Porous Materials, Concept, and Classifications

Porous materials discussed at the International Conference on Materials for Advanced Technologies 2005 included clay minerals, silicates, aluminosilicates, organosilicas, metals, silicon, metal oxides, carbons and carbon nanotubes, polymers and coordination polymers, or metal-organic frameworks (MOFs), metal and metal oxide nanoparticles, thin films, membranes, and monoliths (Zhao, 2006). 

Because of the considerable variety of materials that can be classified as porous, several classifications can be proposed. Thus, according to the distribution of pores within the material, we can distinguish between regular and irregular porous materials, whereas, according to the size distribution of pores, one can separate between uniformly sized and nonuniformly sized porous materials. 

From a structural point of view, porous materials can be viewed as the result of building blocks following an order of construction that can extend from the centimeter to the nanometer levels. Porous materials can range from highly ordered crystalline materials such as aluminosilicates or MOFs, to amorphous sol-gel compounds, polymers, and fibers. This text will focus on materials that have porous structures, so that ion-insertion solids having no micro- or mesoporous structures, such as the metal polycyanometalates, whose electrochemistry was reviewed by Scholz et al. (2005), will not be treated here. To present a systematic approach 

Typical Values for Specific Surface Area of Selected Porous Materials 

Although it does not exhaust the entire range of porous materials, the list attempts to cover those that can be described in terms of extended porous structures and whose electrochemistry has been extensively studied. In addition, since 1990 there has been a growing interest in the preparation of nanostructures of metal and metal oxides with controlled interior nanospace, whereas a variety of nanoscopic poro-gens such as dendrimers, cross-linked and core-corona nanoparticles, hybrid copolymers, and cage supramolecules are currently under intensive research (Zhao, 2006). Several of such nanostructured systems will be treated along the text, although, for reasons of extension, the study in extenso of their electrochemistry should be treated elsewhere. 

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