Synthesis and characterization of Fe₃O₄ nanoparticles coated with organic surfactants: oleic acid and essential oil

Full text: Magnetic nanoparticles, such as Fe₃O₄ coated with organic material, are interesting for technological applications (biomedical and engineering). Several papers show drastic changes in the magnetic properties, which is related to the magnitude of the particle-particle interaction. However, there is no clear explanation of the origin of this relation and the how the surface-to-volume ratio affect that magnetic response. In order to shed a light into these issues, magnetite (Fe₃O₄) nanoparticles with different sizes were synthesized by thermal decomposition method and coating them with oleic acid (AO). Furthermore, aliquots of these samples will be additionally coated with essential oil (EO) extracted from the leaves of Croton Cajucara Benth (SACACA) an amazon plant. The structural, microscopic, and magnetic properties of these samples (Fe₃O₄@AO and Fe₃O₄@AO/OE) were characterized by X-ray diffraction, transmission electron microscopy, FTIR, magnetic measurements and Mössbauer spectroscopy. These characterizations are vital for determining the role of the particle-particle interactions in the magnetic response; and the effects of the surface disorder extent as the nanoparticles size varies. Preliminary results revealed that we obtained Fe3O4 nanoparticles with different sizes, being ~6nm the smallest. The TEM results showed nanoparticles of almost-spherical or polygonal shapes, depending on the synthesis parameters. FTIR spectroscopy confirmed the presence of AO, suggesting the successful surface coating. For the small nanoparticles, magnetic measurements revealed blocked and superparamagnetic states at low and high temperatures, respectively. When the particle size is increased, the transition to the superparamagnetic state shifts to higher temperatures and becomes above 300K, depending on the particle size. Mossbauer spectroscopy data analysis confirms these results. (author)