Potential Theory Isotherms for Single and Mixed Gases

Potential Theory Isotherms for Single and Mixed Gases 

The isotherms derived from the potential theory have found utility in interpreting adsorption by capillary condensation, or pore filling. Thus they are especially useful for adsorption on microporous materials such as activated carbon. However, because the characteristic curve, to be described later, is assumed to be independent of temperature, which applies to adsorption by the temperature-independent dispersion forces, the resulting isotherms are applicable only to relatively nonpolar surfaces. The theory, nonetheless, is general in that it encompasses multilayer adsorption on energetically nonuniform surfaces. 

The potential theory is empirical. It assumes, by Polanyi in 1914 (Yang, 1987), that the cumulated volume of the adsorbed space, V, is a function of the potential, e  

Dubinin (1960) assumed the following empirical form for the adsorbed amount  

The exponent 2 in the D-R equation can be replaced by n, which is called the Dubinin-Astakhov equation (or D-A equation). The value of n empirically ranges from below 1 to about 14 (Kapoor and Yang, 1988 Kapoor et al., 1989a). The parameter n can be related to heterogeneity (Jaroniec and Madey, 1988 Rudzinski and Everett, 1992). The theoretical basis given by Chen and Yang (1994) is also valid for the D-A equation. 

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