BiOBr–carbon nitride heterojunctions: synthesis, enhanced activity and photocatalytic mechanism

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.