Influence of Rare Earth Substitution on the Photocatalytic Efficiency of Spinel Ferrite Nanoparticles

Samarium-substituted cobalt–copper ferrite nanoparticles were synthesized via citrate sol-gel auto-combustion method and applied for photocatalytic degradation of Methylene Blue under simulated sunlight. XRD confirmed single-phase spinel structure (Fd3m), with crystallite size decreasing from 23.06 to 17.33 nm due to increased microstrain induced by Sm ions substitution. SEM-EDX studies confirmed nanocrystallinity and elemental composition. UV–Vis analysis revealed a systematic increase in the optical band gap from 1.84 to 2.42 eV with Sm content, indicating modification of electronic structure and band-edge states. The highest photocatalytic efficiency (94.36% in <200 min) was achieved for x = 0.04 sample. Magnetic recovery enables reuse, making Sm-doped Co–Cu ferrites promising materials for wastewater treatment.