Metal–semiconductor electron-rich interface governs the enhanced activity of spinel ferrite toward heterogeneous electro-Fenton process

Transition metal-based bimetallic spinel ferrites are widely used for heterogeneous Fenton catalysis due to their excellent catalytic activity and fine-tunable physiochemical properties. However, the critical role of incorporating metal species into spinel structures in governing enhanced activity remains ambiguous. Herein, monodisperse variable-valence (Mn, Co, and Cu) and fixed-valence (Ni and Zn) metal-substituted magnetite nanospheres loaded on multiwalled carbon nanotubes (MFe₂O₄/MWCNTs) were solvothermally prepared, and examined as catalysts for the heterogeneous electro-Fenton process within a dual-compartment ceramic membrane reactor that could efficiently produce H₂O₂ in situ. A catalytic performance evaluation indicated a significant promotion in the presence of Cu and Zn, moderate promotion of Ni, and inhibition of Mn and Co, compared to pristine Fe. Various characterizations illustrated that the observed increase in activity can be attributed to the improvement of several important properties (e.g., surface Fe(II) content, MO adsorption capacity, and electron transfer rate) associated with metal doping. Particularly, the formation of metal–semiconductor (Cu⁰–CuFe₂O₄) interfaces in the most active Cu-containing catalysts enables electron transfer from Cu⁰ to CuFe₂O₄, accelerating active Fe(II) regeneration and H₂O₂ conversion to ^[rad]OH. This study enhances the understanding of the activity of spinel oxides and inspires the construction of highly efficient heterogeneous catalysts.