Shape-Selective Synthesis of Palladium Nanoparticles Stabilized by Highly Branched Amphiphilic Polymers

Abstract

Despite the current broad interest in such materials, the synthesis of defined structures in the size range of 10 nm to ca. 1 μm (mesoscopic) is challenging. Few routes shape-selectively afford geometrically regular structures, other than the typical spherical metal particles of 1 to 10 nm. Moreover, these few routes are largely restricted to aqueous systems, however, for catalysis and other applications dispersions in organic solvents are desirable. Carbon monoxide reduction of a palladium(II) compound in combination with stabilization by (readily available) amphiphilic hyperbranched polymers surprisingly affords dispersions of hexagonal platelets selectively with average sizes of thirty to several hundred nanometers in toluene. The size can be controlled by the polymer composition. Transmission electron microscopy (TEM), electron diffraction, and extended X-ray absorption fine structure (EXAFS) spectroscopy demonstrate these palladium(0) platelets to be extremely thin (1-2 nm). Despite this high aspect ratio, the platelets prove quite shear resistant.