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

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.