Synthesis of monodisperse Pt nanocubes and their enhanced catalysis for oxygen reduction

Growth of pagoda-topped tetragonal copper nanopillar arrays

Growth of arrays of pagoda-topped tetragonal Cu nanopillar (length 1- 6 mum; width 150 +/- 25 nm) with {100} side faces on Au/glass is achieved by a simple electrochemical reduction of CuCl(2)(aq) by Al(s) in aqueous dodecyltrimethylammonium chloride. Field-emission measurement shows that the Cu nanopillars can emit electrons (10 muA cm(-2)) at a turn-on field of 12.4 V mum(-1) with a calculated field enhancement factor of 713.

Controlled synthesis of dendritic Au@Pt core-shell nanomaterials for use as an effective fuel cell electrocatalyst

We report the controlled synthesis of dendritic Au@Pt core-shell nanomaterials. The size and morphology of the Au cores and the Pt shell thickness of the Au@Pt core-shell nanostructures could be easily tuned. It was found that the directing agent and the reducing agent play critical roles in the synthesis of dendritic Au@Pt core-shell nanomaterials. For comparison purposes, conventional Au@Pt core-shell nanoparticles and monometallic Pt nanoparticles were also synthesized by the successive reduction method. Transmission electron microscopy (TEM) observations demonstrated the dendritic surface of the products obtained. The UV-visible (UV-vis) spectroscopy results and a comparison of the average diameter between the dendritic Au@Pt and conventional Au@Pt confirmed the relatively loose Pt shells around Au cores for the dendritic Au@Pt. The as-prepared dendritic Au@Pt showed enhanced electrocatalytic activity for methanol oxidation in acid medium, compared to the conventional Au@Pt and monometallic Pt.

Monodisperse platinum nanospheres with adjustable diameters from 10 to 100 nm: synthesis and distinct optical properties

We present a facile and reproducible method for synthesizing monodisperse platinum (Pt) spheres with sizes ranging from 10 to 100 nm in diameter and exceptionally small standard deviations of 3% for large spheres. The reaction takes place in aqueous solution using a multistep seed-mediated approach. The Pt nanospheres consist of several small crystallites resulting in a surface roughness of 5-10 nm. Extinction spectra are measured from particles dispersed in water and calculated for single particles which are found to be in excellent agreement. We obtain a linear correlation between the plasmon extinction maximum (from UV to the visible regions) and the particle diameter which might be of value for experimentalists in the field.

Facile synthesis of highly faceted multioctahedral Pt nanocrystals through controlled overgrowth

Highly faceted Pt nanocrystals with a large number of interconnected arms in a quasi-octahedral shape were synthesized simply by reducing H2PtCl6 precursor with poly(vinyl pyrrolidone) in aqueous solutions containing a trace amount of FeCl3. The iron species (Fe(3+) or Fe(2+)) play a key role in inducing the formation of the multioctahedral structure by decreasing the concentration of Pt atoms and keeping a low concentration for the Pt seeds during the reaction. This condition favors the overgrowth of Pt seeds along their corners and thus the formation of multiarmed nanocrystals. Electron microscopy studies revealed that the multioctahedral Pt nanocrystals exhibit a large number of edge, corner, and surface step atoms. The size of the multioctahedral Pt nanocrystals can be controlled by varying the concentration of FeCl3 added to the reaction and/or the reaction temperature. These multioctahedral Pt nanocrystals were tested as electrocatalysts for the oxygen reduction reaction in a proton exchange membrane fuel cell and exhibited improved specific activity and durability compared to commercial Pt/C catalyst.

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272:1924-1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon-carbon double-bond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes.

Interfacial and solvent effects govern the formation of tris(dibenzylidenacetone)dipalladium(0) microstructures

Organometallic palladium adducts have application as catalysts and as precursors for nanoparticle synthesis. Herein, we study the spontaneous formation of molecular crystals of the organometallic reagent tris(dibenzylidenacetone)dipalladium(0) (Pd(2)(DBA)(3)) in THF/H(2)O binary solvent systems. We report structural and chemical characterization of the resulting diverse structures with shapes including hexagonal platelets, rods, cubes, and stars. Optical microscopy, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectroscopy were used to determine representative structures and corresponding compositions when formed either in a binary solution or upon evaporation on a surface. The difference in Pd(2)(DBA)(3) particle morphology was attributed to differences in the surface tension of growing crystalline faces. The formation of a majority of rods or hexagonal platelets in solution was shown to be determined by the ratio of THF to H(2)O in the solvent, whereas supersaturation effects and interfacial surface tension played a major role in creating the shape of particles formed upon evaporation of Pd(2)(DBA)(3) droplets on a surface.

Morphological control of synthesis and anomalous magnetic properties of 3-D branched Pt nanoparticles

Morphology-controllable platinum nanostructures could be obtained by modulating the growth kinetics in oleylamine. The nanostructures evolve from spherical particles to branched networks with decreasing reaction temperature, and the complexity of the branched-network nanostructures increases with the extended reaction period. Size-dependent magnetic properties and enhanced ferromagnetism in dodecanethiol-capped Pt branched nanostructures indicate that the permanent magnetic moments are probably introduced by broken symmetry and charge transfer because charge transfers more effectively from dodecanethiol than from oleylamine.