Interaction of Hydroxylated Anatase TiO₂ Surfaces and H₂O by Molecular Dynamics Simulation

In this work, the interaction between hydroxylated anatase TiO₂ (101)/(001) surfaces and H₂O was studied by molecular dynamics simulations and the effects of hydroxyl groups on the properties of TiO₂-H₂O interface were obtained. By analyzing the radial distribution functions and bond lengths of Ti_5c-O_w and O_2c-H_w, it is confirmed that the hydroxylated TiO₂ (101)/(001) model and the force field can well simulate the structures and properties of the TiO₂-H₂O system. With the molecular dynamics snapshots, the O_2c adsorption sites on TiO₂ surface had nearly no change before and after hydroxylation, while the Ti_5c adsorption sites on perfect surfaces were replaced by the hydrogen atoms of hydroxyl groups. Further research on the hydrogen bonds between H₂O and TiO₂ was shown, which caused charge transfer on the interface, and the density distribution of H₂O presents hierarchical structures made up of inner Helmholtz layer (IHL), outer Helmholtz layer (OHL) and bulk. Compared with perfect surfaces, hydroxyl groups made the IHL/OHL on TiO₂ (101) surface narrowed, while the IHL of TiO₂(001) surface got narrowed. By analyzing the diffusion properties and average velocity distribution of H₂O molecules, we found the surface structure of hydroxylated TiO₂ (001) is conducive to the movement of H₂O along the surface relative to hydroxylated TiO₂ (101). Based on the charge density distribution of H₂O, it is shown that the hydroxyl group do increase the charge fluctuation on the surface of TiO₂ (101) and (001), and the extreme value of the charge density is obviously improved.