MoS₂ Nanosheet/ZnS Composites for the Visible-Light-Assisted Photocatalytic Degradation of Oxytetracycline

Wastewater management and treatment are crucial to preserve health and life on the planet. To achieve efficient wastewater treatment, MoS2 nanosheet/ZnS-based composites were prepared and tested for the photodegradation of a model wastewater contaminant, oxytetracycline (OTC), a widely used antibiotic. Various parameters, such as contact time, solution pH, and nanocomposite dosage, were studied to obtain the optimal parameters. Among the various composites, that prepared using 0.25 g of the zinc acetate precursor (denoted MoS2/ZnS-0.25) showed the highest photocatalytic activity: 81% OTC degradation in 180 min. The high photocatalytic activity of the nanocomposite can be ascribed to the greater absorption of visible light, enhanced charge carrier transfer, and delayed electron–hole recombination. In addition, first-principles density functional theory calculations were used to understand the mechanism behind the enhanced photocatalytic performance, charge transfer, band alignment, and electronic, optical, and interfacial properties of the MoS2 nanosheet/ZnS composites. Based on the theoretical calculations, we found that the MoS2 nanosheet/ZnS composite band structure ensures that electrons are transferred from ZnS to MoS2 on visible light irradiation. In addition, the potential drop and charge difference at the interface induce a large built-in internal electric field that reduces charge carrier recombination. The results of this study will enable the design of a wider range of two-dimensional van der Waals nanocomposites as photocatalyst materials.