The formation and effect of O-vacancies in doped TiO2†
The formation of O-vacancies along with their local environment and locus of formation for the O-vacancies has been understood using EXAFS and ab initio techniques in a doped (Zn2+) anatase lattice. The local environment around Ti cations shows no significant alterations whereas at the Zn K edge it can be inferred that oxygen vacancies are present due to doping. The EXAFS data also show that there occurs lowering of the lattice parameters resulting in the contraction of the lattice. The ab initio studies after geometry optimization in accordance with the EXAFS studies reveal the presence of O-vacancies near the doped (Zn2+, here) ion in the anatase lattice along with a significant modification in the electronic structure. Electron density near the Zn centre is relatively higher than that near the Ti centre. The effect of O-vacancies on photocatalytic oxidation is understood using Reactive Blue-19 (RB-19) as a model anionic dye. The trend for the photo-degradation of RB-19 utilizing a UV-source using different Zn-doped TiO2 photocatalysts is portrayed as TiO2 > Zn-1 > Zn-5 > Zn-2 > Zn-10 > ZnO and is explained with the above experiments accordingly.