Development and enhancement of charge separation processes for the degradation of RhB using an innovative ZnO/MgIn2S4 S-scheme heterojunction photocatalyst

Abstract

The dye Rhodamine B (RhB), commonly utilized in the textile sector, is linked to carcinogenic and neurotoxic effects, posing a significant risk for a range of human health issues. Photocatalytic systems can be used as an effective and energy-saving technique to degrade dye pollutants. Herein, a novel ZnO/MgIn₂S₄ S-scheme heterojunction photocatalyst was successfully synthesized by a facile method and employed as a highly efficient photocatalyst for the degradation of RhB under visible light irradiation. To optimize the use of the developed photocatalyst for environmental remediation, it was investigated how several factors affect the photocatalytic process. These factors included the initial pH of the reaction medium, the photocatalyst dosage, and RhB concentration. The reaction kinetics of the synthesized photocatalysts followed pseudo-first-order kinetics, and the degradation rate constant was obtained at 1874 × 10⁻⁴ min⁻¹ for the optimized ZnO/MgIn₂S₄ nanocomposite, which was significantly increased compared to the constituent components. Examination of the optical properties demonstrated that the presence of MgIn₂S₄ with a narrow band gap increased the absorption of visible light in the nanocomposite compared to the bare ZnO. Also, photocurrent and electrochemical impedance studies displayed that, the incorporation of MgIn₂S₄ and ZnO facilitated charge separation by controlling the band structure in the constructed heterojunction. The trapping tests identified holes, hydroxyl and superoxide ion radicals as the dominant active species for photodegradation. In addition, the prepared ZnO/MgIn₂S₄ photocatalyst showed significant stability after 4 cycles of the photocatalytic degradation process. Finally, the most probable charge transfer mechanism was proposed by analyzing the experimental results.