Influence of Bi chemical state on the photocatalytic performance of Bi-doped NaTaO3

NaBiO3 and Bi(NO3)(3) were used to synthesize Bi-doped NaTaO3. The influence of the Bi chemical state on the photocatalytic activity was investigated using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and diffused reflectance spectroscopy to study the structure, chemical state and light absorption characteristics, respectively. The photocatalytic activity was evaluated by the H-2 evolution water splitting reaction. The monoclinic phase of NaTaO3 remained intact for the two Bi-doped samples, but the Ta-O-Ta bond was distorted from 180 degrees after Bi doping. XPS results indicated that Bi3+ was doped into NaTaO3 with the Bi(NO3)(3) precursor, while Bi5+ and Bi3+ were doped into NaTaO3 with the NaBiO3 precursor. The two samples showed identical light absorption, where doping with Bi extended the light absorption to long wavelength light as expected. However, Bi3+ doping did not promote the photocatalytic activity of NaTaO3, while Bi5+. and Bi3+ doping did. The distorted Ta-O-Ta bond from 180 degrees due to doping with Bi was detrimental for charge carrier transfer in the photocatalytic process. In contrast, the vacancies or defects in the NaTaO3 lattice induced by Bi doping for charge balance were beneficial for charge carrier separation. The opposing action of these two factors resulted in the activity of the Bi3+-doped sample being comparable with pristine NaTaO3. For Bi5+- and Bi3+-doped NaTaO3, a high concentration of defects was induced by the high valence Bi5+ ion and this led to its higher photocatalytic activity. Our results indicated that charge carrier transfer is a priority factor in the photocatalytic process and the doping of a high valence ion in the ABO(3) structure is a way to promote the separation of charge carriers. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.