Novel C3N4–CdS composite photocatalysts with organic–inorganic heterojunctions: in situ synthesis, exceptional activity, high stability and photocatalytic mechanism

Abstract

Novel organic–inorganic composites composed of two visible light responsive semiconductors of graphitic carbon nitride (C₃N₄) and CdS were successfully synthesized via an “in situ” precipitation–deposition method. The C₃N₄–CdS heterostructures were fabricated by depositing CdS nanoparticles onto the surface of C₃N₄. The morphology and optical property of compsoites can be tuned by adjusting the mass ratio of C₃N₄–CdS, which determines the enhanced level of photocatalytic activity. The optimum activity of 0.7C₃N₄–0.3CdS photocatalyst is almost 20.5 and 3.1 times higher than those of individual C₃N₄ and CdS for the degradation of methyl orange, and 41.6 and 2.7 fold higher for the degradation of 4-aminobenzoic acid, respectively. Moreover, its activity is also much higher than those of C₃N₄–TiO₂ and CdS–TiO₂ composites, as well as N-modified TiO₂. Of special significance is that the present C₃N₄–CdS composites exhibit high stabilities under illumination, in contrast with CdS. The enhancement in both performance and stability should be assigned to the effective separation and transfer of photogenerated charges originating from the well-matched overlapping band-structures and closely contacted interfaces. Our work highlights that coupling semiconductors with well-matched band energies provides a flexible route to improve the activity and stability of photocatalysts, and gives ideas for the design and synthesis of other highly active and stable materials.