%0 Journal Article %J Journal of Physical Chemistry C %D 2012 %T Nanocatalysts Can Change the Number of Electrons Involved in Oxidation-Reduction Reaction with the Nanocages Being the Most Efficient %A Weng, G. %A Mahmoud, M A %A El-Sayed, M. A. %X Eosin Y (EY) is a fluorescein derivative dye that can be reduced by accepting either one or two electrons. The one- or two electron reduction potentials have comparable values. The two-electron reduction pathway dominates when sodium borohydride is used, whereas the reduction pathway changes to a one-electron reduction pathway when gold solid (AuNS) or hollow (AuHS) nanosphere catalysts are used. The reduction reaction of EY by borohydride proceeds via one kinetic stage, whereas in the presence of gold nanocatalysts, three different stages are identified. The first stage has the same reaction rate as in the absence of the nanocatalyst, and no one-electron product is observed (absorption peak at 405 nm). The second stage starts when the rate of the disappearance of EY is suddenly increased; a new peak at 405 nm beings to appear. This stage ends when the rate of the disappearance of EY decreases. The third stage has a rate close to that of the first stage, and the EY is reduced again by accepting two electrons. The lifetime of the first stage is greatly affected by the concentration of the nanocatalyst and decreases as the concentration of the nanocatalyst is increased. The conversion ratio of EY to its one electron reduced form is found to increase proportionally with the concentration of the gold nanocatalyst. In the case of using hollow nanospheres as a catalyst, the conversion ratio is found to be 3 times higher than that when using the solid nanospheres due to the cage effect. %B Journal of Physical Chemistry C %V 116 %P 24171-24176 %8 Nov %@ 1932-7447 %G eng %M WOS:000311190800040 %R 10.1021/jp308869m %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