Green synthesis of magnetite (Fe3O4) and hematite (Fe2O3) nanoparticles using Moringa oleifera and Psidium guajava leaf extracts for sustainable applications
Syeda K. Begum, Dalia Shabnam, Nazmul Haque, Mohammad Jahidul Alam, Jannatul Ferdous, Umme Juharia Binte Nur, Kaniz Fatema, Rayhana Jannat Shabiha, Ronald J. Clarke, Pial Chowdhury, Md. Nizam Uddin
Abstract
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.