Nanostructured hard-template method

The disadvantages of the nanoporous hard-template method are the generally tedious post-synthetic processes, which are required in order to remove the templates, and the destruction of nanostructures during die post-synthetic process, i.e. the formation of undesirable aggregated structures after removal of the templates. 

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. 

Djinovic P, Batista J, Pintar A (2009) WGS reaction over nanostructured CuO-Ce02 catalysts prepared by hard template method characterization, activity and deactivation. Catal Today 147S S191-197... 

Hard template method has been used for the 1-D nanostructures such as nanotubes, nanorods and nanofibers of conducting polymers. The commonly used templates are AAO membrane, and track-etched PC membrane, whose pore size ranges from 10 nm to 100 pm. Hard template methods for synthesizing conducting polymer nanomaterials have been extensively reviewed in recent years [156-160]. 

Martin [21] proposed a mechanism for the growth of the nanostructures prepared by the hard-template method. However, the mechanism is insufficient in explaining the growth of partially filled nanotubes by an electrochemical template synthesis [36]. Recently, Lee and coworkers [37] investigated the electrochemical... 

A number of methods, such as hard and soft template as well as physical methodologies have been used to synthesize conducting polymer nanostructures. In the hard template method, a template membrane is usually required to guide the growth of... 

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. 

Though the hard template method is most efiftcient approach for preparing well controlled and highly oriented nanostructures of conducting polymers, the removal of template is very difficult [18]. 

Synthesis of ordered nanostructured Cu0-Ce02 catalysts by hard template method... 

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. 

P. Djinovic, J. Batista, J. Levee, A. Pintar, Comparison of water-gas shift reaction activity and long-term stabihty of nanostructured CuO-Ce02 catalysts prepared by hard template and coprecipitation methods, Appl. Catal. A Gen. 364 (2009) 156—165. 

Figure 17.2 Schematic illustration of common methods, such as hard-template, and soft-template methods as well as electrospinning technology, for the preparation of conducting polymer nanostructures.

A quite widely used method for the achievement of nanostructured polymers deals with the assistance of templates. Direct templating is particularly suited for getting mesostructures of organic and soft materials such as polymers that, in general, can be easily replicated by adopting hard templates which allow a great synthetic flexibility. 

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. 

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