A new insight into the surface adsorption in the solution phase: A modification of the Langmuir isotherm.

The Langmuir isotherm, originally developed to study the adsorption of gases, has been modified in this research to investigate the adsorption of solutes in the solution phase. The modification considers the adsorption of solvent molecules and the interactions between adsorbed particles and the species in the solution. Three equations have been obtained to calculate the contribution of these additional effects on the Gibbs free energy, enthalpy, and entropy of solute adsorption based on the new isotherm. The study evaluated the efficiency of the new isotherm in the adsorption of some metal ions in an aqueous solution and found that it is more accurate than the Langmuir isotherm and provides a deeper insight into the adsorption process in the solution phase. Practitioner Points: Modification of the Langmuir isotherm for adsorption in solution.Comparison of the efficiency of the Langmuir and modified Langmuir isotherms.Accurate determination of ∆Hadso$$ \Delta {H}_{ads}^o $$ and ∆Sadso$$ \Delta {S}_{ads}^o $$ for Pb(II), Cd(II), and Ni(II) adsorption. [ABSTRACT FROM AUTHOR]