Soft chemical routes

Nanotubes and nanowires of II—VI semiconductor compounds such as CdS and CdSe have been obtained by a soft chemical route involving surfactant-assisted synthesis.28,75 For CdSe nanotubes, the metal oxide was reacted with the selenidizing reagent in the presence of a surfactant such as Triton 1G0X. Substantial amounts of nanotubes were obtained by this method (Fig. 25a and b). Annealing of the as-prepared nano-... 

In custom-designing materials with tailored properties, it is often necessary to s)m-thesize metastable phases that will be kinetically stable under the temperature and conditions of use. These phases are obtainable only through kinetic (chemical) control. In many cases, kinetic control has been achieved via the soft chemical low-temperature (e.g. electrochemical synthesis, sol-gel method) and/or topochemical routes (e.g. intercalation, ion exchange, dehydration reactions), since these routes use nuld synthetic conditions. It should be noted that not all soft chemical routes are topochemical. A reaction is said to be under topochemical control only if it follows the pathway of minimum atomic or molecular movement (Elizabe et al., 1997). Accordingly, topochemical reactions are those in which the lattice of the solid product shows one or a small number of... 

A soft chemical route, known as the sol-gel method, has also been employed for the preparation of nano-oxides with uniform size and shape. This is a multistep process, usually consisting of hydrolysis of a metal alkoxide in an alcoholic solution to yield a metal hydroxide, followed by polymerization by elimination of water (gel-formation), drying off the solvent, and densification of the product to yield an ultrafine powder (Rao and Raveau, 1998 Khaleel and Richards, 2001). 

There is a tremendous research interest in the area of nanotechnology to develop reliable processes for the synthesis of nanomaterials with definite size, shape, and chanical composition to control surface functional properties via soft chemical route. 

Microemulsions allow for the synthesis of nanoparticles of controlled particle size with a narrow size distribution, and are amicable to simple fimc-tionalization routes for decorating the resulting nanoparticle surfaces. Being a soft chemical method, these methods are well suited for encapsulating or... 

Metal-polymer nanocomposites can be obtained by two different approaches, namely, in situ and ex situ techniques. In the in situ methods, metal particles are generated inside a polymer matrix by decomposition (e.g., thermolysis, photolysis, radiolysis, etc.) or chemical reduction of a metallic precursor dissolved into the polymer. In the ex situ approach, nanoparticles are first produced by soft-chemistry routes and then dispersed into polymeric matrices. Usually, the preparative scheme allows us to obtain metal nanoparticles whose surface has been passivated by a monolayer of -alkanethiol molecules (i.e., Crfiin+i-SH). Surface passivation has a fundamental role since it avoids aggregation and surface oxidation/contamination phenomena. In addition, passivated metal particles are hydrophobic and therefore can be easily mixed with polymers. The ex-situ techniques for the synthesis of metal/polymer nanocomposites are frequently preferred to the in situ methods because of the high optical quality that can be achieved in the final product. 

It was pointed out earlier that soft-chemistry routes have been receiving considerable attention recently. It would be instructive to examine a few typical examples of soft-chemical methods of material synthesis (chimie douce). Marchand et al. [6] obtained a new form of TiO by the dehydration of H TiOg-xH O, which in turn was prepared by the exchange of K+with H-tin K Ti O. The mechanism of this transformation has been described recently by Fiest and Davis [7] and we show this schematically in Figure 2.2. Rebbah et al. [8] prepared Ti Nb O by the dehydration of HTiNbOj, the... 

Many of the chemical methods such as the sol-gel synthesis and intercalation are soft-chanicals routes. The synthesis of HAIO from a-LiAlO is an interesting... 

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