A hierarchical flower-like Co3O4/Bi2O2CO3 composite photocatalyst with a p-n heterojunction semicon-ductor structure has been synthesized via two-step hydrothermal process. The composite photocatalyst have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photo-electron spectroscopy (XPS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), BET surface area, UV-vis diffuse reflectance spectra (DRS), electron spin resonance (ESR) and photoluminescence spectroscopy (PL). The photocatalyst exhibits enhanced pho-tocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The ESR results reveal that the superoxide radicals (O-center dot(2)-) were the main active species in the photocatalytic system. The 0.6 wt% Co3O4/Bi2O2CO3 exhibits the highest photocatalytic activity as compared with other sam-ples because of the formation of the p-n junction between p-Co3O4 and n-Bi2O2CO3, which effectively suppresses the recombination of photoinduced electron-hole pairs and increase of the concentration of superoxide radicals ((center dot)O2(-)) involving in the photodegradation process. Moreover, the mechanism of the enhanced photocatalytic properties was proposed. (C) 2016 Elsevier B.V. All rights reserved.