Visible-Light Degradation of Organic Dye Based on a Heterostructure Photocatalyst

Novel highly visible-light active 1.0rGO–ZnBi₂O₄–Bi₂S₃ heterostructure photocatalysts with various weight percentages of Bi₂S₃ were successfully synthesized. First, the 1.0rGO–ZnBi₂O₄ catalyst was synthesized by a simple two-step oxidation–reduction and co-precipitation methods, followed by heating at 450 °C. Then, 1.0rGO–ZnBi₂O₄ was hydrothermally treated with Bi³⁺, and thiourea in ethylene glycol to obtain the 1.0rGO–ZnBi₂O₄–Bi₂S₃ heterostructure photocatalyst. The obtained 1.0rGO–ZnBi₂O₄–Bi₂S₃ heterostructure photocatalysts were characterized by X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Photocatalytic studies were conducted using Indigo carmine and it was found that the heterostructure photocatalyst enabled an almost complete degradation of the pollutants. The enhanced catalytic activity of the 1.0rGO–ZnBi₂O₄–2.0Bi₂S₃ heterostructure photocatalyst is due to the homogeneous distribution of ZnBi₂O₄–2.0Bi₂S₃ over rGO as well as to the efficient electron-transfer from Bi₂S₃ to ZnBi₂O₄ and finally to rGO. More than 97% of Indigo carmine of 50 mg/L was degraded by 1.0rGO–ZnBi₂O₄–2.0Bi₂S₃ in 75 min of visible light irradiation. The reusability of the 1.0rGO–ZnBi₂O₄–2.0Bi₂S₃ was studied, and after four cycles, the Indigo carmine degradation efficiency decreased to 90%.The mechanism of the Indigo carmine degradation by the 1.0rGO–ZnBi₂O₄–2.0Bi₂S₃ catalysis likely consists of to two main processes: first, charge transfer prolongs the lifetime of the electron–hole pairs, and then the electron–hole pairs participate in the reactions that produce free radicals.