Gas Phase Photocatalysis on Large-Scale TiO₂ Nanotube Layers for Pollutant Degradation: Influence of the Nanotube Crystallinity

In this work, for the first time, the influence of the crystallinity of TiO2 nanotube (TNT) layers on their gas phase photocatalytic performance was investigated under ISO standards using two distinct model pollutants, namely, hexane and acetaldehyde. TNT layers (1 mu m thick) on 5 x 10 cm(2) large Ti substrates were employed in this work due to their excellent adhesion to Ti upon annealing at high temperatures. Annealing of the TNT layers was carried out in a temperature range between 300 and 700 degrees C, resulting in TNT layers with different crystallinities, i.e., from the pure anatase phase to an 85% rutile phase. The superior performance of the TNT layers annealed at 600 degrees C with mixed anatase and rutile phase compared to other specimens was observed for both model pollutants, stemming from the band alignment between the two crystalline phases. For higher annealing temperatures, however, the photocatalytic performance of the TNT layers was reduced due to a partial disintegration of the TNTs. No surface contamination of the TNT layers with residues of pollutant degradation products was observed after experiments.