Understanding the Formation of Iron Oxide Nanoparticles with Acicular Structure from Iron(III) Chloride and Hydrazine Monohydrate

Iron oxide nanoparticles, nanowires, and nanobelts were prepared from a 50 vol % ethanol solution of 28 mM iron (In) chloride and 0.3 mM polyethylene glycol (20 kDa) by hydrothermal treatment at 120 C, using hydrazine monohydrate (N2H4) as a reducing agent. Factors governing phase and morphology of the iron oxide nanoparticles were studied. The amount of hydrazine added affected the hydrolysis of iron(III); therefore, the type of iron oxyhydroxide formed; this in turn controlled whether akaganeite, goethite, hematite, or magnetite was obtained after the hydrothermal treatment step. For conditions that favored the formation of magnetite, the addition rate of hydrazine was shown to affect the reduction of iron (III) to iron (II) and, hence, the relative amount of magnetite and goethite in the final product. Increasing the pH of the precursor solution to 14 resulted in the formation of magnetite nanobelts. Phase analysis of the intermediate products showed that the magnetite nanobelts were formed from the dissolution of goethite nanowires at high pH, interspersed with the partial reduction of iron(III) to iron(II) by hydrazine, and reaction between iron(M) and iron(II) to form magnetite on the surface of the goethite nanowires.