Interfacial S-scheme charge transfer in MgIn ₂ S ₄ /ZnO heterojunction for enhanced photodegradation of tetracycline and efficient water splitting

Environmental pollution and high energy costs are among today's most pressing global challenges. Photocatalysis offers a cost-effective and environmentally sustainable strategy to address these issues by enabling efficient pollutant degradation and hydrogen production. This work constructed a nanoflower MgIn₂S₄ and nanorod ZnO heterojunction to enhance photocatalytic performance through an interfacial S-scheme charge transfer mechanism. Unlike most reported ZnO-based heterojunctions in the literature, this approach introduces MgIn₂S₄, a ternary sulfide with a narrow band gap and a high conduction band potential, to form a heterostructure material with a strong redox potential and efficient charge separation. The MgIn₂S₄/ZnO heterojunction exhibited superior photocatalytic activity, achieving a remarkable 94% tetracycline (TCE) degradation efficiency, 1.4 and 3.9 times higher than that of pristine MgIn₂S₄ and ZnO, respectively. Furthermore, the heterojunction demonstrated an improved hydrogen evolution rate of 8.29 mmol h^-1 g^-1, significantly surpassing ZnO (6.96 mmol h^-1 g^-1) and MgIn₂S₄ (6.24 mmol h^-1 g^-1). The enhanced performance is attributed to the efficient interfacial charge transfer, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis and electrochemical characterization, demonstrating charge migration from MgIn₂S₄ to ZnO. Mechanistic investigations further revealed that the S-scheme charge transfer mechanism effectively promoted charge separation and facilitated the generation of reactive radical species, ultimately leading to improved photocatalytic activity. This study highlights the potential of the rationally designed MgIn₂S₄/ZnO S-scheme heterojunction as a highly efficient and sustainable photocatalyst for organic pollutant degradation and hydrogen production under visible light irradiation, providing a promising solution to environmental and energy challenges.