In Situ Single-Atom Decoration of Transition Metal Dichalcogenides by Millisecond Flash Thermal Synthesis Toward High Performance Room Temperature Chemiresistors.

Transition metal dichalcogenides (TMD) are attractive for adsorption-driven reactions, yet their activity is strongly site-dependent. Activity is concentrated at edge motifs, whereas most exposed area resides on inert basal planes. Dual-site designs that enrich edges while activating basal planes with catalysts remain challenging to realize without coarsening and metal aggregation during thermal processing. Here, an intense pulsed light-driven flash thermal synthesis route is demonstrated that directly converts ammonium tetrathiomolybdate ((NH4)2MoS4) into few-layer, edge-rich MoS2 nanoflakes (FTS-MoS2) within 10 ms pulse in ambient-air. Ultrafast photothermal shock (1192-1811°C; ∼105/104°C s- 1 heating/cooling rates) suppresses in-plane coarsening and out-of-plane stacking, while Pt, Ir, or Au single atoms are uniformly anchored on MoS2 via rapid metal-sulfur coordination without aggregation. As a proof-of-concept, FTS-MoS2 exhibits a 23.6-fold higher NO2 response at 5 ppm than solvothermally synthesized MoS2. Pt single atom functionalization (FTS-PtSA-MoS2, 1.2 wt%) further boosts the response by 22.8-fold versus pristine FTS-MoS2 and achieves 100.8% response toward 400 ppb NO2 at room temperature. Density functional theory supports enhanced NO2 adsorption and charge transfer on FTS-PtSA-MoS2. With a low electrical energy input (8.6 kJ g-1) and scalable irradiation, ultrafast FTS enables industrially relevant active-site and single-atom engineering in TMDs for high-performance gas sensors.