Porous crystals classification

The given discussion shows that rather universal and simple classification of porous materials equivalent to classification of crystals is absent. However, one can consider a system of interrelating classifications that take into account order, morphology and sizes at different hierarchical levels, degrees of integrity, structure, heterogeneity of a various type, etc. Such a systematic approach can be used as well for adequate modeling of various hierarchical levels of a porous material structure. 

Bilayer architectures formed in M2(2)3(N03)4 n (where M = Co, Ni and Zn) were one of the first systems of coordination polymers to be shown as porous materials [43]. The bilayer architectures interdigitate with each other leaving small channels in the crystal lattice which were occupied by solvated water molecules. Powder X-ray studies indicate that the water molecules can be removed from the network without causing any distortion or decomposition of the network. The adsorption studies of water removed and dried sample indicated that the material is capable of adsorbing CH4, N2 and 02. About 2.3 mmol of CH4 and 0.80 mmol of N2 or 02 are adsorbed per gram of anhydrous material. The adsorption-readsorption followed the same isotherm, indicating the stability of the network throughout the process. Further, the isotherms for the adsorption-readsorption can be classified as type I in the IUPAC classification [48]. 

Another classification can be made by considering the structure-determining step in manufacturing. These include precipitation (amorphous silica), melting (porous glass), and hydrothermal crystallization (layered materials, zeolites). The... 

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