Remarkable role of annealing time on anatase phase titania nanotubes and its photoelectrochemical response

Pure anatase phase highly ordered titanium dioxide nanotube (TNT) arrays were successfully prepared by a two-step electrochemical anodization of titanium foil for photoelectrochemical (PEC) performance. The effect of annealing time (1, 3, 5, 7 and 9 h) on structural, morphological, optical and their novel photoelectrochemical properties of TNTs were investigated. As-anodized nanotubes were amorphous in nature and the pure crystalline anatase phase was observed after annealing the sample at 480 °C in air atmosphere. The XRD spectra reveal that the crystallinity of nanotubes greatly enhanced with increase in annealing time. The optical band gap energy decreases from 3.037 (2) to 2.812 (3) eV with increase in annealing time. The maximum photoconversion efficiency of 25.5% was observed for the 9 h annealed TNT sample on illumination. These results suggest that the anatase phase with high degree of crystallinity play an important role in improving the photoconversion efficiency.

► Anatase phase of titania is more stable for longer annealing time.
► Longer annealing time improves the crystallinity and photoconversion efficiency.
► Band gap of titania has been effectively reduced by increased annealing time.