%0 Journal Article %J Journal of the American Chemical Society %D 2008 %T A new catalytically active colloidal platinum nanocatalyst: The multiarmed nanostar single crystal %A Mahmoud, M A %A Tabor, C. E. %A El-Sayed, Mostafa A %A Ding, Y. %A Wang, Z.L. %X Nanocatalysts that possess large amounts of atoms on sharp corners and edges and high indexed sites are known to be more catalytically active. We report here on a novel yet simple method to synthesize in large yields a very active platinum nanocatalyst; the multiarmed nanostar single crystal. We utilize a seed mediated method using tetrahedral nanoparticles that are also synthesized by a new and simple technique. High-resolution TEM shows that the nanostar has many arms, varying from a few to over 30, whereby even the largest ones :re found to have single-crystal structures. This strongly suggests that they are formed by a growth mechanism of the seed crystals and not by the aggregation of seed crystals, which should produce twinning planes. Due to the reduction reaction of ferricyanide by thiosulfate, the nanostars are found to have an activation energy, which is nearly 60% of that of the tetrahedral seeds themselves, both having the same PVP capping agent. This is undoubtedly due to the multiarms with edges, corners, and the presence of high indexed facets in the nanostar catalyst. %B Journal of the American Chemical Society %V 130 %P 4590-+ %8 Apr %@ 0002-7863 %G eng %M WOS:000254643900009 %R 10.1021/ja710646t %0 Journal Article %J Journal of Physical Chemistry C %D 2007 %T Effect of the lattice crystallinity on the electron-phonon relaxation rates in gold nanoparticles %A Huang, Wenyu %A Qian, Wei %A El-Sayed, Mostafa A %A Ding, Y. %A Wang, Z.L. %X In order to study the importance of surface phonons on the electron-phonon relaxation in plasmonic nanoparticles, the effect of size, shape, and materials have recently been studied. Gold and silver nanoparticles have shown no dependence on size and shape while copper nanoparticles have shown some size dependence. This suggests that the bulk phonons, which are sensitive to the bulk-phase structure, are solely responsible for the relaxation of the hot electron in gold and silver plasmonic nanoparticles. The importance of bulk phonons should depend on the degree of crystallinity. In the present study, we have found that the electron-phonon relaxation rate decreases greatly when polycrystalline prismatic gold nanoparticles are annealed and transformed into nearly single-crystalline nanospheres. The results are explained by the presence of high-density grain boundaries with dense, high-frequency molecular type vibrations which are effective in removing the energy of the excited electrons in the polycrystalline prismatic nanoparticles. %B Journal of Physical Chemistry C %V 111 %P 10751-10757 %8 Jul %@ 1932-7447 %G eng %M WOS:000248121600002 %R 10.1021/jp0738917