Monodisperse MFe₂O₄ (M = Fe, Co, Mn) Nanoparticles

TLDR

Iron oxide nanoparticles and their dispersions in various media hold promise for magnetic nanodevice and biomagnetic applications. Monodisperse Fe₃O₄, CoFe₂O₄, and MnFe₂O₄ nanoparticles (3–20 nm) are produced by a high‑temperature solution reaction of metal acetylacetonates with 1,2‑hexadecanediol, oleic acid, and oleylamine, and their hydrophobic surfaces can be rendered hydrophilic with bipolar surfactants for aqueous dispersion. The synthesized nanoparticles exhibit a cubic spinel structure, and Fe₃O₄ can be oxidized to Fe₂O₃ as confirmed by XRD, NEXAFS, and SQUID magnetometry.

Abstract

High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3, with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe3O4) nanoparticles. Similarly, reaction of Fe(acac)3 and Co(acac)2 or Mn(acac)2 with the same diol results in monodisperse CoFe2O4 or MnFe2O4 nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe3O4 can be oxidized to Fe2O3, as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.