The BET isotherm builds upon the Langmuir theory by considering multilayer adsorption. The key assumptions include:
- Adsorption occurs in layers. - The first layer's adsorption enthalpy is different from subsequent layers. - There is no interaction between adsorbed molecules in adjacent layers.
Where \( P \) is the equilibrium pressure of the gas, \( P0 \) is the saturation pressure, \( V \) is the volume of gas adsorbed, \( Vm \) is the monolayer capacity, and \( C \) is the BET constant related to the energy of adsorption.
