Enhanced photocatalytic degradation of Congo red by a BiVO₄/ZnIn₂S₄ composite: performance and mechanism

High-performance visible-light-driven photocatalysts have emerged as a research hotspot in environmental pollution; however, the photocatalytic degradation mechanisms of Congo red using bismuth semiconductor composites are not fully understood. Herein, BiVO₄/ZnIn₂S₄ was successfully synthesized via a hydrothermal method, and the photocatalytic performance of the composite was assessed by carrying out photocatalysis experiments to decompose Congo red. The phase composition, carrier separation capability, interface electron interactions, and morphological features were characterized by XRD, PL, XPS, and TEM analyses, respectively. The results showed that a Z-scheme heterostructure was successfully constructed between the BiVO₄ and ZnIn₂S₄. Electrons in the conduction band of BiVO₄ migrated to the valence band of ZnIn₂S₄, which effectively enhanced the separation of photogenerated charge carriers and improved the degradation capability. Compared with pure BiVO₄, 7% BiVO₄/ZnIn₂S₄ displayed superior photocatalytic capability and could completely remove Congo red (100 mg L^-1) in 60 min under visible light. Radical trapping experiments combined with electron paramagnetic resonance characterization revealed that the superoxide anion (˙O₂ ^-) and holes (h⁺) acted as the key reactive species driving Congo red degradation. In addition, six cycles of experiments were performed to verify that the BiVO₄/ZnIn₂S₄ composite retains its high stability. This study provides a feasible strategy for fabricating effective photocatalysts to treat organic pollutants in wastewater.