Adsorption Isotherm (Langmuir-Freundlich)

Adsorption isotherms describe the equilibrium uptake of a substance on a solid surface as a function of gas or solution phase concentration at constant temperature. The Langmuir isotherm (1918) and Freundlich isotherm (1906) are classical empirical models. The Langmuir model assumes monolayer coverage and is mechanistic; the Freundlich model is empirical and describes multilayer or heterogeneous adsorption. These isotherms are essential for designing separation processes (activated carbon filters, molecular sieves) and understanding pollutant sorption.