The effect of oxygen vacancies on the photocatalytic activity of BiOCl nanocrystals prepared by hydrolysis and UV light irradiation

We report the prepared gray bismuth oxychloride (BiOCl) with oxygen vacancies by UV light irradiation. The presence of oxygen vacancies and unpaired electrons was confirmed by characterizing the gray BiOCl with X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), photoluminescence (PL) and Ultraviolet–visible-light diffuse reflectance spectroscopy (UV–vis DRS) techniques. The gray BiOCl nanocrystals exhibited excellent visible-light-driven photocatalytic activities for methylene blue (MB) degradation, which was much higher than that of white BiOCl. The photocatalytic mechanism of gray BiOCl with oxygen vacancies under visible light irradiation was tentatively discussed. The intermediates and the final products of degradation were observed by high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry (HPLC–ESI-DAD-MS) and the possible photodegradation pathway of MB was subsequently proposed. The roles of different kinds of reactive oxygen species in the photocatalytic degradation process were investigated by using certain radical scavengers. The reduction of the total organic carbon (TOC) and the formation of inorganic products i.e. SO42− and NO3−, suggesting that it is a promising photocatalyst for the complete mineralization of aqueous methylene blue (MB).