Langmuir adsorption model

The Langmuir adsorption model describes adsorption on a uniform surface with a fixed number of identical sites, each holding at most one adsorbed molecule.

Langmuir adsorption isotherm: An equation relating the fraction of occupied adsorption sites to adsorbate pressure or concentration at constant temperature. It is the model’s quantitative expression for how site occupancy rises and approaches saturation.
Adsorption: The accumulation of atoms or molecules at a surface or interface. The model is a particular account of how surface accumulation depends on available sites.
Freundlich adsorption isotherm: An empirical equation relating adsorbed amount to solution concentration or gas pressure, often used for heterogeneous surfaces. Unlike Langmuir’s finite identical sites, it represents adsorption across a range of surface energies.
Langmuir probe: An electrode inserted into a plasma to infer properties such as electron temperature and density from its current–voltage response. Its current analysis uses Langmuir’s name but is distinct from the adsorption model.
Surface coverage: The fraction of a surface occupied by adsorbed atoms or molecules. The model predicts coverage as a function of adsorbate pressure or concentration.
Adsorption site: A position on a surface where an atom or molecule can bind. Identical, independently occupied sites are the model’s central surface assumption.
BET theory: A model of multilayer gas adsorption on solid surfaces used to estimate specific surface area. It extends monolayer adsorption assumptions to successive layers rather than stopping at one.
Gas adsorption: The attachment of gas molecules to a solid surface, often measured as uptake versus pressure. Pressure-dependent uptake can be fitted to estimate monolayer capacity and affinity.
Adsorption equilibrium constant: A constant that quantifies the equilibrium preference of an adsorbate for a surface relative to the fluid phase. It sets how strongly pressure or concentration shifts the model’s predicted coverage.
Physisorption: Adsorption held primarily by intermolecular forces rather than formation of chemical bonds. It can approximate reversible adsorption when surface sites behave uniformly.

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