Synthesis and Characterization of Enhanced Photocatalytic Activity with Li+-Doping Nanosized TiO2 Catalyst.

Abstract

The photocatalytic efficiency of TiO2 is reduced by rapid electron–hole recombination. An effective approach to address this limitation is to have TiO2 doped with various metal ions or heteroatoms. Herein, we prepared a series of Li+-doped TiO2 nanoparticles showing high photocatalytic activities through the sol–gel method. The samples were characterized by X-ray diffraction (XRD) and surface area analyses. Effects of Li+ doping on the Brunauer–Emmett–Teller (BET) surface area, crystallite size, phase transformation temperature, and phase composition were studied. The results showed that Li+ doping can promote the generation of the rutile crystal phase in TiO2, lower the anatase-to-rutile transformation temperature, and generate the mixed-crystal effect. The photocatalytic degradation of methyl orange (MO) was used as a probe reaction to evaluate the photoactivity of the nanoparticles. Parameters affecting the photocatalytic efficiency, including the Li+ doping amount, calcination temperature, and catalyst amount, as well as the kinetics of the photocatalytic process toward the degradation of MO, were investigated. The mixed-crystal TiO2, which was doped with 1.0 mol % Li+ and calcined at 550 °C containing 27.1% rutile and 72.9% anatase phase, showed a 2.2-fold increase in the photoactivity on the basis of the rate constant of MO decomposition as compared with the undoped TiO2. The existence of a definite quantity of rutile phase could effectively inhibit the recombination of the electron–hole pairs, thus promoting photocatalytic activity.