Colloidal metal particles

At short interparticle distances, the van der Walls forces show that two metallic particles will be mutually attracted. In the absence of repulsive forces opposed to the van der Walls forces the colloidal metal particles will aggregate. Consequently, the use of a protective agent able to induce a repulsive force opposed to the van der Walls forces is necessary to provide stable nanoparticles in solution. The general stabihzation mechanisms of colloidal materials have been described in Derjaguin-Landau-Verway-Overbeck (DLVO) theory. [40,41] Stabilization of colloids is usually discussed... 

Electron transfer processes leading to a product adsorbed in the interfacial region o are of practical interest. These processes include the deposition of a metal such as Cu or Pd at ITIES, the preparation of colloidal metal particles with catalytic properties for homogeneous organic reactions, or electropolymerization. 

Living Colloidal Metal Particles from Solvated Metal Atoms Clustering of Metal Atoms in Organic Media... 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

A synthetic alternative to this is the chemical reduction of metal salts in the presence of extremely hydrophilic surfactants have yielded isolable nanometal colloids having at least 100 mg of metal per litre of water [105], The wide range of surfactants conveniently used to prepare hydrosols with very good redispersibility properties include amphiphilic betaines A1-A4, cationic, anionic, nonionic and even environmentally benign sugar soaps. Table 3.1 presents the list of hydrophilic stabilizers used for the preparation of nanostructured colloidal metal particles, and Table 3.2 shows the wide variety of transition metal mono- and bi-metallic hydrosols formed by this method [105,120],... 

A.D. (1997) Structure and reactivity of colloidal metal particles immersed in water. Solid State Ionics 101-103 1235-1241 Blesa, M.A. Marinovich, H.A. Baumgartner,... 

Boutonnet M, Kizling J, Stenius P (1982) The Preparation of Monodisperse Colloidal Metal Particles from Micro-Emulsions. Colloids Surf 5 209-225... 

It is important to state the difference between particles and particulate films at the onset of this section. Particles are separate nanometer- to micron-sized colloids dispersed in solution. Physically interconnected colloidal metal particles constitute a particulate film which may be supported by a monolayer floating on an aqueous subphase or be deposited on a solid substrate. 

Physically interconnected colloidal metal particles supported by a monolayer, a BLM, or a solid substrate. 

Finally, as an alternative to colloidal metal particles it is possible to use hydrogenase,133,153 186 187-200,202,238"248 normally from Desulphovibrio vulgaris, or a synthetic analogue derived from Fe4S4 clusters248 in the presence of bovine serum albumin, as the redox catalyst for production of hydrogen from MVf and protons. 

Metal labels have been proposed to resolve problems connected with enzymes. Metal ions [13-16], metal-containing organic compounds [17,18], metal complexes [19-21], metalloproteins or colloidal metal particles [22-28] have served as labels. Spectrophotometric [22,25], acoustic [25], surface plasmon resonance, infrared [24] and Raman spectroscopic [28] methods, etc. were used. A few papers have been dealing with electrochemical detection. However, electrochemical methods of metal label detection may be viewed as very promising taking into account their high sensitivity, low detection limit, selectivity, simplicity, low cost and the availability of portable instruments. 

If the sonolysis is done in the presence of a support or porous host, then colloidal metal particles are formed. These powders have a surface area over a hundred times greater than powders commercially available and are amorphous. Such materials are generally considered for catalytic reactions and not for magnetic applications. 

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

Originally, the goal of this technique was to determine the rates of exchange of a nucleus between two environments in solution, when the lifetimes are comparable to the spin lattice relaxation times and long with respect to the inverse of the frequency difference (43). However, it has also been used for indirect detection of a broad resonance in one of the two environments by monitoring a narrow resonance in the other environment. The exchanging unit was the "CO molecule, which occurred either as a solute in the solvent or as an adsorbate on a colloidal metal particle. The broad line (the adsorbed state) could not be detected directly with the liquid high-resolution equipment used (see Section IV.D). 

The hydrosilylation reaction can also be conventionally conducted by reaction of an olefin and an SiH-f mctional polydimethylsiloxane in the presence of a standard transition metal catalyst, and after the reaction the catalyst can be extracted with an ionic liquid. In some cases, the use of an ionic liquid in the hydrosilylation process even improved the quality of the polyethersiloxanes with respect to color compared to the standard process. An explanation might be the avoidance of catalyst reduction leading to the formation of colloidal metal particles, which tend to color the product slightly brownish. In other words, the ionic liquid seems to have a stabilizing effect on the catalyst. 

Mixing a preformed metal sol with a support material also provides a method for the preparation of supported catalysts with the colloidal metal particles attached to supports such as alumina - o, titania5. 52 d pumice.53 While this procedure gives catalysts having essentially a single size metal particle, the particles are not strongly bonded to the support which makes these materials primarily useful for vapor phase reactions. An added complication is that the citric acid commonly used to prepare the sols > >52 qj. the micellar material in which they are stabilized, can also be adsorbed on the support and, possibly, inhibit the activity of the resulting catalysts. 

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