Cobalt ion-incorporated nanocrystalline spinel cubic zinc ferrite for targeted magnetic hyperthermia and sensing applications†

Abstract

To enhance the therapeutic efficacy of magnetic hyperthermia, the effective anisotropy energy barrier of magnetic nanoparticles must be optimized since it affects relaxation dynamics and self-heating capabilities. Tuning the magnetic anisotropy of soft zinc ferrite nanoparticles was achieved in this work via doping of ferromagnetic cobalt ions for controlled hyperthermia therapy. We synthesized four nanocrystalline zinc ferrites doped with cobalt ions of varying concentrations [Co_xZn_1−xFe₂O₄ (x = 0.00, 0.10, 0.30, and 0.50)] using the standard chemical co-precipitation method. The role of doping Co²⁺ ions in modifying the physical properties, including microstructural, electronic, optical and magnetic characteristics, of pure zinc ferrite nanoparticles was thoroughly investigated using several characterization techniques. The obtained TEM images verified good homogeneity in both the size and shape of the studied nanocrystalline ferrites. The optical indirect bandgap was estimated to be 1.55 ± 0.03 eV for the nanosized ferrites. Substitution of ferromagnetic cobalt ions in appropriate amounts improved the magnetic responses of the doped zinc ferrite nanoparticles, and thereby, several magnetic parameters such as coercivity, magnetic anisotropy and magnetization were observed to increase gradually. The tunable magnetic anisotropy energy barrier of pristine ZnFe₂O₄ nanoparticles was achieved via Co²⁺ ion doping, and consequently, the induction heating efficiency of the doped ferrite samples improved. Owing to the incorporation of magnetic cobalt ions, the blocking temperature was found to increase, which highly affected the relaxation dynamics and superparamagnetic behavior of the zinc ferrite nanoparticles. The presence of one semicircle in the Cole–Cole plot suggested that the grain boundaries played a more significant role than the conductive grains in determining the dielectric properties of the nanoferrites. The as-synthesized nanomaterials were further explored for the sensing of the herbicide metribuzin. It was observed that the conductivity of the Co²⁺ ion-doped zinc ferrite nanoparticles decreased in the presence of metribuzin, with 50% cobalt ion-doped zinc ferrite nanoparticles exhibiting a better performance compared with the pristine sample in metribuzin herbicide sensing. The limit of detection (LOD) was determined to be 1 ppm. Hence, it was successfully demonstrated that cobalt ion-incorporated zinc ferrite nanoparticles showed potential for use in magnetic hyperthermia and metribuzin herbicide sensing applications.