Banana Peel Modified with Deep Eutectic Solvents for Pharmaceutical Water Remediation

Banana peel (BP) has gained attention as a sustainable, low-cost biosorbent for removing pharmaceuticals from aquatic environments. In this study, BP was modified using a choline chloride/methanesulfonic acid (ChCl/MSA) deep eutectic solvent to produce a chemically and structurally enhanced material (BP-ChCl/MSA) for pharmaceutical adsorption from water. The modified biosorbent was comprehensively characterized by FTIR, TGA, and SEM analyses, and its performance was systematically compared with BP treated solely with methanesulfonic acid (BP–MSA). MSA induced holocellulose hydrolysis and ChCl/MSA increased the lignin content in the biosorbent. Propranolol (PRO), metformin, and tinidazole were used as model drugs. BP-ChCl/MSA showed selective adsorption for PRO, with almost 90% of removal efficiency achieved from an initial concentration of 20.0 mg L–1, without requiring pH adjustment at 25 °C. The PRO adsorption kinetics for both BP-MSA and BP-ChCl/MSA were best described by the pseudo-second-order (PSO) model, with adsorption occurring in less than 500 min. Isotherms were well described by the Sips model, indicating adsorption on a heterogeneous surface, with BP-ChCl/MSA exhibiting higher maximum adsorption capacity value (284.6 mg g–1) than BP-MSA (238.1 mg g–1). Thermodynamic analysis using the partition model provided more consistent results, with ΔadsG◦ ranging from −24.1 to −21.9 kJ mol–1 as the temperature increased from 25 to 40 °C, showing an endothermic process (ΔadsH◦ = 23.5 kJ mol–1) that is entropy-driven (ΔadsS◦ around 0.15 kJ mol–1 K–1). Overall, ChCl/MSA treatment enhanced the interactions between the remaining lignin functional groups and PRO, mainly through electrostatic interactions and hydrogen bonding. Moreover, the material showed good reusability, maintaining more than 75% of removal efficiency after 3 adsorption cycles. These results demonstrate that treatment with the ChCl/MSA DES significantly improved the adsorption capacity of BP through an efficient and eco-friendly approach, yielding a sustainable and promising material for drug adsorption in aqueous media.