Comparative study of the activation of peroxymonosulfate and persulfate by ferrocene for bisphenol A degradation

Persulfate-based advanced oxidation processes (PS-AOPs) exhibit enhanced oxidant stability and radical persistence compared to traditional H₂O₂-AOPs. This study comparatively evaluates redox-active ferrocene (Fc/Fc⁺) for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS) toward bisphenol A (BPA) degradation. The Fc/PMS system demonstrates superior BPA removal efficiency and kinetics relative to Fc/PDS, mechanistically attributed to the lower activation barrier for asymmetric PMS (accepting 0.91 e⁻ from Fc) versus symmetric PDS (accepting 0.88 e⁻ from Fc), as quantified by density functional theory (DFT) with Bader charge analysis. Sulfate (SO₄^•−) and hydroxyl ^(•OH) radicals were identified as the dominant reactive species in both systems. Crucially, O₂-mediated Fc-to-Fc⁺ oxidation promotes electrostatic migration of anionic persulfates to the catalyst surface, enhancing activation efficiency. Both systems sustain contaminant removal through Fc⁺ reduction by persulfates, demonstrating regenerative catalytic behavior. For practical application, future work should prioritize catalyst design strategies to accelerate Fc⁺ recycling kinetics and enhance system resilience under oxygen-limited conditions.