In addition to alkanethiols and phosphine derivatives, alkylamines have been investigated as capping agents in the synthesis of organically dispersible gold nanoparticles. However, reports pertaining to gold nanoparticle derivatization with alkylamines are relatively scarce and their interaction with the underlying gold support is poorly understood. In this paper, we attempt a more detailed examination of this problem and present results on the Fourier transform infrared spectroscopy, thermogravimetry, nuclear magnetic resonance, and X-ray photoemission (XPS) characterization of gold nanoparticles capped with the alkylamines laurylamine (LAM) and octadecylamine (ODA). The capping of the gold nanoparticles with the alkylamines was accomplished during phase transfer of aqueous gold nanoparticles to chloroform containing fatty amine molecules. Thermogravimetry and XPS analysis of purified powders of the amine-capped gold nanoparticles indicated the presence of two different modes of binding of the alkylamines with the gold surface. The weakly bound component is attributed to the formation of an electrostatic complex between protonated amine molecules and surface-bound AuCl/AuCl ions, while the more strongly bound species is tentatively assigned to a complex of the form [AuCl(NHR)]. The alkylamine monolayer on the gold nanoparticle surface may be place exchanged with other amine derivatives present in solution.
Development of simple and reliable protocols for the immobilization of catalytically active metal nanoparticles is an important aspect of the nanomaterials field. Amine groups bind very strongly to platinum and palladium nanoparticles; therefore, we have attempted to entrap aqueous platinum and palladium nanoparticles on the surface of micron-sized zeolite particles functionalized with amine groups. In this paper, we demonstrate that platinum and palladium nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na-Y zeolites are excellent heterogeneous catalysts for hydrogenation and Heck reactions. The assembly of platinum or palladium nanoparticles on the zeolite surface occurs via an interaction with the amine groups present in APTS leading to a new class of catalyst. The synthesized catalysts were well-characterized by UVvis, FTIR, TGA, XRD, XPS, and TEM. TEM images of the fresh and used catalysts indeed show that the platinum and palladium nanoparticles supported on amine-functionalized zeolites remain unchanged at the end of the reactions. The rate of hydrogenation and Heck reactions over these catalysts was much higher than those obtained using conventionally prepared catalysts.
The surface modification of aqueous silver colloidal particles with the amino acid cysteine and the cross-linking of the colloidal particles in solution is described. Capping of the silver particles with cysteine is accomplished by a thiolate bond between the amino acid and the nanoparticle surface. The silver colloidal particles are stabilized electrostatically by ionizing the carboxylic acid groups of cysteine. Aging of the cysteine-capped colloidal solution leads to aggregation of the particles via hydrogen bond formation between amino acid molecules located on neighboring silver particles. The aggregation is reversible upon heating the solution above 60°C. The rate of cross-linking of the silver particles via hydrogen bond formation may be accelerated by screening the repulsive electrostatic interactions between the particles using salt. The process of aggregation and heat-induced dispersion of the particles has been studied by UV-vis spectroscopy, laser light scattering, and transmission electron microscopy measurements.
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