Synthesis of platinum nano-particles in high-temperatures and high-pressures fluids

Colloidal dispersions of platinum nano-particles have been synthesized by the reduction of platinum ion(IV) in the high-temperature and high-pressure water, ethanol, and water–ethanol mixtures in the presence of the protective polymer of poly(N-vinyl-2-pyrrolidone) (PVP). The syntheses have been tested at various temperatures (from 100 to 300 °C) and pressures (from 5 to 25 MPa). The diameter and the composition have been examined by UV-Vis, extended X-ray absorption fine structure (EXAFS), and transmission electron micrograph (TEM), respectively. At 200 °C and 25 MPa, colloidal dispersions of platinum particles of small size (2.6±0.5 nm) were synthesized from 1:1 mixture of water and ethanol within a few seconds. From the analysis of the EXAFS, it is suggested that the elementary particle size obtained under the present condition is larger than that obtained under the ambient condition. We have also succeeded in producing the colloidal dispersions in aqueous solution, although the size and its distribution were relatively larger than the case of water–ethanol mixture. In ethanol solution we could not synthesize a well-dispersed colloidal solution at high temperatures. The possibility of the regulation of the particle size and distribution is discussed.