Green synthesis of magnetite (Fe3O4) and hematite (Fe2O3) nanoparticles using Moringa oleifera and Psidium guajava leaf extracts for sustainable applications

Magnetite (Fe₃O₄) and hematite (Fe₂O₃) nanoparticles hold significant potential for catalysis, environmental remediation, biomedicine, and energy generation. However, conventional synthesis methods for iron-oxide nanoparticles (IONPs) are often complicated or involve hazardous reagents, limiting scalability. Although plant extract-mediated green synthesis offers better alternatives, many rely on rare or expensive biomaterials and hazardous precursors or pH-adjusting chemicals, compromising eco-friendliness and cost-effectiveness. To address these challenges, we developed a truly green, efficient, and economical protocol for synthesizing the nanoparticles smaller than 50 nm. Widely available Moringa oleifera (Moringa) and Psidium guajava (Guava) leaf extracts, along with a relatively low-cost, non-toxic FeSO₄·7 H₂O precursor at an optimized concentration, were employed without any harmful chemicals for pH adjustment. Additionally, a unique calcination strategy was applied. This method produced nanoparticles with an average size of 20-30 nm, confirmed by Field Emission Scanning Electron Microscopy (FESEM). Crystalline structures of the magnetite and hematite nanoparticles were validated by X-Ray Diffraction (XRD), and Fe-O bonding with organic capping was identified by Fourier Transform Infrared Spectroscopy (FTIR). These nanoparticles exhibited superparamagnetic behavior with saturation magnetization of 6-13 emu/g, measured by Vibrating Sample Magnetometry (VSM), and strong optical absorption with band gaps from 1.52 to 4.78 eV, determined by UV-Vis spectroscopy and Tauc's plots. Preliminary antibacterial and photocatalytic tests showed moderate bioactivity, highlighting potential environmental and biomedical uses. This eco-friendly, scalable approach combines abundant natural extracts and avoids the use of harmful chemicals, advancing sustainable production of magnetite and hematite nanoparticles and addressing a critical gap in green nanotechnology.