Nanocomposite materials pore size

The sol-gel method has been extensively used for the preparation of n-metal oxides and organic compounds. The important examples are n-NiO, n-Mn02, n-W03 and n-Fe203 etc. which have homogeneous particles, pore sizes and densities. This method affords easy control over the stoichiometry and homogeneity which is not possible with conventional methods. Further, the materials with special shapes monoliths, fibers, films and powders of uniform and very small particle sizes can also be prepared. The most important attribute of NMs prepared by this method is that they also contain pores of similar dimensions. These pores may be filled with another phase to form a nanocomposite which has proved to be of significant use to the HEMs community [98]. 

In 1992, researchers of the Mobil Oil Company introduced a new concept in the synthesis of mesoporous materials. They used supramolecular arrays of surfactant molecules as templating agents in order to obtain mesostructured silicates or alumosilicates which retain after calcination an ordered arrangement of pores with diameters between 2 and 10 nm and a narrow pore size distribution comparable to that of zeolites. These materials called M41S phases give access to the regime of the mesopores which is very interesting for different kinds of new size selective applications, e.g., molecular sieves, catalysis and nanocomposites [1]. 

Sol-gel-derived materials are popular for developing sensors.16 40"13 The physicochemical properties within these sol-gel-derived nanocomposites is an important factor in designing platforms for sensing applications.18 20 22 44-53 Factors such as polarity, microviscosity, pore size, pore wall chemistry, microscopic phase separation, partition coefficient, and solubility coefficient can dramatically alter the behavior of active dopants within a nanocomposite and may lead to undesirable properties. 

Microporous materials with regular pore architectures comprise wonderfully complex structures and compositions.[1,2] Their fascinating properties, such as ion-exchange, separation, catalysis, and their roles as hosts in nanocomposite materials, are essentially determined by their unique structural characters, such as the size of the pore window, the accessible void space, the dimensionality of the channel system, and the numbers and sites of cations, etc. 

Microporous materials with regular pore architectures comprise wonderfully complex structures and compositions. Their fascinating properties, such as ion-exchange, separation, and catalysis, and their roles as hosts in nanocomposite materials, are essentially determined by their unique structural characters, such as the size of the pore window, the accessible void space, the dimensionality of the channel system, and the numbers and sites of cations, etc. Traditionally, the term zeolite refers to a crystalline aluminosilicate or silica polymorph based on comer-sharing TO4 (T = Si and Al) tetrahedra forming a three-dimensional four-connected framework with uniformly sized pores of molecular dimensions. Nowadays, a diverse range of zeolite-related microporous materials with novel open-framework stmctures have been discovered. The framework atoms of microporous materials have expanded to cover most of the elements in the periodic table. For the structural chemistry aspect of our discussions, the second key component of the book, we have a chapter (Chapter 2) to introduce the structural characteristics of zeolites and related microporous materials. 

Several significant advantages justify its extensive use. First, as mentioned above, the self-removal of the template favors a reduction on the production time and costs. Second, BF allows the employment of a large variety of materials ranging from polymers to hybrid nanocomposites thus leading to porous films with diverse properties. Finally, as will be analyzed throughout this chapter, the external parameters (temperature, air humidity,. ..) and those related with the preparation procedure (solvent, polymer concentration, polymer features,. ..) are directly related to the pore dimensions and shape obtained. Thus, by controlling these parameters the pore sizes can be easily manipulated. 

Polystyrene nanospheres can be also used as a specific template for the preparation of nanocomposites with organic materials. In fact, the electropolymerization can be carried out within the voids of polystyrene nanospheres giving rise to RANI honeycomb films with desirable pore size, pore wall widths, and film thickness [245]. 

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