Influence of Ho³⁺/La³⁺-doping on photocatalytic activity of TiO₂ for methyl orange degradation

The un-doped and Ho³⁺/La³⁺-doped TiO₂ nanoparticles were prepared by sol-gel method with Ti (OC₄H₉)₄ as raw material and characterized with X-ray diffraction (XRD) and UV-Vis absorption spectra (UV-Vis), and their photo-catalytic activity were evaluated in the methyl orange (MO) degradation in aqueous suspension under UV irradiation. XRD shows that all samples preserve anatase structure. Ho³⁺/La³⁺-doping inhibites the increase of crystallite size, and leads to the lattice expansion and aberrance. A tiny blue-shift of the absorption profile in Ho³⁺-doped samples and a red-shift of the absorption profile in La³⁺-doped samples are found. Ho³⁺-doping and La³⁺-doping improve photocatalytic activity of TiO₂ markedly. In the experiment condition, the optimum Ho³⁺ concentration is about 0.3% for the maximum photocatalytic degradation, and the optimum La³⁺ concentration is about 0.1%. The photocatalytic degradation efficiency of Ho³⁺-doping is almost equal to La³⁺-doping in their optimum doped concentration.