Heterojunction is an effectively construction to improve the photocatalytic activity due to the excellent photo-induced carrier separation efficiency. In this paper, g-C3N4/Bi4O5I2 heterojunction was prepared and characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic data showed that g-C3N4/Bi4O5I2 heterojunction had higher activity than pure g-C3N4 and Bi4O5I2. At an optimal ratio of 1.0 mol% (11.4 wt% of Bi4O5I2), g-C3N4/Bi4O5I2 photocatalyst showed the highest photocatalytic reduction activity for CO2 conversion with 45.6 mu mol h(-1) g(-1) CO generation. Photocurrent and electrochemical impedance (EIS) spectroscopy revealed that higher photo-induced carrier separation efficiency of g-C3N4/Bi4O5I2. Z-scheme charge transfer mode was proved by redox mediator existence and superoxide radical (O-2(center dot-)) and hydroxyl radical ((OH)-O-center dot) quantification experiments. (C) 2016 Elsevier B.V. All rights reserved.