Facile Synthesis of Gold Octahedra by Direct Reduction of HAuCl₄ in an Aqueous Solution

This paper describes a water-based protocol that provides a simple, convenient, and environmentally benign route to the synthesis of Au octahedra. Specifically, we obtained single-crystal Au octahedra (ca. 85% of the product) with an edge length of 32.4+/-2.3 nm and singly twinned, truncated bipyramids (ca. 15%) by reducing HAuCl(4) with N-vinyl pyrrolidone in an aqueous solution in the presence of a proper amount of cetyltrimethylammonium chloride (CTAC). Our mechanistic study indicates that the formation of Au octahedra could be explained by oxidative etching, a pathway that has already been validated for the synthesis of nanocrystals for a number of different noble metals.