Templating methods, chemical approaches

Over the past few years, a large number of experimental approaches have been successfully used as routes to synthesize nanorods or nanowires based on titania, such as combining sol-gel processing with electrophoretic deposition,152 spin-on process,153 sol-gel template method,154-157 metalorganic chemical vapor deposition,158-159 anodic oxidative hydrolysis,160 sonochemical synthesis,161 inverse microemulsion method,162 molten salt-assisted and pyrolysis routes163 and hydrothermal synthesis.163-171 We will discuss more in detail the latter preparation, because the advantage of this technique is that nanorods can be obtained in relatively large amounts. 

The imprinting of polymer supports is an exciting development in the immobilization of transition metal complexes. The process involves the copolymerization of an inorganic or an organic template into a crosslinked polymer network. In a subsequent step, the template is chemically removed leaving an imprint of molecular dimensions in the resin. Ideally, the imprint retains chemical information related to the size and shape of the template. This approach has been used to prepare chiral imprints in otherwise achiral polymer networks. The method is outlined in Scheme... 

As mentioned above, metal/CPs with core-sheath structure can be prepared by the template method. However, the approach based on the template technique is complicated and non-economical because of the need to remove the templates. In fact, metal/CPs with core-sheath structure can be fabricated via a one-step chemical polymerization [83-87]. Niu and co-workers demonstrated that Au/PANI coaxial nanocables could also be fabricated by the redox reaction between chloroauric acid and aniline in the presence of d-CSA [85]. In that case, CSA acted not only as a dopant, but also as a surfactant or a soft template. In addition to Ag/PPy and Au/PANI nanocables, cable-like Au/poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures have been synthesized in the absence of any surfactant or stabilizer through one-step interfadal polymerization of EDOT dissolved in dichloromethane solvent and HAuCl dissolved in water [86]. Microscopy studies showed (Figure 13.6) that the outer and inner diameters of Au/PEDOT nanocables were aroimd 50 and 30 nm, respectively. 

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

---