Hydrophobic Deep Eutectic Solvent-Coated Silica Gel for NSAID Adsorption From Water: Performance and Interfacial...

Pharmaceutical residues in aquatic environments require reusable sorbents capable of removing structurally diverse contaminants under competitive conditions. Here, a hydrophobic natural deep eutectic solvent-coated silica composite (DES-SOT) was prepared by functionalizing silica gel with n-octyltriethoxysilane followed by immobilization of a thymol:oleic acid deep eutectic solvent. Characterization confirmed formation of a DES-rich organic interfacial layer. DES-SOT showed higher adsorption capacities than unmodified silica and Si-OTES for diclofenac, ibuprofen, mefenamic acid, and tolfenamic acid, with equilibrium reached within 20 min at pH 6. Kinetic and isotherm analyses described heterogeneous adsorption behavior, while reusability, desorption, and molecular dynamics results were consistent with hydrophobic partitioning and weak noncovalent interactions. Molecular dynamics simulations supported analyte-dependent association with the DES-rich interface, consistent with experimental adsorption trends. DES-SOT maintained adsorption performance in groundwater and lake water and remained reusable over five adsorption-desorption cycles. This study demonstrates a simple DES-based adsorption interface for pharmaceutical removal from water.