Mesoporous materials synthesis strategies

Series of Special Issues cover various aspects of microporous molecular sieves, metal-organic frameworks and ordered mesoporous materials. Synthesis principles, templating, formation mechanisms, characterization methods, functionalization strategies, and applications are discussed in excellent and comprehensive review articles and more specific research reports. 

Ordered macroporous materials can be templated by colloidal crystals or emulsions. In comparison to microporous and mesoporous materials, the synthesis strategy of macroporous materials is relatively simple. 

It is important to emphasize that the situations described above are different synthesis strategies that expectedly lead to composite and porous materials that have distinctly different properties. In the preparation of mesoporous materials, procedural variables define a very complex system in which kinetic parameters (time, basic operations sequence) may play a determinant role. 

The present book consists of nine chapters, with the synthetic and structural chemistry of microporous and mesoporous materials as the core. Five chapters (Chapters 3, 4, 5, 6, and 8) are allocated to cover the synthetic aspects of the topic. Chapter 3 introduces the synthesis and related fundamental principles, synthetic strategies, and techniques for the major microporous materials such as zeolites and microporous aluminophosphates. This Chapter serves as Part I of the synthetic aspects of the microporous compounds. 

This paper describes a new synthesis strategy of preparing thermally stable mesostructured transition metal oxides, namely, two-step synthesis (TSS). Basically, the synthesis course involves two steps (1) formation of a mesostructured transition metal oxide solid mediated by surfactant in a basic aqueous solution and (2) treatment of the solid product in an acidic organic solvent containing the respective precursor from which the solid product was produced. The final material synthesized according to such a method is thermally stable and structurally mesoporous with high surface area and uniform pores arranged disorderedly. 

The morphology of ordered mesostructured carbons is another important factor with respect to their practical applications. Various macroscopic morphologies are required, for example, films (in sensor, separation and optical applications), uniformly sized spheres (in chromatography) or transparent monoliths. Using suitable synthesis strategies, it is possible to control the external shape of the templated mesoporous carbon materials to generate powders, films and membranes, spheres, hollow spheres, rods, fibres, nanowires, nanotubes and monoliths. 

Ozin and coworkers recently extended the supra-molecular I S+ assembly into the synthesis of binary mesoporous yttrium oxide-stabilized-zirconium oxide materials.These materials were synthesized by a modified sol-gel method under basic conditions, where zirconium ethoxide and yttrium acetate were used as the precursors for the transition metal oxides, and CTAB was used to form the supramolecular templates. The use of ethylene glycol with coordinating capability as a cosolvent may play a role in controlling the hydrolysis rate and solubility of zirconium(IV) and yttrium(III). This synthesis strategy is similar to that of so-called polymerizable-complex method, which was widely used to prepare multicomponent single-phase oxides. The yttrium content in these binary materials can be tuned from 12-56 wt%, and no phase segregation of yttrium and zirconium oxides was observed. These materials could be applied in designing new solid oxide fuel-cell electrode materials. 

Another possible approach to model mesoporous materials is to mimic the synthesis process of the real material. This strategy has been used by Gelb and Gubbins [62] to develop realistic models for Vycor and controlled pore glasses. The input of such an approach is the representation of the templating surfactants using simplified potentials to describe the interactions involved in the system. Siperstein et al. [63]... 

Pal, N., and Bhaumik, A. (2013) Soft templating strategies for the synthesis of mesoporous materials inorganic, organic-inorganic hybrid and purely organic solids. Adv. Colloid Interface Set, 189-190,21-41. 

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