Existence form of lathanum and its improving mechanism of visible-light-driven La-F co-doped TiO2

The existence form and effect of La on the phase composition, morphology, recombination of photocarriers, and optical absorptivity of La-F codoped TiO2 were investigated. Experimental results indicate that all the phase composition of samples is anatase TiO2, the grain sizes decrease with the increasing of La content. The catalysts have a well-defined spherical structure with an average size of 12 -14 nm, and the doping elements are uniformly dispersed. Compared with pure TiO2, the absorption edge of La1.5F5-TiO2 red shifts from 388 to 437 nm, accordingly the energy gap (E-g) reduces from 3.2 to 2.84 eV. Besides, the recombination rate of electron-holes in La1.5F5-TiO2 is the weakest among the prepared samples, and the specific surface area of La1.5F5-TiO2 reaches 105.27 m(2)/g. The apparent reaction rate constant k of La1.5F5-TiO2 for methylene blue (MB) degradation under visible light obtained from the apparent first-order model achieves 0.0166 +/- 0.52 min(-1), which is greater than 0.0033 +/- 0.09 min(-1) of TiO2. Moreover, high-resolution transmission electron microscopy (HRTEM) observation reveals that there coexist La2O3 particles in the co-doped TiO2. (C) 2019 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.