Nanosized metal materials

The well-defined large bimetallic Au—Ag cluster as [(Ph3P)i2AuigAg2oCli4] can achieve nearly two orders of magnitude of attenuation of high-intensity laser power and, consequently opens the door to a new class of optical materials based on nanosized metal clusters 3269... 

The materials described in this chapter are denoted in the literature mostly as metal clusters or metal nanoclusters . However, the terminology metal clusters spans various scientific disciplines and has consequently multiple meanings, including plasmonic nanoparticles and various nanosized metallic structures. Therefore alternative names have been given, although they are at the moment supported only by a fraction of the scientific community quantum clusters [26], nanodots [27], metal quantum dots [25] and superatoms [28]. 

Significant new insight has been gained into the formation of small clusters and nanosized metallic particles [501,502]. This fundamental information is not only inherently fascinating, but it is vitally important for the construction of new generations of advanced nanostructured materials. Evolution of nanosized metallic particles from non-metallic clusters and the chemistries of these species will, therefore, be discussed in the following sections. 

Fine tuning of the Fermi levels of nanosized metallic and size-quantized quasi-metallic particles by adsorbing (or desorbing) charges, ions, or molecules opens the door to the construction of tailor-made advanced materials [538]. 

These difficulties have stimulated the development of defined model catalysts better suited for fundamental studies (Fig. 15.2). Single crystals are the most well-defined model systems, and studies of their structure and interaction with gas molecules have explained the elementary steps of catalytic reactions, including surface relaxation/reconstruction, adsorbate bonding, structure sensitivity, defect reactivity, surface dynamics, etc. [2, 5-7]. Single crystals were also modified by overlayers of oxides ( inverse catalysts ) [8], metals, alkali, and carbon (Fig. 15.2). However, macroscopic (cm size) single crystals cannot mimic catalyst properties that are related to nanosized metal particles. The structural difference between a single-crystal surface and supported metal nanoparticles ( 1-10 nm in diameter) is typically referred to as a materials gap. Provided that nanoparticles exhibit only low Miller index facets (such as the cuboctahedral particles in Fig. 15.1 and 15.2), and assuming that the support material is inert, one could assume that the catalytic properties of a... 

Interest in the application of nanostructured catalysts stems from the unique electronic structure of the nanosized metal particles and their extremely large surface areas. Nanostructured metal colloids can be defined as isolable particles between 1 and 50 nm that are prevented from agglomerating by protecting shells. They can be prepared to be redispersed in both water ( hydrosols ) and organic solvents ( organosols ). Here we hope to provide a synopsis of the wet chemical syntheses of these materials and their application as precursors of electrochemical catalysts. 

The fabrication of well-ordered arrays of well-defined nanoparticles or clusters is of fundamental and technological interest. As this is a difficult task, different techniques have been employed. An elegant approach would be to link well-defined building blocks in a chemically straightforward procedure yielding a monodisperse or a completely homogeneous material. We succeeded now to cross-link assembled nanosized metal-oxide-based clusters/composites - novel supramolecular entities - under one-pot conditions. 

In this chapter we discuss a novel approach to the concept of nanostructuring, which is based on coating metal or semiconductor nanoparticles with silica, so that the final morphology involves a silica sphere of the desired size containing a core placed precisely at its center. Although such concepts have been proposed before, it has only recently been possible to synthesize such coated materials in a reproducible manner. These composite spheres can then be used as the building blocks of the nanostructured material. The interest of these systems is due to the unique optical and electronic properties of nanosized metal and semiconductor particles. 

Microemulsion-mediated synthesis has attracted the attention of many researchers [10-18, 44-120]. In the specific case of oxide materials, the clearest achievement of the work to date is the demonstration that a wide variety of nanosize metal oxides—binary oxides from... 

Jacob DS, Bitton L, Grinblat J, Felner I, Koltypin Y, Gedanken A. Are ionic liquids really a boon for the synthesis of inorganic materials A general method for the fabrication of nanosized metal fluorides. Chem Mater 2006 18(13) 3162. 

Nanosized metals are characterized by novel thermodynamic, chemical, catalytic, optical, magnetic, and transport properties which are much different from those of corresponding massive metals. For this reason a 3-D periodic table of elements has been frequently proposed by chemists working in this material science field (36). 

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