Evidence for Seed-Mediated Nucleation in the Chemical\nReduction of Gold Salts to Gold Nanoparticles

Abstract

Central to the concept of seed-mediated growth of nanoparticles is that small nanoparticle\nseeds serve as nucleation centers to grow nanoparticles to a desired size. We have examined\nthis common assumption in a model system, the wet chemical synthesis of gold nanoparticles\nvia reduction of a gold salt, by transmission electron microscopy and electronic absorption\nspectroscopy. We find that changing the seed concentration does affect the size of the product\nnanoparticles, but the method of reagent addition drastically affects the outcome even more.\nFor fast addition of reducing agent, the presence of seeds appears to promote the formation\nof more seeds instead of growth. The observed nucleations are drastically enhanced (99%)\ncompared to particle growth. For slow addition of reducing agent, the seeds do grow, but\nthe product nanoparticle's degree of homogeneity in shape is compromised. For higher\nconcentrations of seeds, nanoparticle growth is better controlled for slow addition of reducing\nagent compared to fast addition of reducing agent. We propose a mechanistic step to explain\nthe commonly observed size distribution.