Metal organosols

Figure 7. Metal organosols accessible via the NR4(Bet3H) route (Equation (2)). (Reprinted from Ref. [53], 2007, with permission from Wiley-VCH.)...

Fig. 2.10 Structural representation of NR4X-stabilized metal organosols. Reproduced with permission from Elsevier Science [91].

Table 2.2 summarizes some typical examples of mono- and bi-metallic organosols prepared via the reductive stabilization pathway. 

Hydrogenation of olefinic ligands in zerovalent complexes is a fadle method for the synthesis of metal organosols. Hydrogenation of (cydooctadiene)(cydo-octatriene)ruthenium, Ru(COD)(COT), yidds metaUic ruthenium, and, in the presence of polymers such as PVP, ceUulose nitrate, and cellulose acetate, ruthenium sols form. [23, 113] For the PVP stalnlized sol, the partide rize is very small (ca. 1 nm). Similar reactions of Ni(COD)2, Pt(COD)Q2, or mixtures of the two have been used to prepare PVP stabilized mono- and tnmetallic organosols of these metals. [114]... 

The preparation of metal organosols by electrolysis in a two-layer bath proved to be more suitable than electrochemical polymerization. The upper organic layer of the electrolytic bath is a dilute solution of a polymer in an orgaific solvent, sometimes, supplemented with a small amormts of surfactant. The polymer interacts with the nascent colloidal metal particles near the interface between layers. 

This is the basis of a generally applicable multigram synthesis routes to isolable 1-10 nm organosols of the transition metals that are easily redispersible in high concentration in organic phases (Figure 7) [3,183]. 

Typically the [NR4] -stabilized raw organosols contain 6-12 wt% metal but for metals such as rhodium they can be converted to pure colloids containing... 

Depending on the nature of these protecting shells, the resulting metal colloid may be taken into organic (organosols) or aqueous (hydrosols) medium. Lipophilic protective agents such as... 

While there are extensive reviews of organosols and the catalysts therefrom in the literature, hy-drosols are relatively unknown in spite of the promising electrocatalysts that can emerge from them. Hydrosols of mono-, bi- and multimetallic nanoparticles as isolable precursors for producing supported metal catalyst are an economically beneficial alternative to the traditional wet impregnation of active metal components on carrier surfaces [25],... 

Bonnemann, H. and Brijoux, W., The preparation, characterization and application of organosols of early transition metals, Nanostruct. Mater., 5, 135, 1995. 

In the literature, metal nanoparticles have been obtained in hydrocarbon media in different ways. Thus, Brust et al.5 synthesized thiol-derivatized gold nanoparticles in a two-phase liquid—liquid system by transferring the metal salt from the aqueous medium to toluene using tetraoctylammoniumbromide as the phase-transfer reagent. Thiol-derivatized nanoparticles of Au, Pt, and Ag have been prepared as organosols, by the... 

For plastisol/organosol technology, high-molecular-weight PVC powder is slurried in liquid plasticizer, and poured, dip- or spread-coated onto metal, fabric, or paper to produce dishwasher racks, upholstery, and wallpaper, respectively. 

The reduction of TiBr4-2THF with KfBEtjH] yields a hydrogen-free organosol Ti-0.5THF which seems to consist of very small Ti particles in the zerovalent state stabilized by THF molecules.83 This nanoparticulate metal colloid is extremely oxophilic, very soluble in THF but insoluble in hydrocarbons. 

Samples of a palladium colloid were prepared by concentrating the original organosols to l-2 metal concentration (a factor of 5-10) filtering as before, and exposing the concentrated solution to 99 at lat. 

Interest in the application of nanostructured catalysts stems from the unique electronic structure of the nanosized metal particles and their extremely large surface areas. Nanostructured metal colloids can be defined as isolable particles between 1 and 50 nm that are prevented from agglomerating by protecting shells. They can be prepared to be redispersed in both water ( hydrosols ) and organic solvents ( organosols ). Here we hope to provide a synopsis of the wet chemical syntheses of these materials and their application as precursors of electrochemical catalysts. 

Table 1 THF-Stabilized Organosols of Early Transition Metals...

This modification [Eq. (6)] of the organoaluminum protecting shell can be used to tailor the dispersion characteristics of the original organosols. A vast spectrum of dissolubilities of the colloidal metals in hydrophobic and hydrophilic media (including water) has been achieved this way. 

Figure 10 Differential TEM/STEM study of a Pd organosol showing that the metal core (size = /tem) is surrounded by a monolayer of the surfactant (thickness A = ((5 tem — c stm 2)-(From Ref. 60.)...

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