Cobalt nanopartides

An alternative method of preparing cobalt nanopartides is based on the thermal decomposition of Co2(CO)g in the presence of a suitable surfactant [27]. A typical recipe involves the injection of a solution of Co2(CO)g in diphenylether (solution A) into the hot (200 °C) mixture of oleic acid and TOP or TBP, dissolved also in diphenylether (solution B). The mixture is then heated at 200 °C for 15-20 min. Decomposition of the cobalt carbonyl, under the conditions described above, results in Co nanopartides with a so-called multiply-twinned face-centered cubic (mt-fee) lattice (Figures 3.115b and (3.116)d). The multiply-twinned particles are composed of domains with a distorted fee lattice, this structure being similar to that observed in multiply-twinned, icosahedral gold particles [27]. Post-preparative size-selection... 

A magnetic field, when applied perpendicularly to the substrate, induces the formation of 2-D hexagonal superlattices of individual Co nanoparticles [30] Pileni et al. [28] observed the formation of a hexagonal network of about 1 [tm dot-shaped aggregates made from 8nm cobalt nanopartides. CoPts nanociystals (4nm), when deposited under a magnetic field of 0.9 Tapplied perpendicularly to the substrate, can... 

Son, S.U., Lee, S.I., Chung, Y.K., Kim, S.-W. and Hyeon, T. (2002) The first intramolecular Pauson-Khand reaction in water using aqueous colloidal cobalt nanopartides as catalysts. Organic Letters, 4, 277-9. 

The magnetic metals were also prepared by a method [25] based on the rapid expansion of supercritical fluid solutions (RESS) coupled with chemical reduction to produce nickel, cobalt, iron, and iron oxide nanopartides of reasonably narrow size distribution. Under the protection of a polymer stabilization agent, the largely amorphous metal nanopartides form stable suspensions in room-temperature solvents. 

Wizel later extended her study and included another metallic nanopartide, cobalt, and an additional polymer, poly(methylmethacrylate), in her metal-polymer composite research [58]. A significant difference in the solubility of the iron-poly(methylacrylate) and cobalt-poly(methylacrylate) in various solvents was observed. While the iron-poly(methylacrylate) composite (FePMA) and iron-poly(methylmethacrylate) composite (FePMMA) dissolved in chloroform, acetone, and toluene at room temperature, the corresponding cobalt-poly(methylacrylate) composite (CoPMA) was insoluble in these solvents at room temperature. At elevated temperatures (45 °C), dissolution of CoPMA in these solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron-poly(methylacrylate) this interaction is weakened due to the formation of an iron complex. The Mw of the various polymers and composites as a function of the metal-to-monomer weight ratio was measured and reported. 

Synthesis of CoPtj Magnetic Alloy Nanocrystals The synthetic approach developed for the preparation of elemental nanopartides can be further extended to intermetallic compounds. Thus, high-quality CoPt3 nanocrystals can be synthesized via the simultaneous reduction of platinum acetylacetonate and the thermal decomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic add (ACA) and hexadecylamine (HDA) as stabilizing agents [65]. 

The preparation of core-shell -type magnetic nanopartides was reported [92,93] as a two-step synthesis in which nanopartides of one metal served as the seeds for growth of the shell from another metal. Thus, the reduction of platinum salts in the presence of Co nanopartides would allow the preparation of air-stable CocorePtsheii nanopartides [92]. The thermal decomposition of cobalt carbonyl in the presence of silver salt led to the formation of AgcoreCOgheii nanopartides [93]. The syntheses of these multicomponent magnetic nanostructures are discussed in Section 3.3.2.4. 

The issue whether the true catalyst is the metal(O) nanoparticles or their aggregated form bulk metal has not been address in that report. However, the sole stabilizer present in the system for all of the precursors used [162] is the weakly coordinating chloride anion which cannot provide enough stabilization for the metal(O) nanoclusters, not imexpectedly, based on a previous study ranking the anions in the order of their abilities to stabilize the metal(O) nanoparticles, whereby the chloride anion has been found to be the weakest stabilizer for the iridium(O) nanopartides [163]. Consequently, ruthenium(O), rhodiiun(0), cobalt(O), and pal-ladium(0) nanoparticles putatively generated could not be stabilized by chloride anions and... 

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