The characterization of MgFe2O4@CeO2 superparamagnetic nanocomposites was thoroughly investigated using powder X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), dispersive X-ray analysis (EDX), elemental mapping (MAP), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and UV–Vis diffuse reflectance spectroscopy (DRS) analyses. The photocatalytic activity of the synthesized samples was evaluated as a novel magnetic nanocatalyst for degrading Congo red (CR) dye in an aqueous solution under visible light at room conditions. The results demonstrate that the efficiency of photocatalytic degradation is higher than that of absorbance and photolysis. The degradation efficiency of photodegradation is 93% within 49% of total organic carbon removal performance. The prepared MgFe2O4@CeO2 magnetic nanocomposites (MNCs) can be easily recovered and recycled for five repeated cycles, demonstrating potential extensive efficiency in magnetic nanocomposites in wastewater and water treatment. The nanoscale morphology of MgFe2O4@CeO2 MNCs was characterized as spherical, with a size range of 35–40 nm, utilizing SEM and TEM techniques. The saturation magnetization (Ms) of the resulting nanocomposites was analyzed by VSM, revealing a value of 3.58 emu/g. Furthermore, the surface area was determined to be 27.194 m2/g using BET analysis, and the band gap was identified as 2.85 eV through DRS analysis.
