Comparison of doping limits among sonochemically prepared metal-doped TiO2 nanopowders in view of physicochemical properties

According to binding energy calculations in a unit cell model of anatase TiO₂, the doping limits for Cr, V, W, Mo, Zr, and Nb are predicted to increase in this order. In our experimental test of doping limits, Cr and W are considered in this series of transition metals, since their low doping limits suggest greater difficulty of doping into anatase structure than the others, thereby providing a challenging test for the prediction. Besides, noble metals such as Ag and Pt are selected for doping into TiO₂ for comparison. Thus, our investigation includes twofold research activities. One is to prepare metal-doped TiO₂ nanopowders of four different kinds, and the other is to determine the doping limit of each resulting powder. For the former, a sonochemical process has been used to produce metal-doped TiO₂ nanoparticles. For the latter, we resorted to electron probe microanalysis. In addition, we performed analysis by X-ray diffraction, transmission electron microscopy, and diffuse reflectance spectroscopy, as well as photocatalytic reaction with methylene blue. Thus, the resulting physicochemical properties of our metal-doped nanoparticles are expected to provide a basis for comparison of doping limits among them.