Synthesis of Metal Nanoparticles

This sub-chapter is divided into two parts. In the first part, attention is focused on particles, except for a few examples that consist mainly of noble metals. Nanoparticles of noble metals, in particular, have a long tradition and the fundamental synthetic strategies associated with these materials have long been known. Thus, the aim here is not to describe the vast number of synthetic pathways for metal nanopartides, but rather to summarize the recognized syntheses (although some novel procedures have been included in so far as they complement traditional procedures). 

The second part of the sub-chapter deals exclusively with magnetic particles, which have attracted much attention during the past decade. The reason for this relates to the manifold future applications in nanodevices. This second part also describes the most important properties of these partides. 

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Scheme 1 Illustration of the general synthetic method followed in our group for the synthesis of metal nanoparticles i decomposition of the precimsor, nucleation ii first growth process in ripening or coalescence leading to size and shape controlled objects through addition of stabilizers which prevent the full precipitation of the metal (iv)...

The synthesis of metal nanoparticles via the controlled decomposition of pre-prepared organometallic complexes or metal carbonyls where the metals are already in the zero valent or low-valent state has been known since 1970. The first examples were Pd- and Pt-dibenzylideneacetone complexes where the coordinated ligands detached using either hydrogen of carbon monoxide under mild conditions to give the respective metal nanoparticles [310]. 

The intention of this chapter is to provide a general survey on the preparative methodologies for the size- and shape-selective synthesis of metallic nanoparticles that have emerged from the benches of chemical basic research during the last few decades and become established as practical standard protocols. Industrial scale-up, however, has only just started to test the economic viability of these procedures and to determine whether they can meet the challenges of a number of very specific applications. The commercial manufacture of such thermodynamically extremely unstable nanoparticles in defined sizes and shapes on the kilo-scale is still confronted by a number of major problems and it remains to be seen how these can be solved. 

Gold electrodes coated by nanostructured self-assembled monolayer of TMPP and Cl2 are used as template for in situ synthesis of metallic nanoparticles (Figure 2). 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Figure 4. Synthesis of metal nanoparticles by SCCO2 treatment and subsequent dry H2-reduction. (a) Mesoporous silica, (b) impregnation of mesoporous silica with metal ions, (g) SCCO2 treatment for high dispersion, (h) formation of small metal nanoparticles.

Size and Shape Selective Synthesis of Metal Nanoparticles by Seed-Mediated Method and the Catalytic Activity of Growing Microelectrodes (GME) and Fully Grown Microelectrodes (FGME)... 

Size and Shape Selective Synthesis of Metal Nanoparticles... 

In conclusion, we can say that the synthesis of metal nanoparticles and tuning of their sizes is achievable through seed-mediated synthetic route. Again, this method helped us to obtain shape selective evolution of... 

Because ultrasound can be an efficient driving force in the synthesis of metal nanoparticles [86], it is important to point out the specific effects of the combination [87] (in contrast to the use of both techniques alone) but the intensity of the effects depends on the experimental set up used ... 

Although various techniques have been reported, sonochemical reduction technique for the synthesis of metal nanoparticles in an aqueous solution are reviewed in this chapter. 

The use of dendrimers constitutes an attractive stabilization mode for the synthesis of metal nanoparticles for several reasons ... 

Dendrimer interior functional groups and cavities can retain guest molecules selectively, depending on the nature of the guest and the dendritic endoreceptors, the cavity size, the structure, and the chemical composition of the peripheric groups. Two main methods are known for the synthesis of metal nanoparticles inside dendrimers. The first method consists of the direct reduction of dendrimer-encapsulated metal ions (Scheme 9.4) the second method corresponds to the displacement of less-noble metal clusters with more noble elements [54]. 

PS-PEO reverse spherical micelles have been used as nanoreactors for the synthesis of metallic nanoparticles, as shown by the works of Moller and coworkers [102] and Bronstein et al. [103]. 

Fig. 3. Schematic illustration of the synthesis of metal nanoparticles within dendrimer templates. The composites are prepared by mixing of the dendrimer and metal ion, and subsequent chemical reduction. These materials can be immobilized on electrode surfaces where they serve as electrocatalysts or dissolved in essentially any solvent (after appropriate end-group functionalization) as homogeneous catalysts for hydrogenation and other reactions...

The structures of unsymmetrical photochromic 42, which is also intended for the use in the synthesis of metal nanoparticles enclosed by dihetarylethenes (07CC1355), and fluorescent 43, which was prepared in 05JOC5545, are illustrated. 

This section is concerned with the mechanism of formation and growth of metal nanoparticles in homogeneous solutions. As mentioned in the section on synthesis of metal nanoparticles, there are many kinds of synthetic methods. Each method has its own process and mechanism. However, there are four main processes ... 

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