Influence of porosity on the adsorption enthalpies of a non-ionic surfactant onto carbonaceous materials

The adsorption of a non-ionic surfactant (Triton X-100 (TX-100)) from aqueous solutions onto a set of carbon blacks and activated carbons has been compared by a calorimetric study. Different behaviours in the progress of the adsorption enthalpy as a function of surface coverage are obtained. However, irrespective of the nature of the carbon support, the process can be related to the same types of interactions since the evolution of adsorption enthalpy in these systems depends mainly on the porosity of the samples but not on the chemistry surface composition. The results at low coverage, indicate two kinds, at least, of adsorption behaviour: the first related to the adsorption of TX-100 in the narrowest pores with a suitable width, and the second on more open surfaces. In the narrowest micropores, the adsorption enthalpy can be twice that for a non-microporous surface as can be expected for slit-shaped micropores accommodating only one molecule. At higher coverage, the retention is due to interactions between surfactant molecules at the adsorbent-solution interface leading to the formation of interfacial aggregates.