Polymorphism and phase-selective synthesis of MoS2 under hydrothermal conditions

Molybdenum disulfide (MoS 2 ), a two-dimensional transition metal dichalcogenide, exhibits various polymorphic forms (1T, 2H, and 3R). The distinct MoS 2 polymorphs exhibit markedly different properties and application potentials. However, the polymorphism of MoS 2 under hydrothermal conditions has not been systematically investigated, leaving a gap in the rational design and selective synthesis of targeted polymorphs. In this study, the polymorphism of MoS 2 under hydrothermal conditions was systematically investigated, focusing on the effects of temperature, reaction time, and drying conditions on phase formation. The Rietveld refinement method was employed to unambiguously distinguish the MoS 2 polymorphs and to establish reliable criteria for their accurate identification. Complementary characterization techniques, including X-ray photoelectron spectroscopy and Raman spectroscopy, further confirmed the reliability of the Rietveld method for identifying MoS 2 polymorphs. The phase transition behavior of MoS 2 was investigated under both hydrothermal conditions and solid-state conditions under vacuum, using as-prepared intercalated 1T-MoS 2 as the precursor. The differences in phase transition behavior between these environments were discussed. Based on these insights, a two-step synthesis strategy was developed to fabricate 2H–MoS 2 /α-Fe 2 O 3 composites with well-defined nanosheet morphology, combining hydrothermal synthesis at 200 °C to preserve the α-Fe 2 O 3 nanosheets with subsequent annealing at 250 °C to achieve the 2H–MoS 2 phase. These findings provide a robust framework for tailoring MoS 2 -based materials for specific applications in catalysis, optoelectronics, and energy storage. Schematic illustration of the phase evolution of MoS₂ under different thermal and environmental treatments. • Polymorphism of MoS 2 under hydrothermal conditions was systematically investigated. • Rietveld refinement was employed for unambiguous identification of MoS 2 polymorphs. • Phase transition behaviors of MoS 2 were clarified under both hydrothermal and solid-state conditions. • A two-step strategy was developed for fabricating 2H–MoS 2 /α-Fe 2 O 3 composites with desired morphology. • The findings provide a framework for phase-engineering MoS 2 -based composites for catalytic applications.