The Effect of Cryochemical Synthesis Parameters of Iron Oxide Nanoparticles on Their Size, Structure and Magnetic Properties

In this work, cryochemical approaches are used to obtain nanoparticles of magnetic iron oxides of various compositions and morphologies. Cryochemical coprecipitation of iron(II) and (III) salts with an ammonia solution in the temperature range from –30 to –50°C leads to the formation of single-domain superparamagnetic maghemite nanoparticles with an average size of 6 ± 2 nm, which is smaller than the average particle size (20 ± 2 nm) obtained by the classical coprecipitation method. However, cryochemical coprecipitation leads to the formation of goethite impurity. Single-domain superparamagnetic magnetite nanoparticles with an average diameter of 10 ± 2 nm without goethite impurity can be obtained by cryochemical precipitation of iron(II) sulfate with ammonia in air. Thermal decomposition of cryomodified iron salts allows obtaining maghemite nanoparticles of 40–300 nm in size in the case of iron(III) acetylacetonate and iron(III) formate, as well as micron-sized maghemite and goethite particles of complex shape in the case of iron(III) ammonium citrate and iron(II) gluconate.