Fabrication, characterization and mechanism of a novel Z-scheme photocatalyst NaNbO3/WO3 with enhanced photocatalytic activity.

Development of semiconductor photocatalysts with simultaneous high photooxidation and photoreduction performance is always a hot topic in the photocatalytic field. In this article, a highly active Z-scheme NaNbO3/WO3 photocatalyst was prepared by a facile ball milling method, even though either NaNbO3 or WO3 exhibited relatively much lower photocatalytic activity. The photocatalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron spin resonance technology (ESR), photoluminescence (PL) spectra and UV-Vis diffuse reflection spectroscopy (DRS). The OH radicals produced during the photocatalytic process were detected by a terephthalic acid photoluminescence probing technique (TA-PL). The photocatalytic activity was evaluated by photocatalytic oxidation of rhodamine B (RhB), methylene blue (MB) and reduction of Cr2O7(2-). The results showed that the photocatalytic activity of the composite was much higher than that of single NaNbO3 and WO3. The first-order kinetic constant of photocatalytic degradation of RhB and MB for NaNbO3/WO3 is 4.9 times and 3.4 times that of pure WO3. The optimum amount of NaNbO3 is 0.5 wt%. The composite photocatalyst shows good stability. It is proposed that the photoexcited electrons in the CB of WO3 and photogenerated holes in the VB of NaNbO3 are quickly combined, so the accumulated rich electrons in the CB of NaNbO3 and holes in the VB of WO3 have powerful potential to produce ˙O2(-) and ˙OH, respectively. The ˙OH, ˙O2(-) and direct h(+) oxidation of WO3 play major roles in the degradation of RhB or MB in the NaNbO3/WO3 system.