Solar photocatalytic activities of porous Nb-doped TiO2 microspheres prepared by ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis method was used to prepare Nb-doped TiO2 porous microspheres with an average diameter of 500 nm for solar photocatalytic applications. The effect of Nb-doping on morphology, structure, surface area, as well as spectral absorption properties of TiO2 microspheres was investigated with SEM, TEM, XRD, Raman spectra, BET, and UV–Vis absorption spectra. The Nb-doping decreased the grain size of TiO2 porous microsphere, and influenced its surface area and pore size distribution dependent on the doping concentration, but changed negligibly the morphology and size of TiO2 microspheres. Moreover, the Nb-doping was observed to extend the spectral absorption of TiO2 into visible spectrum, and the absorption onset was red-shifted for about 88 nm at a doping level of 5% compared to pristine TiO2 microspheres. Under solar or visible irradiation, Nb-doped TiO2 microspheres showed higher photocatalytic activity for methylene blue degradation compared with TiO2 microspheres, which could be ascribed to the extended light absorption range and the suppression of electron-hole pair recombination.