Iodine Ions Mediated Formation of Monomorphic Single-Crystalline Platinum Nanoflowers

Well-defined and strikingly monomorphic single-crystalline Pt nanoflowers were successfully synthesized through the addition of a large amount of iodine ions into polyol process (5 mM H2PtCl6, 30 mM KI, and 50 mM PVP in ethylene glycol solution at 160 degrees C). The detailed structures of the Pt nanoflowers were studied with high-resolution TEM, indicating that high-quality production of the Pt nanoflowers could be obtained when the KI concentration was increased to six times of H2PtCl6. The size of Pt nanoflowers could be tuned by changing the concentration of H2PtCl6 with the constant Pt/I ratio (1:6). The formation process of the nanoflowers was investigated by the UV-vis and EXAFS spectroscopic studies, demonstrating that the iodine ions played a key role in inducing the formation of the single-crystalline Pt nanoflowers. After the addition of iodine ions into the polyol synthesis, the Pt-I complex was formed and reduced by different kinetics compared with that of H2PtCl6 to induce the overgrowth of Pt nanocrystals. Additionally, a small portion of iodine element was found to be strongly adsorbed on the surfaces of Pt nanoflowers, which probably also favored the anisotropic overgrowth of Pt nanocrystals resulting in the single-crystalline Pt nanoflowers. A comprehensive set of systematic studies on the synthesis factors (the concentrations of Pt precursor, iodine ions and PVP, reaction temperature, different kinds of Pt precursors and reaction atmosphere) was also reported.