Gram-scale synthesis of monodisperse gold colloids by the solvated metal atom dispersion method and digestive ripening and their organization into two- and three-dimensional structures

We describe a synthetic procedure for preparation of large quantities of monodisperse thiol-stabilized gold colloids in toluene solution. The method is based on the solvated metal atom dispersion technique (SMAD), which is very suitable for preparation of large amounts of metal colloidal solutions, as well as of metal sulfide, metal oxide, and other types of dispersed compounds in different solvents. A combination of two different solvents like acetone and toluene is used for the preparation of the gold colloids. The necessity of initially carrying out the SMAD reaction in acetone comes from its high degree of solvation of gold particles. Acetone acts as a preliminary stabilizing agent. After its removal from the system, the particles are stabilized by dodecanethiol molecules, which enable their very good dispersion in toluene solution. A digestive ripening procedure is carried out with the gold-toluene colloid, and for this purpose pure toluene as solvent is necessary. This has a dramatic effect on the narrowing of particle size distribution and almost monodisperse colloids are obtained (some discussion of the probable mechanism of this remarkable digestive ripening step is given). These colloidal solutions have a great tendency to organize in two- and three-dimensional structures (nanocrystal superlattices, NCSs). We believe that this procedure provides a real opportunity to synthesize large amounts of gold nanocrystals as well as NCSs.     

Letters to the editor

Abstract

An X-ray topographic method for investigating migration of point defects is described as a summary of previous work carried out on self-interstitials in ice. Since the method presented is based on in situ observations of dislocation climb in a thick specimen, the advantages of synchrotron-radiation topography for this method is emphasized. It is shown that the diffusion coefficients of the point defects can be determined as functions of both temperature and pressure.     

Reactions of VX, GB, GD, and HD with nanosize Al(2)O(3). Formation of aluminophosphonates.

Room-temperature reactions of VX, GB, GD, and HD with nanosize Al(2)O(3) (AP-Al(2)O(3)) have been characterized by (31)P, (13)C, and (27)Al MAS NMR. Nerve agents VX, GB, and GD hydrolyze to yield surface-bound complexes of their corresponding nontoxic phosphonates. At sufficiently high loadings, discreet aluminophosphonate complexes, Al[OP(O)(CH(3))OR](3), are generated which are identical to synthesized model compounds. Thus the reaction with phosphonic acids is not just surface-limited, but can continue to the core of alumina particles. HD mainly hydrolyzes at lower loadings to yield thiodiglycol (TG, 71%) and a minor amount of the CH-TG sulfonium ion (12%), although some elimination of HCl is also observed (17%). The reactive capacity for HD is evidently exceeded at high loadings, where complete conversion to TG is hindered. However, addition of excess water results in the quantitative hydrolysis of sorbed HD to CH-TG. On AP-Al(2)O(3) dried to remove physisorbed water, (13)C CP-MAS NMR detects a surface alkoxide consistent with that of TG.     

Organogallium compounds from metallic gallium through using metal-vapor synthesis

The first syntheses of organogallium compounds utilizing metallic gallium and alkyl halides (bromides and iodides) are presented. Metal-vapor synthesis methods were used, and it is proposed that gallium atoms are the reactive species involved. Gallium also reacted with alkyl halides as fine particles in slurry form, but only when deposited in, or co-deposited with, alkylaluminum compounds. Rationale for this finding is based on irregularity of the clusters due to incorporation of aluminum (or its compounds) and probably also on smaller particle sizes.     

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).     

Nanoparticle adsorption at liquid-vapor surfaces: influence of nanoparticle thermodynamics, wettability, and line tension

We developed a statistical mechanical theory that describes the adsorption of nanoparticles (NPs) at liquid-vapor surfaces. This theory accounts for the surface to bulk NP thermodynamic equilibrium, as well as the NP mechanical equilibrium, wettability, and line tension at liquid-vapor surfaces. The theory is tested by examining the adsorption of 5 nm diameter dodecanethiol-ligated gold NPs at the liquid-vapor surface of a homologous series of n-alkane solvents, from n-nonane to n-octadecane, where the NP wettability decreases with an increasing n-alkane chain length.