Effect of Nd3+ Doping on Photocatalytic Activity of TiO2 Nanoparticles for Water Decomposition to Hydrogen

The undoped TiO2 and Nd3+-doped TiO2 samples were prepared by the sol–gel method and characterized by X-ray diffraction, diffuse reflectance UV-visible spectroscopy, transmission electron microscopy, and N2 adsorption. The correlation of the photocatalytic activity for hydrogen evolution with the phase composition, BET surface area, and light absorption intensity in the UV region was investigated. For the undoped TiO2 sample, the particle size and agglomeration increased while the BET surface area and the light absorption intensity in the UV region decreased with increasing calcination temperature. The anatase to rutile phase transformation started at 600°C and completed at 800°C. The photocatalytic activity of undoped TiO2 decreased with increasing calcination temperature, and the sample calcined at 600°C was the best because of the coexistence of a certain proportion of rutile/anatase mixed phase. For the Nd3+/TiO2 samples, Nd3+ doping inhibited the crystal phase transformation and the rutile phase appeared at 800°C. Moreover, Nd3+ doping restrained the growth of grain size, improved the dispersivity of the particles, and raised BET surface area. The more the doping amount, the larger the BET surface area. As the calcination temperature increased, the decreasing extent of the light absorption intensity of Nd3+/TiO2 in the UV region was lower than that of undoped TiO2. Nd3+ doping raised the photocatalytic activity for hydrogen generation, and the optimum amount of Nd3+ doping was 0.1%, at which the photocatalytic activity of Nd3+/TiO2 was 3.5 times that of undoped TiO2.