Mechanistic Study of Seed-Mediated Growth of Gold Rhombic Dodecahedra

It is a viable approach to tailor the optical and catalytic properties of noble-metal nanocrystals by controlling their geometric shapes. Among various shapes, rhombic dodecahedra are considered particularly difficult to synthesize owing to the higher energy of {110} facets relative to other low-index facets. Here we report a facile synthesis of Au rhombic dodecahedra with high uniformity and purity through seed-mediated growth in N,N-dimethylformamide (DMF) containing a small amount of water. The success of this synthesis critically relied on the use of single-crystal seeds with a spherical shape, the capability of DMF to selectively cap the {110} facets, and the balance between deposition and surface diffusion. We systematically investigated the effects of the amounts of poly(vinylpyrrolidone) (PVP), seeds, and water on the synthesis, as well as reaction temperature and time. Under the condition optimal for layer-by-layer growth and with the use of 10 nm seeds, the edge lengths of the rhombic dodecahedra could be tuned from 18-36 nm by increasing the duration of growth time. This method also offers a facile route to Au nanocrystals with other shapes. For example, by varying the amount and molecular weight of PVP, as well as temperature, the same protocol could be adapted to obtain trisoctahedra and octahedra, respectively, in high yield and quality.