Investigation On Formation And Properties Of The TiO₂ Nanotubes And Nanotube Arrays By Density Functional Theory

As an important wide-band gap versatile semiconductor, TiO₂ has been widely applied in a lot of research fields. And the experiment study shows the dominant peaks of anatase and rutile nanotubes are (101) and (110). Therefore, we investigated the TiO₂ nanotubes constructed by wrapping rutile (110) sheet in this study. We proposed a general method for the formation of TiO₂ nanotubes from the pristine or reconstructed single trilayer rutile TiO₂ (110) thin sheets, which was similar to the formation of carbon nanotubes from a graphene sheet.It was found that the electronic properties of TiO₂ nantubes depended on the chirality, coordination environment and so on. The structures, identified from the density functional theory calculations, could exist in single or mixed phases depending on the temperature from molecular dynamics simulation. The result is according with the geometry optimize. TiO₂ nanotube arrays can be synthesized by several experimental procedures. Here we constructed the first theoretical model of the array. Based on the density functional theory calculations, the formation energy of theTiO₂ nanotube array was nearly the same with that of rutile TiO₂ (110) surface.The thermodynamic properties of H₂O splitting on the TiO₂ nanotube and nanotube arrays have been discussed using the density functional theory calculation sand Gibbs free energy diagrams. The over potential of H₂O splitting is 0.51 and 1.0 eV on the outside and inside of nanotube and 1.13eV on the inside TiO₂ nanotube of an array. Fuethermore, based on the thermodynamic point of view from the Gibbs free analysis, we can find that the rate-limiting step is to obtain the OH from the dissociation of the first H₂O on both TiO₂ nanotube and nanotube arrays.