“Cubic” Colloidal Platinum Nanoparticles

Transition metals have long been used as catalysts in the form of dispersions stabilized on inorganic substrates such as silica gel, alumina, and activated charcoal.1 More recently, colloidal platinum nanoparticles have been used as catalysts and photocatalysts in solutions.2 Aqueous colloidal platinum particles are mostly prepared by the reduction of a platinum salt by hydrogen, photochemical, pulse-radiolytical, or thermal methods.2 Catalytic reactivity of metal particles is undoubtedly linked to the nature of surfaces involved in the catalysis. Determining the particle shape and consequently the atomic arrangements in the crystal planes forming the surfaces is essential to our understanding of the whole phenomena of catalysis and the design of more “ideal” catalysts for different chemical transformations. In this letter, we are reporting on the synthesis of platinum nanoparticles of cubic shapes in an aqueous medium, without a substrate and at 25 °C, for the first time. These cubic-shaped nanoparticles were not observed previously in the gas phase or in the colloidal phase without a substrate. The synthesis of the cubic-shaped nanoparticles adds a new structure to the list of already known shapes, i.e., tetrahedra, icosahedra, and cubooctahedra, of platinum particles. The cubic particles have large surface-to-volume ratios and may prove to have significantly different reactivity and selectivity in catalysis.