Hard template method materials

Ordered Mesoporous Carbons The first ordered mesoporous carbons were synthesized by hard templating methods (141). The use of porous inorganic silica templates allowed the preparation of series of ordered mesoporous carbon materials, designated as CMK-x materials (carbon molecular sieves Korean Advanced Institute of Science and Technology). The hrst one, CMK-1, was prepared using MCM-48 as a template and sucrose as the carbon source impregnated in the... 

The other method for preparing ordered mesoporous materials is the so-called hard template method using hard mesoporous silica or replicated carbon templates. The metal precursors are filled into hard templates. In this method, heat treatment can be performed at a higher temperature without structural collapse and highly crystallised materials can be obtainedl ° ] (Figure 3.6). 

A limitation of the hard template method is that the resulting materials must be stable in HF or NaOH solution and that the precursors must not react with the silica template at a high temperature. For example, in the formation of lithium containing transition metal oxides, it is necessary to first form the transition metal oxide as a mesoporous solid to prevent reaction of the alkali metal Li with the silica template and then to react the mesoporous transition metal solid with a lithium source, such as LiOH. 

Mesoporous crystalline M0O3 and WO3 were obtained in thin films. Ordered mesoporous WO3 was first produced using the soft template method. By changing formation conditions, cubic and hexagonal mesoporous structures were obtained. The hard template method using SBA-15 or KIT-6 produced ordered mesoporous crystalline WO3 materials. With SBA-15 as a template, a porous single crystal was formed, while polycrystalline porous WO3 materials were formed with a KrT-6 template,although reaction conditions were similar. 

Figure 4.1 Schematic illustration of hard template method for the preparation of porous carhon materials from porous inorganic templates. Reprinted with permission from T. Kyotani, Bull. Chem. Soc. Jpn., 79, 1322. Copyright (2006) The Chemical Society of Japan...

Soft-template technique offers advantage of scalability [39]. In hard-template method, a porous membrane of inorganic or polymeric material serves as a rigid mold for chemical or electrochemical replication of stracture. This method provides an easy marmer for production of 1-D nanostractures, but with difficulties of scale up. Hard templates such as silica or carbon spheres are also ideal for synthesis of hollow strac-tures (11 Chen et al. 2003). Classical examples where the template enables the control of morphology of a-Fe Oj nanoparticles can be found in literature (Table 1). 

This is a powerful and controllable method to synthesize the nanostructure materials of inorganic semiconductors, metals, and polymers. In the hard template method, the growth of the nanostructures takes place within the pores or channel of template membrane by polymerization and then the template is removed after the polymerization. The porous membrane is the basic and most important part of the hard template method. Porous membrane such as polycarbonate and alumina can be used as the hard template to produce conducting polymer nanotubes and nanowires as shown in Fig. 9. 

The use of polystyrene-based materials has also been investigated for porous carbon formation with the hard template method using amorphous silica gel, mesoporous alumina, and microporous zeolites as inorganic templates [90]. 

Organic nano-objects such as rods, tubes, and wires have been widely applied in many fields [154—159]. One of the most commonly used methods for fabrication of organic nanostmctures is the hard-template method using AAO templates [160-163]. Porous AAO templates can be prepared by conventional two-step anodization [164, 165], yielding pores of defined size that can be used as shape-defined molds for infiltration of organic materials. The infiltration of desired monomers or... 

Besides cooperative pathways, also tme liquid crystal templating (TLCT) and the hard template route (Section 9.3.7) have been developed for the synthesis of ordered mesoporous materials. In the case of the TLCT, a preformed surfactant liquid crystalline mesophase is loaded with the precursor for the inorganic materials (140). The nanocasting route, on the other hand, is a clearly distinct method (141). Here, no soft surfactant template is used but, instead, the pore system of an ordered mesoporous solid is used as the hard template serving as a mold for preparing varieties of new mesostructured materials, for example, metals, carbons, or transition metal oxides. 

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