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

Abstract

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 Cr₂O₇²⁻. 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.