Metallic nanoclusters

What makes metal nanoclusters scientifically so interesting The answer is that they, in many respects, no longer follow classical physical laws as all bulk materials do, but are correctly to be considered by means of quantum mechanics. This is not only valid for metals. In principle any other solid or in some cases even liquid material exhibit so-called nano-effects when reaching a critical size. Nanoscience and nanotechnology are based on those effects. In the course of only 1-2 decades nanosciences and nanotechnology have developed to such an extent that our daily life already is and will be increasingly influenced in a way that cannot be compared with any other technological development in mankind s history [2]. A few examples will help to better understand what is meant. 

Metal Nanoclusters in Catalysis and Materials Science The Issue of Size Control Edited by B. Corain, G. Schmid and N. Toshima... 

Metal Nanoclusters Synthesis and Strategies for their Size Control... 

Since the surface areas of metal nanoclusters are enormous relative to their masses, they have an excess surface free energy comparable to the lattice energy, making them... 

Figure 3. Double autocatalytic pathway for the metal nanocluster formation. (Reprinted from Ref. [299], 2005, with permission from American Chemical Society.)...

Finke s system discovered in 1994 represents a special subclass of transition metal nanocluster [167,288,289]. A zerovalent transition metal core consisting of, e.g., 300-900 atoms is doubly stabilized by a cationic surfactant (e.g., and by an assembly of polyoxoanions... 

It should be mentioned here that Finke s group has added a whole plethora of significant contributions to the field of metal nanoclusters [295-299] including a recent study on the mechanism for the self-assembly of transition metal nanoparticles [294]. 

Heterogeneous supports, like stabilizers, can prevent metal nanoclusters from agglomerating and they can also... 

The oxides of Si, Al, Ti, Zr, Ca, Mg, and Zn have often served as convenient supports for metal nanoclusters [358-362]. Conductive glassy carbon or graphite materials have proved to be suitable carriers for electrocatalytic applications [363,364]. 

Similarly, Pd, Ag, and Pd-Ag nanoclusters on alumina have been prepared by the polyol method [230]. Dend-rimer encapsulated metal nanoclusters can be obtained by the thermal degradation of the organic dendrimers [368]. If salts of different metals are reduced one after the other in the presence of a support, core-shell type metallic particles are produced. In this case the presence of the support is vital for the success of the preparation. For example, the stepwise reduction of Cu and Pt salts in the presence of a conductive carbon support (Vulcan XC 72) generates copper nanoparticles (6-8 nm) that are coated with smaller particles of Pt (1-2 nm). This system has been found to be a powerful electrocatalyst which exhibits improved CO tolerance combined with high electrocatalytic efficiency. For details see Section 3.7 [53,369]. 

Finke has reported remarkable catalytic lifetimes for the polyoxoanion- and tetrabutylammonium-stabi-lized transition metal nanoclusters [288-292]. For example in the catalytic hydrogenation of cyclohexene, a common test for structure insensitive reactions, the lr(0) nanocluster [296] showed up to 18,000 total turnovers with turnover frequencies of 3200 h [293]. As many as 190,000 turnovers were reported in the case of the Rh(0) analogue reported recently. Obviously, the polyoxoanion component prevents the precious metal nanoparticles from aggregating so that the active metals exhibit a high surface area [297]. 

An important field of development is the batched flow production of metal nanoclusters attached to biomolecules such as DNA under GMP laboratory standards. This conjures up hopes of applying metallic nanomaterials coupled with drugs, antibodies, or with oligonucleotides for cell-specific cancer diagnosis and therapy. With the help of such nanometallic tools, it can be expected that diseases or predispositions to diseases will be diagnosed earlier with the help of nanodrugs than is possible at present. 

Metal Nanoclusters Electronic Aspects and Physico-Chemical Characterization... 

Different approaches have been discussed up to now how to reach this size scale and consequently how to bridge the size gap between the conventionally fabricated circuit elements of some ten nanometers in size and at least the true atomic or molecular scale. In that concern noble metal nanoclusters have attracted much attention. 

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