Nanoparticles organometallic precursors

Recently, Dupont and coworkers described the use of room-temperature imi-dazolium ionic liquids for the formation and stabilization of transition-metal nanoparticles. The potential interest in the use of ionic liquids is to promote a bi-phasic organic-organic catalytic system for a recycling process. The mixture forms a two-phase system consisting of a lower phase which contains the nanocatalyst in the ionic liquid, and an upper phase which contains the organic products. Rhodium and iridium [105], platinum [73] or ruthenium [74] nanoparticles were prepared from various salts or organometallic precursors in dry 1-bu-tyl-3-methylimidazolium hexafluorophosphate (BMI PF6) ionic liquid under hydrogen pressure (4 bar) at 75 °C. Nanoparticles with a mean diameter of 2-3 nm... 

Scheme 15.3 Preparation of soluble iridium nanoparticles from in situ reduction of the organometallic precursor [ir(COD)Cl]2 in imidazolium ionic liquids.

Similar to chemical vapor deposition, reactants or precursors for chemical vapor synthesis are volatile metal-organics, carbonyls, hydrides, chlorides, etc. delivered to the hot-wall reactor as a vapor. A typical laboratory reactor consists of a precursor delivery system, a reaction zone, a particle collector, and a pumping system. Modification of the precursor delivery system and the reaction zone allows synthesis of pure oxide, doped oxide, or multi-component nanoparticles. For example, copper nanoparticles can be prepared from copper acetylacetone complexes [70], while europium doped yttiria can be obtained from their organometallic precursors [71]. 

MetalHc cobalt nanoparticles were synthesized by the decomposition of THE solution of an organometallic precursor Colij -CgHia) )[197]... 

The decomposition of organometallic precursors is probably the simplest method to use to prepare nanoparticles. This decomposition may be driven by heat... 

The IBM nanoparticle synthesis route is a combination of the polyol method and the thermolysis routes. The rapid injection of the organometallic precursor into a hot solution containing the polyol stabilizing agents allows for the immediate formation of nuclei. 

Recent work by Lukehart et al. has demonstrated the applicability of this technique to fuel-cell catalyst preparation [44g,h]. Through the use of microwave heating of an organometallic precursor that contains both Pt and Ru, PtRu/Vulcan carbon nanocomposites have been prepared that consist of PtRu alloy nanoparticles highly dispersed on a powdered carbon support [44g]. Two types of these nanocomposites containing 16 and 50 wt.% metal with alloy nanoparticles of 3.4 and 5.4 nm, respectively, are formed with only 100 or 300 s of microwave heating time. The 50 wt.% supported nanocomposite has demonstrated direct methanol fuel-cell anode activity superior to that of a 60 wt.% commercial catalyst in preliminary measurements. 

Similar studies in an organic solvent yielded almost the same product [66]. Nanostructured particles of amorphous carbon-activated palladium metallic clusters have been prepared (in situ) at room temperature by ultrasound irradiation of an organometallic precursor, tris-//-[dibenzylideneacetone]dipalladium [(p-CH= CH-CO-CH=CH-5 )3Pd2] in mesitylene. Characterization studies show that the product powder consists of nanosize particles, agglomerated in clusters of approximately 800 A. Each particle is found to have a metallic core, covered by a carbonic shell that plays an important role in the stability of the nanoparticles. The catalytic activity in a Heck reaction, in the absence of phosphine ligands, has been demonstrated. 

A number of techniques have been used for producing nanoparticles, including vapour phase techniques [72], sol-gel methods [73], sputtering [74], coprecipitation [75] etc. Two main methods can be employed for the preparation of metal nanoparticles coprecipitation and chemical reduction. In both cases, the presence of surfactant is required to govern the growth process. Typically, the coprecipitation reactions involve the thermal decomposition of organometallic precursors [76 ]. The chemical reduction occurring in colloidal assemblies... 

InP nanocrystals can be made by dehalosilylation of InCls and (MesSi) 3P with subsequent thermolysis at 200 - 400 Monodisperse and soluble InP nanocrystals are obtained by thermolysis reactions in trioctylphosphine oxide. InP nanoparticles can also be obtained by the decomposition of organometallic precursors. A novel route has been developed to prepare nanocrystalline InP by the reaction of InCls, P4, and KBH4 at temperatures as low as 80°C, which is the lowest temperature reported for InP nanocrystals. The synthesis of InP nanotubes by laser ablation is also reported. 

Organometallic precursors may also be used for the direct preparation of metal oxide nanoparticles. 

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