Precursors templating techniques

By applying the template technique, Kyotani et al. and Che et al. succeeded in preparing Pt and Pt/Ru metal-filled uniform carbon nanotubes in which the metal is present as either nanorods or nanoparticles. It should be noted that no metal was observed on the outside wall of the tubes. This is due to the preparation procedure, in which the metal precursor was loaded into the carbon-deposited alumina film before the dissolution of alumina by HF (see Fig. 10.1.9). Thus, there is no other space for metal to be loaded except in the channels. 

More effective nanoporous carbons have been obtained by the template technique. A nitrogenated precursor is introduced in a nanoporous scaffold and subsequently pyrolyzed then the nitrogen-enriched replica is obtained by etching the host with hydrofluoric acid. The first materials of this... 

We will not discuss here models for pores in carbons, as this topic is treated in Chapter 5, and elsewhere in specialist [15] or general reviews [106, 107]. For similar reasons, we will not discuss porosity control [44, 108] in detail. However, porous carbons prepared by the template technique, especially the ordered ones, deserve special attention. Ordered mesoporous carbons have been known to scientists since 1989 when two Korean groups independendy reported their synthesis using mesoporous silicas as templates [109, 110]. Further achievements have been described in more recent reports [111, 112]. One might have expected that the nanotexture of these materials would merely reflect the nature of the precursor used, namely phenol-formaldehyde [109] or sucrose [110] in the two first ordered mesoporous carbon syntheses (as is well known, these two precursors would have yielded randomly oriented, isotropic carbon had they been pyrolyzed/activated under more conventional conditions). However, the mesopore walls in some ordered mesoporous carbons exhibited a graphite-like, polyaromatic character [113, 114], as described in Chapter 18. This information was obtained by nitrogen adsorption at low relative pressures, as in classical... 

As an alternative to the two-step approach, mesoporous silica with organic moieties covalently linked to their internal surface could be obtained in a single-step cocondensation of siloxane and organosiloxane precursors using similar supramolecular templating techniques as those for the synthesis of pure silica. Successful one-step syntheses of MCM-41 silicas modified with alkyl, phenyl, vinyl. cyanoethyL amine, thiol, and propylsulfonic acid moieties were reported in the literature.Similar preparations were extended to MCM-48 silica and to meso-... 

Surface/Template Derivatized method Template techniques are common to some of the previous mentioned methods and use two types of equipments hard-templates (porous solids as carbon or silica) and soft-templates (surfactants). Surface-mediated and template-nanoparticles precursors have been used to synthesize self-assembled systems [47]. 

Ordered nanostructured materials were prepare by the template technique. This method consists of a thermal decomposition of the sol—gel precursor within the pores of a membrane. The template is dipped into the sol for 10 min and taken out for heating at r>400 °C resulting in the formatimi of nanomaterial within the template pores. Different types of template have been widely investigated such as anodic alununum oxides (AAO), porous polymer and nano-channel glass templates. The final nano-specimens are obtained by dissolutimi the template composites in 6 mol NaOH solutimi. The template method with porous membranes of AAO has... 

Abstract A review of the thermolytic molecular precursor (TMP) method for the generation of multi-component oxide materials is presented. Various adaptations of the TMP method that allow for the preparation of a wide range of materials are described. Further, the generation of isolated catalytic centers (via grafting techniques) and mesoporous materials (via use of organic templates) is simimarized. The implications for syntheses of new catalysts, catalyst supports, nanoparticles, mesoporous oxides, and other novel materials are discussed. 

As described in this chapter, the sonochemical reduction technique appears to be a promising method for the preparation of various types of metal nanoparticles in an aqueous solution. By choosing more efficient organic additives, easily-reducible metal precursors, supports and templates with an appropriate role, more advanced functional nanoparticles could be synthesized successfully using the sonochemical reduction technique. In future, it is also possible to develop effective synthetic methods by combining the sonochemical method with other chemical methods. 

The variety of finely divided silica known as hexagonal mesoporous silica (HMS) [6,34] is generally prepared by the copolymerization of a silica precursor such as tetraethylorthosilicate (TEOS), in presence of a suitable template. This acid or base catalyzed reaction follows the sol-gel route and it has been found [28] that during silica preparation by this technique, it is also possible to add an organotriethoxysilane [RSi(OEt)3] that would... 

Using the template mediation technique, mixed hexakisadducts with different types of addends are also easily available [26]. Here the precursor is not but a adduct with an incomplete octahedral addition pattern. The possible structures of mixed hexakisadducts with two different addends in octahedral positions are depicted in Figure 10.12. 

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