Biogenic Zinc Oxide Nanoparticles: A Comprehensive Review on Green Synthesis, Characterization, and Environmental Applications
Ebtehaj Ahmed, Rasha A. Al-husseiny
Abstract
Nanotechnology has revolutionized material science by enabling nanoscale material synthesis with unique properties, primarily due to a high surface area-to-volume ratio. Zinc oxide nanoparticles (ZnO NPs) have attracted extensive interest because of their semiconducting behavior, high photostability, broad-spectrum antimicrobial activity, and environmental compatibility. However, conventional physical and chemical synthesis methods raise serious ecological and health concerns due to the involvement of toxic reagents, high energy consumption, and hazardous by-products. In response, green synthesis approaches—utilizing biological agents such as plants, fungi, bacteria, and algae—have emerged as viable, eco-friendly alternatives for ZnO NP production. This review provides a comprehensive evaluation of biological synthesis mechanisms, contrasting their efficiencies, nanoparticle characteristics, environmental impacts, and scalability. Key characterization techniques and functional applications in biomedicine, water treatment, cosmetics, and food preservation are also discussed. Visual frameworks and comparative charts are incorporated to facilitate understanding of biological sources and mechanistic pathways. Despite significant progress, the field faces challenges related to standardization, variability in biological extracts, and reproducibility of nanoparticle properties. Future research should focus on scaling up biogenic synthesis, integrating bioinformatics to identify phytochemical mediators, optimizing process control, and elucidating molecular mechanisms behind biological activity. This review highlights critical insights, emerging trends, and strategic research directions aimed at enhancing the industrial viability and environmental sustainability of ZnO NP synthesis.