Ion-Exchange Synthesis of Molybdenum Blue Dispersions: Colloidal Properties, Self-Assembly and Thermal Phase Transformation

High-purity precursors are often required for the targeted synthesis of functional nanomaterials. Molybdenum blue (MB) dispersions are promising precursors for the production of functional materials based on molybdenum oxides and carbides. Here, a facile, spectator-ion-free synthesis of molybdenum blue dispersions via a tailored ion-exchange strategy is reported. By eliminating extrinsic counter-ions, we achieve uniform toroidal nanoclusters (~3.5 nm) of {Mo154} wheel-type molybdenum blue with a precise mixed-valence Mo5+/Mo6+ framework and long time aggregative and sedimentation stability. Moderate reduction ratios yield crystalline monoclinic MoO2, whereas high reduction ratios drive an in situ carbothermal reduction, selectively yielding hexagonal β-Mo2C/η-MoC phases. This approach establishes a versatile, scalable pathway for engineering molybdenum blue nanoparticles as precursors for oxide- and carbide-based advanced functional materials.