Microwave-assisted versus conventional green synthesis of CuO nanoparticles: A DFT-guided structure–property–performance relationship

CuO nanoparticles were synthesized using Clerodendron viscosum leaf extract through conventional green synthesis and microwave-assisted green synthesis, and their structural, electronic, photocatalytic, antibacterial, and cytotoxic properties were systematically investigated using experimental characterization and DFT + U calculations. First-principles calculations confirmed monoclinic CuO as an indirect band-gap semiconductor with a GGA + U band gap of 0.753 eV, while scissors-corrected optical analysis provided insights into its electronic and optical behavior. XRD analysis verified the monoclinic CuO, with microwave-assisted synthesis reducing the crystallite size from 18.0 nm to 13.21 nm and improving crystallinity from 79.51% to 88.43%. SEM analysis further revealed a reduction in average particle size from approximately 27 nm to 18.43 nm after microwave treatment. FTIR and EDS analyses confirmed Cu–O formation along with plant-derived surface functionalities. The microwave-assisted CuO nanoparticles exhibited improved photocatalytic activity toward methylene blue degradation, achieving 79.2% removal within 120 min compared with 60.3% for conventionally synthesized CuO, along with an increased apparent rate constant from 0.0069 to 0.01238 min⁻¹ . Antibacterial assessment against Staphylococcus aureus and Escherichia coli demonstrated concentration-dependent activity, with MIC analysis confirming effective inhibition at low nanoparticle concentrations. Brine shrimp lethality analysis showed concentration- and time-dependent toxicity; however, the estimated LC₅₀ values are considered preliminary due to the limited concentration range investigated. Statistical analysis using one-way ANOVA followed by Duncan’s multiple range test confirmed significant differences in cytotoxic responses (p < 0.05). Overall, microwave-assisted green synthesis enhanced the structural quality and multifunctional performance of CuO nanoparticles, while further comprehensive toxicity studies are required before practical environmental or biomedical applications.