Structure and dynamics of water in TiO₂ nano slits: The influence of interfacial interactions and pore sizes

The interaction of water with TiO₂ surfaces is of enduring interest because of wide applications of the TiO₂ materials in aqueous environments. The structure and dynamic properties of water molecules in TiO₂ nanopores are crucial as increasingly TiO₂ materials are synthesized into nanoporous structures. In this work, the structural and dynamic properties of water molecules in nanoscale slit pores of TiO₂ are investigated, by using three sets of force field models for the water- TiO₂ interaction, as well as four TiO₂ slit pore widths. It is concluded that the water- TiO₂ interaction dominates the interfacial structure of water molecules, while the dynamic properties of water molecules are primarily influenced by the slit width in both interfacial and central regions. These findings indicate that both of the fluid properties and the interactions of fluids with pore wall will determine the transport properties of fluid in nanopores. If the pore size is large enough, e.g. 1.0 nm or larger in this work, the transport properties will be determined most by the fluids themselves. For the cases of pores whose sizes are in the range of interfacial region, the influences of pore size and interfacial interaction will interfere each other.