Structural characterization of the V 2O 5/TiO 2 system obtained by the sol–gel method

Abstract

The influence of the vanadium load and calcination temperature on the structural characteristics of the V 2O 5/TiO 2 system was studied by X-ray diffraction and X-ray absorption spectroscopy (XAS) techniques. Samples of the V 2O 5/TiO 2 system were prepared by the sol–gel method under acid conditions and calcined at different temperatures. The rutile phase was found to predominate in pure TiO 2 calcined at 450 °C as a result of the reduction of phase transition temperature promoted by the sol–gel method under acid conditions. The anatase phase became predominant at 450 °C as the amount of vanadium increased from 6 to 9 wt%. A structural change in the TiO 2 phase from predominantly anatase to totally rutile with increased calcination temperature was observed in 6 wt% samples. An analysis of the vanadium X-ray Absorption Near Edge Structure (XANES) spectra showed that the oxidation state of vanadium atoms in the samples containing 6 and 9 wt% of vanadium and calcined at 450 °C was predominantly V 4+. However, the presence of V 5+ atoms cannot be ruled out. A qualitative analysis of extended X-ray absorption fine structure (EXAFS) spectra of the samples containing 6 and 9 wt% of vanadium calcined at 450 °C showed that the local structure around vanadium atoms is comparable to that of VO 2 crystalline phase, in which vanadium atoms are fourfold coordinated in a distorted structure. For the sample after calcination at 600 °C, the EXAFS and XANES results showed that a significant portion of vanadium atoms were incorporated in the rutile lattice with a V x Ti (1− x) O 2 solid solution formation. The conditions of sample preparation used here to prepare V 2O 5/TiO 2 samples associated with different amounts of vanadium and calcination temperatures proved to be useful to modifying the structure of the V 2O 5/TiO 2 system.