Enhancement mechanism of novel heterojunction Z-scheme-type composite BiOBr/ZnIn2S4 to degrade Congo red

Abstract

Most of the intrinsic photocatalysts with visible-light response and the forbidden bandwidth less than 2.32 eV can produce only one active radical due to the limitation of their energy band structure, which limits their photocatalytic degradation performance. Herein, a novel visible-light-driven binary catalyst (BiOBr/ZnIn₂S₄) was prepared by a hydrothermal method. Compared with pure BiOBr, the prepared binary composite exhibited stronger photocatalytic decomposition ability for pollutants under visible light. The Congo red solution (100 mg L⁻¹) was completely degraded after 40 min under visible light. Repeated cycling experiments showed that BiOBr/ZIS-7 had excellent stability and reusability. The enhanced photocatalytic ability was attributed to the formation of a heterojunction between BiOBr and ZnIn₂S₄, which promoted the separation efficiency of photogenerated electron–hole pairs. Electron paramagnetic resonance and radical capture experiments were used to determine the radicals produced by BiOBr/ZnIn₂S₄ under visible light, indicating that ·O₂⁻ and ·OH are the main active species for the decomposition of Congo red in the photocatalytic process.