Shape-controlled synthesis of Pt nanocrystals: an evolution of the tetrahedral shape

Platinum nanocrystals with sizes smaller than 10 nm are obtained by H-2-reduction of aqueous K2PtCl6 in the presence of different concentrations of poly (N-vinyl-2-pyrrolidone; PVP: M-w approximate to 360 000) at pH = 2.5-7.0. Tetrahedral Pt nanocrystals (3-10 nm) are produced with high selectivity (73-83% by number) at moderate PVP:K2PtCl6 ratios. The co-existing round/spheroidal crystallites are found to be smaller than the tetrahedrally shaped ones in the systems of varying K2PtCl6:PVP ratios. Careful examinations of the particle size and shape evolution of the crystallites at different stages of the crystal growth with transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy (UV-vis) suggest that the tetradedrally shaped Pt crystallites share the same type of nuclei with the round ones at the early stage of the crystal formation. Evolution of the tetrahedral shape happens in the later slow crystal growth. Copyright (c) 2006 John Wiley & Sons, Ltd.