Polyol Synthesis of Platinum Nanoparticles:  Control of Morphology with Sodium Nitrate

Abstract

Morphological control over platinum nanoparticles was realized by varying the amount of NaNO 3 added to a polyol process, where H 2 PtCl 6 was reduced by ethylene glycol to form PtCl 4 2- and Pt 0 at 160 °C. As the molar ratio between NaNO 3 and H 2 PtCl 6 was increased from 0 to 11, the morphology of Pt nanoparticles evolved from irregular spheroids with rounded profiles to tetrahedra and octahedra with well-defined facets. Absorption spectroscopy studies suggest that nitrate was reduced to nitrite by PtCl 4 2- in the early stage of the synthesis, and the nitrite could then form stable complexes with both Pt(II) and Pt(IV) species. As a result, the reduction of Pt precursors by ethylene glycol was greatly slowed. This change in reaction kinetics altered the growth rates associated with different crystallographic directions of the Pt nanocrystals and ultimately led to the formation of different morphologies.