= Solution
The <Langmuir adsorption model> assumes equivalent independent sites, a maximum of one adsorbate per site, no lateral adsorbate interactions, reversible adsorption-desorption equilibrium and non-dissociative <adsorption> here. Surface coverage obeys $\theta=bC/(1+bC)$ for the solution analogue.
<BET adsorption> allows multiple layers: occupation of one layer creates sites for further <adsorption> above it, and higher-layer binding is treated differently from first-layer binding, commonly using a condensation-like energy. Langmuir saturation is monolayer saturation; the BET model is not simply Langmuir with a different numerical equilibrium constant.
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