Architecture-engineered Fe₃O₄-MnO₂ composite for peroxydisulfate activation: Visible light-enhanced redox cycling mechanism

Unlike conventional Fe₃O₄-MnO₂ composites, an architecture-engineered Fe₃O₄-MnO₂ (FM-21) heterostructure was constructed by anchoring Fe₃O₄ nanoparticles onto α-MnO₂ nanorods. Under visible light irradiation, the FM-21/PDS system achieves 96.5 % Orange II degradation within 60 min with a kinetic rate constant of 0.0596 min −1 , significantly outperforming its individual components and dark condition controls. Multiple characterization techniques confirm that the unique interfacial configuration establishes a direct Z-scheme charge transfer pathway, substantially enhancing charge carrier separation efficiency. XPS analysis provides direct evidence that visible light accelerates the co-cycling of Fe 3+ /Fe 2+ and Mn 4+ /Mn 3+ redox pairs, thereby maintaining highly efficient PDS activation. Quenching experiments and EPR analysis further reveal that the synergistic effect between radical and non-radical pathways, which is dominated by singlet oxygen ( 1 O₂) and holes (h + ), drives the degradation process. This mechanism enables the degradation of various pollutants with minimal dependence on their charge characteristics, demonstrating the catalyst's broad applicability. The catalyst also exhibits practical advantages including magnetic separability and stable performance over five consecutive cycles. This study demonstrates that the synthesized FM-21 exhibits significant potential for visible light-enhanced PDS activation in eliminating recalcitrant organic pollutants.