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.

The high recombination rate of photogenerated charges is the main problem that limits the photocatalytic activity of semiconductor photocatalysts. Herein, we have reported novel heterojunctions of BiOBr–carbon nitride (BiOBr–C₃N₄) fabricated by depositing BiOBr nanoflakes onto the surface of C₃N₄. These visible light responsive heterojunctions possess intimately contacted interfaces and well-aligned straddling band-structures, which are propitious to the effective separation and transfer of photogenerated charges, bringing an improved performance. Their photocatalytic activities were evaluated by degrading Rhodamine B in aqueous solution induced by visible or indoor light. The optimum photocatalytic activity of the 0.5BiOBr–0.5C₃N₄ heterojunction was almost 4.9 and 17.2 times as high as those of individual BiOBr and C₃N₄ under visible light irradiation, and 1.5 and 48.9 times as high under indoor light irradiation, respectively. Moreover, its activity was also much higher than those of TiO₂ (P25), BiOBr–TiO₂, and C₃N₄–TiO₂ heterojunctions. On the basis of experimental and theoretical results, the photocatalytic mechanism was proposed, which revealed that organic molecules were mainly oxidized by holes concentrated in the valence band of C₃N₄. Our work highlights that the design of heterojunctions with well-aligned straddling band-structures by combining two visible light responsive semiconductors provides an efficient method to prepare new photocatalysts working with natural light.