Frumkinisotherm

Frumkinisotherm

The Frumkin isotherm is a model for adsorption that incorporates lateral interactions between adsorbed molecules on a surface. It extends the Langmuir isotherm by including a factor that accounts for interactions among neighboring adsorbates, using a mean-field approach.

The standard form, in terms of fractional surface coverage θ, is:

θ/(1 − θ) = K p exp(−g θ)

where p is the adsorbate pressure (or bulk concentration), K is a Langmuir-type adsorption constant, and g is the dimensionless Frumkin parameter related to the adsorbate–adsorbate interaction energy divided by RT. The exponential term modulates adsorption as coverage increases: g > 0 indicates repulsive interactions, g < 0 indicates attractive interactions, and g = 0 reduces the equation to the Langmuir isotherm.

An equivalent rearrangement for p is: p = (1/K) [θ/(1 − θ)] exp(g θ).

The model assumes a homogeneous surface, monolayer adsorption, and mean-field lateral interactions; it does not capture pore effects or multilayer adsorption. It is used to fit experimental adsorption data to estimate K and g, providing insight into the strength and nature of lateral interactions and how adsorption behavior changes with temperature. Limitations include potential oversimplification for heterogeneous surfaces and systems with complex cooperative effects beyond the mean-field approximation.

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