Size control and shape evolution of single-twinned platinum nanocrystals in a room temperature colloidal synthesis

Abstract

Platinum nanocrystals in the size range of a few nanometers are especially interesting candidates for catalytic applications. We present an easy, low-temperature procedure, which allows for a precise size control of this material. Uniform platinum nanoparticles were obtained by reduction of platinum(IV)chloride with tetrabutylammonium borohydride in toluene solution at room temperature. Dodecylamine served as a ligand. The size of the resulting particles could be controlled in the range between 2 and 5 nm by slow addition of platinum monomers and the reducing agent to preformed 2 nm seeds. Furthermore, particles with a tetrapod shape could be synthesized. In contrast to the usual kinetic control leading to the formation of elongated structures, the analysis of the growth process of the tetrapods suggests a reaction-controlled growth process. Their structure was investigated by powder X-ray diffraction and high-resolution electron microscopy, which revealed that two branches of the tetrapods grow along the 〈111〉 direction, while the other two show growth in the 〈220〉 direction. This uncommon shape of the tetrapods is attributable to the presence of a twin defect parallel to the 〈220〉 direction. Thus, the method presented in the article allows for the formation of platinum particles with a single twin defect with a high yield.