High resolution gas adsorption study on illites permuted with various cations: Assessment of surface energetic properties

Ar and N2 high resolution adsorption volumetry coupled to the Derivative Isotherm Simulation method was applied on nine homoionic illite samples (Li-, Na-, K-, Rb-, Cs-, Mg-, Ca-, Sr- and Ba-illites). By comparing the adsorption isotherms it appears that the nature of the surface cation strongly influences the adsorption mechanisms. The lateral and basal surface areas can only be derived from argon adsorption on monovalent samples. The argon adsorption energies vary with the nature of the surface compensating cation. Both cation size and electronegativity are involved. These interactions can, in first approach, be expressed in terms of surface tensions γsvLW. Specific interactions appear when nitrogen is used revealing high energy adsorption sites located on basal faces. These sites could be related to some polar properties of the surface.