Comparison of HO Adsorption and Dissociation Behaviors on Rutile (110) and Anatase (101) Surfaces Based on ReaxFF Molecular Dynamics Simulation.

The relationship between structure and reactivity plays a dominant role in water dissociation on the various TiO crystallines. To observe the adsorption and dissociation behavior of HO, the reaction force field (ReaxFF) is used to investigate the dynamic behavior of HO on rutile (110) and anatase (101) surfaces in an aqueous environment. Simulation results show that there is a direct proton transfer between the adsorbed HO (HO) and the bridging oxygen (O) on the rutile (110) surface. Compared with that on the rutile (110) surface, an indirect proton transfer occurs on the anatase (101) surface along the H-bond network from the second layer of water. This different mechanism of water dissociation is determined by the distance between the 5-fold coordinated Ti (Ti) and O of the rutile and anatase TiO surfaces, resulting in the direct or indirect proton transfer. Additionally, the hydrogen bond (H-bond) network plays a crucial role in the adsorption and dissociation of HO on the TiO surface. To describe interfacial water structures between TiO and bulk water, the double-layer model is proposed. The first layer is the dissociated HO on the rutile (110) and anatase (101) surfaces. The second layer forms an ordered water structure adsorbed to the surface O or terminal OH group through strong hydrogen bonding (H-bonding). Affected by the H-bond network, the HO dissociation on the rutile (110) surface is inhibited but that on the anatase (101) surface is promoted.