Metallic nanoparticles chemical synthesis control

The science of nanocatalysis is enabled by the ability to synthesize nanoparticles of well-controlled shape, size, and composition. To explore how structnral factors impact catalytic performance, we need to decouple these interacting structural and compositional factors of an industrial catalyst through chemical synthesis [3-12], For example, to explore potential snrface-structnre-dependent catalytic activity or selectivity we could keep the size and composition of nanoparticles of a catalyst the same but vary shape of a catalyst. The surface strueture of a catalyst with a different shape can be varied through chemical synthesis [13-17]. Chapter 2 reviews the control of nanocatalyst structural parameters through chanical synthesis by which shape, composition, and nanostructure can be controlled. In this chapter, the fundamental mechanisms of growth of metal nanoparticles are introduced. Controlled syntheses of intermetallic nanocatalysts, nanostructured catalyst particles, and coreshell nanoparticles are reviewed. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

Since nanoscale metal nanoparticles are applicable to a number of areas of technological importance, the nano-structured materials chemistry will occupy much attention of scientists. It is certain that controlling the primary structures of metal nanoparticles, that is, size, shape, crystal structure, composition, and phase-segregation manner is still most important, because these structures dominate the physical and chemical properties of metal nanoparticles. Now the liquid phase synthesis facilitates the precise control of the primary structures. 

In this chapter the potential of nanostructured metal systems in catalysis and the production of fine chemicals has been underlined. The crucial role of particle size in determining the activity and selectivity of the catalytic systems has been pointed out several examples of important reactions have been presented and the reaction conditions also described. Metal Vapor Synthesis has proved to be a powerful tool for the generation of catalytically active microclusters SMA and nanoparticles. SMA are unique homogeneous catalytic precursors and they can be very convenient starting materials for the gentle deposition of catalytically active metal nanoparticles of controlled size. 

Electrochemical Synthesis of Bimetallic Particles. Most chemical methods for the preparation of metal nanoparticles are based at first on the reduction of the corresponding metal ions with chemical reagents to form metal atoms and then on the controlled aggregation of the obtained metal atoms. Instead of chemical reduction, an electrochemical process can be used to create metal atoms from bulk metal. Reetz and Hclbig proposed an electrochemical method including both oxidation of bulk... 

Figure 13.15 Schematic representation of synthesis and surface modification of nanoparticles [54]. (Reproduced with permission from W.J. Rieter et al., Surface modification and functionalization of nanoscale metal-organic frameworks for controlled release and luminescence sensing, Journal of the American Chemical Society, 129, 9852-9853, 2007. 2007 American Chemical Society.)...

In the present work, we consider the two approaches for synthesis of nanoparticles designed for metal particles and being in the progress for ultraflne semiconductors. They allow to fabricate nanocomposites of the type nanoparticles-in-dielectrics with amorphous and crystalline matrices. The first one is based on the sol-gel technique producing dielectric silica films with nanoparticles incorporated within silica matrix [1]. Nanoparticles provide an optical response of the material due to the plasmon resonance [2] with variable spectral position and band shape. In the second approach nanoparticles are produced within the crystalline zeolite matrices which stabilize both the few-atomic clusters (e.g., Agg) and metal particles in the size range of 1-20 nm [3], Chemical routes of their synthesis admit easy control of size and optical properties. The metal nanoparticles in zeolites can be transformed into semiconductors without destroy of the zeolite matrix and with incorporation of zeolite microcrystals into transparent silica films. This construction... 

Production of any predetermined size of the particles can be generated through radiation chemical synthesis by controlling an easy-to-control parameter, radiation dose. Even a very small size can be obtained with monodispersity. Good crystallinity can be achieved and different phases of metal sulfide nanoparticles can be prepared just by choosing different nonmetallic sources and solvents (Qiao et al. 1999). A variety of nanocrystalline semiconductor materials has been synthesized so far in different media (Table 23.4). 

Further detailed informadon on each of these methods is available in Ref. [29]. Solution-phase chemical syntheses are commonly used for the preparation of colloids of magnedc metal nanoparticles. Several general approaches can be used to control the size and shape of nanoparticles in solution-phase synthesis. 

Dispersions of metallic nanoparticles can be obtained by two main methods (i) mechanic subdivision of metallic aggregates (physical method) or (ii) nucleation and growth of metallic atoms (chemical method). The physical method yields dispersions where the particle size distribution is very broad. Traditional colloids are typically larger (>10nm) and not reproducibly prepared, giving irreproducible catalytic activity. Chemical methods such as the reduction of metal salts is the most convenient way to control the size of the particles. Today, the key goal in the metal colloid area is the development of reproducible nanoparticle (or modem nanocluster) syntheses in opposition to traditional colloids. As previously reported, nanoclusters should be or have at least (i) specific size (1-10 nm), (ii) well-defined surface composition, (iii) reproducible synthesis and properties, and (iv) be isolable and redissolvable ( bottleable )- ... 

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