Tetraoctylammonium bromide

About: Tetraoctylammonium bromide is a research topic. Over the lifetime, 219 publications have been published within this topic receiving 7289 citations.

Surface Binding Properties of Tetraoctylammonium Bromide-Capped Gold Nanoparticles

Abstract: Surface interaction of gold nanoparticles with solvents and functionalized organic molecules is probed using the changes in the surface plasmon absorption band. A red shift in the surface plasmon band is observed with increase in solvent dielectric constant for solvents that do not complex with metal surface. A plot of the square of the observed position of the surface plasmon bands of Au nanoparticles in these solvents as a function of medium dielectric function shows a linear dependence. Interestingly, the surface plasmon band position remains unaffected in polar solvents (with nonbonding electrons) and is attributed to the direct interaction of these solvents with the gold surface. Binding of gold nanoparticles with organic molecules containing functional groups such as −SCN or −NH2 were found to dampen the surface plasmon bands. Binding of phenyl isothiocynate (PITC) and 15N-labeled benzylamine to gold nanoparticles was probed using NMR techniques, and in both cases, two sets of signals were observed,...

Synthesis and characterization of surfactant-stabilized Pt/C nanocatalysts for fuel cell applications

Abstract: Platinum nanocatalysts supported on Vulcan XC-72 carbon have been synthesized through the reduction of chloroplatinic acid with formic acid, using surfactant tetraoctylammonium bromide (TOAB) as the stabilizer in the solvent tetrahydrofuran (THF). These nanocatalysts are synthesized by changing the molar ratio of TOAB to chloroplatinic acid, i.e., N/Pt ratio of 0.76, 0.38, and 0.19. A control catalyst that does not contain TOAB is also synthesized by this method for comparison purposes. Comparison of the morphological properties of these catalysts by transmission electron microscopy (TEM) reveals that the N/Pt ratio of 0.76 catalyst has well-separated smaller particles (2.2 nm) than the other lower molar ratio and control catalysts. X-ray diffraction (XRD) analysis indicates the presence of platinum in the fcc phase and the average size of the particles calculated from the XRD peak widths agreed well with the TEM results. X-ray photoelectron spectroscopic (XPS) measurement of the 0.76 ratio catalyst reveals that a higher amount of Pt exists in its metallic state (73.64% of Pt(O) and 26.36% Pt(II)) and the data are on par with that of the E-TEK catalyst. Stabilization effect of the TOAB on the surface of platinum particles has been discussed with respect to the different N/Pt molar ratios. The XPS technique has been exploited to prove the presence of coverage of TOAB and its subsequent removal from the surface of the Pt particles, which is considered to be the crucial step prior to the electrochemical measurements. Electrochemical measurements have demonstrated that the surface area of the 0.76 ratio catalyst is higher than that of the lower molar ratios (0.38 and 0.19).

Various ligand-stabilized metal nanoclusters as homogeneous and heterogeneous catalysts in the liquid phase

Abstract: Ligand-stabilized noble metal nanoclusters, prepared by various chemical methods by different research groups in Japan and Germany, were characterized and examined by a common method for application to the catalysis for hydrogenation of olefins in homogeneous and heterogeneous systems in the liquid phase. The mean diameters of palladium, platinum, rhodium and Pd/Pt nanoclusters stabilized by various ligands range from 1.3 to 3.2 nm if prepared by a single reaction, and from 2.2 to 4.0 nm if prepared by a stepwise growth method. The Stokes radii of metal nanoclusters stabilized by surfactants range from 1.7 to 2.1 nm, suggesting a thickness of the protective layer from 1.1 to 1.4 nm, whereas those stabilized by polymers give much larger values, suggesting the formation of aggregates. The catalytic activities of the metal nanoclusters, evaluated by hydrogenation of 1,3-cyclooctadiene and methyl acrylate, depend mainly upon the particle size, i.e. the smaller the size, the higher the activity. However, a strongly interacting ligand like tetraoctylammonium halide and 1,10-phenanthroline can disturb the hydrogenation. In contrast, the activities of heterogeneous catalysts supported on charcoal depend strongly on the covering strength of the stabilizer. Copyright © 2001 John Wiley & Sons, Ltd.

Iridium nanocrystal synthesis and surface coating-dependent catalytic activity.

Abstract: Iridium (Ir) nanocrystals were synthesized by reducing (methylcyclopentadienyl)(1,5-cyclooctadiene)Ir with hexadecanediol in the presence of four different capping ligand combinations: oleic acid and oleylamine, trioctylphosphine (TOP), tetraoctylammonium bromide (TOAB), and tetraoctylphosphonium bromide (TOPB). The oleic acid/oleylamine-capped nanocrystals were of the highest quality, with the narrowest size and shape distribution. The Ir nanocrystals were tested for their ability to catalyze the hydrogenation of 1-decene as a model reaction. The oleic acid/oleylamine and TOP-capped nanocrystals were both catalytically dead. TOAB and TOPB-coated nanocrystals both catalyzed 1-decene hydrogenation, with the TOPB-coated nanocrystals exhibiting the highest turnover frequencies. Recycling through several catalytic reactions increased the catalytic activity, presumably as a result of ligand desorption and increased exposure of the metal surface, with ligand desorption eventually leading to precipitation and s...

Nucleation Control of Size and Dispersity in Aggregative Nanoparticle Growth. A Study of the Coarsening Kinetics of Thiolate-Capped Gold Nanocrystals

Abstract: The thermal coarsening (180 °C) of decanethiolate-capped Au nanocrystals is studied at various tetraoctylammonium bromide concentrations. The coarsening kinetics are determined by measuring nanocrystal size distributions (CSDs) as a function of time. The results are shown to be consistent with aggregative nucleation and growth. For each kinetic trial, the time dependence of the aggregative nucleation rate is extracted from the early time CSDs and fitted by a Gaussian profile. The height of the profile is the maximum nucleation rate, Γmax, and the 2σ width is the time window for nucleation, Δtn. These nucleation parameters are shown to control the final mean size and size distribution of the coarsened nanocrystals. The coarsening kinetics are influenced by tetraoctylammonium bromide concentration because the nanocrystals are partially electrostatically stabilized.