A highly efficient visible-light-driven acidified g-C3N4 (ACNS)/g-C3N4 isotype heterojunction photocatalysts were synthesized by ultrasonic dispersion assisted electrostatic self-assembly strategy for the first time. The photocatalytic oxidation ability of the novel photocatalysts were evaluated using methyl orange (MO) as a target pollutant. The obtained ACNS/g-C3N4 photocatalysts were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FTIR), UV-vis diffuse reflection spectroscopy (DRS), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) methods. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO under visible light illumination (lambda > 420 nm) compared with the pristine ACNS and g-C3N4 solely. The optimal ACNS content for the photocatalytic activity of the heterostructured composites was determined. The 30 wt.% ACNS/g-C3N4 exhibited the highest photo-catalytic activity, which showed a reaction rate constant as high as 0.0216 min(-1), 4.3 times higher than that of bare g-C3N4. The mechanism of the photocatalysts was investigated by determination of reactive species in the photocatalytic reactions and photoluminescence technique. The quenching effects of different scavengers displayed that the reactive h(+) and center dot O-2(-) played major role in the reaction systems. The synergic effect between the ACNS and g-C3N4 was found to lead to an improved photo-generated carrier separation and hence the photocatalytic activities of the composite photocatalysts were increased significantly. (C) 2016 Published by Elsevier B.V.