Construction of Z-scheme BiOI/g-C3N4 heterojunction with enhanced photocatalytic activity and stability under visible light

BiOI/g-C 3 N 4 binary catalysts with different loading ratios were prepared by a mild one-step stirring method. The optimum loading ratio of BiOI was selected by photocatalytic degradation of 20 mg/L methyl orange (MO) under visible light irradiation. The experimental results of photocatalytic degradation of MO indicated that the loading of BiOI improves the photocatalytic performance of g-C 3 N 4 . The structure and morphology of the catalyst were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and fourier transform infrared spectroscopy (FT-IR). The characterization results showed that BiOI and g-C 3 N 4 were well complexed together, the Z-type heterojunction between them increased the utilization of visible light by g-C 3 N 4 and reduced the recombination rate of photogenerated electron–hole pairs. In addition, the effects of catalyst loading, initial concentration of solution and initial pH on the photocatalytic degradation of MO by BiOI/g-C 3 N 4 under visible light were explored. As a result, it was found that the optimum dosage of the binary catalyst was 1.25 g/L, and the photocatalytic efficiency against MO decreased as the initial concentration increased. In addition, the initial pH of the MO solution had a complicated effect on the photocatalytic efficiency of the binary catalyst, which was related to the existence form of MO in different environments. Finally, the main factors of photocatalytic degradation of MO were confirmed by free radical trapping experiments. Based on the results, the possible mechanism of photocatalytic degradation of MO by BiOI/g-C 3 N 4 was inferred. Enhanced visible light photocatalytic activity was obtained due to light trapping of photogenerated carriers, high transfer efficiency, and enhanced separation efficiency by Z-type heterojunction.