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

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.