TiO2 nanotubes constructed from anatase TiO2 layers were investigated with DFT methods employing the periodic CRYSTAL code. Films of thickness from one to three TiO2 layers (1-3 ml) have been considered. The dependence of strain energies, structural and electron properties on the tube diameter was investigated in the 10-70 Å range. Relative stabilities have also been considered. We found that the most stable nanotubes are in the region of D > 50 Å: lepidocrocite, fluorite-1 ml and 001-3 ml nanotubes differ in energy by less than 0.1 eV/TiO2. This is in agreement with experimental observations of tubes that have a size that range between 50 and 100 Å. At D < 20 Å, nanotubes with a 1 ml thickness (fluorite and 101 nanotubes) show higher stability. In addition, present calculations indicate that anatase films with a thickness of 1 to 3 ml only single walled nanotubes can be constructed. All investigated nanotubes possess a high (∼5-5.5eV) band gap compared to bulk TiO2 phases (4.3 eV for anatase calculated with the same functional and basis set) that differs by less than 0.1-0.3 eV from the corresponding flat slab and approaches smoothly this reference value.
ASJC Scopus subject areas
- Materials Chemistry