Porous solids template synthesis

The variety of porous solid materials that can be used as templates for nanostructure synthesis has been reviewed by Ozin (1992). In the template-assisted synthesis of nanowires, the pores or voids of the template are filled with the chosen material using a number of approaches. Nanowires have been derived via pressure injection, electrochemical deposition, and vapor deposition, as described in the following sections. 

Curved structures are not only limited to carbon and the dichalcogenides of Mo and W. Perhaps the most well-known example of a tube-like structure with diameters in the nm range is formed by the asbestos mineral (chrysotil) whose fibrous characteristics are determined by the tubular structure of the fused tetrahedral and octahedral layers. The synthesis of meso-porous silica with well-defined pores in the 2-20 nm range was reported by Beck and Kresge.6 The synthetic strategy involved the self-assembly of liquid crystalline templates. The pore size in zeolitic and other inorganic porous solids is varied by a suitable choice of the template. However, in contrast to the synthesis of porous compounds, the synthesis of nanotubes is somewhat more difficult. 

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 methods of soft chemistry include sol-gel, electrochemical, hydrothermal, intercalation and ion-exchange processes. Many of these methods are employed routinely for the synthesis of ceramic materials. - There have been recent reviews of the electrochemical methods, intercalation reactions, and the sol-gel technique. The sol-gel method has been particularly effective with wide-ranging applications in ceramics, catalysts, porous solids and composites and has given rise to fine precursor chemistry. Hydrothennal synthesis has been employed for the synthesis of oxidic materials under mild conditions and most of the porous solids and open-framework structures using organic templates are prepared hydro-thermally. The advent of supramolecular chemistry has started to make an impact on synthesis, mesoporous solids being well known examples. ... 

Hentze, H.P. Antonietti, M. Template synthesis of porous organic polymers. Cun Opin. Solid State Mater. Sci. 2001. 5. 343. 

Researchers have devised a synthesis strategy that entails the use of a sacrificial porous solid support on which the template is immobilized. An example that demonstrates the feasibility of this approach is represented in Fig. 12 [42]. Presently, this new concept is explored further and the imprinting of other immobilized templates has been published [43]. 

H.-P. Hentze, M. Antonietti, Template synthesis of porous organic polymers. Current Opinion in Solid State and Materials Science 5 (2001) 343-353. 

Template Molecule or siufactant that dictate the morphology of the resultant material, often by moderating growth. For instance a DNA molecule can serves as a pattern for the synthesis of another macromolecule such as RNA. Also any porous solid such as a porous polymer that serves as a pattern to the synthesis of another or porous solid of a different... 

Synthetic pathways to porous solids are manifold and often depend strongly on the targeted product. The early synthesis of porous solids was considered an art rather than science. A scientific approach to the synthesis of porous materials began in the first half of the 20th century [9], when the synthesis of materials such as activated carbons and silica gels was studied more systematically. Nowadays, one relies on scientific manipulation of preparation parameters and design principles, by which adjustment of the chemical and physical properties of the materials is possible. A notable example is the so-called template synthesis [9-11]. 

Controlled electrochemical synthesis of conductive polymer nanotubes in a porous alumina template has been studied as a function of monomer concentration and potential in the case of PEDOT the electropolymerization leads either to solid nanowires or to hollow nanotubes depending on the template pore diameter, the applied oxidation potential and the monomer concentration [265], Nanowires are formed at slow reaction rate and high concentration monomer supply in fact monomeric molecules should have enough time to diffuse into and fill the pores, from the bulk solution. On the other hand, nanotubes are predominantly formed with fast reaction rate and low monomer concentration, because the monomers that diffuse from the bulk solution can be deposited along the pore wall thanks to the interaction of the polymer with the wall surface. 

Ch, Kaiser, G, Buechel, S, Luedtke, I. Lauer, and K.K. Unger Processing of microp-orous/mesoporous submicron-size silica spheres by means of a template-supported synthesis, Characterization of Porous Solids IV(B. Me Enaney, T.J. Mays, J. Rouquerol, F. Rogriguez-Reinoso, K,S,W, Sing, K.K. Unger, eds The Royal Society of Chemistry, London (1997)... 

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