Submicrometer intermediates in the citrate synthesis of gold nanoparticles: new insights into the nucleation and crystal growth mechanisms.

The reduction of tetrachloroaurate by citrate ions in aqueous solutions yielding gold nanoparticles (GNPs) has been studied using in situ tapping mode atomic force microscopy (AFM), UV-vis absorption and dynamic light scattering (DLS) spectroscopies, small-angle X-ray scattering (SAXS) along with ex situ TEM, EDX and XPS. Special attention is given to mesoscale intermediates responsible for the intense coloring of the transient solutions and their role in nucleation and crystal growth. AFM detects liquid droplet-like domains, globules 30-50 nm in diameter arranged in submicrometer aggregates in the gray and blue solutions, and well separated individual particles in the final red sols.

Formation of gold and gold sulfide nanoparticles and mesoscale intermediate structures in the reactions of aqueous HAuCl4 with sulfide and citrate ions.

The effects of the molar ratio of sodium sulfide to chloroauric acid in the range of 0.5 to 5 and the time factor on the formation of the nanoparticles (NPs) of metallic Au, Au(2)S or their mixtures have been studied applying in situ and ex situ techniques (UV-Vis absorption spectroscopy, potentiometry, TEM, SPM, SERS, XPS). The products and intermediates have been compared with those for the reduction of chloroaurate with citrate ions and combinations of citrate and sulfide ions.

Reversible transformations of gold nanoparticle morphology.

Herein is reported a metamorphosis taking place in a gold nanosized system. The observed phenomenon of shape and size transformations was found to be completely reversible. Unlike most procedures in the literature where shape and size control occur in the synthetic step by adding growth- and shape-controlling agents such as surfactants or polymers, in this system postsynthetic changes in shape and size can be carried out simply by changing the ratio of reactive, competing reagents, more specifically, alkylthiols versus tetralkylammonium salts.

Novel halogen and interhalogen adducts of nanoscale magnesium oxide.

The difference in the adsorption properties of magnesium oxide in two different physical forms--large micron-sized crystals (CM-MgO) and nanoscale crystals (AP-MgO)--is described. The highly energetic surface of the nanoparticles is significantly more active than the bulk surface in adsorption of nonpolar halogens (Cl(2), Br(2), and I(2)) and dipole interhalogen molecules (ICl, IBr, and ICl(3)). The nanocrystalline and microcrystalline MgO adducts with halogens and interhalogens were characterized by thermogravimetric analysis (TGA), UV-vis and Raman spectroscopies, and transmission electron microscopy (TEM).

Gold nanoparticles as catalysts for polymerization of alkylsilanes to siloxane nanowires, filaments, and tubes.

Nanoparticles of gold prepared by condensation of gold vapor in cold pentanone serve as active catalysts for the polymerization of an alkylsilane C18H35SiH3 with water, to form nanowires and filaments. This reaction takes place under relatively mild conditions (refluxing pentanone).