Influence of annealing temperatures on TiO<inf>2</inf> nanotubes formation

Abstract

Herein, we report on the influence of annealing temperature on the formation of anatase and rutile phase of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . 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 Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> assigned as Raman vibrational mode E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> and A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1g</sub> , respectively.