Enhanced photocatalytic activity in TiO2 mixed phase nanostructures

Abstract

Titanium dioxide (TiO2) is one of the most effective n-type semiconductors for photocatalytic applications. Compared with the bulk TiO2 nanostructures, the one-dimensional (1D) TiO2 nanostructures have elicited great interest due to its various advantageous properties such as high surface-volume ratio, high chemical stability, strong oxidizing power, nontoxicity and low cost. TiO2exists mainly in two crystalline phases namely anatase and rutile. When different phases of TiO2are combined, they have better charge transport and light absorption properties than pristine nanotubes and nanorods. In reference to that, mixed phases play an important role in the modification of the photocatalytic properties.In the present work, three different nanostructures (TiO2 nanotubes, nanorods and mixed phase nanohybrids) are fabricated by electrochemical anodization and hydrothermal processes, respectively. TiO2 nanotubes are synthesized by electrochemical anodization of highly pure titanium foil in a solution containing ethylene glycol, ammonium fluoride and distilled water, TiO2 nanorods are grown on fluorine-doped tin oxide (FTO) using a hydrothermal method and hybrid TiO2 nanostructures consisting of rutile TiO2 nanorods synthesized by hydrothermal method on anodized TiO2 nanotubes in a high temperature and high-pressure condition with titanium-n-butoxide as the reaction precursor. The three different morphologies of nanotubes, nanorods and nanohybrids are investigated using scanning electron microscopy (SEM). The crystallinity of the TiO2 nanotubes, nanorods and nanohybrids are studied using Raman spectroscopy and X-ray diffraction (XRD) techniques. TiO2 nanotubes, nanorods and nanohybrids are crystalized in anatase, rutile and mixed phase (anatase and rutile), respectively. The structural transformation of the formed TiO2 nanohybrid is compared with TiO2 nanorods and nanotubes that further be explored for photocatalysis by degradation of methylene blue (10 μM) under xenon lamp in the presence of catalysts. It is observed that overall photocatalytic activity of mixed phase TiO2 nanohybrids is better than TiO2 nanotubes and nanorods owing to better electron hole separation and transportation.