In this work, visible-light-active silver halide AgX(X = Cl and Br) deposited on the protonated graphitic carbon nitride (pCN) photocatalyst was developed by a sonication-assisted deposition-precipitation route at room temperature. The surface morphology, phase structure, chemical composition, optical property and electronic band structures of the AgX-hybridized pCN (AgX/pCN) hybrid nanocomposites were systematically characterized. Subsequently, the photocatalytic performance of the AgX/pCN was evaluated by the reduction of CO2 to CH4 in the presence of H2O vapor under a low-power energy-saving daylight bulb at atmospheric pressure and ambient temperature. The optimal 30AgBr/pCN presented the highest photocatalytic activity, achieving a total CH4 evolution of 10.92 mu mol g(catalyst)(-1), which was 34.1 and 4.2 times greater than those of single-phase AgBr and pCN, respectively. Furthermore, by comparing different halide ions, the photoactivity of 30AgBr/pCN was higher (by a factor of 1.3) than that of the optimal 30AgCl/pCN. The enhanced photocatalytic activity was accredited to (1) the surface plasmon resonance (SPR) effect from Ag and (2) the formation of heterojunction structure between pCN and AgBr in the AgBr/pCN hybrid photocatalysts for efficient charge transfer and separation to retard the recombination process as evidenced by the photoluminescence analysis. The effective charge separation was attributed to the matching of electronic band potentials of pCN and AgBr, exhibiting the Type II heterojunction, in comparison to that of AgCl/pCN (Type I heterojunction). Lastly, the plasmon-enhanced photocatalytic mechanisms associated with both Ag/AgBr/pCN and Ag/AgCl/pCN hybrid nanoarchitectures were critically discussed. (C) 2015 Elsevier B.V. All rights reserved.