Chemical hard-template method

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...

Nanoporous Hard-Template Methods PANI-NTs have been prepared by the chemical oxidative polymerization of aniline within the pores of PC nanoporous membranes... 

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). 

Fig. 4 Illustration of hard template method for porous carbon production. Modified and adapted with permission from [86] Copyright 2011 American Chemical Society...

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. 

Chemical Oxidative Polymerization of Aniline Hard (Physical) Template Methods... 

Template-free techniques have been extensively studied for the fabrication of conducting polymer nanomaterials fabrication. Compared with hard and soft template methods, these methodologies provide a facile and practical route to produce pure, uniform, and high quality nanofibers. Template-free methods encompass various methods such as electrochemical synthesis, chemical polymerization, aqueous/organic interfacial polymerization, radi-olytic synthesis, and dispersion polymerization. 

The conventional chemical polymerization of polyaniline only produces nonfibrous or irregular shaped morphologies [237,238], In the past several years, a variety of chemical methods were reported that yield polyaniline nanofibers, such as use of hard templates [239,240], soft templates [241], electrospinning [242], interfacial polymerization [237], and seeding polymerization [238]. Recently, Chiou and Epstein discovered that polyaniline nanofibers can be directly synthesized in dilute chemical polymerization... 

Conductive polymeric nanostructures can be prepared by using hard or soft templates or with template-free methods. The template method has been extensively used because of its simplicity, versatility and controllability. Some further features on this topic are reported in Section 1.3. A typical hard template material can be a thin porous film of aluminum oxide or polycarbonate and polymeric materials ean be deposited into the pores to form nanotubes or nanowires. The electrochemical template method enables a better control of the dimensions compared with the chemical methods. In addition, the nanostructures produced by the electrochemical method are in solid contact with a base electrode that is beneficial for further processing steps when building an electrochemical device. 

Depending on the desired materials properties and structure, these approaches have been explored for sol-gel processing of alkoxide-based precursors and further developed in combination with many experimental parameters that can also be adjusted to control the sol composition and particle size, including alkoxide/ water ratio, concentration of the precursors, reaction temperature, reaction time, drying methods, choice and concentration of the catalyst, and the solvent used [42]. Besides the well-known hydrolytic sol-gel processes, even nonhydro-lytic approaches have been reported as a powerful method in the synthesis of mixed oxide materials and will be discussed in more detail subsequently [43]. Another processing option to tailor the material properties is the application of soft or hard templates [44]. In addition to the chemical parameters, drying and thermal treatments or firing processes determine the final architecture, chemical... 

Recently, attention has been paid to porous carbon materials, owing to their large surface area, large pore volume, chemical inertness, and electrical conducting properties. Porous carbon materials with controlled architecture, morphology, and relatively narrow pore size distribution are usually prepared by a templating (hard or soft) method followed by carbonization processes. The main synthetic way to produce ordered mesoporous carbons relies on the use of ordered mesoporous silica with interconnected pore structures as a hard template. This synthetic route (see Fig. 16.6 for the hard template route) requires (1) preparation of... 

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