Controlled Growth of Sub-10 nm Gold Nanoparticles Using Carbon Monoxide Reductant

Abstract

There is a need to develop aqueous-phase synthesis methods of sub-10-nm Au nanoparticles (NPs), given their many exciting possibilities in catalysis, sensing, biomedical, and other water-based applications. Synthesizing Au NPs by reducing Au salt onto preformed NPs as seeds is a useful approach because final particle size can be finely predicted and controlled, though few studies have reported successful synthesis of Au NPs in the 1 and 10 nm size range. Here we report that water-suspended Au particles with a diameter ∼2.8 nm can be grown as large as ∼12 nm with sub-nanometer control, as verified through detailed ultraviolet−visible spectroscopy, small-angle X-ray scattering, and transmission electron microscopy measurements. With carbon monoxide as the reducing agent, this seeded-growth method results in colloidally stable Au sols. The reaction mechanism most likely involves the catalyzed oxidation of CO into CO2 accompanied by electron transfer to the gold hydroxide-chloride ionic species through the growing particle.