Preparation, physicochemical characterization, and AC induction heating properties of colloidal aggregates of ferrimagnetic cobalt ferrite nanoparticles coated with a bio-compatible polymer

AC induction heating properties of colloidal nano-aggregates of ferrimagnetic cobalt ferrite magnetic nanoparticles (MNPs) are reported in this study. Bio-compatible chitosan polymer-coated CoFe2O4 MNPs are synthesized using a co-precipitation method. Powder X-ray diffraction indicates the formation of mixed spinel structures for the uncoated (CP) and chitosan-coated (CP-CHN) MNPs, which is also supported by the cation distributions obtained from the Mo center dot ssbauer spectra. The presence of chitosan coating on the surface of the CPCHN MNPs is confirmed using X-ray photoelectron and Fourier transform infrared spectroscopy studies. Transmission electron microscopy shows primary particle sizes of -13 nm, which is larger than the superparamagnetic size limit of the CoFe2O4 MNPs. Hence, the CP and CP-CHN MNPs exhibit ferrimagnetic behaviour at room temperature with estimated saturation magnetization values of -77.4 emu/g and -74.4 emu/g, respectively. The average hydrodynamic diameter is found to be -90 +/- 8 nm for an aqueous dispersion of the CP-CHN MNPs, which indicate the formation of colloidal nano-aggregates due to the ferrimagnetic interaction of the primary MNPs. The CP-CHN sample exhibits a significantly high AC induction heating efficiency of -267.2 +/- 4.0 W/gFe, where the higher heating efficiency is attributed to the combination of hysteresis and relaxationmediated magneto-thermal energy conversion, as confirmed using Stoner-Wohlfarth model-based dynamic hysteresis loop calculations. Further, the heating efficiency decreases with increasing sample concentration due to an increase in dipolar interaction, which is confirmed using semi-empirical calculations, where a lowering of the initial susceptibility is observed at higher concentrations. The higher AC induction heating efficiency, coupled with the demonstrated significant bio-compatibility during in vitro cytotoxicity studies, make the cobalt ferrite nano-aggregates potential candidates for magnetic hyperthermia.

Automated summary

This study investigates the AC induction heating properties of colloidal nano-aggregates of ferrimagnetic cobalt ferrite magnetic nanoparticles (MNPs). CoFe2O4 MNPs coated with bio-compatible chitosan polymer were synthesized using co-precipitation. The presence of chitosan coating was confirmed by various spectroscopy studies. The MNPs exhibited ferrimagnetic behavior at room temperature, and the CP-CHN sample showed significantly high AC induction heating efficiency. The cobalt ferrite nano-aggregates have potential applications in magnetic hyperthermia due to their high heating efficiency and bio-compatibility.