Nano-sized metal particles

For metal catalysts used for hydrogenations and, in combination with acid functions, in hydrocarbon reforming reactions, the advantage of nano-size metal particles has been well known. More recently it has been demonstrated that metals on... 

Nano-sized metal particles are usually present in the supported metallic catalysts used industrially. The smaller the particle size, the larger the fraction of metal surface atoms exposed, which are therefore accessible to reactants. However, as the size of the metal particles decreases to the molecular range, their properties and, consequently, their catalytic behavior change. Both well-defined metal clusters and small metal aggregates can be generated by applying proper activation... 

Iron carbonyls have been also used to fabricate nanostructures of potential use in catalysis. In this context, the preparation at room temperature of nano-sized a-Fe single crystals over carbon micro-grid films has been reported. The particles were prepared by electron beam induced deposition using Fe(CO)s as precursor [77]. The use of a focused electron beam to induce metal deposition from carbonyl compounds opens a new route for the preparation of nano-sized metal particles. 

For the beautiful tetracapped octahedral Os cluster, [OsioC(CO)24]2- with an interstitial C atom in the octahedral core, shown in Figure 3.10, the predicted eve count is 14(6) + 2 + 4(12) = 134, which agrees with that of the observed stoichiometry. It s a little bit harder to count the sep but give it a try. Each tetrahedral cap consists of an Os(CO)3 fragment and the other six fragments are Os(CO)2 so we have (4x2 + 6x0 + 4 + 2)/2 = 7 appropriate for an octahedron. If you look ahead in Chapter 6 (Exercise 6.1), you will find that this trigonal bipyramidal ten-atom core can be excised from a cubic close-packed metal lattice (ABC layers). [OsioC(CO)24]2- can be considered a nano-sized metal particle stabilized by the ligands in the same manner as Ni atoms are stabilized when removed from Ni metal by CO as Ni(CO)4 in the Mond process. 

The intense research interest to nano-sized metal particles and clusters is explained by their unique properties that differ significantly from properties of bulk metals. For example, luminescence from clusters has received an increasing attention, while the process is unlikely in case of bulk metals since they do not have band gaps. Luminescence of nano-sized transition metal particles can be of great practical importance in various fields of science, medicine and industry. 

PHYSICAL AND CHEMICAL PROPERTIES OF NANO-SIZED METAL PARTICLES... 

Rao CNR, Kulkami GU, Thomas PJ, Agrawal W, Gautam UK, Ghosh M (2003b) Nanocrystals of metals, semiconductors and oxides novel synthesis and applications. Curr Sci 85 1041-1045 Rao CNR, Kulkami GU, Thomas PJ (2005) Physical and chemical properties of nano-sized metal particles. In Nicolais L, Carotenuto G (eds) Metal-polymer nanocomposites. WUey, Hoboken, New Jersey, pp 1-36... 

The investigation of the chemistry that occurs on the surface of colloidal metal particles is important for our imderstanding of many properties of nano-particles, such as their catalytic effects, their growth, and their electrochemical and photochemical behaviour. The electronics of nano-sized metal particles are changed when chemical events occur on the surface, and, consequently, certain physical properties such as their optical absorption are affected. On the other hand, optical measurements can often be used to trace the chemical modifications on the surface. 

The study of fluorescence of molecules situated near nano-sized metal particles has been the subject of considerable experimental interest in recent years, largely due to important biological applications and the emergence of nano-technology. The spectroscopic properties of molecules interacting with small solid-state particles was investigated theoretically and experimentally over two decades ago. The work pointed to a competition between enhanced radiative processes and additional non-radiative chaimels introduced by the presence of particles. It was found that the specific optical properties of the solid played an important role, as well as the geometric shape of the particle, and the location of the molecule relative to the particle. 

In nano-size metal particles or thin band semiconductors the above mentioned effect of giant oscillator strength is much stronger due to a large number of electrons on the Fermi level and the possibility collective exdtation Migdal type [53]. This effect can be interpreted as a coherent vibration of all electrons or... 

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. 

Surface-adsorbed polystyrene spheres as a template for nano-sized metal particle formation. Optical properties of nano-sized Au particle, H. Takei, J. Vac. Sci. Technol. B, 1999,17, 1906. 

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