Capped Vapor–Liquid–Solid Growth of Vanadium-Substituted Molybdenum Disulfide Ultrathin Films for Enhanced Photocatalytic Activity

The exceptional and tunable physicochemical properties of 2D transition metal dichalcogenides (TMDCs) have made them model catalysts for fundamental studies and applications. Activating the inert basal plane holds the key to utilizing wafer-scale TMDCs in artificial photosynthesis. To address this challenge, we report a SiO₂-capped vapor-liquid-solid (VLS) growth method that assists in substituting vanadium into the molybdenum disulfide ultrathin film and introducing sulfur vacancies to form S_vac-Mo_1-<i>x</i>V_<i>x</i>S₂. By optimizing the thickness of solid precursors and the SiO₂-capping layer (membrane layer), as well as the growth temperature, we demonstrate control over the film thickness, vanadium concentration, and film uniformity. Our results reveal the presence of the V-S_vac pairs, manifesting in the enhanced S_vac concentration and charge density transfer among V-S-Mo atoms, with multifaceted benefits, including increasing light absorption, photoluminescence quenching, crystal structure distortion, efficient binding of CO₂ or H₂O on the surface, improved charge transfer/transport, and a suitable energy band diagram. Furthermore, the 2D S_vac-Mo_1-<i>x</i>V_<i>x</i>S₂ model catalyst films, with abundant V-S_vac pair active sites, exhibit a stable and boosted photocatalytic CO₂ reduction to CO, specifically yielding ∼5 times more than that of pristine MoS₂. Our study demonstrates the origin of V-S_vac pairs in host MoS₂, leading to basal plane activation. This suggests a foundation for future research on pairing dopants or alloying elements with defects for efficient photocatalyst design.