Adsorption of propranolol onto montmorillonite: Kinetic, isotherm and pH studies

The objective of this study was to explore the potential use of the smectite clay mineral montmorillonite (Mt) as adsorbent in the removal of water containing the emerging compound propranolol. The Mt was deeply characterized by X-ray diffraction (XRD), Zeta potential and thermogravimetric analysis (DSC-TG), before and after adsorption experiments, and their isotherms and kinetic models were fitted to assess the adsorption of propranolol. The incorporation of propranolol in the interlayer was demonstrated by XRD and DSC-TG. The results obtained by Zeta potential indicated no adsorption of propranolol in the surface. Kinetic of propranolol adsorption onto Mt. was evaluated using pseudo-first-order, pseudo-second-order, intra-particle diffusion and Elovich models. Pseudo-second order was the kinetic model that best described the adsorption of propranolol (R-2 > 0.999). It was possible to obtain a removal efficiency of approximately 96% in < 1 min. The adsorption equilibrium isotherm was fitted with the Langmuir, Freundlich and Dubinin-Radushkevitch mathematical models to obtain the respective parameters. Freundlich and Dubinin-Radushkevitch were the models that best fitted the experimental data (R-2 > 0.999). Due to the cationic form of propranolol, the adsorption by ionic exchange between charged propranolol and sodium cations onto the interlayer space was the most favorable pathway proposed. Results indicate that adsorption onto Mt proved to be an efficient method for removing propranolol, thus being a viable alternative for the treatment of water contaminated with this drug.