In heterogeneous electro-Fenton (EF) catalysis, achieving selective H2O2 generation with efficient •OH production remains challenging due to poor oxygen reduction reaction (ORR) selectivity and cycling stability. This study employs an interfacial spin-state engineering strategy to construct CoFe solid solutions/Fe3O4 heterostructures (CoFess/Fe3O4) through controlled Co doping. Co incorporation induces Fe0 lattice expansion, forming CoFess phases that creates oxygen-bridged heterointerfaces with Fe3O4 (CoFess–O–Fe2+), altering the coordination environment and facilitating the Fe2+ spin-state transition from high-spin (t2g4eg2 S = 2) to intermediate-spin (t2g5eg1 S = 1) configuration at the interface. This modulation optimizes electron transfer dynamics, steering ORR toward the 2-electron ORR pathway with H2O2 selectivity of 75.9%. Co0.1Fess/Fe3O4 (with a 0.1 Co/Fe molar ratio) exhibits exceptional tetracycline degradation performance, achieving 95.0% removal within 60 min, outperforming the undoped catalyst. The degradation involves •OH as the dominant reactive species, with •O2– and 1O2 contributing synergistically to drive tetracycline degradation through hydroxylation, demethylation, and ring-opening pathways. The catalyst demonstrates broad-spectrum pollutant removal and excellent cycling stability, with negligible metal ion leaching. Ecotoxicity assessments confirm that degradation intermediates exhibit low toxicity to aquatic organisms, ensuring high environmental safety. This work elucidates heterometallic doping as an effective spin-state engineering strategy through interfacial electronic reconstruction, providing insights for efficient EF catalysts in antibiotic wastewater treatment.
Li et al. (2026) studied this question.