The BiOCl, BiOCl/Bi2O2CO3 composites and Bi2O2CO3 were successfully fabricated by a facile composition-controlled preparation technology at room temperature for the first time. The X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) adsorption isotherm, UV-vis diffuse reflectance spectra (UV-vis DRS) and first-principles methods were employed to characterize the phase structures, morphologies, surface areas, optical properties, and photocatalytic mechanism of as-prepared samples. The BiOCl/Bi2O2CO3 composites exhibited the higher photocatalytic activity than individual BiOCl and Bi2O2CO3 for the degradation of MO under simulated sunlight irradiation. The COD removal efficiency of MO solution over BiOCl/Bi2O2CO3 composite achieved 95% after 8 h reaction time. In addition, the formation mechanism and excellent photocatalytic activity of BiOCl/Bi2O2CO3 composite have been investigated and discussed in detail. The enhanced photocatalytic performance of BiOCl/Bi2O2CO3 composites is closely related to the suitable conduction band (CB) interaction and efficient separation of photo-induced electron-hole pairs by the synergistic effect of BiOCl and Bi2O2CO3 under the simulated sunlight irradiation. Combined with the theoretical and experimental findings, the photocatalytic mechanism of BiOCl/Bi2O2CO3 composite and the charge carrier transfer process between Bi2O2CO3 and BiOCl semiconductors have been proposed and investigated. (C) 2014 Elsevier B.V. All rights reserved.