Assessing optimal photoactivity on titania nanotubes using different annealing temperatures

Photocatalytic activity of titania nanotubes, during degradation of reactive blue 69 (RB-69) dyes, was correlated with its optical properties and compared with commercial photocatalyst P25. Titania nanotubes made up of two structural layers walls were prepared by an alkali thermal reflux treatment at atmospheric pressure from an anatase precursor with sodium hydroxide. Annealing titania nanotubes at 473-673 K, red-shifted the fundamental transition edge of titania, showing a maximum at 573 K with a band gap energy of 2.97 eV and an additional visible absorption band was originated due to the clehydroxylation of strongly deformed TiO6 octahedral layers on the curved nanotubular structure. Temperatures above 673 K brought about the collapse of TiO6 octahedra layers of the nanotubular walls yielding anatase domains inhibiting the light absorption in the visible region and blue shifting the UV absorption to a band gap energy of 3.2 eV. The higher the red-shift of the transition edge of titania the higher the photocatalytic activity in degradation of the dye compound. Titania nanotubes annealed at 573 K showed similar photodegradation activity (per mass unit) of RB-69 to commercial photocatalysts Degussa-P25, both with band gap energies of 2.97 and 3.0 eV, respectively. (C) 2010 Elsevier B.V. All rights reserved.