Sonophotocatalytic degradation of methylene blue with magnetically separable Zn-Doped-CoFe₂O₄/α-Fe₂O₃ heterostructures

This work reports an approach of highly active sonophotocatalysts through the combined Zn-doping and heterojunction of CoFe₂O₄/α-Fe₂O₃ heterostructures. The novelty lies in the combined Zn-doping and α-Fe₂O₃ coupling strategy to tune the electronic structure and enhance charge separation of spinel-based magnetic nanocatalyst. A sol–gel auto-combustion method was used to synthesize Zn_0.3Co_0.7Fe₂O₄ nanoparticles with ~12% α-Fe₂O₃ content. The Zn-doping increased the magnetization saturation from ~65 to 86 emu/g and narrowed the optical bandgap from ~1.48 to 1.62 eV compared to undoped CoFe₂O₄, indicating a modified electronic structure. Under sonophotocatalysis, near complete methylene blue decomposition was achieved in 45 min for both catalysts, with a 30% synergistic effect observed. The Zn-doping also activated the semiconductor photocatalysis mechanism. The combined Zn-doping and heterojunction approach enables highly active sonophotocatalysts to effectively degrade dye pollutants and mitigate water pollution.