Fitting A Square Peg Into A Round Hole: Shape Control In Phase Transfer Of Cubic Gold Nanoparticles

Although nanomaterials are widely involved in technological applications, common synthetic recipes for such colloids are restricted to special, optimized conditions, particularly for anisotropic shapes. Ligand exchange is frequently necessary for further functionalization. While such protocols are well established for spherical particles, it is more demanding to keep the corpus for thermodynamically less stable shapes. We highlight the temperature as one key for the formation of anisotropic gold nanoparticles, but also for ligand exchange protocols under shape retention or deliberate reshaping at the example of gold nanocubes. In the first part, the synthesis of CTAB capped gold nanocubes in aqueous solution is examined highlighting the narrow temperature window in which selective adsorption site blocking by bromide ions leads to the formation of gold nanocubes. While too low temperatures yield multiple particle shapes due to a low surface mobility, temperatures above the appropriate window result in more thermodynamically favored shapes. Furthermore, two protocols are presented for the exchange of the ammonium ligand CTAB by oleylamine as an organic amine including water removal from a slurrish water-amine paste through the gas phase. In turn, precise temperature control allows to either maintain the cubic shape or induce a reshaping process towards other, thermodynamically preferred shapes such as for example truncated octahedra.