Hard-template approach

XRD patterns of Left - (a) MCM-41 (b) Silica-carbon composite (c) NCCR-41. Right - (a) CMK-3 (b) Silica-carbon composite (c) SBA-15. 

NCCR-56 IITM-56 sucrose 5.1 2.40 1367 2.7 Selvam et al. (2010b 2010c) 

FDU-16 F108/F127 Phenol/ formaldehyde lesin 11.6 0.50 1030 3.2 Zhang et al. (2006) 

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For the oxides that cannot he synthesized by the surfactant self-assembly, the hard-templating approach is a good choice. The key point for the nanocasting method is to increase the loading level of the precursors in the mesopore channels of the templates. Evidently, improving the interactions between template and precursor and between precursors themselves are essential in the hard-templating approach [11]. 

Chiral nematic mesoporous films of Eu " doped Zr02 have been produced via a hard-templating approach using nanoctystalline cellulose-templated silica (Fig. 11). It was found that these chiral nematic nanostructures are capable of modulating the spontaneous emission of the Eu ions. The emission lines of the Eu " at 596 nm, 613 and 625 nm were significantly suppressed, and an increase in the luminescence lifetime is observed. It was suggested that these new chiral luminescent nanomaterials could find potential applications in sensing and new optical nanodevices. 

Fig. 11 A schematic diagram of the fabrication of EDCNMZ-n by a hard-templating approach. Calcination was conducted at 600 °C for 6 h. Reproduced from ref. 87 with permission from the Royal Society of Chemistry.

As a rather unusual application of 1,2,4-triazine, it is necessary to mention the preparation of highly ordered and graphitic mesoporous carbon nitride with an ordered porous structure and a high nitrogen content by a nano-hard-templating approach through a simple polymerization of 3-amino-l,2,4-triazine inside the pore channels of a mesoporous silica template (13JMCA2913). 

The chemical methods for the preparation of nanomaterial could be categorized as either template-directed or template-free. The template synthesis methods commonly used for the production of one-dimensional nanostructured PANI are further subdivided into hard template (physical template) synthesis and soft template (chemical template) synthesis approach according to the solubility of the templates in the reaction media. Non-template routes for the synthesis of one-dimensional nanostructured PANI such as rapid-mixing reaction method, radiolytic synthesis, interfacial polymerization, and sonochemical synthesis have also been reported [56], Other approaches like combined soft and hard template synthesis are also known. An overview of hard-template, soft-template, and template-free procedures are presented in the following paragraphs. 

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. 

In summary, highly cubic ordered cobalt oxides with crystalline walls have been synthesized by an accurately controlled incipient wetness approach using mesoporous silica as hard template and cobalt nitrate as the precursors. Compared with the previously reported solution impregnation processes, this technique is facile, time-saving and economical. This technique can be used to synthesize ordered mesoporous metal oxides, and we expect that rvith this approach various kinds of mesoporous oxides or other materials can be synthesized, which may benefits their applications in many areas such as in catalysis, sensors, clean energy and electronics. 

Dopant-Free Template-Free Method PANI-NTs have been prepared by the oxidative polymerization of anihne with APS in water without added acid (Figure 2.18) [199,350,380,381]. This is a facile and efficient approach to synthesize PANI-NTs because it not only omits hard templates and post-treatment template removal, but also simplifies reagents. A modification of the dopant-free template-free method of PANI-NTs synthesis... 

Hard-tcmplatc synthesis can provide micro- and nanocontainers with a controlled geometric shape. However, this approach requires complicated synthetic steps, including the dissolution of the template in corrosive media. Collapse of the hollow structure after template removal is also a critical problem. Therefore, the potential drawback of using hard templates forced scientists to search for more efficient and facile routes to prepare CPCs. Among these newly developed approaches, the soft-template method is considered a powerful tool as an alternative strategy to hard-template synthesis. 

However, each currently developed method has its own disadvantages. Hard-template methods, for instance, are a universal and controlled approach to obtaining conducting-polymer nanostructures, but the requirement of a template and the post-treatment for template removal not only results in a complex preparation process, but can also destroy the formed structures. Moreover, the size and morphology of available templates is limited. The soft-template method is another relatively simple, cheap, and powerfid approach to obtain CPCs via a self-assembly process. However, the morphology and size control of the self-assembled nanostructures obtained is poor. Therefore, finding a facile, efficient, and controlled route to prepare CPs nanostructures is desirable. 

Hard Templating by Carbon Materials The work on carbon templating by Jacobsen and coworkers [156] has stimulated dramatic growth in the synthesis of mesoporous/hierarchical zeolites. This approach uses an excess of zeolite gel inside an inert, mesoporous carbon matrix, wherein the zeohte grows over and... 

A complementary approach to the fabrication of nanotubes involves the use of hard templates as tools. Hard templates are either nanofibers or porous host materials. In the former case, the nanofibers are at first coated with the waU material of the tubes or a corresponding precursor. Subsequently, the template fiber, that is, the core of the hybrid fiber thus obtained, is selectively removed so that a shell of the material initially deposited onto the template nanofiber is conserved. Template fibers can, for example, be produced in high... 

Only few attempts have been made to rationally design the mesoscopic fine structure of nanotubes fabricated by wetting nanoporous hard templates with polymeric solutions. Chen et al. infiltrated solutions of PS-fo-PAN in DMF into AAO. As described above, the PAN was at first crosslinked and then carbonized. However, the PS domains were converted into holes, and porous amorphous carbon nanotubes could be fabricated [89]. hi a similar approach, Rodriguez et al. used a solution of PS-fo-PVP and carbohydrates associated with the PVP blocks via hydrogen bonds in DMF into AAO and obtained mesoporous amorphous carbon nanotubes with the positions of the mesopores determined by the positions of the PS domains. Solvent annealing of the BCP/hydrocarbon films in DMF/benzene vapor led to a significantly... 

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