Nonaqueous synthesis of magnetite nanoparticles via oxidation of tetrachloroferrate anions by pyridine-N-oxide

• Published in: Solid state sciences Vol. 92; pp. 81 - 88
• Main Authors: Kamura, Atsuo, Idota, Naokazu, Sugahara, Yoshiyuki
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 01-06-2019
• Subjects: Magnetite; Nanoparticles; Nonaqueous synthesis; Pyridine-N-oxide; Superparamagnetism; Nanoparticles; Nonaqueous synthesis; Superparamagnetism; Magnetite; Pyridine-N-oxide
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2018.10.018

Fe3O4 nanoparticles were prepared from a salt comprising a tetrachloroferrate anion and a methyltrioctylammonium cation in toluene using ethylenediamine as a reductant and pyridine-N-oxide as an oxygen donor and an oxidant. The X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy showed that the product was Fe3O4. Water content measurement with a Karl Fischer moisture meter showed the presence of only a small amount of water in the present system, indicating a limited contribution of water to the formation of Fe3O4 nanoparticles. The Fe3O4 nanoparticle size based on transmission electron microscopy (TEM) observation was approximately 10–30 nm, a result consistent with the crystallite diameter estimated by Scherrer's equation (15.7 nm). A possible reaction mechanism involves the reduction of Fe3+ to Fe2+ by ethylenediamine, coordination of both ethylenediamine and pyridine-N-oxide to Fe2+, and oxidation of a part of Fe2+, leading to a mixed-valence iron-oxygen network, which was a precursor of Fe3O4 nanoparticles. As concerns magnetic properties, saturation magnetization of the product was 57 emu g−1. Both the coercivity and remanent magnetization were nearly zero and the similar decreases in magnetization were observed above the blocking temperature in the zero-field-cooled and field-cooled curves, results indicating the formation of superparamagnetic Fe3O4 nanoparticles.
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•Fe3O4 nanoparticles were prepared via oxidation of FeCl4− in a nonaqueous medium.•Iron valence was controlled by ethylenediamine and pyridine-N-oxide.•Fe3O4 nanoparticles showed the particle size range of 10–30 nm.•Fe3O4 nanoparticles exhibited superparamagnetic behavior.