Özge Demir, Nilay Baylan, Şah İsmail Kirbaşlar
Abstract BACKGROUND Copper oxide nanoparticles ( CuO NPs ) have emerged as promising adsorbent materials due to their affordability, expansive surface area, abundant active sites, and robust adsorption capacity. Utilizing green chemistry principles, this study aimed to synthesize CuO NPs via a precipitation method in a deep eutectic solvent ( DES ) composed of choline chloride, ethylene glycol, and water, and to evaluate their effectiveness in removing metronidazole ( MTZ ), a pharmaceutical contaminant, from aqueous solutions. RESULTS The synthesized CuO NPs were characterized by BET , SEM , FTIR , and XRD analyses, confirming their optimal morphology, crystalline structure, and monoclinic phase. The average crystallite size was calculated as 70.42 nm via the Debye–Scherrer equation. HPLC analysis demonstrated efficient MTZ adsorption, reaching a maximum monolayer adsorption capacity of 29.39 mg/g. The adsorption process followed the Langmuir isotherm and pseudo‐second‐order kinetics, indicating monolayer adsorption on homogeneous surfaces. Thermodynamic studies revealed that MTZ adsorption on CuO NPs was spontaneous and endothermic, highlighting the significance of the DES ‐mediated nanostructure in enhancing removal efficiency. CONCLUSION This work demonstrates that the use of a ternary DES ( ChCl : EG : H 2 O ) as both green solvent and surface modifier enables the synthesis of CuO NPs with a well‐developed nanostructure and high adsorption performance for MTZ . The DES ‐mediated process provided enhanced adsorption capacity, showing the potential of this eco‐friendly synthesis route for water treatment applications. © 2025 Society of Chemical Industry (SCI).