Metallic nanoparticle composites size distribution

Fig. 2. Composite size distribution of metal nanoparticles (from left to right) ...

Pt/Pd bimetallic nanoparticles can be prepared by refluxing the alcohol/water (1 1, v/v) solution of palla-dium(II) chloride and hexachloroplatinic(IV) acid in the presence of poly(A-vinyl-2-pyrrolidone) (PVP) at ca. 95 °C for Ih [15,16,48]. The resulting Pd/Pt nanoparticles have a Pt-core/Pd-shell structure with a narrow size distribution and the dispersion is stable against aggregation for several years. The core/shell structure was confirmed by the technique of EAXFS. Composition of Pt/Pd nanoparticles can be controlled by the initially feed amount of two different metal ions, i.e., in this case one... 

This chapter concerns composite films prepared by physical vapor deposition (PVD) method. These films consist of dielectric matrix containing metal or semiconductor (M/SC) nanoparticles. The structure of films is considered depending on their formation by deposition of M/SC onto dielectric substrates as well as by layer-by-layer or simultaneous deposition of M/SC and dielectric vapor. Data on mean size, size distribution, and arrangement of M/SC nanoparticles in so obtained different composite films are given and discussed in relation to M/SC nature and matrix properties. Some models of nucleation and growth of M/SC nanoparticles by the diffusion of M/SC atoms/molecules over a surface or in volume of dielectric matrix are proposed and analyzed in connection with experimental data. 

The chemical reactivity of nanoparticle surfaces, presents interesting additional opportunities for evaluating nanoparticle surface composition. Some noble metal particles (Pd and Au in particular) can be extracted from the PAMAM dendrimer interiors into organic solution with long-chain thiols [37]. The resulting nanoparticles, referred to as Monolayer Protected Clusters (MPCs), retain the size distributions and spectroscopic characteristics of the original DENs and allow for recycling the expensive dendrimer [16]. 

The morphology, size distribution, and composition of the metal nanoparticles as well as magnetic properties of Fe-, Co-, and Ni-containing composites and electric properties of polyethylene-based composites have been studied. 

Nanoporous carbon with narrow pore-size distribution can be prepared directly via a one-step nanocasting technique by carbonization of cyclodextrin-silica organic-inorganic hybrid composite.[260] The method consists of preparing a cyclodextrin-templated silica mesophase via soft chemistry, followed by direct carbonization of the occluded cyclodextrins. The nanocasting procedure provides granules (in millimeter scale) or monoliths (in centimeter scale). Cyclodextrins can be employed not only as structuredirecting templates but also as carriers for metal nanoparticle precursors. 

In the particle synthesis, metal atoms produced by the heating collide with the inert gas atoms to decrease the diffusion rate of the atoms fi-om the source region. The collisions also cool the atoms to induce the formation of small clusters of fairly homogeneous size. The clusters grow mainly by cluster-cluster condensation to give nanoparticles with a broader size distribution. A convective flow of the inert gas between the warm region near the vapour source and the cold surface carries the nanoparticles to the cooled finger, where they are let to deposit. The inert gas pressure, the evaporation rate, and the gas composition can control the characteristics... 

In recent years simultaneous progress in the understanding and engineering of block copolymer microstructures and the development of new templating strategies that make use of sol-gel and controlled crystalHzation processes have led to a quick advancement in the controlled preparation of nanoparticles and mesoporous structures. It has become possible to prepare nanoparticles of various shapes (sphere, fiber, sheet) and composition (metal, semiconductor, ceramic) with narrow size distribution. In addition mesoporous materials with different pore shapes (sphere, cyHndrical, slit) and narrow pore size distributions can be obtained. Future developments will focus on applications of these structures in the fields of catalysis and separation techniques. For this purpose either the cast materials themselves are already functional (e.g., Ti02) or the materials are further functionalized by surface modification. 

For the sample PPX -f Cu the calculated fractal dimension Df is equal to 2.609 [70]. It should be noted that the above-mentioned size distribution of metal nanoparticles leads to the mutual charging of such particles in the percolation cluster. This effect is discussed in the following section in coimection with catalysis by nanoparticles. As stated in reference 70, the specific low-temperature peak of dielectric losses in the synthesized composite samples PPX -t-Cu is probably due to the interaction of electromagnetic field with mutually charged Cu nanoparticles immobilized in the PPX matrix. The minor appearance of this peak in PPX -i- Zn can be explained by oxidation of Zn nanoparticles. 

Recently, an alternative strategy has been adopted to synthesize metal or semiconductor nanomaterials by exposing precursor metal-organic frameworks (MOFs) to an electron beam. Jacobs et al. (2011) demonstrated the formation for ZnO particles with narrow and tunable size distributions using different Zn-based MOFs. They showed that the composition, size, and morphology of the nanoparticles are determined by the chemistry and structure of the MOF, as well as the electron beam properties. 

---