Citrate-capped iron oxide nanoparticles: ultrasound-assisted synthesis, structure and thermal properties

The present work describes the synthesis of iron oxide magnetic nanoparticles (IONP) and citrate-capped IONP (IONP-citrate), via conventional chemical routes and ultrasound-assisted approaches. IONP and IONP-citrate samples were characterized by x-ray diffraction (XRD), vibrational spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic light scattering (DLS). XRD analyses allowed the crystalline structure determination, evidencing the formation of magnetite phase in all samples. FTIR provided evidence of chemical structures involving hydroxylated species at IONP surface, replaced by citrate during capping, to obtain IONP-citrate samples. Mean particle size, determined from DLS, varied from (approximately) 172 to 34 nm, decreasing as the energy transferred from the ultrasound device during synthesis increases. SEM images showed a regular spherical morphology, regardless the capping or perturbation imposed during synthesis.