Sonochemical synthesis of BiOI-TiO2heterojunction with enhanced visible-light-driven photocatalytic activity

Construction of p-n heterostructured semiconductor photocatalysts is of great attention. Herein, BiOI-TiO2p-n heterojunction photocatalysts with different molar ratios have been successfully synthesized by ultrasonic-assisted method. On the basis of the XPS analysis, Ti-O-Bi bonds are formed between BiOI nanosheets and TiO2nanoparticles rather than a simple overlap of single material. Compared to the pure BiOI and TiO2, the BiOI-TiO2p-n heterojunctions show prominently enhanced photocatalytic activity for degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Especially, 80% BiOI-TiO2possesses the highest photocatalytic reaction rate constant, which is 3.9 and 12.2 times higher than that of BiOI and TiO2, respectively. The superoxide radical species (•O2−) has been regarded as the predominant active species in the reaction process, confirmed by the trapping experiments and Electron spin resonance (ESR) results. In addition, efficient separation and transfer of photogenerated electron-hole pairs rendered by the heterojunctions are proved employing photocurrent experiments, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL). Moreover, the positions of the conduction bands (CB) and valence bands (VB) of the samples are investigated by Mott–Schottky measurements. It can be deduced that the existence of internal electric field caused by p-n junction leads to effective separation of electron hole pairs, resulting in the production of a large number of active species for the MO degradation.