Preparation of Ta-Doped TiO₂ Using Ta₂O₅ as the Doping Source

A novel method for preparing Ta-doped TiO₂ via using Ta₂O₅ as the doping source is proposed. The preparation process combines the hydrothermal fluorination of Ta₂O₅ and the subsequent formation of Ta-doped TiO₂ sol. The results show that the doped sample annealed at 393 K generates an unstable intermediate NH₄TiOF₃, which converts into anatase TiO₂ with the increase of temperature. After annealing at ≥673 K, the Ta-doped TiO₂ nanocrystals with the grain size <20 nm are obtained. Both the XRD and TG-DSC results confirm that Ta doping prevents the anatase-rutile crystal transition of TiO₂. The band gap values of the doped samples, as obtained by UV-vis diffuse reflectance spectra, are smaller than that of pure anatase TiO₂. The first-principle pseudopotential method calculations indicate that Ta⁵⁺ lies in the TiO₂ lattice at the interstitial position.