Nanocast materials

Lu, A. H. Schuth, F. 2006. Nanocasting A versatile strategy for creating nano-structured porous materials. Adv. Mater. 18 1793-1805. 

In either the transcriptive or synergistic strategy, removal of the organic template by extraction or calcination renders the inorganic mesoporous structure. For synthetic schemes that are not compatible with the formation of stable template assemblies, an alternative approach is to use a preformed, templated inorganic host, such as mesoporous silica, as a mold to nanocast the desired material as an inverse replica of the host, such as that seen in Figure 14. ... 

Nanocasting allows us to create mesoporous materials with new compositions, controllable structure, and specific functionality. Figure 8.44 illustrates the nanocasting pathway. For practical applications, the nanocasting pathway provides an opportunity to create the... 

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. 

Ordered mesoporous silica seems to be an ideal hard template, which can be used as a mold for other mesostructures with various compositions, such as ordered mesoporous carbon and metal oxides. Mesoporous silicas with various different structures are available, and silica is relatively easily dissolved in HF or NaOH. Alternatively, mesoporous carbons with a solid skeleton structure are also suitable choices as hard templates due to their excellent structural stability on thermal or hydrothermal and chemical treatment. A pronounced advantage of carbon is the fact that it is much easier to remove than silica by simple combustion. The nanocasting synthesis of mesoporous carbon by using mesoporous silica as template will be discussed in detail in the section on mesoporous carbon. In many cases, silica is unsuitable for synthesizing framework compositions other than carbon, since the leaching of the silica typically affects the material which is filled into the silica pore system. 

Zeolites were already employed as templates in the synthesis of microporous carbon with ordered structures.[247] The discovery of ordered mesoporous silica materials opened new opportunities in the synthesis of periodic carbon structures using the templating approach. By employing mesoporous silica structures as hard templates, ordered mesoporous carbon replicas have been synthesized from a nanocasting strategy. The synthesis is quite tedious and involves two main steps (i) Preparation and calcination of the silica mesophase, and (ii) filling the silica pore system by a carbon precursor, followed by the carbonization and selective removal of the silica framework. 

Recently carbon based mesoporous materials have been synthesized via a technique using the inorganic mesoporous framework as a template [40], The approach is designated nanocasting [17]. In fact, these materials were the first to illustrate the existence of the mesoporosity of SBA-15 materials [41],... 

Yang Z, Xia Y, Sun X and Mokaya R (2006), Preparation and hydrogen storage properties of zeolite-templated carbon materials nanocast via chemical vapor deposition effect of the zeolite template and nitrogen doping , J Phys Chem B, 110, 18424. 

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