Bipyramidal Nanocrystals of Noble Metals: From Synthesis to Applications

Shape control has been a major theme of nanocrystal research in terms of synthesis, property tailoring, and optimization of performance in a variety of applications. Among the possible shapes, bipyramids are unique owing to their symmetry, planar defects, and exposed facets. In this article, we focus on the colloidal synthesis of noble-metal nanocrystals featuring a triangular bipyramidal shape, together with highlights of their properties and applications. We start with a brief discussion of the general classification and requirements for the nucleation and growth of bipyramidal nanocrystals, followed by specific aspects regarding the synthetic methods with a focus on the roles of reduction, etching, and capping, as well as controls of facet, size, aspect ratio, and corner truncation. In the end, we illustrate how these aspects affect the properties of bipyramidal nanocrystals for plasmonic and catalytic applications, together with future perspectives.