The theoretical structures of armchair (6,6) and zig-zag (12,0) TiO2 nanotubes were constructed by rolling the (101) layer of an anatase TiO2 crystal. The (101) layer was made by cutting the cleavage plane (101) of the anatase TiO2 crystal. Based upon these structures, the basic properties of TiO2 nanotubes were investigated using molecular statics. Molecular dynamics simulations were used to investigate the status and permeation of water through the TiO2 nanotubes. Structural analysis showed that both the inner and outer walls of the structures were terminated by oxygen atoms. The thicknesses of single tube walls were smaller than that of a perfect triple layer (2.20Å) in bulk anatase. With regard to the bulk Ti-O bond length, the Ti-O bonds in the outer layer were elongated, and were shortened in the inner layer. Molecular dynamics simulation showed that the water molecules in the nanotubes moved back and forth, as in one-dimensional Brownian motion. The penetration properties of TiO2 nanotubes were associated with their radii; with TiO2 nanotubes having larger radii exhibiting better penetration properties. When used for filtration, armchair TiO2 nanotubes were expected to be better than zig-zag TiO2 nanotubes.

Theoretical Study of the Permeation of Water through TiO2 Nanotubes using Molecular Dynamics Simulation. Yang, W., Fang, J., Liu, P., Li, J., Cai, K.: Molecular Physics, 2011, 109[6], 969-74