With sodium polyacrylate (NaPA: M_w≈2100) as a protector, H_2 reduction of aqueous K_2PtCl_4 and K_2PtCl_6 were performed for shape- controlled synthesis of platinum (Pt) nanocrystals. It was found that the hydrolysis of the Pt precursors affected significantly the shape of Pt nanocrystals synthesized. Aqueous K_2PtCl_4, which was frequently used in earlier literature works for producing cubic Pt nanocrystals, proved not stable in the present work, it was hydrolyzed to fonn a black deposit when the solution was aged in dark for a week. While the aqueous K_2PtCl_6 was fairly stable in the dark aging, synthesis with fresh K_2PtCl_6 solution produced mainly truncated- octahedral Pt nanocrystals by H_2 reduction with NaPA as the protector. An exposure to ambient light was shown to induce a hydrolysis of [PtCl_6]~(2-) in the K_2PtCl_6 solution. When the characteristic absorption of [PtCl_6]~(2-) ions (260 ran) disappeared entirely by exposing the K_2PtCl_6 solution to the ambient light, cubic Pt nanocrystals enclosed with {100} facets were produced selectively (ca. 80%) from thereafter H2 reduction under NaPA protection. It is emphasized that a proper control of the hydrolysis or light-induced hydrolysis of the Pt precursora is crucial for the synthesis of cubic Pt nanocrystals.

Key words: PLATINUM, HYDROGEN, POTASSIUM PLATINUM CHLORIDE, HYDROLYSIS, GRAIN, NANOPHASE MATERIALS, REDUCTION