Periodic density functional calculations are carried out to investigate the structure and the stability of hydrated/hydroxylated TiO2 layered compounds, nanosheets, and nanotubes. Due to a very efficient interlayer hydrogen bonding, the ABA-stacked “step 3” H2Ti3O7 compound is found to be the most stable bulk phase, in agreement with the experiment. For single sheets in a water-rich environment other forms are instead favored, all close in energy, namely, “step 2” titanates, hydroxylized-anatase-like layers, and lepidocrocite-TiO2. Finally, it is shown that a lepidocrocite-TiO2 sheet, when hydroxylated only on one side, spontaneously forms a scroll-like nanotube. The nanotube diameter estimated from our models perfectly matches the3 nm value observed for the internal diameters of Na-free titania nanotubes.
First Principles Study of Hydrated/Hydroxylated TiO2 Nanolayers: From Isolated Sheets to Stacks and Tubes
CASARIN, MAURIZIO;
2009
Abstract
Periodic density functional calculations are carried out to investigate the structure and the stability of hydrated/hydroxylated TiO2 layered compounds, nanosheets, and nanotubes. Due to a very efficient interlayer hydrogen bonding, the ABA-stacked “step 3” H2Ti3O7 compound is found to be the most stable bulk phase, in agreement with the experiment. For single sheets in a water-rich environment other forms are instead favored, all close in energy, namely, “step 2” titanates, hydroxylized-anatase-like layers, and lepidocrocite-TiO2. Finally, it is shown that a lepidocrocite-TiO2 sheet, when hydroxylated only on one side, spontaneously forms a scroll-like nanotube. The nanotube diameter estimated from our models perfectly matches the3 nm value observed for the internal diameters of Na-free titania nanotubes.Pubblicazioni consigliate
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