One-step solid state synthesis of cappedγ-Fe2O3 nanocrystallites

Abstract

The thermally induced solid state synthesis of soluble organophilic maghemite(γ-Fe2O3) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt stateof Fe(NO)3·9H2O andRCOOH (R = C11H23, C15H31)at 240 °C. The method yields well-crystallized nanoparticles ofγ-Fe2O3 functionalized with the corresponding aliphatic acid. Transmission electron microscopy(TEM) and atomic force microscopy (AFM) observations reveal composite particles withfaceted magnetic cores and average size of 20 nm, which are well capped with thesurrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermalanalysis suggest a bimodal configuration of the organic shell including chemicallycoordinated and physisorbed molecules of aliphatic acid. The chemical bonding of thecarboxylate groups to the surface iron atoms is also indicated by a paramagnetic doubletwith unchanged area in the variable temperature Mössbauer spectra. The spinelγ-Fe2O3 particles exhibit perfect structural and magnetic ordering, includingthe almost ideal ratio of octahedral to tetrahedral positions(5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy.Magnetic measurements demonstrate the suitable properties required in various(bio)magnetic applications like superparamagnetic behavior at room temperature, highsaturation magnetization achievable at low applied fields and suppressed magneticinteractions.