Plant Extract-Mediated Synthesis of CuO Nanoparticles from Lemon Peel Extract and Their Modification with Polyethylene Glycol for Enhancing Photocatalytic and Antioxidant Activities

Plant extract-mediated synthesis is a simple, eco-friendly, and inexpensive method for the preparation of efficient antioxidant and photocatalytic nanoparticles. In this study, lemon peel aqueous extract was used to synthesize CuO nanoparticles (NPs) and then the obtained CuO NPs were modified using polyethylene glycol (PEG). The characteristics, optical properties, antioxidant, and photocatalytic activities of the synthesized nanoparticles were investigated. The CuO NPs and CuO/PEG NPs exhibited sphere-like morphology with an average size of 34 nm and 45 nm and optical bandgap energies of 1.2 eV and 1.5 eV, respectively. The antioxidant activity tests showed that the CuO/PEG NPs exhibited significant scavenging activity with IC 50 values of 104.6 μg/mL for the β-carotene scavenging assay and 38.1 μg/mL for the ABTS scavenging assay, while CuO showed lower antioxidant activity of about 150.54 μg/mL for β-Carotene linoleic acid bleaching assay and 59.63 μg/mL for the ABTS scavenging assay. In terms of photocatalytic degradation, CuO/PEG NPs demonstrated higher activity compared to CuO NPs alone. They achieved degradation rates of 99.7% for 4-bromophenol (BP) dye and 99.5% for toluidine blue (TP) dye after 90 min, whereas CuO NPs achieved slightly lower rates. The CuO NPs and CuO/PEG NPs displayed significant photocatalytic degradation activity against amoxicillin (antibiotic), with degradation rates of 91% and 98%, respectively, after 120 min. The reaction kinetics of CuO/PEG NPs and CuO NPs followed a pseudo-first order model, with CuO/PEG NPs exhibiting a higher rate constant than CuO NPs. Overall, modifying the CuO NPs with PEG demonstrated excellent photocatalytic properties for environmental remediation and exhibited antioxidant activity, suggesting their potential use in wastewater treatment and therapeutic applications. Graphical Abstract