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 aqueo us solutions onto a set of carbon blacks and activated carbons has been com pared 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 rela ted to the same types of interactions since the evolution of adsorption ent halpy in these systems depends mainly on the porosity of the samples but no t on the chemistry surface composition. The results at low coverage, indica te two kinds, at least, of adsorption behaviour: the first related to the a dsorption of TX-100 in the narrowest pores with a suitable width, and the s econd on more open surfaces. In the narrowest micropores, the adsorption en thalpy can be twice that for a non-microporous surface as can be expected f or slit-shaped micropores accommodating only one molecule. At higher covera ge, the retention is due to interactions between surfactant molecules at th e adsorbent-solution interface leading to the formation of interfacial aggr egates. (C) 2001 Elsevier Science B.V. All rights reserved.