Using oxalate as a stabilizing agent, stable colloidal solutions of platinum nanoparticles of different shape distributions were prepared by reducing K_2[Pt(C_2O_4)_2], K_2PtCl_6 and K_2PtCl_4 with hydrogen. The mean diameters of the Pt nanoparticles prepared from the above mentioned precursors were 6.5, 3.5 and 7.9 nm, respectively. UV-vis and transmission electron microscopy (TEM) studies on the preparation processes and the products indicated that not only the rate of reduction and the particle size but also the shape distributions of the prepared Pt nanoparticles depended on the used precursors. Pt nanoparticles prepared from K_2[Pt(C_2O_4)_2] had quite narrow size- and shape-distributions. The selectivity of cubic nanoparticles was 93%. When the prepared Pt colloidal solutions were exposed to air, oxidizing decomposition of oxalate in the solution was catalyzed by the Pt nanoparticles, which led to Pt nanoparticles to aggregate in a linear shape. After treating with hydrogen, the linear aggregations of the Pt nanoparticles fused into Pt nanowires.

Key words: PLATINUM, NANOPHASE MATERIALS, COLLOID, OXALIC ACID, AGGREGALES