Magnetic nanoparticles such as cobalt ferrite are investigated under clinical hyperthermia conditions for the treatment of cancer. Cobalt ferrite nanoparticles (CFNPs) synthesized by the thermal decomposition method, using nonionic surfactant Triton-X100, possess hydrophilic polyethylene oxide chains acting as reducing agents for the cobalt and iron precursors. The monodispersed nanoparticles were of 10 nm size, as confirmed by high-resolution transmission electron microscopy (HR-TEM). The X-ray diffraction patterns of CFNPs prove the existence of cubic spinel cobalt ferrites. Cs-corrected scanning transmission electron microscopy–high-angle annular dark-field imaging (STEM–HAADF) of CFNPs confirmed their multi-twinned crystallinity due to the presence of atomic columns and defects in the nanostructure. Magnetic measurements proved that the CFNPs possess reduced remnant magnetization (M_R/M_S) (0.86), which justifies cubic anisotropy in the system. Microwave-based hyperthermia studies performed at 2.45 GHz under clinical conditions in physiological saline increased the temperature of the CFNP samples due to the transformation of radiation energy to heat. The specific absorption rate of CFNPs in physiological saline was 68.28 W/g. Furthermore, when triple-negative breast cancer cells (TNBC) in the presence of increasing CFNP concentration (5 mg/mL to 40 mg/mL) were exposed to microwaves, the cell cytotoxicity was enhanced compared to CFNPs alone.

This study evaluates the effect of equimolar substitution of manganese by cobalt or nickel in hexacyanoferrate (HCF) open frameworks as electrode materials for Na-ion batteries. As the stability of Mn–N bonds is crucial to obtain long term stability and cyclability of manganese (Mn–HCF), the samples were analyzed thoroughly using several spectroscopic and structural methods. The XPS and infrared experiments reveal that the charge density around Fe is modulated by the presence of Co or Ni, which is associated with their high polarizing power, leading to decreased cell distortion as revealed by XRD. The Rietveld refinement demonstrated that the octahedra built by 3d metals and the cyanide nitrogen were distorted with the axial bond distances being larger than the equatorial distances. This octahedral distortion promotes the spin behavior of 3/2 for Mn²⁺ confirmed by magnetic experiments; the arising of this spin state is attributed to d orbital splitting determined by UV-Vis experiments. Therefore, the changes upon Mn substitution are related to the modification of the covalent character of Mn–N bonds, modulated by the effect of the Ni and Co polarizing power. All these properties improve the electrochemical stability of the Ni or Co substituted materials as Na-ion batteries, leading to higher capacity retention even at higher C-rates (5C) and good capacity recovery, in comparison with those obtained for Mn–HCF.