Light-independent dye degradation using MoS₂-Bi₂O₃ nanocomposites: a dual-mode approach for wastewater treatment

Developing multifunctional and energy-efficient materials for sustainable wastewater treatment is an important challenge. In this study, a series of MoS₂-Bi₂O₃ nanocomposites was synthesised via a hydrothermal method and evaluated for their dual-mode degradation of methylene blue (MB) under visible-light and dark conditions. Structural, morphological, and compositional properties were systematically investigated using XRD, FESEM, HR-TEM, XPS, BET, UV-Vis, UPS, EPR, and EIS analyses. The results confirmed the formation of well-coupled MoS₂-1.5Bi₂O₃ type-II heterojunctions with increased surface area and improved electronic structures, enabling efficient charge separation. Among the samples, the MoS₂-1.5Bi₂O₃ composite showed the best performance, achieving 95% MB degradation within 30 min under visible light with a rate constant of 0.08289 min^-1. Notably, it also removed 98% of MB at low dye concentration (10 ppm) in the absence of light due to strong adsorption and surface-mediated reactions. Enhanced activity was attributed to improved charge transfer and reactive oxygen species generation. These results highlight the potential of MoS₂-Bi₂O₃ composites as low-energy, multifunctional materials for sustainable wastewater treatment.