Porous inorganic solids, templated

A typical infrared spectrum is collected between 400 and 4000cm , which enables most of the fundamental bands from the framework and hydroxyls to be measured. Some spectrometers permit measurement in the near IR (up to 7000cm ), so that overtones and eombination bands (much weaker than the fundamental resonances) ean also be measured. For porous inorganic solids empty of adsorbed speeies, fundamental hydroxyl stretches are observed in the range 3200-3800 cm and framework vibrations are observed in the range 400-1200 cm Organic species present (such as templates or the organic parts... 

Two kinds of template, viz. hard template and soft template, are usually available for nanocasting processes. The true liquid crystal templating synthesis can be considered a soft-template process. In general, the hard template means an inorganic solid. For example, mesoporous silica as a template to replicate other materials, such as carbon or metal oxides, by which the pore structure of the parent can be transferred to the generated porous materials. A 3-D pore network in the template is necessary to create a stable replica. Mesoporous silica and carbon are commonly used templates for nanocasting synthesis. 

Curved structures are not only limited to carbon and the dichalcogenides of Mo and W. Perhaps the most well-known example of a tube-like structure with diameters in the nm range is formed by the asbestos mineral (chrysotil) whose fibrous characteristics are determined by the tubular structure of the fused tetrahedral and octahedral layers. The synthesis of meso-porous silica with well-defined pores in the 2-20 nm range was reported by Beck and Kresge.6 The synthetic strategy involved the self-assembly of liquid crystalline templates. The pore size in zeolitic and other inorganic porous solids is varied by a suitable choice of the template. However, in contrast to the synthesis of porous compounds, the synthesis of nanotubes is somewhat more difficult. 

The fluoride route of synthesis seems very rich and already provided four among the six most open frameworks described up to now in the litterature in the category of microporous compounds (0 < A) VSB-1 [22] cloverite [11], ULM-5 [23] and ULM-16 [24] with tunnels limited by 24, 20,16 and 16 polyhedra respectively. These four solids are really porous, the porosity being generated by the elimination of the template either by thermal or chemical methods which preserve the inorganic framework. 

The methods of preparing inorganic membranes with tortuous pores vary enormously. Some use rigid dense solids as the templates for creating porous structures while many others involve the deposition of one or more layers of smaller pores on a premanufactured microporous support with larger pores. Since ceramic membranes have been studied, produced and commercialized more extensively than any other inorganic membrane materials, more references will be made to the ceramic systems. 

The so-called template-based technique has been found to be particularly suitable for the synthesis of carbons whose porosity is not only uniform in size and shape, but also periodically ordered in some cases. In this approach, the porous carbon is prepared through infiltration of an organic precursor into the nanochannels of an appropriate inorganic material (the template), followed by carbonization and then liberation of the resultant carbon from the template. Different nanospaces in templates have been used to confine the carbon precursors. The first templates used included, e.g., silica gel or porous glass [84,85], layered clays such as montmorillonite ortaeniolite [86,87], or pillared clays [88-90]. Several detailed reviews on this topic have been published [75,91-95] that cover the areas of microporous and, especially, mesoporous solids. Here, some illustrative examples will he presented in some detail rather than reviewing systematically the literature. 

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