Caffeine adsorption from aqueous solutions onto polymeric sorbents: The effect of surface chemistry on the adsorptive affinity and adsorption enthalpy

Abstract Measurements of the adsorption equilibria and the adsorption enthalpies are used to characterize the thermodynamics of caffeine adsorption from aqueous solutions onto three polymeric sorbents which vary in their ability to donate π electrons for adsorptive interactions. Measured adsorption enthalpies, by both the temperature dependence of the adsorption affinities and calorimetric methods, are in qualitative agreement and demonstrate that the sorbents with the highest adsorption affinity for caffeine also display the largest adsorption enthalpy. These observations support the contention that caffeine adsorption is driven predominantly by specific enthalpic interactions of the solute with the delocalized π electrons on the surface of the sorbents.