In this study, we prepared Pt nanoparticles through the reduction of H2PtCl6 solutions containing poly(vinylpyrrolidone) (PVT) as a capping agent and investigated the effects of several reaction parameters, such as the reducing agent-to-Pt molar ratio and the concentration and molecular weight (M-w) of PVP, on the size, size distribution, and stability of the particles in the resulting Pt colloids. When PVT (Mw 10,000) was added at a PVT-to-Pt molar ratio of 0.38 in the presence of NaOH, we obtained quasi-spherical nanoparticles having average sizes ranging from 2.0 to 4.0 nm. The particle size increased upon decreasing the molecular weight of PVP; increasing the PVP concentration had only a stabilizing effect. The particle size of the monodisperse Pt nanoparticles, we obtained in the presence of NaOH were larger than those formed in the presence of NaHCO3, indicating that the of rate reduction of [PtCl6](2-) ions is an important factor influencing the growth of these particles. Furthermore, increasing the reducing agent-to-Pt molar ratio also increased the particle size. To understand their mechanism of formation, we used transmission electron microscopy (TEM) and UV-Vis spectrophotometry to monitor the stabilities and size distributions of the Pt nanoparticles.

Keywords: Pt nanoparticles; poly(vinylpyrrolidone) (PVP); capping agent; reducing agent; stability; chemical reduction