Role of Ionic Liquids in Hydrothermal Synthesis of Li‐Doped CuO Nanoparticles: Improved Photocatalytic, Electrochemical, and Antibacterial Properties

ABSTRACT Lithium‐doped copper oxide nanoparticles (Li‐CuO NPs) were synthesized via an ionic‐liquid‐assisted hydrothermal method to examine the role of ionic liquids in tailoring structural and functional properties. PXRD analysis confirmed phase‐pure monoclinic CuO (JCPDS/PDF No. 45‐0937), with a reduction in crystallite size from 46 nm (CuO) to 39 nm upon Li incorporation. BET analysis revealed mesoporous characteristics with a specific surface area of 85 m 2 g − 1 and an average pore diameter of 10 nm. Optical studies showed a red shift in absorption and a band gap narrowing from 2.61 eV (CuO) to 2.35 eV (Li‐CuO), indicating enhanced visible‐light absorption. The photocatalytic performance of Li‐CuO NPs was evaluated using Evans Blue dye under visible‐light irradiation, achieving 96.67% degradation within 2 h, along with good stability over repeated fourth cycles. The effects of various parameters, including pH, catalyst loading, dye concentration, illumination intensity, and the recyclability and reusability of the catalyst, were also investigated. Electrochemical studies demonstrated enhanced redox activity and improved charge‐transfer behavior for dye sensing. In addition, Li‐CuO NPs exhibited significant antibacterial activity, attributed to lithium‐induced defects, and increased surface reactivity. These findings highlight ionic‐liquid‐assisted lithium doping as an effective approach for improving the multifunctional performance of CuO‐based nanomaterials.