Review on Green Chemistry of Manganese Oxide Nanoparticles Using Plant Extracts: Characterization and Recent Applications

The rapid expansion of nanotechnology has led to significant advancements across biomedical, environmental, and energy sectors. Manganese oxide nanoparticles (MnO NPs) have garnered considerable attention due to their magnetic properties, redox activity, biocompatibility, and low toxicity. However, conventional synthesis methods often involve hazardous chemicals and energy-intensive processes. In response, green synthesis approaches – particularly plant-mediated methods – have emerged as sustainable, cost-effective, and environmentally benign alternatives. Utilizing phytochemicals such as flavonoids, terpenoids, and phenolics, plant extracts function as natural reducing and stabilizing agents during nanoparticle formation. This review highlights various plant species employed in MnO NP synthesis, including Azadirachta indica, Camellia sinensis, and Ocimum sanctum, and discusses key characterization techniques such as UV-Vis, XRD, FTIR, SEM, TEM, and DLS. Additionally, it explores recent real-world applications of green-synthesized MnO NPs in biomedicine (e.g., drug delivery, MRI imaging, antibacterial activity), environmental remediation (e.g., water purification, pollutant degradation), and energy storage and conversion (e.g., supercapacitors, lithium-ion batteries, fuel cells). The review underscores the promise of plant-based green synthesis as a scalable and eco-friendly route to advanced nanomaterials for diverse technological applications.