Effect of the Ti/Na molar ratio on the acidity and the structure of TiO2 nanostructures: Nanotubes, nanofibers and nanowires

TiO2 nanotubes were prepared by the hydrothermal treatment of TiO2 particles with different NaOH concentrations (5, 7, 10 and 12 N) at 140 °C; afterwards, HCl was added until reaching pH 1. Both the crystalline phase and coordination of the TiO2 nanotubes, composed principally of H2Ti3O7 and H2Ti4O9·2H2O, were significantly affected by the NaOH rinsing treatment. Likewise, the surface area, pore volume and pore size of the TiO2 nanotubes changed with the NaOH rinsing treatment. Finally, the NaOH rinsing treatment exerted a notable effect on the generation of Brِnsted sites, which is shown by the following sequence: NT7 > NT10 > NT12 > NT5; meanwhile Lewis sites were only present on the NT5 sample.