Soft template synthesis

Soft templates, usually molecules and molecular associations such as amines, thermolabile organic polymers, and surfactants, can be removed by heat treatment. In addition, vesicles, ionic liquids, self-assembled colloidal crystals, and air bubbles have been used for soft templating synthesis. 

Soft-Template Synthesis Strategy for Ordered Mesoporous Carbons... 

Zhao and co-workers have made major advances in the soft-template synthesis of mesoporous carbons. They reported the self-assembly of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) and resol mixtures and successful removal of the templates including F127, F108 and P123 at a series of temperatures to produce mesoporous polymer and carbon materials. " ° Eigure 4.10 illustrates the five-step synthesis procedure reported by Meng et Low-... 

Mikhailov, O. V. Soft template synthesis of Fe(II,III), Co(II,III), Ni(II) and Cu(II) metalmacro-cyclic compounds into gelatin-immobilized matrix implants. Rev. Inorg. Chem., 30(4), 199273 (2010). 

Recently, a facile soft template synthesis was developed for fabricating PPy nanotubes against the hard template synthesis [153,249]. PPy nanotubes could be readily produced through a cylindrical micelle templating in re-... 

FIGURE 7 Schematic of the mechanism of the soft-template synthesis of different conducting polymer nanostructures. 

Schematic of the mechanism of the soft-template synthesis of different conducting polymer nanostructures (a) micelles acted as soft-templates in the formation of nanotubes. Micelles were formed by the self-assembly of dopants, and the polymerization were carried out on the surface of the micelles (b) nanowites formed by the protection of dopants. The polymerization were carried out inside the micelles (c) monomer droplets acted as soft-templates in the formation of microsphere and (d) polymerization on the substrate producing aligned nanowire arrays. Nanowires were protected by the dopants, and polymerization preferred to cany out on the tips of nanowires.

Figure 2.15 General concept of the syntheses of mesoporous materials (a) mesoporous silica synthesis with soft template (b) mesoporous carbon synthesis with hard template.

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. 

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. 

The templates used in the synthesis of mesostructured and mesoporous materials can be classified into two categories The first class of templates includes soft templates, which are ordered arrays of self-assembled surfactant micelles, similar to the ones used by the researchers at Mobil. Alternately, mesoporous materials can themselves be used as templates to synthesize new mesostructured materials, and such templates can be termed as rigid templates. In the following sections, we focus on the use of supramolecular assemblies of surfactants as well as on the use of rigid templates as the templates for the synthesis of mesostructured materials. 

In the Pt-doped hexagonal mesophase formed from CPCI (cetyl pyridinium chloride), platinum ions are adsorbed at the surface of the surfactant cylinders. They are reduced radiolytically into a metal layer as a nanotube of around 10 nm diameter and a few hundred nm long (Fig. 3f). Extraction of all these nanostructures is achieved by dissolution of the soft template using alcohol. This possible easy extraction constitutes a marked advantage over the synthesis in hard templates, such as mesoporous silica or carbon nanotubes, the dissolution of which is more hazardous for the metal nanostructures. 

Although traditional synthetic methods can be used for preparing a variety of porous materials, the development of template synthesis strategies has prompted an explosive-like growth of synthetic methods. Template synthesis roughly involves the use of a structure-directing reagent that facilitates the porous material to adopt the desired structure, followed by the template release. Three main types of templates, soft, hard, and complex, can be used (Zhao, 2006). 

PbS hollow nanospheres with diameters of 80-250 nm have been synthesized by a surfactant-assisted sonochemical route from Pb(CH3COO)2, thioacetamide, and sodium dodecylbenzenesulfonate [3]. 200-400 nm hollow silica spheres with mesoporous walls were prepared by the application of ultrasound to a mixture of nonionic polyoxyethylene surfactant and tetraethylorthosilicate. The presence of surface-active agents during ultrasonic synthesis was proved to be effective because surfactants can act as soft templates as well as structure directing agents for the assembly and subsequent... 

Successful nanocrystals synthesis has also been carried out employing soft templates such as the water pool in a reverse micelle, the interface of two... 

Several reviews covering the synthesis, properties and applications of porous carbons, especially mesoporous carbon materials, can be found in the literature. In this chapter, we summarise the recent developments in the synthesis and characterisation of templated porous carbon materials. Particular attention is paid to the synthesis of structurally ordered porous carbon materials with narrow pore size distribution via both hard and soft template methods. We especially emphasise those so-called breakthroughs in the preparation of porous carbon materials. The chapter is divided into three sections according to the pore size of carbon materials we first consider the synthesis of microporous carbon materials using zeolites and clays as hard template, then summarise the preparation of mesoporous carbon materials via both hard template and self-assembly... 

The pore size of mesoporous carbon is of importance with respect to practical applications. When mesoporous carbon is synthesised via soft-template methods, the self-assembly of organic-organic species and pore size can be influenced by synthesis conditions, including surfactant type and concentration, and synthesis temperature. For example, Meng et al. observed that the pore size of mesoporous carbon derived from soft-templated mesoporous polymer composites decreased from 7.4 to 5.9 nm when the pyrolysis temperature increased from 400 to 800 How-... 

In the case of soft-template self-assembly synthesis, mesostructure assembly and morphology growth can be controlled concurrently. Due to the versatility of the solvent-based soft-template self-assembly process, highly ordered mesoporous carbons can be produced relatively easily with different morphologies such as thin film and membrane, " monolith,fibre,sphere, rod, single-crystal, " and discus-like crystal. Initially, mesoporous carbons synthesised with soft templates were exclusively in the form of films. " ... 

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