Preparation, phase analysis and electrochemistry of magnetite (Fe3O4) and maghemite (γ-Fe2O3) nanoparticles

Magnetite and maghemite superparamagnetic nanoparticles were prepared via co-precipitation synthetic route. The phases of the iron nanoparticles were quantitatively confirmed from their powder X-ray diffraction patterns (XRD) and cyclic voltammetry. UV-Visible, Fourier transform infrared (FT-IR), Energy dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM) were used to differentiate both types of iron nanoparticles. Cyclic voltammetry showed that magnetite nanoparticles exhibited one redox couple while maghemite had both a redox couple and an irreversible anodic peak. The results shows that aqueous ammonia was more desirable for the synthesis of narrow sized and mono-phased magnetite nanoparticles. The iron oxides prepared from sodium hydroxide showed pronounced energy bandgap reduction in comparison to those obtained from aqueous ammonia. Selected area electron diffraction (SAED) patterns of the as-prepared iron oxides nanoparticles confirmed the nanoparticles were crystalline. Superparamagnetism of magnetite nanoparticles was confirmed from the hysteresis loop; magnetisation saturation (Ms) value was 69.3 emug -1 while the BET surface area was 110.31 m²/g. The average particle sizes of the nanoparticles were 13 nm. The bandgap values were 3.9 and 2.6 eV for magnetite and maghemite nanoparticles, respectively.