Efficient Extraction of Nanoplastics from Aqueous Media Using Natural Deep Eutectic Solvents: Experimental and Molecular Insights

Abstract

Microplastics and nanoplastics are persistent contaminants of global concern due to their ubiquity in aquatic systems and their potential ecological and toxicological impacts. Conventional solvent-based extraction methods are often inefficient or environmentally harmful, emphasizing the need for greener alternatives. In this study, natural deep eutectic solvents (NADES) composed of thymol (Thy), menthol (Men), and fatty acids were prepared and evaluated for the extraction of polystyrene (PS) nanoplastics from aqueous media. Extraction experiments were performed at 25 °C under controlled agitation, and the influence of pH (3.0–9.0) and solvent composition on extraction efficiency was systematically investigated. The Thy:Men (1:1) system exhibited the highest extraction efficiencies of 97.14 ± 0.49%, 75.35 ± 20.90%, and 78.19 ± 1.36% at pH 3.0, 7.0, and 9.0, respectively, reaching equilibrium after approximately 2 h. Molecular dynamics (MD) simulations were employed to elucidate the molecular mechanisms underlying the extraction process. The results revealed that menthol molecules preferentially accumulate at the water–NADES interface, forming hydrogen bonds with water while engaging in van der Waals interactions with PS. Thymol contributes primarily through π–π stacking interactions with the aromatic backbone of PS, resulting in strong stabilization within the NADES phase.