Structure and photoactivity of titania derived from nanotubes and nanofibers.

Photoactivity under UV irradiation for the decomposition of methylene blue in water and for the oxidation of NO gas was studied on titania powders derived from titanate nanotube (TNT) and nanofiber (TNF) by annealing at high temperatures, comparing with granular titania (ST-01). Rate constant for methylene blue decomposition k(MB) increased with increasing annealing temperature above 300 degrees C after the conversion from titanate to tinania. It tended to decrease above 700 degrees C, mainly due to the phase transformation from anatase to rutile. The dependences of k(MB) on full width at half maximum intensity (FWHM) were common for three samples, a sharp maximum at around 0.4 degrees in FWHM, but TNF-derived sample gave much higher maximum than ST-01. Change in fraction of oxidized NO with annealing temperature showed a plateau at around 50% and then decreased abruptly by high temperature annealing. Starting from TNT and TNF has an advantage to form fine particles by annealing above 300 degrees C, giving high photoactivity due to high crystallinity and high adsorptivity particularly for methylene blue.