Síntese de nanoestruturas de óxido de ferro para aplicações em hipertermia magnética

Abstract

In this work, the structural and magnetic properties of iron oxide nanoparticles synthesized via the hydrothermal method were investigated. Sodium phosphate and sodium sulfate were added to control the morphology of the nanostructures. A reduction process using a gas mixture (N2 95% - H2 5 was employed to ensure the formation of the magnetite phase (Fe3O4) in the final samples. Structural characterization was performed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns confirmed the crystalline Fe3O4 phase in all studied samples. The average size of the crystallites, estimated by the full width at half maximum of the XRD peaks extracted from the Rietveld refinement and using the Scherrer equation, indicated that nanoparticles diameters are in the range from 22 to 40 nm range. TEM images revealed morphologies such as spheres, rods, tubes, and rings, depending on the phosphate/sulfate ratio. Magnetic characterization included magnetization measurements as a function of field (M vs. H) and temperature in the Zero Field Cooling – Field Cooling (ZFC/FC) mode. These results indicate that the nanoparticles are not in a superparamagnetic state at room temperature, suggesting sizes larger than the typical magnetic single-domain limit. Furthermore, the data point to a highly interacting system. Magnetic hyperthermia measurements, conducted under an AC magnetic field of 32 kA/m and a frequency of 311 kHz, showed a temperature increase of 7 °C within 100 to 200 s. Analysis of these results yielded Specific Absorption Rate (SAR) values between 260 to 510 W/g. Notably, the sample with ring-like morphology proved to be the most promising for hyperthermia treatment applications.