Molten salt-assisted controlled synthesis of two-dimensional molybdenum carbide

Abstract

The present investigation examines the carbothermal reduction synthesis of two-dimensional molybdenum carbide (2D Mo₂C) using sodium carbonate (Na₂CO₃) as a molten salt diffusion promoter and sodium sulfide (Na₂S) as a solid-state intercalation agent. Raw molybdenum disulfide (MoS₂) powder undergoes carbothermal reduction facilitated by activated carbon and Na₂CO₃ above 800 °C to produce 2D Mo₂C layers intercalated by Na₂S. The diffusion of Na₂S can be enhanced by the fluidity of molten salt Na₂CO₃, leading to the expansion of the Mo₂C layer spacing to 29 nm under the influence of the temperature field. Na₂S intercalation prevents layer shrinkage during cooling while molten Na₂CO₃ directs 2D growth, yielding 10 nm-thick sheets. The product maintains hexagonal β-Mo₂C structure up to 950 °C with microflowers of accordion-shaped nanosheets. Ultrasonication exfoliates the weakly bound Mo₂C layers into uniform, freely suspended flakes around 10–100 nm in lateral size. This work demonstrates the tuning of 2D Mo₂C morphology in high-temperature reactions by utilizing molten salts. The principal results are the synthesis of micrometer-sized Mo₂C sheets with controlled nanoscale thickness and uniform nanosheet dispersions, enabled by molten salt-directed diffusion of intercalated species. The major conclusion drawn is that solid-liquid synergistic diffusion can guide precision synthesis of layered nanomaterials.