Experimental and theoretical study of oxygen vacancy induced La-doped mesoporous TiO2 for enhanced thermal stability

We report a facile synthesis of mesoporous TiO2 with a large specific surface area and rich oxygen vacancies using La-doped TiO2 through high-temperature annealing. Such integration of a unique mesoporous structure and oxygen vacancies provides effective carrier transport and increased surface active sites. The effects of lanthanum on mesoporous TiO2 were studied experimentally and theoretical calculations were performed. Thermal treatment was conducted at temperatures ranging from 350 to 900 °C. The x-ray diffraction analyses confirm that the formation of anatase TiO2 remains stable until 650 °C for pure TiO2 and 850 °C for the La doped sample. It was noted that there was a phase transformation from anatase to rutile with an increase in temperature. Morphological analysis confirmed a mesoporous structure with lanthanum covering the surface of the TiO2 mesospheres. Elemental analysis confirms the presence of La in the TiO2 composition and increased oxygen vacancies with increased lanthanum concentration. The density functional theory calculations reveal that the oxygen vacancy heavily alters the electronic structure of TiO2. The distance between the oxygen vacancy and lanthanum was shown to play an important role in altering the bandgap of TiO2. When lanthanum was near the oxygen vacancy, the bandgap was larger than that of all the models. Lanthanum, when away from the vacancy, leads to the lowest bandgap among all the models.