Structural and magnetic studies of Cobalt-Substituted copper ferrites for efficient photocatalytic dye degradation

In this work, cobalt-substituted copper ferrites with the composition CoxCu1-xFe2O4 (0.0 <= x <= 1.0) were synthesized using the sol-gel autocombustion method with citric acid as fuel. The influence of cobalt ion substitution (Co2+) on the structural, magnetic, optical, and photocatalytic properties was systematically studied. A range of characterization techniques, including X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), UV-visible spectroscopy, and vibrating sample magnetometry (VSM), were used to analyze the properties of the synthesized materials. XRD analysis revealed that the crystallite sizes of the samples ranged between 20-25 nm, with interplanar distances, bond lengths between cations, and crystallite size varying according to the degree of cobalt substitution. The formation of the spinel structure and the successful incorporation of cobalt ions into the lattice were confirmed by FTIR spectroscopy. Magnetic measurements showed that increasing the cobalt content enhanced the saturation magnetization while also influencing the Curie temperature and coercivity. The photocatalytic efficiency of the CoxCu1-xFe2O4 samples was evaluated for the degradation of Methylene Blue, Congo Red, and Malachite Green dyes under visible light irradiation. The photocatalytic degradation rates were strongly influenced by the copper-to-cobalt ion ratio, with cobalt-rich compositions demonstrating superior activity. The best photocatalytic performance was observed for intermediate cobalt concentrations (x = 0.4 and x = 0.6), where particle size and dielectric constant behavior led to efficient electron-hole separation and improved degradation rates. Methylene Blue decomposition was significantly enhanced in an alkaline medium (pH 10) due to better adsorption and charge interaction between the dye and the photocatalyst surface. Fitting the experimental data to the Langmuir-Hinshelwood and Weibull models further highlighted the increased degradation rates with increasing pH and cobalt content, supporting the conclusion that cobalt-substituted copper ferrites are highly effective photocatalysts.