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

NaBiO 3 and Bi(NO 3 ) 3 were used to synthesize Bi-doped NaTaO 3 . 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 NaTaO 3 remained intact for the two Bi-doped samples, but the Ta–O–Ta bond was distorted from 180° after Bi doping. XPS results indicated that Bi 3+ was doped into NaTaO 3 with the Bi(NO 3 ) 3 precursor, while Bi 5+ and Bi 3+ were doped into NaTaO 3 with the NaBiO 3 precursor. The two samples showed identical light absorption, where doping with Bi extended the light absorption to long wavelength light as expected. However, Bi 3+ doping did not promote the photocatalytic activity of NaTaO 3 , while Bi 5+ and Bi 3+ doping did. The distorted Ta–O–Ta bond from 180° due to doping with Bi was detrimental for charge carrier transfer in the photocatalytic process. In contrast, the vacancies or defects in the NaTaO 3 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 Bi 3+ -doped sample being comparable with pristine NaTaO 3 . For Bi 5+ - and Bi 3+ -doped NaTaO 3 , a high concentration of defects was induced by the high valence Bi 5+ 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.