The effect of organics on the structure and magnetization of electro-synthesised magnetite nanoparticles

An electro-oxidation method was used to produce magnetite (Fe₃O₄) nanoparticles in the presence of several different organic molecules. The synthesis was carried out in a thermostatic electrochemical cell at 60 °C with two iron electrodes, using an electrolyte which was an aqueous solution of sodium sulfate, and either thiourea, propylamine, sodium butanoate, hexamethylene-tetra-amine, β-cyclodextrine, or tetrabutylammonium bromide. All the nanoparticle samples were characterized by X-ray diffraction, electron microscopy, magnetometry, and Mössbauer spectrometry. Electron microscopy images confirmed that the mean magnetite particle size is in the range 20–90 nm, and depends critically on the type of organic additive. Room-temperature saturation magnetization of the samples ranges from 19 to 91 Am² kg⁻¹, again depending on the type of organic molecules. Mössbauer spectra, which were recorded at 18 and 290 K for all the samples using a Co⁵⁷ source, are typical of non-stoichiometric Fe_3-δ O₄, with a small excess of Fe³⁺, 0.05 ≤ δ ≤ 0.10. In most cases, there was relatively little organic material associated with the magnetite nanoparticles, but for molecules with carboxylic groups, the strong coulombic interaction led to an association between the negatively charged carboxylate and Fe³⁺, leading to the formation of a secondary paramagnetic phase.