Metal colloid synthesis nanoparticles

In this chapter, we intend to introduce to the reader some of the most popular preparation methods of noble metal colloids, but do not intend by any means to thoroughly review the scientific literature on metal colloid synthesis. We have chosen examples of synthesis in aqueous and organic solvents, and differentiate between spherical and anisotropic nanoparticles (nanorods and nanoprisms). Additionally, in section 3 we shall describe one of the most popular recent procedures to assemble metal colloids into nanostructured materials (layer-by-layer assembly), as well as the properties of the resulting structures. 

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

A new method to synthesis nanoparticles of group VIII-X elements has been developed by Choukroun et al. [178] by reduction of metalUc precursors with CP2V. Mono- and bimetallic colloids of different metals (stabilized by polymers) have been prepared in this way (Fe, Pd, Rh, Rh/Pd). These colloids are then used as catalysts in various reactions such as hydrogenation of CC, CO, NO or CN multiple bonds, hydroformylation, carbonylation, etc. 

Common methods for the fabrication of metallic nanoparticle arrays are electron beam lithography, photolithography, laser ablation, colloidal synthesis, electrodeposition and, in recent time, nanosphere lithography for which a monodisperse nanosphere template acts as deposition mask. A review on advances in preparation of nanomaterials with localized plasmon resonance is given in [15]. 

The formation and stabilization of noble metal colloids in the aqueous phase are widely known. Platinum and palladium are most widely used in hydrogenation of C=C bonds but some results have been described with rhodium. Generally, surfactants are investigated as stabilizers for the preparation of rhodium nanoparticles for biphasic catalysis in water. In many cases, ionic surfactants, such as ammonium salts, which provide sufficiently hydrophilic character to maintain the catalytic species within the aqueous phase, are used. The obtained micelles constitute interesting nanoreactors for the synthesis of controlled size nanoparticles due to the confinement of the particles inside the micelle cores. Aqueous colloidal solutions are then obtained and can be easily used as catalysts. 

The outline of the paper is therefore as follows In section 1 we introduce the main interaction forces acting on colloidal particles, as well as the concept of nanostructured materials, in the form of 2D and 3D assemblies. We discuss the main stabilization techniques employed in the synthesis of nanoparticles in solution. Then we outline in section 2 the procedures involved in silica coating, and discuss its advantages as a general stabilization technique. Section 3 deals with the special properties of both metal and semiconductor nanoparticles, summarizing their... 

The synthesis of metallic colloids in the nanometer size range was already performed by Faraday [86], who studied for the first time gold sols in a systematic way. The great interest which this sort of systems is still raising mainly arises from the very small dimensions that can be achieved, which give properties to the particles that are very different from those of bulk metals. Several reviews have been published about the special electronic properties of metallic [87-90] and semiconductor [87,91-93] nanoparticles, which are due to a decrease in the density of states within the valence band and the conduction band when the particle size is decreased. Particles which exhibit such quantum size effects represent... 

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 )- ... 

The synthesis methods used for the preparation of carbon supported PtRuMo nanoparticles could be classified as adsorption of metal colloids onto the carbon surface, or impregnation of carbon support with metals precursor solution. Additionally, the incorporation of the metals has been carried out in a (1) one step method or with simultaneous incorporation of the three metals, and in (2) two step methods or sequential incorporation of Mo and PtRu nanoparticles ... 

The methods used for the synthesis of metal NPss in colloidal solution are very important as they control the size and shape of NPs, which in turn affects their properties. Moreover, successful utilization of NPs in biological assays relies on the availability of nanomaterials in desired size, their morphology, water solubility and surface functionality, Several reviews on the synthesis of nanoparticles are available [93], Some reviews dedicatedly covered the synthesis of gold nanoparticles [109,127,140], Synthesis methods of CG (and other metal colloids) can arbitrarily be divided into following two major categories ... 

The main role of stabilizers (surfactants or polymers) is to provide a steric or an electrostatic barrier between particles, thereby preventing inhibition of aggregation. Furthermore, stabilizers play an essential role in the control of both size and shape of nanoparticles. Generally, polymers are recommended as stabilizers for metal colloids due to their transparent, permeable, and nonconductive properties and also because they do not influence the optical, electrical, and catalytic properties of the nanoparticles. In addition, investigation of polymer-stabilized MNPs appears as a suitable way for solving the stability of MNPs. For this reason, great attention has been focused on the incorporation of MNPs into a polymer matrix, a procedure based on the synthesis of nanometer-sized metallic filler particles (Giannazzo et al. 2011). 

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