Metal nano-dispersed

In contrast to traditional energy sources, microwave, laser, and sonic energy can be delivered to specific solid sites or small areas by fine-tuning frequencies and energy levels. It is especially suitable for preparation of nano-structured catalyst. For example, inherent eggshell catalysts can be produced with sonochem-ical preparation by which nano-dispersed metal particles are formed with instantaneous decomposition of metal solution by high-intensity irradiation of ultrasound in local area. In the preparation of M02C on ZSM-5 with ultrasound at 20 kHz, narrowly distributed particles of about 2nm in diameter are uniformly dispersed on the outer surface of the ZSM-5 support. ... 

Noble metals are known to actively catalyze reduction and oxidation reactions of many organic compounds. The catalytic activity depends on the metal surface area avadable to the reacting molecides. From the viewpoint of economy the most beneficial are nano-dispersed metal catalysts. However, nanoparticles tend to agglomerate, so that the catalyst gradually loses its activity. Size stabilization of the catalyst nanoparticles can be achieved by immersing them into a polymeric matrix with an optimized size of cavities that incorporate the metal clusters. HypercrossUnked polystyrene offers such an opportunity. 

The support for the metal nano-particles turns out to be as important as the nano-particles for providing their dispersion and stability. Studies on electron transfer are particularly important for carbon-based materials because those materials, such as glassy carbon, graphite, fullerene, and diamond with different electronic and structural properties, have been proved to possess distinctly different electrochemical properties from each other (Ramesh and Sampath, 2003). Carbon supports provide high electronic conductivity, uniform catalyst dispersion, corrosion resistance, and sufficient access of gas reactants to the catalyst (Ismagilov et al, 2005). In addition to electrical conductivity and surface area, hydrophobicity, morphology, porosity, and... 

Various disciplines such as colloid chon.istry, electrochemistry, electron microscopy, and solid state physics come together in the investigation of metallic nano-particles in solution. In the studies described above, photo- and radiation chemical methods play an important role in both the preparation of nano-particles and the initiation of surface chemical processes. In fact, the field of free radical chemistry has been enriched by the studies on the interaction of radicals with the surface of finely dispersed metals. The examples mentioned here are to give the reader an impression of the many aspects which one encounters in these investigations. For more details and aspects, the reader s attention is called to recent reviews. ... 

CNT dispersions Sputtered ITO ITO Nano-metal ICP dispersion dispersions dispersions ... 

Recently, various sol-gel based recipes incorporating metal colloids have been shown to result in successful SERS substrates (49, 50, 52-57). Large Raman enhancements have been found for nano-sized metal particles dispersed in the resulting gel structure, in part, due to the large stabilized metal surface areas available to molecular-sized scatterers. In contrast, the sol-gel derived SiOa SERS substrate produced by the procedure described here is covered by immobilized clustered aggregates of monodispersed sized gold nano-particles that have been grown in-situ. 

Breakthrough in this field has been achieved through the development of cleverly designed carbon-metal composites, hi an oversimphfied way, these composites may be described as formed by small-size, metal particles dispersed within a carbon matrix. The carbon matrix, while maintaining in its core the nano-sized metal particle configuration that helps in containing the volume stress, supplies an overall compact structme that assmes stability and provides high tap density. 

Nano-composites (NCs) are materials that comprise a dispersion of particles of at least one of their dimentions is 100 nm or less in a matrix. The matrix may be single or multicomponent. It may include additional materials that add other functionalities to the system such as reinforcement, conductivity and toughness (Alexandre and Dubois, 2000). Depending on the matrix, NCs may be metallic (MNC), ceramic (CNC) or polymeric (PNC) materials. Since many important chemical and physical interactions are governed by surface properties, a nanostructured material could have substantially different properties from large dimensional material of the same composition (Hussain et ah, 2007). 

Evaporation of volatile byproducts and solvents is often used to obtain the solid metal nanoparticles. The residue may contain metal nanoparticles and protective reagents. When the nanoparticles are well protected by ligands or polymers, then the solid residues can be dispersed again without coagulation of the particles. When the nanoparticles are not well protected, however, the evaporation often results in aggregation of the nano-particles. 

Figure 6. Schematic representation of the micro- and nanoscale morphology of nanoclustered metal catalysts supported on gel-type (a) and macroreticular (b) resins [13]. The nanoclusters are represented as black spots. Level 1 is the representation of the dry materials. Level 2 is the representation of the microporous swollen materials at the same linear scale swelling involves the whole mass of the catalyst supported on the gel-type resin (2a) and the macropore walls in the catalyst supported on macroreticular resin (2b). The metal nanoclusters can be dispersed only in the swollen fractions of the supports, hence their distribution throughout the polymeric mass can be homogeneous in the gel-type supports, but not in the macroreticular ones (3a,b). In both cases, the metal nanoclusters are entangled into the polymeric framework and their nano-environment is similar in both cases, as shown in level 4.

Our studies on graphite - transition metal systems [11] have shown the methods of chemical deposition of nano-scaled metal particles on the surface of graphite supporter to be powerful technique for production of CM with well dispersed, nanoscaled homogeneously distributed modifier component. 

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