Adsorption of ibuprofen on organo-sepiolite and on zeolite/sepiolite heterostructure: Synthesis, characterization and statistical physics modeling

A synthesized zeolite/sepiolite nanoheterostructure (Zeo-Sep) and a modified organo-sepiolite (O-Sep) have been employed as clay-based adsorbents to study the adsorption mechanism of ibuprofen (IBP) from aqueous solution. New equilibrium data of IBP adsorption were determined at 20–60 °C, which were utilized to perform a theoretical analysis of the removal mechanism using statistical physics models. To interpret the IBP adsorption mechanism at molecular level, three advanced statistical physics models were employed. Modeling results indicated that IBP adsorption on Zeo-Sep and O-Sep was associated to the formation of two layers. It has been deduced that the IBP adsorption occurred by horizontal and non-horizontal orientations on both adsorbents depending on the temperature thus reflecting that the adsorption was a multi-docking and multi-molecular process, respectively. At high temperature (i.e., 60 °C), it was found that the number of captured IBP molecules is around two reflecting that the IBP was aggregated (i.e., formation of a dimer) in solution. IBP adsorption capacity at saturation was higher on O-Sep than that of Zeo-Sep at all tested temperatures indicating that the O-Sep adsorbent was more suitable for the removal of this pharmaceutical. The interactions between IBP and both adsorbents (IBP/O-Sep, and IBP/Zeo-Sep) and between IBP molecules (IBP- IBP) have been calculated to further characterize the adsorption mechanism, which was found to be a physisorption process. These new findings provided microscopic explanations regarding the IBP adsorption mechanism using clay-based adsorbents.