Derivation and constants determination of the Freundlich and (fractal) Langmuir adsorption isotherms from kinetics

Abstract

The Freundlich adsorption isotherm is mostly presented as an empirical equation and the (fractal) Langmuir adsorption isotherm is derived from kinetics. However, their constants are determined by thermodynamic approach. As yet, both are used as an independent tool for determining the type of adsorption, just physical or chemical adsorption. This study aims to introduce an alternative way of driving Freundlich adsorption isotherm from kinetics, to elaborate its relation with the (fractal) Langmuir adsorption isotherm, and to determine their constants simultaneously by kinetics approach. An alternative way of determining the constants in both isotherm equations by kinetics approach was introduced. The results were then compared with that obtained by the conventional method. The study is theoretical but the validity of determination technique is based on the statistical tests on data adapted from literature. The Freundlich adsorption isotherm is introduced; the isotherm is the (fractal) Langmuir adsorption isotherm at relatively low concentration. It is irrelevant to use both adsorption isotherm separately. The new method is more reliable and its represent the reaction.