Facile Synthesis of Gold Icosahedra in an Aqueous Solution by Reacting HAuCl4 with N-Vinyl Pyrrolidone

Herein we describe a protocol that generates An icosahedra in high yields by simply mixing aqueous solutions of HAuCl4 and N-vinyl pyrrolidone. Our mechanistic study reveals that water plays an important role in this synthesis: as a nucleophile, it attacks the gold-vinyl complex, leading to the production of an alcohol-based Au-1 intermediate. This intermediate then undergoes a redox reaction in which Au-1 is reduced to Au-0, leading to the formation of Au atoms and then Au icosahedra of about 18 nm in size at a yield of 94%, together with a carboxylic acid in the final product. This new protocol has also been employed to prepare multiply twinned nanoparticles of Ag (15-20 nm in size), spherical aggregates (25-30 rim in size) of Pd nanoparticles, and very small nanoparticles of Pt (2 urn in size). Since no organic solvent, surfactant, or polymer stabilizer is needed for all these syntheses, this protocol may provide a simple, versatile, and environmentally benign route to noble-metal nanoparticles having various compositions and morphologies.