Metallic nanoparticles formation

Scheme 15.5 The pseudo-elementary step concept proposed by Finke and coworkers to monitor transition-metal nanoparticle formation.

Since the micellar characteristics of the PEO-b-P2VP-Pd block copolymer aggregates in a given solvent and at a given pH may influence the catalytic properties, this was another important variable for the present system. PEO-fe-P2VP forms micelles in water whose characteristics are mainly preserved after metallation (incorporation of a metal salt and metal nanoparticle formation) [49], but the behavior of this system in the presence of isopropanol is more complicated. To clarify the effect of solvent composition and pH on micellar characteristics, TEM and atomic force microscopy (AFM) studies of the key reaction mixtures were performed. Table 3.2 summarizes the catalytic data and mean diameters of the micelles and micellar aggregates obtained from AEM. 

NANOSTRUCTURED POLYMERIC NANOREACTORS FOR METAL NANOPARTICLE FORMATION... 

FIGURE 2.10 Transmission electron microscopy images of silver nanoparticles from plant samples irrigated with (a) 10 g/L Ag as AgNOj and (b) 10 g/L Ag as Ag(NH3)2N03. (With kind permission from Springer Science + Business Media from Journal of Nanoparticle Research, Haverkamp and Marshall. The mechanism of metal nanoparticle formation in plants Limits on accumulation, 11, 2008, 1453-1463.)... 

Shuetz, P., and Caruso, F. (2004). Semiconductor and metal nanoparticle formation on polymer spheres coated with weak polyelectrol5fte multilayers. Chem. Mater. 16, 3066-3073. 

I C Colloidal Dispersion of Metallic Nanoparticles Formation and Functional Properties... 

Bronstein, L. H., S. N. Sidorov, P. M. Valetsky, J. Hartmann, H. Colfen, andM. Antonietti. 1999. Induced micellization by interaction of poly(2-vinylpyridine)-block-poly(ethylene oxide) with metal compounds. Micelle characteristics and metal nanoparticle formation. Langmuir 15 (19) 6256-6262. 

Formation of Metallic Nanoparticles Beneath Langmuir Monolayers... 

Figure 25. Formation of an artificial structure of metal nanoparticles by dip pen nanolithography using an AFM (a), tip to transport functionalized thiol molecules onto a gold surface (b) and to trap the nanoparticles (c).

Figure 3. Schematic illustration of core/shell nanoparticle formation via redox transmetalation process. Metal ions (Mu) of reactant metal complexes (Mn-L ) are reduced on the surface of Mi nanoparticles while neutral Mi atoms are oxidized to Mi " by forming a Mi-ligand complex (Mi-Lj) as a resultant reaction byproduct. Repeating this process results in the complete coverage of shell layers on core metals. (Reprinted from Ref [145], 2005, with permission from American Chemical Society.)...

Formation of single-walled carbon nanotubes (SWNTs) was found to be catalyzed by metal nanoparticles [207]. Wang et al. [114] investigated bimetallic catalysts such as FeRu and FePt in the size range of 0.5-3 nm for the efficient growth of SWNTs on flat surfaces. When compared with single-component catalysts such as Fe, Ru, and Pt of similar size, bimetallic catalysts Fe/Ru and Fe/Pt produced at least 200% more SWNTs [114]. 

The acidic conditions of standard SBA-15 synthesis [35] cause the precipitation of metal nanoparticles without silica encapsulation, or the formation of amorphous silica due to the presence of the polymer used for nanoparticle synthesis. Therefore, the SBA-15 framework was synthesized under neutral condition using sodium fluoride as a hydrolysis catalyst and tetramethylorthosilicate (TMOS) as the silica precursor. Pt particles with different sizes were dispersed in the aqueous template polymer solution sodium fluoride and TMOS were added to the reaction mixture. The slurry aged at 313 K for a day, followed by an additional day at 373 K. Pt(X)/SBA-15-NE (X = 1.7, 2.9, 3.6, and 7.1nm) catalysts were obtained by ex-situ calcination (see Section 3.2). TEM images of the ordered... 

Besides electronic effects, structure sensitivity phenomena can be understood on the basis of geometric effects. The shape of (metal) nanoparticles is determined by the minimization of the particles free surface energy. According to Wulffs law, this requirement is met if (on condition of thermodynamic equilibrium) for all surfaces that delimit the (crystalline) particle, the ratio between their corresponding energies cr, and their distance to the particle center hi is constant [153]. In (non-model) catalysts, the particles real structure however is furthermore determined by the interaction with the support [154] and by the formation of defects for which Figure 14 shows an example. 

In this Section we want to present one of the fingerprints of noble-metal cluster formation, that is the development of a well-defined absorption band in the visible or near UV spectrum which is called the surface plasma resonance (SPR) absorption. SPR is typical of s-type metals like noble and alkali metals and it is due to a collective excitation of the delocalized conduction electrons confined within the cluster volume [15]. The theory developed by G. Mie in 1908 [22], for spherical non-interacting nanoparticles of radius R embedded in a non-absorbing medium with dielectric constant s i (i.e. with a refractive index n = Sm ) gives the extinction cross-section a(o),R) in the dipolar approximation as ... 

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