Green synthesis of iron oxide nanoparticles using Terminalia bellirica and Moringa oleifera fruit and leaf extracts: Antioxidant, antibacterial and thermoacoustic properties

This study presents a facile biogenic synthesis of iron (Fe) NPs using aqueous extracts of three plant sources: Terminalia bellirica (TB); Moringa oleifera fruit (MOF) and Moringa oleifera leaves (MOL). The total phenolic content was highest for TB extract (3581.36 +/- 2.38 mu g/ml equivalent of gallic acid). The synthesized Fe NPs were characterized using UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). FT-IR spectra of the extracts and nanosuspensions were similar, with peaks observed at around 3300-3400 cm(-1), 1600 cm(-1), 1050-1150 cm(-1) and 500 cm(-1), corresponding to O-H, C=O, C-O and C-H stretching, indicating the participation of biomolecules in the nanomaterial synthesis process. TEM and SEM images show single spherical particles for T-Fe (21.32 nm), and irregular shaped MOF-Fe and MOL-Fe (particle size of 45 nm). XRD analysis confirmed the presence of hematite (alpha-Fe2O3) and ferric oxyhydroxide (FeOOH) in the Fe NPs. The antioxidant activity of the aqueous extracts was higher than that of the biogenic Fe NPs, with TB extract the highest among all, given its higher phenolic content. The antimicrobial activity of Fe-NPs was higher than the extract alone, with T-Fe and MOL-Fe the most potent towards S. aureus and B. subtilis. The thermal conductivity of the Fe NPs dispersed in propylene glycol: water base fluid was determined. The high thermal conductivity of Fe NPs in glycol - water mixtures showed its potential as a possible nanofluid for various heat transfer applications.