Structural, magnetic, and acidic properties of cobalt ferrite nanoparticles synthesised by wet chemical methods

A detailed investigation on the effect of preparation method on the structural, magnetic, and acidic properties of cobalt ferrite nanoparticles prepared by sol–gel and co-precipitation is presented. Citric acid and ethylene glycol were used as gelling agents, while sodium hydroxide and aqueous ammonia were used as precipitating agents. The resulting ferrites were calcined at 450°C and 750°C. Sharper X-ray diffraction (XRD) peaks were observed for the samples calcined at 750°C, indicating greater crystallinity of the samples calcined at higher temperature. Average crystallite sizes fell in the ranges of 7.1–21.1 nm and 30.4–42.1 nm for the samples calcined at 450°C and 750°C, respectively. The infrared spectra revealed two main absorption bands, the high frequency band ν₁ around 600 cm^-1 and the low frequency band ν₂ around 400 cm^-1 arising from stretching vibrations of the oxygen bond with the metal in the tetrahedral (A) and octahedral (B) sites in the spinel lattice. Agglomeration of particles was observed in the scanning electron microscopy (SEM) images. Magnetic parameters of CoFe₂O₄ nanoparticles greatly depended on calcination temperature and preparation techniques. Ammonia temperature programmed desorption (TPD) measurements indicated that weak acid sites predominate medium strength sites, while the number of strong acid sites is the least. Cumulative acidity decreased for the samples calcined at higher temperature. The results underline the effect of preparation conditions on the morphology, crystallite size, and magnetic properties of nano ferrites.