© A.W.Marczewski 2002

A Practical Guide to Isotherms of ADSORPTION on Heterogeneous Surfaces

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Langmuir plot Data analysis:
Linear Isotherm-specific plots

(Used mostly for raw isotherm data)

See other plot types: Graham | φ-plot | t-plot | αs-plot

Linear plots: L / Everett / BET / LF / GL / Jov / F / DR / DA / HJ / FHH

Try simple linear dependencies using only (if possible) experimental data of adsorption and concentration (or their functions, e.g. logarithms) - methods are equation-specific and you must decide what type of equation should be checked:

Warning. (LSq) Line fitting cannot be treated as a remedy for all troubles. It also brings in its own problems related to the scaling of measured data (i.e. adsorption and concentration or pressure) and data errors. In order to obtain reliable parameters, one has to take error scaling into account - by weighted LSq fitting, by orthogonal fitting (minimization of both x,y errors) - if x,y are independent - and/or by taking into account x,y-error correlation ( see discussion on LSq fitting problems).

NOTE 1. Some of the methods may require adsorption monolayer (adsorption capacity), am or e.g. characteristic micropore filling concentration, co, to be know in advance (estimated by independent method or LSQ-fitted - in this case, linear plot is only a verification).
NOTE 2. Replace concentration, c, by pressure, p, for gas adsorption. In dilute solute adsorption x=c/cs and in vapour adsorption x=p/ps, where index "s" indicates saturation concentration or pressure, respectively.

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