A novel TiO2 composite for photocatalytic wastewater treatment

A novel TiO2 composite consisting of Anatase interacting with a Ti3+-containing Rutile phase was synthesized by heating a mixture of TiO2 (Hombikat) and Ti2O3 in air at different temperatures ranging from 300 °C up to 900 °C. The preparation of the samples was analyzed by Thermal Gravimetric Analysis (TGA), and the resulting composites characterized by X-ray powder diffraction (XRD), Raman and UV–Vis spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) spectroscopy, and Scanning Electron Microscopy. Characterization data show a phase transformation from Ti2O3 to Ti3+-containing Rutile at temperatures of around 600 °C. Moreover, Hombikat is gradually converted from amorphous to crystalline Anatase. The Ti3+-content and the degree of Anatase crystallinity are respectively inversely and directly proportional to an increasing preparation temperature. The composite which was synthesized at 600 °C showed the highest photocatalytic rate in the decolorization of Methyl Orange (MO). The rate constant was significantly larger than obtained for Evonik P25 after identical thermal treatment (600 °C). Photodeposition of Pt further not only enhanced the photocatalytic activity of the optimized composite, but surprisingly also the stability. The methyl orange degradation results are discussed on the basis of hole and electron transfer phenomena between Anatase and Rutile phases, the latter containing (surface) oxygen vacancies (Ti3+). The presence of surface oxygen vacancies and/or Pt nanoparticles is proposed to be of benefit to the rate determining oxygen reduction reaction.