Ionic liquid-assisted growth of single-crystalline dendritic gold nanostructures with a three-fold symmetry

Hierarchical, three-fold symmetrical, single-crystalline gold dendrites were synthesized by the reaction between a zinc plate and a solution of HAuCl4 in the ionic liquid [BMIM][PF6]. The unique dendritic gold nanostructures show a three-order hierarchy (i.e., a three-fold symmetrical < 111 > -oriented trunk, three groups of trident-like < 111 > -oriented branches grown on the trunk, and many < 111 > -oriented nanorod leaves grown on the branches symmetrically), indicating an interesting fractal growth. According to the investigation on the growth process of the gold dendrites, it was proposed that gold nuclei nanocrystals first formed on the zinc substrate through a direct surface reaction and that the subsequent crystal growth preferentially took place on the preformed gold crystals through a primary cell reaction, leading to the formation of the final hyperbranched dendrites under nonequilibrium conditions. In contrast, AuZn alloy dendrites consisting of aggregated primary nanoparticles were produced when the ionic liquid solution was replaced by an aqueous solution. It was proposed that the significantly lowered ion diffusivity and reaction rate in the ionic liquid medium could largely contribute to the formation of the pure single-crystalline gold dendrites. Moreover, electrocatalytic measurements performed in alkaline solution suggested that the obtained dendritic gold nanostructures exhibited good electrocatalytic activity toward the oxidation of methanol, which might be related to the special three-order hierarchical architectures.