Gas adsorption in porous nanostructured materials

Krishna (2000), starting from the fundamental concepts of Maxwell J. C. and Stefan X, describes the conhguration diffusion, also called surface diffusion, within zeolite crystals by means of the following set of equations, namely the generalized MS approach (Kapteijn et al, 2000 Krishna, 2000). Nevertheless, this set of equations can also be used to describe diffusion in other nanostructured materials such as carbon nanotubes  

0 = C / Cf where C is the molecular coverage expressed in molecules of adsorbed gas per unit cell of zeolite, whereas C is the saturation coverage 

Using Equation [17.6], it is easy to verify that the familiar transport or phenomenological Pick coefficient can be obtained as the product of the corrected diffusivity (MS diffusivity) and the thermodynamic factor P, defined 

The term (0) is the MS diffusivity in the limit of zero coverage, namely 

2 Chemical structure of the Silicalite-1 zeolite (a), schematic representation of a functionalized silica nanotube (b), chemical formula of silane functional group used in the silica nanotube (c). 

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