Thermodynamic study of triclosan adsorption from aqueous solutions on activated carbonModelling of experimental adsorption isotherm and calorimetry data

The change in the thermodynamic properties of triclosan adsorption on three activated carbons with the different surface chemistry was studied through immersion calorimetry and equilibrium data; the amount adsorbed of triclosan (Q) during calorimetry was determined and correlated with the energy associated with adsorbate–adsorbent interactions in the adsorption process. It was noted that triclosan adsorption capacity decreases with an increase in oxygenated surface groups. For an activated carbon oxidized with HNO3 (OxAC), the amount adsorbed was 8.50 × 10−3 mmol g−1, for a activated carbon without modification (GAC) Q = 10.3 × 10−3 mmol g−1 and for a activated carbon heated at 1073 K (RAC1073) Q = 11.4 × 10−3 mmol g−1. The adsorbed amounts were determined by adjusting the isotherms to the Sips model. For the activated carbon RAC1073, the immersion enthalpy (ΔHimm) was greater than those of the other two activated carbons due to the formation of interactions with the solvent (ΔHimmOxAC = − 27.3 J g−1 < ΔHimmGAC = − 40.0 J g−1 < ΔHimm RAC1073 = − 60.7 J g−1). The changes in the interaction enthalpy and Gibbs energy are associated with adsorbate–adsorbent interactions and side interactions such as the adsorbate–adsorbate and adsorbate–solvent interactions.