Adsorption in microporous solids

W. C. Conner, Physical adsorption in microporous solids. NATO Adv.Study Inst. C 33... 

M. Molina-Sabio, F. Rodriguez-Reinoso, D. Valladares and G. Zgrablich, A lattice-gas model for adsorption in microporous solids, in J. Rouquerol, F. Rodriguez-Reinoso,... 

As an example of the above statement. Fig. 17.3 contains the Nj adsorption isotherms for powder AC vidth different adsorption capacities [3]. These isotherms, compared with those in Figs. 17.1 and 17.2, clearly demonstrate that the adsorption isotherms do not permit neither to distinguish the ACF from the AC nor to deduce differences in the pore size distribution. However, the unique fiber shape and porous structure of the ACF are advantages that permit to deepen into the fundamentals of adsorption in microporous solids [31]. ACFs are essentially microporous materials [13, 31], with sht-shaped pores and a quite uniform pore size distribution [42, 43]. Thus, they have simpler structures than ordinary granulated ACs [31] and can be considered as model microporous carbon materials. For this reason, important contributions to the understanding of adsorption in microporous solids for the assessment of pore size distribution have been made using ACF [31, 33, 34, 39, 42-46], which merit to be reviewed. 

We see that as the characteristic energy increases the adsorption is stronger as the solid has stronger energy of interaction with adsorbate. One observation in that equation is that the slope of the adsorption isotherm at zero loading is not finite, a violation of the thermodynamic requirement. This will be discussed in greater detail in Chapter 4, where we will deal with adsorption in microporous solids. 

Type I isotherm is the Langmuir isotherm type (monolayer coverage), typical of adsorption in microporous solids, such as adsorption of oxygen in charcoal. Type II typifies the BET adsorption mechanism. Type III is the type typical of water adsorption on charcoal where the adsorption is not favorable at low pressure because of the nonpolar (hydrophobic) nature of the charcoal surface. At sufficiently high pressures, the adsorption is due to the capillary condensation in mesopores. Type IV and type V are the same as types II and III with the exception that they have finite limit as P Pq due to the finite pore volume of porous solids. 

Chapter 3 Practical approaches of Pure Component Adsorption Equilibria Chapter 4 Pure Component Adsorption in Microporous Solids Chapter 5 Multicomponent Adsorption Equilibria... 

Chapter 4 Pure Component Adsorption in Microporous Solids... 

Physical adsorption in microporous solids shows type I isotherms because the micropores limit the adsorption to a few molecular layers. Using a kinetic approach, Langmuir described the type I isotherm, considering that adsorption was limited to a monolayer (32). This approach assumes that the adsorption energy is constant and is independent of the fraction of the surface occupied by the adsorbed molecules. 

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