Engineered interfaces of MoS2-heterojunctions for dye removal: Strategies and perspectives of electron–hole dynamics

The remediation of persistent and toxic pollutants, including synthetic dyes from textile, leather, and printing industries, discharged into the aquatic bodies, demands the development of efficient photocatalysts. MoS2-based materials have recently gained significant attention in photocatalysis. Bulk MoS2 has an indirect bandgap (∼1.2 eV),whereas its monolayer counterpart shows a direct bandgap of ∼1.8–1.9 eV, along with exciton binding energies of ∼0.3–0.6 eV and carrier mobilities of ∼10–200 cm2 V-1 s-1. The conduction-band potential of MoS2 (≈−0.1 to −0.3 V vs NHE) is close to the O2/·O2- level (−0.33 V), enabling moderate superoxide radical generation, while its valence band (+1.5 to +1.7 V) is less positive than the ·OH/H2O potential, which weakens hydroxyl radical formation unless heterostructures are engineered. ESR and trapping studies often prove that ·O2- is accountable for ∼40–70 % of dye degradation, whereas holes contribute to ∼20–40 %, and ·OH to less than 20 % removal in pristine systems. Engineered composites exhibit significantly enhanced photocurrent densities (5–50 μA cm⁻²) compared to pure MoS₂ (∼0.5–2 μA cm⁻²), along with a corresponding increase in quantum efficiency from ∼0.1–1% to ∼2–15%. Herein, the review discusses the interface design involving construction of p–n junctions, Schottky contacts, and Z- and S-scheme architectures, which significantly enhance charge separation, prolong carrier lifetimes from picoseconds to nanoseconds or microseconds, and promote reactive oxygen species generation. Such strategies, integrated with defect engineering, doping, and coupling with oxides or carbon materials, improve light harvesting, interfacial transport, and catalytic durability. These quantitative insights highlight the potential of MoS2 as a photocatalytic component while emphasizing the need for a standardized protocol for testing, mineralization studies, and scalable reactor integration for practical wastewater remediation.