Medium-property relationships and compensation effect in the adsorption of heteroaromatic compounds from aqueous acetonitrile solutions

Abstract

The thermodynamics of the adsorption of heteroaromatic compounds of the 1,3,4-oxadiazole and 1,2,4,5-tetrazine series from aqueous acetonitrile solutions was studied in Henry’s region under the conditions close to equilibrium using the dynamic method. The applicability of the adsorption retention models to the description of medium-property relationships at different temperatures was evaluated. The effect of the composition of the solution on the thermodynamic characteristics of adsorption was studied. The effect of the acetonitrile concen-tration on the enthalpy and entropy of adsorption cannot be described by simple plots, since it is determined by the nature of the adsorbate. At the same time, the Gibbs free energy change of adsorption is characterized by a monotonic dependence on the acetonitrile concentration. Linear relationships between changes in the enthalpy and entropy of adsorption of the same substance from water-acetonitrile media of different compositions were established. The character of these relationships is determined by the adsorbate nature and explains the dependence of its thermodynamic characteristics of adsorption on the solution composition. The compensation of the values of enthalpy and entropy changes in a series of the studied adsorbates measured for the constant composition of the solution was discovered. The concentration of acetonitrile significantly affects the character of this compensation.