Preparation of Transition Metal Disulfide Nano-Dots via Hydroxyl Radicals-Mediated Cutting Metal-Sulfur Bonds.

The preparation of low-dimensional transition metal disulfides (MS₂, M = Mo, W) from mineral bulk-MS₂ via ultrasonication-assisted liquid-phase exfoliation, is proven to be advantageous in terms of sulfurizing reagent-free conditions and operational safety. Nevertheless, mechanical energy input alone is insufficient to effectively cut metal-sulfur bonds to form small-sized MS₂ nano-dots. Herein, we develop an innovative strategy based on hydroxyl radicals-mediated cutting metal-sulfur bonds to prepare MS₂ nano-dots with 10 nm of lateral dimension and 2 nm of height, through ultrasonication treatment of bulk-MS₂ in the presence of a mixture of ammonium citrate/N-Methylpyrrolidone ((NH₄)₃CA/NMP). A pivotal aspect of this strategy is the in-situ generation of hydroxyl radicals from citrate ions (CA^3-), which can effectively cut metal-sulfur bonds of the submicron-sized sheet that was as-exfoliated by NMP. Furthermore, the introduced CA^3- adsorbs onto the surfaces of MS₂ nano-dots, preventing their re-aggregation in the disperse system. This work provides a facile strategy for the direct preparation of metal disulfide nano-dots from their bulk-minerals.