No abstract

Magnetic Co 3 O 4 nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co 3 O 4 NPs were prepared via sol-gel method and encapsulated with a layer of TiO 2 , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co 3 O 4 spinel with TiO 2 . The Co 3 O 4 cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO 2 . According to the neutral red uptake assay, the coating of the cores with TiO 2 significantly decreases the cytotoxic character of the Co 3 O 4 particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co 3 O 4 @TiO 2 core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.

In this work, multiferroic composites were produced from CoFe 2 O 4 and KNbO 3 mixtures via control of the heat treatment temperature. For this, CoFe 2 O 4 nanoparticles were produced by sol-gel method, while KNbO 3 was synthesized by microwave-assisted hydrothermal synthesis. The powders were homogenized and subjected to heat treatment at 300, 400 and 500 • C for 5 h. The structural, electrical and magnetic properties were characterized. The results of X-ray diffraction indicated that there was no formation of secondary phases with heat treatment. Raman vibrational modes confirmed the presence of KNbO 3 and CoFe 2 O 4 in the prepared composites. SEM analysis showed that the composite microstructure consists of smaller ferrite particles arranged on the surface of largest cubic KNbO 3 particles. The improvement of coercivity (H C = 382.1Oe) and dielectric constant (ϵ'~7860) was observed for the composite thermally treated at 300 • C. The obtained results show the potential application of KN:CFO composites for multifunctional devices.