Can the Langmuir adsorption coefficient be used to derive the adsorption Gibbs energy?

To explore the inhibition mechanism of corrosion inhibitors for metals in aqueous solution, the Langmuir adsorption isotherm has been widely used to ascertain the adsorption mode of the inhibitors on the metal surface. Meanwhile the obtained Langmuir adsorption coefficients have been further applied to calculate Gibb free energy change in the adsorption processes. However, the relationship between the Langmuir adsorption coefficients and Gibbs free energy change of adsorption has been misused for plant extracts (as inhibitors) whose composition and/or content were unknown. Herein, the relationship between the Langmuir adsorption coefficients and Gibbs free energy change is derived detailedly. And the applicable conditions of the relationship are analyzed and discussed for correct application and avoiding misuse.