A dual strategy to construct flowerlike S-scheme BiOBr/BiOAc1-xBrx heterojunction with enhanced visible-light photocatalytic activity

For broad-band-gap semiconductors like BiO(CH3COO) (denoted as BiOAc), constructing heterojunctions with a narrow-band-gap semiconductor or forming solid solution is an effective strategy to improve visible-light-driven photocatalytic activity. Herein, by combining two strategies, a novel step-scheme (S-scheme) heterojunction BiOBr/BiO(CH 3COO)(1-x)Br-x (denoted as BiOBr/BiOAc1-xBrx) was synthesized via a facile co-precipitation method at room temperature. The as-prepared BiOBr/BiOAc1-xBrx, with feeding molar ratio of Br/Bi at 0.8 exhibited outstanding visible-light photocatalytic activity for tetracycline (TC) and rhodamine B (RhB) degradation, with degradation efficiency of 99.2% and 99.4%, respectively, which was higher than those of BiOAc (17.3% and 34.8%), BiOBr (57.2% and 62.7%), solid solution BiOAc1-xBrx (x = 0.4) (68.6% and 68.2%) and heterojunction BiOBr/BiOAc (69.9% and 88.1%). The enhanced photocatalytic activity could be attributed to two main aspects. Firstly, the formation of the solid solution BiOAc1-xBrx could not only enlarge visible light response of BiOAc, but also successfully transform type-I heterojunction of BiOBr/BiOAc to typical S-scheme heterojunction of BiOBr/BiOAc1-xBrx which thus prolong the lifetime of charge carriers with stronger redox ability. Secondly, by adding urea to the reaction system as a morphology modifier, uniform ultrathin nanosheet-based flowerlike BiOAc was obtained, and more importantly, the heterojunction BiOBr/BiOAc1-xBrx inherited the flowerlike contour of BiOAc and thus improved the dispersion, which benefit to the transfer of carriers at the interfaces and onto the surface of nanoparticles. In addition, the as-prepared S-scheme heterojunction also possessed desirable photodegradation efficiency for TC and RhB in real wastewater or in the presence of some electrolytes. This study provides a simply and energy-saving strategy for simultaneously optimizing energy band structures and microstructure to highly efficient heterojunction photocatalysts.