Beyond Conventional Heating: Unlocking the Synergy Between Microwave Irradiation and pH Control for High-Efficiency Fabrication of Phyto-Copper Oxide Nanoparticles

Introduction: Sustainable nanotechnology requires synthesis approaches that are environmentally benign while maintaining high efficiency, yield, and functionality. Plant-mediated synthesis combined with advanced heating techniques offers a promising route to achieve these goals. Methods: Phyto-copper oxide nanoparticles (Phy-CuO-NPs) were synthesized using Psidium guajava leaf extract under different pH conditions via two approaches: conventional heating (Series A) and microwave-assisted synthesis (Series B). The influence of pH and heating mode on nanoparticle formation was systematically evaluated. The synthesized nanoparticles were characterized using physicochemical and morphological techniques, and their antibacterial activity was assessed against Staphylococcus aureus and Pseudomonas aeruginosa. Results: Microwave-assisted synthesis significantly altered pH-dependent nucleation pathways, resulting in nanoparticles with enhanced crystallinity, more uniform morphology, higher copper content, and improved colloidal stability, particularly under alkaline conditions. Series B nanoparticles showed a 34% increase in maximum yield (up to 80 mg/g) while achieving a 92% reduction in energy consumption compared to the conventional method. Antibacterial assays revealed strong inhibitory activity against both tested strains, with greater efficacy against Gram-negative bacteria. Discussion: The improved antibacterial performance is attributed to the bio-capped nature of the nanoparticles, which facilitates cellular entry and promotes intracellular copper ion release, leading predominantly to reactive oxygen species generation rather than direct ionic toxicity. This study highlights the synergistic role of microwave irradiation and pH control in enhancing both sustainability and functionality.