100) surface, C-O-O-C on the (110) surface, and C-O on the (111) surface, respectively. During heat treatment, carbon atoms can be oxidized to CO or CO2, causing mass loss. Furthermore, the diamond shows different degrees of graphitization under three orientations. This work provides a theoretical basis for understanding the surface oxidation modification mechanism of nano-diamond from an atomistic perspective.