Re-evaluation of the century-old Langmuir isotherm for modeling adsorption phenomena in solution

One of the first reported equations to describe adsorption at equilibrium is the Langmuir model (J. Am. Chem. Soc. 1918, 40, 1361-1403). Initially, the model was used to describe adsorption from the gas phase, along with adsorption from the liquid phase. Herein, the shortcomings of the Langmuir model for adsorption processes from liquid phase are revealed. This study reports a revised form of the Langmuir isotherm model that provides further insight on the nature of adsorption and desorption processes in condensed phases. This approach is anticipated to provide a theoretical background for universal calculation of the adsorption thermodynamic parameters. We also provide an overview of the methods that use the Langmuir equilibrium constant for calculation of thermodynamic parameters of adsorption and source of their limitations are highlighted.