Seed-Mediated Synthesis of Monodisperse Concave Trisoctahedral Gold Nanocrystals with Controllable Sizes

Concave trisoctahedral (TOH) gold nanocrystals (NCs) with uniform and customizable sizes were synthesized by a seed-mediated growth method using cetyltrimethylammonium chloride (CTAC) as the capping agent. Analysis of the projection angles and the atomic arrangement in the edge-on facets suggests that the surface of the TOH NCs was bounded by high-index {hhl} facets, such as {221}, {331}, and/or {441}. The size of the TOH gold NCs could be increased stepwise from 55 to 120 nm by applying the seed-mediated growth in succession. The TOH gold NCs displayed size-dependent surface plasmon resonance (SPR) properties, with the SPR peak red shifting with the increase in the NC size. The presence of the high-index {hhl} facets on the TOH surface was confirmed by cyclic voltammetric features that are distinctively different from those of cubic and octahedral gold NCs. The formation of these TOH NCs was kinetically driven and governed by two main factors: (i) the preferential face-blocking adsorption of CTA⁺ on high-index facets and (ii) a favorable reduction rate of the metal ions in the growth solution. The uniformity of the TOH NCs in size and shape facilitated NC self-assembly into ordered hexagonal or square packing structures simply by solvent evaporation on a substrate.