Reduction metallic nanoparticle composites

In the present study the property of the aminociays wherein protonation of the amino groups in water is accompanied by exfoliation has been exploited.15 Thus metal nanoparticle composites formed by the exfoliated aminoclay sheets by carrying out the reduction of metal precursors in the presence of the clay have been investigated. Besides being entirely water soluble, the exfoliated sheets of aminoclay-Au nanoparticle composites move to the organic/aqueous interface in the presence of an alkanethiol. 

In case of fuel cell cathodes, theoretical considerations were directed towards optimizing catalysts for O2 reduction [103]. This has led to the synthesis of Pt3Co/C nanocatalyst systems and preliminary results again indicate perfect agreement between the calculations and the wet electrochemical results obtained with metal nanoparticles of the composition which theory had recommended [106]. 

This alcohol reduction method is applied to the control of size and composition of not only the noble metal/noble metal [7] but the 3d-transition metal/noble metal nanoparticles [8] like magnetic FePt nanoparticles. 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

Dendrimer interior functional groups and cavities can retain guest molecules selectively, depending on the nature of the guest and the dendritic endoreceptors, the cavity size, the structure, and the chemical composition of the peripheric groups. Two main methods are known for the synthesis of metal nanoparticles inside dendrimers. The first method consists of the direct reduction of dendrimer-encapsulated metal ions (Scheme 9.4) the second method corresponds to the displacement of less-noble metal clusters with more noble elements [54]. 

Fig. 3. Schematic illustration of the synthesis of metal nanoparticles within dendrimer templates. The composites are prepared by mixing of the dendrimer and metal ion, and subsequent chemical reduction. These materials can be immobilized on electrode surfaces where they serve as electrocatalysts or dissolved in essentially any solvent (after appropriate end-group functionalization) as homogeneous catalysts for hydrogenation and other reactions...

Dendrimers containing Pt " or Pt-metal nanoparticles are easily attached to Au and other surfaces by immersion in a dilute aqueous solution of the composite for 20 h, followed by careful rinsing and drying [59,129]. Therefore it is possible to use X-ray photoelectron spectroscopy (XPS) to determine the elemental composition and the oxidation states of Pt within dendrimers. For example, Pt(4f7/2) and Pt(4f5/2) peaks are present at 72.8 eV and 75.7 eV, respectively, prior to reduction, but after reduction they shift to 71.3 eV and 74.4 eV, respectively, which is consistent with the change in oxidation state from -i-2 to 0 (Fig. 13 a]. 

Another approach for H2 photocatalytic production is reported by Mizukoshi et al. [9] that described the syntheses of noble metal nanoparticles Ti02 composite photocatalysts by the sonochemical reduction method for hydrogen evolution from ethanol aqueous solutions at room temperature. 

Controlling the primary structures of metal nanoparticles (i.e., size, shape, crystal structure, and composition) is one of the most important missions for colloid science, especially for nanoparticle science and technology because these structures determine the chemical and physical properties of metal nanoparticles. Here, chemical methods are dealt with to control the compositions and structures of various bimetallic nanoparticles by making use of the difference in the reduction (decomposition) rate or the reduction sequence of two kinds of metal species. When two kinds of metal ions are simultaneously reduced, the reduction rates of metal ions usually determine the hnal structure of bimetallic nanoparticles (i.e., a core/shell structure or an alloy structure). The successive reduction of two kinds of metal ions, however, generally gives bimetallic nanoparticles with a core/shell structure. As a representative of the chemical properties of such bimetallic nanoparticles, their catalytic properties for... 

Crystallization and reduction of sol-gel prepared zinc oxide films derived from zinc acetate by irradiation with an UV lamp (185 and 254 nm) was studied (Asakuma et al. 2003). UV irradiation induced the formation of hexagonal ZnO crystals from amorphous ZnO films preheated at 100 C, while irradiation of porous ZnO films preheated at 60 C led also to formation of metallic zinc. Composite ZnO/Cu and ZnO/Ag/Cu nanostructures were prepared via the photocatalytic reduction (wavelength 310-390 nm) of cuprous chloride and silver nitrate over the chemically prepared ZnO nanoparticles in aqueous solution (Shvalagin et al. 2004). Amorphous ZnO thin films were prepared... 

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