Simultaneous adsorption of acetaminophen, diclofenac and tetracycline by organo-sepiolite: Experiments and statistical physics modelling

Abstract

Non-selective and simultaneous adsorption of pharmaceutical compounds represents a real approach and a challenging task for researchers. Herein, the single and ternary adsorption of three pharmaceuticals acetaminophen (ACE), diclofenac (DFC) and tetracycline (TTC) on an organo-sepiolite (O-Sep) was studied via statistical physics modeling. A set of physical models was employed to calculate steric and energetic parameters related to the adsorption of ACE, DFC and TTC. An adsorption model based on the formation of a double layer was used to understand the adsorption of tested pharmaceuticals in single solutions, while an adsorption model that assumed that these compounds were adsorbed on three different functional groups was applied to analyze the ternary systems. Experimental and theoretical investigations indicated that O-Sep showed the highest adsorption capacities of DFC in solutions with one and three pharmaceuticals. Adsorption energies were also calculated indicating that endothermic and physical interactions were involved in the removal of these pollutants with the tested adsorbent. Overall, it was obtained that the density of functional groups of DFC and its adsorption energy were higher than those obtained for other pharmaceuticals in solutions with one and three pharmaceuticals, which agreed with the higher saturation capacities observed for this compound. This paper contributes with new interpretations of the adsorption mechanisms of pharmaceuticals on an organo-sepiolite, which is a promising adsorbent for water treatment.