Lemon Peel‐Extracted Recyclable Copper Oxide Nanoparticles for Methylene Blue Dye Adsorption: Optimization, Isotherms, Kinetics, Thermodynamics, and Reusability Study

Abstract Researchers are exploring sustainable methods for synthesizing metal oxide nanoparticles to address wastewater pollution, which poses a global threat to aquatic life and human health. The present research aims to biosynthesize recyclable Lemon peel‐extracted copper oxide nanoparticles (CuO NPs) to remove methylene blue dye via adsorption. Our approach involves a comprehensive range of techniques, such as FTIR, XRD, SEM‐EDX, Zeta potential, and UV‐VIS, to thoroughly characterize the NPs. SEM analysis confirmed that the CuO NPs, with an average size of 64.5 nm and a nearly spherical shape, exhibited a zeta potential value of – 16.34, indicating their relative stability. Optimized conditions for the 92.20% adsorption efficiency for methylene blue dye were pH at 6, contact time of 90 min, 0.06 g of adsorbent dose, 10 ppm dye conc., and Temp. 27 °C. Langmuir 1‐based maximum adsorption capacity (qm) was 617.28 mg/g for CuO NPs. Langmuir 1 and Freundlich are the most suitable isotherm models for experimental data, supporting Physi‐chemisorption and chemisorption as rate‐limiting steps in the exothermic adsorption process. A reusability study of up to three cycles proved the sustainability of the materials.