TiO2 nanorods for gas phase photocatalytic applications

Abstract

Anatase TiO2 nanorod photocatalysts were prepared following a two-step procedure, consisting first in the alkaline hydrothermal treatment at 150°C for 24h of commercial Aeroxide TiO2 P25, and a subsequent calcination at a temperature between 350°C and 700°C. The final calcination led to the transformation of dried TiO2(B) nanotubes into pure anatase TiO2 nanorods, together with a decrease in surface area as well as with the maintain of both one-dimensional morphology and anatase phase with the temperature increase. In the case of the methanol degradation, an optimum in terms of performances was obtained for TiO2 nanorods calcined at 500°C, with a surface area of 122m2/g. This resulted from balanced physicochemical properties with increasing the temperature, with the increase in TiO2 crystallinity, beneficial for lowering the recombination rate, and the decrease in surface area, associated to the increase in the anatase crystallite size, that lower both adsorption capacity of TiO2 nanorods and ability to produce OH radicals. By contrast, the optimum in terms of conversion or sulfur removal rate was observed for nanorods calcined at 380°C in the more rarely studied photocatalytic oxidation of H2S, for which the accumulation at the surface of sulfates as ultimate reaction products deactivates the photocatalyst. Indeed, TiO2 nanorods calcined at a lower temperature of 380°C suffered from a strongly less marked deactivation than the Aeroxide TiO2 P25 reference and nanorods calcined at lower as well as at higher temperatures. They might take advantage of a higher surface area of 219m2/g for overcoming their detrimental lower crystallinity and thus improving their resistance to deactivation, by allowing the storage of larger amounts of poisoning sulfates.