Adsorption isotherms are important for the prediction of the extent of adsorption. The most commonly used models are
Langmuir and Freundlich isotherms. The experimental results are fitted to these isotherm equations. Freundlich isotherm model expresses the heterogeneity of the adsorbent material and multi layer coverage of adsorbate. Langmuir isotherm model was developed assuming that there is limited area available for adsorption, the surface of adsorbent is homogeneous, the adsorbate is adsorbed in one molecule layer and the adsorption is a reversible process [11,20].
Freundlich isotherm model equation and its linear form are given in Eq. (2) and (3).