1% defect enriches MoS₂ quantum dot: catalysis and blue luminescence

Defects in solids are typically recognized as unfavorable, leading to degradation of the structure and properties of the material. However, defects occasionally provide extraordinary benefits as the active sites of catalysts and chemical reactions, and can result in the creation of new electronic states. In particular, a low-dimensional material can become a defect-rich material due to the unique ratio of surface area to volume, giving many dangling bonds. Herein, we report the rapid (20 min) synthesis of MoS₂ quantum dots (QDs) with a diameter of 4 nm at room temperature using nanosecond pulsed laser ablation in a binary solvent. The MoS₂ QDs are crystalline particles composed of 3-5 layers and contain sulfur vacancies at an atomic concentration of 1% acting as a functional defect. The MoS₂ QDs exhibit excellent electrocatalytic performance (Tafel slope = 49 mV dec^-1) for the hydrogen evolution reaction and high quantum yield blue photoluminescence with a large Stokes shift.