Molecular metal nanoparticles with pseudo-plasma absorption band

ABSTRACT Metal nanoparticles include molecular nanoclusters and metallic nanocrystals. Investigating the critical transition sizes from nanoclusters to nanocrystals is appealing. However, achieving precise size control near the critical size region remains challenging, especially for not-so-noble metal nanoparticles (Ag, Cu etc.). Herein, we introduced an active metal anti-galvanic doping strategy to resolve both stability and multi-dispersity issues and demonstrated the gram-scale synthesis (2.40 g of crystals, more than 200 times the existing crystal output record for over 100-metal-atom nanoparticles) of a 1796-atom Ag–Zn nanoparticle. Furthermore, we successfully de-alloyed the Ag–Zn nanoparticles with the remaining structure essentially unchanged via a ligand-exchange method, obtaining 1.03 g of mono-Ag nanoparticle crystals in a one-pot reaction. Such a surgery-like de-alloying was not previously reported. Both of the as-obtained nanoparticles exhibit penta-twinned face-centered cubic (fcc) structures with well-defined shape–number arrangements and display plasmon-like absorptions yet exist in molecular states, as evidenced by ultrafast dynamics measurements. Furthermore, crystallization-induced photothermal enhancement and size-dependent absorbance were observed.