Insight into magnetite nanoparticle phase evolution in solvothermal synthesis through a simple method based on iron chloride and metallic iron

Abstract

This paper presents the development and optimization of the synthesis of magnetic nanoparticles composed of iron oxides by a solvothermal method with benzyl alcohol using iron(III) chloride hexahydrate as a metallic precursor in the substitution of iron(III) acetylacetonate. The synthesis parameters were studied and varied to obtain a high yield of magnetite. Metallic iron was evaluated as a reducing agent and iron source. Furthermore, the use of urea as a precipitation agent was crucial to increasing the yield of magnetite, at once reducing the acidity of the medium and inducing the precipitation of Fe²⁺ ions. Longer treatment times and no stirring led to an increase in the yield of magnetite, whose formation process followed the Ostwald step rule. The particles were characterized by X-ray diffraction, Mössbauer spectroscopy, FTIR, TEM, SEM-FEG and VSM (Vibrating Sample Magnetometry). The phases were quantified by the Rietveld method and Mössbauer spectroscopy, and a 97% maximum yield of magnetite was achieved. The polymerization of benzyl alcohol during the solvothermal treatment was shown to play an important role in the nanoparticle capping. The polymerized resin was characterized by FTIR and NMR-¹H, and a mechanism for the polymerization reaction was proposed to elucidate the synthetic route and its relationship to particle formation and stability.