Thermodynamic study of seven micropollutants adsorption onto an activated carbon cloth: Van't Hoff method, calorimetry, and COSMO-RS simulations.

Abstract

The thermodynamic of the adsorption of seven organic pollutants, namely benzotriazol, bisphenol A, caffeine, carbamazepine, diclofenac, ofloxacin, and pentachlorophenol, was studied on a microporous-activated carbon fabric. The isosteric adsorption quantities (Gibbs energy, enthalpy, and entropy variations) at high coverage ratio (around 1mmol/g) have been determined from the adsorption isotherms at three temperatures (13, 25, and 40°C). The adsorption heats at very low coverage (about 10-5mmol/g) have been measured by flow micro calorimetry. The experimental adsorption energies were correlated to the adsorbate-adsorbent and the adsorbate-solvent interaction energies calculated by simulations using the COSMO-RS model. The main role of the van der Waals forces in the adsorption of the studied molecules was established. The bulkier the adsorbate is, the lower the adsorption Gibbs energy variation at high coverage deduced from the isotherms. The heterogeneity of the adsorption sites was brought out by calorimetric measurements. At high coverage, a physisorption phenomenon was observed. At very low coverage, high values of the adsorption heats were found (ranging from -58 to -110kJ/mol), except for pentachlorophenol characterized by an athermal adsorption controlled by Pi-anions interactions.