Metallic nanoparticles metal properties

Bulk nanostructured materials are soUds with nanosized microstructure. Their basic units are usually nanoparticles. Several properties of nanoparticles are useful for applications in electrochemical sensors [67], However, their catalytic behavior is one of the most important. The high ratio of surface atoms with free valences to the total atoms has led to the catalytic activity of nanostructured SEs being used in electrochemical reactions. The catalytic properties of nanoparticles could decrease the overpotential of electrochemical reactions and even provide reversibility of redox reactions, which are irreversible at the bulk metal SE [68], Multilayers of conductive nanoparticles assembled on electrode surfaces produce a high porous surface with a controlled microenviromnent. These structures could be thought of as assemblies of nanoelectrodes with controllable areas. 

Decrease in the size of a metal particle below a critical dimension results in dramatic changes in the electronic properties of the bulk metal. Properties like conductivity, magnetism, light absorption, luminescence, electrochemical, and catalytic activity depend on the particle size. Many heterogeneous catalysts are based on finely divided metal particles on various supports. However, this section deals with the catalytic properties of unsupported nanoparticles. 

Synthesis of polymer/nanoparticles composite materials is very important for the advanced material science. Materials of this type combine unique properties of nanoparticles with properties of polymers, and even reveal new properties not specific for their components. Moreover, a polymer also plays a role of stabilizer for extremely active nanoparticles. Metal oxides are an interesting class of inorganic nanoparticles due to optical, magnetic and electronic features [1-3],... 

It is worthwhile mentioning a new direction in physicochemistry of nanoparticles chemistry of gigantic clusters. A number of synthesis methods for com-pormds with metal-metal links whose nuclearity reaches several hundreds have been elaborated lately. It was noted earlier that severe conditions of synthesis (i.e., the large specific area Sjp of nanoparticles, which is also characterized by small-size morphological elements) can induce variations in the nanoparticles physicochemical properties and even the violation of the expected atomic structure. Extremely high (or low) temperatures and velocities of the processes and various outer effects (e.g., fast condensation or quenching) assist in formation of nonequilibrium, so-called frozen states in growing y-nuclei particles. 

As was briefly mentioned above, the increased reactivity of small Au nanoparticles may be the result of the unique electronic characteristics of small Au clusters. There is a clear shift from the bulk metal properties which readily allow electron transfer between the valence and conduction bands of the metal due to small energy differences between these states. In reducing the size of a metal particle to the nanometer size scale, we lose the band structure... 

Noble metal nanoparticles can go beyond acting as labels recent advances show that changes in nanoparticle optical properties can act as the signal transduction mechanism in chemosensing and biosensing events. Van Duyne and coworkers have exploited the extreme LSPR sensitivity of NSL-fabricated nanoparticles to changes in local refiactive index in order to sense small molecules, amino acids, proteins, and antibodies. The LSPR shifts systematically to lower energies as the local dielectric constant increases ... 

K. L. Kelly, T. R. Jensen, A. A. Lazarides and G. C. Schatz, Modeling metal nanoparticle optical properties,... 

M. Vaseem, A. Umar, Y. B. Hahn, ZnO nanoparticles Growth, properties, and applications. Metal oxide nanostructures and their applications, A. Umar and Y. B. Hahn (eds.) 5 Chapter -IV (2010), American Scientific Publishers, pp. 1-36. 

Clusters are intennediates bridging the properties of the atoms and the bulk. They can be viewed as novel molecules, but different from ordinary molecules, in that they can have various compositions and multiple shapes. Bare clusters are usually quite reactive and unstable against aggregation and have to be studied in vacuum or inert matrices. Interest in clusters comes from a wide range of fields. Clusters are used as models to investigate surface and bulk properties [2]. Since most catalysts are dispersed metal particles [3], isolated clusters provide ideal systems to understand catalytic mechanisms. The versatility of their shapes and compositions make clusters novel molecular systems to extend our concept of chemical bonding, stmcture and dynamics. Stable clusters or passivated clusters can be used as building blocks for new materials or new electronic devices [4] and this aspect has now led to a whole new direction of research into nanoparticles and quantum dots (see chapter C2.17). As the size of electronic devices approaches ever smaller dimensions [5], the new chemical and physical properties of clusters will be relevant to the future of the electronics industry. 

Metallic and semiconductor nanoparticles or nanocrystals —chunks of matter intennediate in size and physical properties between single atoms and tire macroscopic bulk materials—are of great interest botli for tlieir... 

The optical properties of metal nanoparticles have traditionally relied on Mie tlieory, a purely classical electromagnetic scattering tlieory for particles witli known dielectrics [172]. For particles whose size is comparable to or larger tlian tire wavelengtli of the incident radiation, tliis calculation is ratlier cumbersome. However, if tire scatterers are smaller tlian -10% of tire wavelengtli, as in nearly all nanocrystals, tire lowest-order tenn of Mie tlieory is sufficient to describe tire absorjDtion and scattering of radiation. In tliis limit, tire absorjDtion is detennined solely by tire frequency-dependent dielectric function of tire metal particles and the dielectric of tire background matrix in which tliey are... 

Stella A ef al 1996 Comparative study of thermodynamic properties of metallic and semiconducting nanoparticles in a dielectric matrix Mater. Res. Soc. Symp. Proc. 400 161... 

RAFT polymerization lends itself to the synthesis of polymers with thiol end groups. Several groups have utilized the property of thiols and dilhioesLers to bind heavy metals such as gold or cadmium in preparing brushes based on gold film or nanoparticles1 8 761 763 and cadmium selenide nanoparticles.763 76 1... 

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