Adsorption of propranolol hydrochloride from aqueous solutions onto thermally treated bentonite clay: A complete batch system evaluation

Abstract

Sustainability is an increasingly prominent issue in our modern society. Propranolol, a β-blocker mainly indicated for the control of hypertension, is an emerging contaminant that has already been reported as non-biodegradable, highly persistent, partially removed by the conventional treatment processes of water and wastewater and harmful to aquatic organisms. The removal of propranolol hydrochloride by batch adsorption using calcined Verde-lodo, a thermally modified bentonite clay, was assessed in this work. pH analysis indicated that natural pH could be used in the experiments. The kinetic study, conducted at 25 °C and deeply evaluated by rate laws and mass transfer models, achieved the equilibrium after 15 h, with pseudo-second order model showing the best fit and resistance to mass transfer in external film as the limiting step of adsorption. The isotherms’ study, conducted at 20, 30 and 40 °C, showed a maximum adsorptive capacity of 0.468 mmol.g−1. The thermodynamic analysis revealed a spontaneous, endothermic and entropy-governed adsorptive process (with increase in randomness and disorder level at the solid/liquid interface), and that clay surface is energetically heterogeneous. The energies of the electron-rich and electron-deficient sites, as well as the quantum chemical parameters (based on DFT theory), were determined for propranolol. The effects of molecular sieving could be ignored. Experimental data was supported by characterization results of the clay before and after adsorption, which indicated that the process modified its surface by the effective removal of the drug from aqueous solutions.