Influence of annealing temperatures on TiO2 nanotubes formation

Herein, we report on the influence of annealing temperature on the formation of anatase and rutile phase of TiO₂. Electrochemical anodization was carried out in two electrodes bath consisting of excess Fluorine ions. The anode is a 0.1 mm thick Ti foil and the cathode is Pt electrode. Anodization was conducted at 20 V in 1M Na₂SO₄ electrolyte. The anodized foil was subjected to morphological and structural characterizations using field emission scanning electron microscope and Raman spectroscopy. As-anodized foil was found to be amorphous or weakly crystalline. When the oxide was heat treated, Raman spectroscopy analysis showed the diminishing of anatase peaks for samples annealed at 500 °C at Raman frequency 149.41 cm^-1. This indicates that the transformation occurs at this range of temperatures with a more complete transformation at higher temperature. Annealing at higher than 600 °C the pattern shows a peak belonging to the rutile peak and it induces thickening of the nanotubes wall and at above 700 °C, the nanotubes structure has completely disappeared. For Rutile phase structural appeared at Raman frequency 633.59 cm^-1 assigned as Raman vibrational mode E_g and A_1g, respectively.