Controlled synthesis of vertically aligned honeycomb TiO2 nanotube arrays: effect of high-temperature annealing on physical properties

Abstract

Vertically aligned honeycomb titania (TiO2) nanotube arrays grown on Ti foil were synthesized by electrochemical anodization method. The changing of morphology, crystalline structural, and optical properties of anodic titania nanotube (ATNT) arrays systematically studied. A novel annealing approach is proposed to retain the ATNT arrays at high temperatures ranging from 700 to 900 °C. At 700 and 800 °C, FESEM images showed that the nanotubular structures were preserved from annihilation and the morphology of the structure was a mixture between anatase and rutile. However, the highlight of this research was the successful synthesis of the high-quality rutile ATNT arrays at 900 °C. The X-ray diffractometer measurements proved that the variations in the mean crystallite sizes of anatase and rutile phase occurred during annealing of ATNT samples. The corresponding optical bandgaps were determined by extracting the reflectance values and combining Kubelka–Munk function with the indirect Tauc plot for transition phases of ATNT arrays for high-temperature annealed films.