Stable anatase TiO2 formed by calcination of rice-like titania nanorod at 800 °C exhibits high photocatalytic activity

This paper demonstrates the complete retention (>98%) of anatase TiO2 crystalline phase after high temperature (800 degrees C) thermal treatment of rice-like TiO2 nanorods (length = 81-134 nm, diameter = 8-13 nm) relative to 100% conversion of the rutile phase after calcination of P25-TiO2 under similar conditions. The existence of the anatase phase at >800 degrees C was further confirmed by the presence of characteristic vibrational bands (144, 395, 513 and 639 cm(-1)) in the Raman spectra. It was found that TiO2 nanorods undergo fragmentation to a highly crystalline irregular morphology (60-70 nm), nanopolygons (91-110 nm) and smaller rod-shaped particles (length 60-110 nm and diameter 7-12 nm), accompanied by a gradual increase in their crystallite size (from 16 to 40 nm) and decrease in surface area (from 79 to 31 m(2) g(-1)) with increased calcination temperatures from 200 to 900 degrees C. This TiO2 anatase phase displayed enhanced photocatalytic oxidation rate (similar to 2-11 times higher than rutile TiO2) for methyl parathion (a neurotoxic pesticide) degradation to various intermediate products and ultimately to CO2, whereas 1.0 wt% Au-TiO2 significantly improved the photoactivity.