Explain the Langmuir and Freundlich adsorption isotherms.

The Langmuir isotherm assumes monolayer adsorption on homogeneous surfaces with finite sites: q = q_max*K*C/(1+K*C). The Freundlich isotherm is empirical for heterogeneous surfaces: q = K*C^(1/n). Langmuir predicts saturation at high concentrations; Freundlich does not. BET isotherm extends Langmuir for multilayer adsorption. These models are essential for designing adsorption systems, determining capacity, and predicting breakthrough curves.