Sirajudheen Palliyalil, Nabeena Chettithodi Poovathumkuzhi, Sivakumar Vigneshwaran
Abstract The continuous discharge of synthetic dyes into aquatic systems poses significant environmental and public health risks, necessitating the development of efficient remediation strategies. Among advanced oxidation processes (AOPs), photocatalysis using molybdenum disulfide (MoS₂) has emerged as a promising approach due to its unique electronic structure and visible-light responsiveness. This review provides a systematic and critical analysis of MoS₂-based Type-I and Type-II heterojunction photocatalysts for dye degradation, with a particular emphasis on elucidating their charge-transfer mechanisms and structure–activity relationships. The uniqueness of this work lies in establishing a direct correlation among band alignment, interfacial charge migration pathways, and reactive oxygen species generation, offering a unified mechanistic framework that has not been comprehensively addressed before. Further, the discussion covers the structural and electronic features of MoS₂ polymorphs (1T, 2H, and 3R) and their influence on photocatalytic behaviour. Key characterization techniques, including UV–Vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), and electron paramagnetic resonance (EPR), are critically evaluated to link optical properties, charge dynamics, and radical formation with photocatalytic performance. Beyond conventional dye degradation studies, the review also considers catalyst stability, reusability, mineralization efficiency (COD and TOC), and applicability in real water matrices. A comparative assessment reveals that Type-II heterojunctions enhance charge separation efficiency, whereas Type-I systems retain stronger redox potentials but suffer from recombination losses. Overall, this review provides practical design insights and a comprehensive foundation for the rational development of advanced MoS₂-based photocatalysts for sustainable wastewater treatment.