Gold colloids preparation

Adsorbed molecules or ions formed during the various syntheses of colloidal metals have been observed by SERS. A silver hydrosol prepared by ferrous reduction of Ag in the presence of citrate showed enhanced Raman intensity corresponding to adsorbed citrate, [213] and gold colloids prepared from [Au(CN)2]" by reduction with borohydride showed SER bands due to adsorbed CN". [214] The Raman spectrum of [Pt(CN)4] adsorbed on a 1.6 nm platinum colloid has been measured, [215] but it was concluded that the slight intensity increase observed (a factor of 7) for the CN mode at 2215 cm might be due to other enhancement mechanisms. It has also been shown that ligands such as (N-4-dimethylaminoazobenzene-4 -sulfonyl)aspartate [216] adsorbed on colloidal silver are highly Raman active as a result of this phenomenon. Polymer films con-... 

Historically, Michael Faraday must be credited with some of the earliest work on small particles, his gold colloid preparations are still used today over 200 years later. In 1925, Richard Zsigmondy received the Nobel Prize for his study of colloidal metal solutions. Today microclusters of metals constitute one of the most important of man s synthetic materials they are vital in heterogeneous catalysis on which 20% of the GNP of the United States is dependent. Among other numerous applications of small metal particles are thin films and coatings, latent image development, and photographic films. 

Gold colloid preparation accord ng to Slot>Geuze [7]... 

The use of tetraoctylammonium salt as phase transfer reagent has been introduced by Brust [199] for the preparation of gold colloids in the size domain of 1-3 nm. This one-step method consists of a two-phase reduction coupled with ion extraction and self-assembly using mono-layers of alkane thiols. The two-phase redox reaction controls the growth of the metallic nuclei via the simultaneous attachment of self-assembled thiol monolayers on the growing clusters. The overall reaction is summarized in Equation (5). 

This method is especially valid for the preparation of gold NPs mixed with activated carbon, which are active and stable for the selective oxidation of hydrocarbons and alcohols in water. Over activated carbon gold could not be directly deposited as NPs by using the techniques described above, such as DP and even by GG. Gold colloids with mean diameters from 2.5 to lOnm stabilized by poly vinyl alcohol or poly vinyl p5rrolidone are used. 

Thus, we see that the digestive ripening process leads to highly monodispersed nanoparticles that can come together to form ordered superstructures similar to atoms or molecules that form crystals from a supersaturated solution. Then if the superstructure formation can indeed be related to atomic/molecular crystallization, it should also be possible to make these supercrystals more soluble in the solvent with a change of temperature. Indeed, the optical spectra of the three colloids prepared by the different thiols discussed above exhibit only the gold plasmon band at 80 °C suggesting the solubilization of these superlattices at the elevated temperatures [49]. 

Figure 5.9 Synthesis of gold nanoparticles within Zr02. A gold colloid is first prepared then coated with silica using a modified Stober process [75]. The silica is removed using NaOH. Reproduced with permission from [74],...

Mix a stabilizing amount of antibody plus an additional 10 percent with the appropriate volume of colloidal gold. For example, Geoghegan (1988) found that an addition of 10-14 pg of antibody per ml of gold colloid resulted in stable preparations. Mix well after addition of antibody to the gold suspension. 

Duff, D.G. and Baiker, A., Preparation and structural properties of ultrafine gold colloids for oxidation catalysis, in Preparation of Catalysts VI, Poncelet, G., Martens, J., Delmon, B., Jacobs, P.A., and Grange, P., Eds., Elsevier, Amsterdam, 1995, p. 505. 

J. D. Grunwaldt, C. Kiener, C. Wogerbauer, and A. Baiker, Preparation of supported gold catalysts for low-temperature CO oxidation via size-controlled gold colloids, J. Catal. 181(2), 223—232 (1999). 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Gold colloid will aggregate with age. Use within 3 d of preparation. 

Kameo A, Suzuki A, Torigoe K, Esumi K (2001) Fiber-like Gold Particles Prepared in Cationic Micelles by UV Irradiation Effect of Alkyl Chain Length of Cationic Surfactant on Particle Size. J Colloid Interface Sci 241 89-292... 

Potable Gold. In the KoUoid-Zeitschrift, H. Losner discussed the history of colloidal gold and quoted several early recipes for the preparation of red gold sols, or potable gold (Trinkgold). Preparations such as this were made by Creiling (1730), Valentin Krautermann (1717), G. E. Stahl (1744), and George Wilson (126). 

Copper, silver, and gold colloids have been prepared by Chemical Liquid Deposition (CLD) with dimethoxymethane, 2-methoxyethyl ether, and ethylene glycol dimethyl ether. The metals are evaporated to yield atoms which are solvated at low temperatures and during the warm-up process colloidal sols with metal clusters are obtained. Evaporation of the solvent was carried out under vacuum-generating metal films. These films are showing very low carbon/hydrogen content and were characterized by elemental analyses and infrared spectroscopy (Cardenas et al., 1994). 

Fig. 1. Formvar grid coated with a colloidal suspension of 14-nm gold particles prepared using the method of Slot and Geuze (4). Most gold particles are spherical singlets, duplets, or triplets (g). Occasionally, the particles are tetrahedral (t) or in clusters (c). Electron micrograph ><125,000.

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