Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

Unaggregated La0.82Sr0.18MnO3+delta perovskite nanoparticles with a mean crystallite size of 22 nm were successfully synthesized through an aqueous combustion process (Glycine Nitrate Process, GNP) which takes advantage of exothermic, fast and self-sustaining chemical reactions between metal nitrates and glycine as a suitable organic reducing agent. The influence of G/N molar ratio on the phase purity, crystallite size and manganese valency was screened. Fuel-rich conditions were selected to improve chelation of the cations in acidic pH and ensure an accurate control of the cationic composition. Fast calcination was optimized to enhance crystallinity of the nanoparticles and subsequent milling step was performed to favour their desaggregation. The manganite nanoparticles were thoroughly characterized by X-ray diffraction (XRD), elemental chemical analysis, Mohr salt titration and transmission electron microscopy (TEM). According to a process derived from the Stober's method, they were uniformly coated with a 5 nm thick silica shell, as evidenced by TEM, infrared spectroscopy, zeta potential measurements and dynamic light scattering experiments. Preliminary heating experiments in a ac magnetic field showed these core@shell nanoparticles fulfill the requirements for self-controlled magnetic fluid hyperthermia, considering their size (20-70 nm) and their maximum heating temperature (43 degrees C) which is controlled by the Curie temperature of the magnetic cores.