Supermagnetic Mn-substituted ZnFe₂O₄ with AB-site hybridization for the ultra-effective catalytic degradation of azoxystrobin

Spinel ferrites with magnetic properties have great potential for the decontamination of aqueous systems due to their ease of recycling by magnetic separation. Herein, the purpose is to enhance ZnFe₂O₄ spinel properties in terms of magnetization and catalytic performance via Mn substitution into the crystal structure. Zn_1−xMn_xFe₂O₄ (x = 0-1) nanoclusters were successfully synthesized via an optimal hydrothermal process, in which additives (i.e., citric acid and ammonia) play key roles in inhibiting impurity phase formation via homogenizing the distribution of metal ions and slowing down the reaction rate. At a Zn/Mn ratio of 1 : 3, the nanocluster Zn_0.25Mn_0.75Fe₂O₄ (ZMF_0.75) composed of nanoparticles with sizes ranging from 5 to 10 nm shows the highest saturation magnetization (Ms = 68 emu g⁻¹, which is ∼5 times greater than that of ZnFe₂O₄) and the best catalytic performance, with >99% azoxystrobin (AZX) degradation in a Fenton-like system. Moreover, the findings unveiled that the balance of Zn and Fe occupation in the polyhedron centres in the spinel crystal is broken upon replacing Zn with Mn. In all probability, the Zn/Fe/Mn cross-occupation phenomenon is essential for enhancing the activity of Fe and Mn multivalent metal atoms. A plausible mechanism for the synergistic effect of multiple active sites in ZMF_0.75 on the formation of HO˙ and HO₂˙ radicals is proposed. This work proves that Mn-substituted ZnFe₂O₄ could be an efficient heterogeneous Fenton-like catalyst for EOC decontamination in aqueous systems with ease for recycling via magnetic separation.