Shape-Controlled Synthesis of Pd Nanocrystals in Aqueous Solutions

This article provides an overview of recent developments regarding synthesis of Pd nanocrystals with well-controlled shapes in aqueous solutions. In a solution-phase synthesis, the final shape taken by a nanocrystal is determined by the twin structures of seeds and the growth rates of different crystallographic facets. Here, the maneuvering of these factors in an aqueous system to achieve shape control for Pd nanocrystals is discussed. L-ascorbic acid, citric acid, and poly(vinyl pyrrolidone) are tested for manipulating the reduction kinetics, with citric acid and Br- ions used as capping agents to selectively promote the formation of {111} and {100} facets, respectively. The distribution of single-crystal versus multiple-twinned seeds can be further manipulated by employing or blocking oxidative etching. The shapes obtained for the Pd nanocrystals include truncated octahedron, icosahedron, octahedron, decahedron, hexagonal and triangular plates, rectangular bar, and cube. The ability to control the shape of Pd nanocrystals provides a great opportunity to systematically investigate their catalytic, electrical, and plasmonic properties.