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Spinel cobalt ferrite (CoFe2O4) nanoparticles have garnered significant interest due to their versatile properties and potential applications. Among the various factors influencing their properties, annealing temperature stands out as a crucial parameter. In this comprehensive analysis, we studied the effects of various annealing temperatures (400, 500, 600, and 700 °C) on the structural, optical, morphological, magnetic, and photocatalytic characteristics of CoFe2O4 nanoparticles. X-ray powder diffraction (XRD) studies reveal the crystalline structure of CoFe2O4 nanoparticles. The crystallite size was increased from 13.544 nm to 20.312 nm with the increasing annealing temperature from 400 to 700 °C. The effect of annealing temperature on cationic-anionic interaction of the nanomaterials is studied through Fourier transform infrared spectroscopy (FTIR). Morphological and elemental composition of the nanomaterials is evaluated through Field Effect Scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Changes in annealing temperature lead to variations in particle size, morphology, and surface area, influencing their catalytic activity. UV–visible spectroscopy (UV–Vis) and photoluminiscene spectroscopy (PL) were employed to investigate the optical properties of CoFe2O4 nanoparticles. Annealing temperature variation influences the band gap energy, affecting the absorption and emission properties of the nanoparticles. Tauc's plot was employed to obtain the band gap of the nanomaterials. The band gap was decreased from 2.33 eV to 1.92 eV with rise in annealing temperature. An emission peak at 465.80 nm was observed through PL spectroscopy. The magnetic properties of CoFe2O4 nanoparticles, including saturation magnetization and coercivity, are examined using a vibrating sample magnetometer (VSM). The sample annealed at 400 °C has shown highest magnetic parameters with saturation magnetization, coercivity, and remanent magnetization of 51.53 emu/g, 1860 Oe, and 17.5 emu/g respectively. Annealing temperature variation alters the magnetic behavior, affecting the nanoparticles' utility in magnetic and photocatalytic applications. The photocatalytic performance of CoFe2O4 nanoparticles is examined through degradation of methylene blue dye under UV–Visible irradiation. The sample annealed at 400 °C exhibited the highest photocatalytic efficiency, achieving 74.46% discoloration. The involvement of hydroxyl ion (OH−) and singlet oxygen ion (O2−) was verified through a Scavenger test using Isopropyl Alcohol (IPA) and Disodium Ethylenediaminetetraacetic Acid (EDTA 2NA), respectively. The kinetics of dye removal was analyzed using various rate models. Additionally, the material's stability was evaluated by calculating its recycling efficiency over four successive cycles. [ABSTRACT FROM AUTHOR]

The change in the behavior of pristine cobalt ferrite on doping it with rare-earth (RE) metal ions has been investigated. The CoFe2-xDyxO4 (where x = 0–0.1, with stepsize of 0.02) nanomaterials were synthesized by the co-precipitation method and corresponding morphological, structural, optical, and magnetic properties were observed. The x-ray diffraction (XRD) spectra revealed that all the prepared samples show a crystalline nature and that the crystallite size reduces with increasing dysprosium (Dy) concentration from 21 to 9 nm for x = 0.02 to x = 0.1. The Fourier-transform infrared spectroscopy (FTIR) spectra in the 4000–400 cm−1 range supported the material formation. Diffused reflectance spectroscopy (DRS) was used for the energy bandgap calculation. Field-emission scanning electron microscopy (FESEM)–energy dispersive x-ray spectroscopy (EDAX) spectra showed the surface morphology and elemental composition of the materials and no peaks corresponding to other elements were observed. Room-temperature Vibrating sample magnetometer (VSM) studies at a field of 7 T revealed that the sample with x = 0.02 had the highest value of saturation magnetization at 77.39 emu/g, which is even greater than the CoFe2O4 sample, while the sample composition x = 0.1 had the least saturation magnetization of 36.41 emu/g. This reduction was brought on by the lower magnetic interactions between the RE3+ and Fe3+ ions. Such materials can have applications in optoelectronic, magnetic hyperthermia, and high-frequency devices. [ABSTRACT FROM AUTHOR]