Phase Composition and Photocatalytic Properties of La3+-doped TiO2 Nanopowders

A sol-gel method was used to prepare La3+-doped TiO2 nanopowders. The sample was characterized with XRD, TEM, HRTEM, STEM-EDS, XPS and ultraviolet-visible (UV-Vis) spectroscopy. The changes of the La3+-doped TiO2 in the phase transition were discussed on the aspects of its phase composition, the average grain size, the microstructure, the chemical states and UV-Vis absorption spectroscopy. The results show that doping with La3+ significantly suppresses the phase change and grain growth of TiO2. It effectively improves the TiO2 dispersibility and reduces the average particle size of TiO2. With the increase of the calcination temperature, the second phase La4Ti19O24 gradually precipitates from the La3+-doped TiO2 and forms an incoherent interface with the brookite TiO2 phase, which precipitates in the form of irregular spheres on the surface of the TiO2 base. Secondary phases are originated from segregation of point defects La.(Ti)', at grain boundaries in La3+ doped TiO2. The segregation driving force is mainly the elastic strain energy. With the increase of calcining temperature, the atomic fraction of the O-IS in the La3+-doped TiO2 gradually decreases, and that of the La-3d gradually increases. There is an energy loss peak at the higher binding-energy side of the main peak of the La-3d, and Ti3+ exists after the calcination. La3+ doping makes the optical absorption band edge of the TiO2 red-shift. But with increasing the calcination temperature, the optical absorption bandedge blue shifts.