Dramatic visible light photocatalytic activity of MnOx–BiOI heterogeneous photocatalysts and the selectivity of the cocatalyst

Abstract

Charge separation is very important for increasing the activity of semiconductor-based photocatalysts. Here we show that the main active species of BiOI are photo-induced holes, rather than ˙OH and O₂˙⁻, under visible light irradiation. Based on this finding, the cocatalyst MnO_x was used to enhance the transfer of the photo-induced holes, resulting in much higher photocatalytic activity, compared with the photocatalyst without MnO_x. MnO_x–BiOI heterogeneous nanostructure photocatalysts have been prepared by photo-deposition in Mn(NO₃)₂ solution, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy. As-prepared MnO_x–BiOI exhibited higher photoactivity than BiOI and Pt–BiOI for the degradation of Rhodamine B (RhB) dye under visible light irradiation. The PL spectrum showed that MnO_x enhances the separation efficiency of the photo-induced electrons and holes of BiOI. Finally, BiOI was selectively combined with a deriving-hole-type cocatalyst to enhance the photocatalytic activity, and the reason for the cocatalyst selectivity is also discussed. This finding may be useful in bismuth-based photocatalysts to construct highly efficient solar energy conversion systems.