Modulation of Charge‐Ordered Carriers Within 3D Fe ₃ S ₄ Polyurethane Foam (Fe ₃ S ₄ ‐PUF) for Efficient Iron Redox Cycling and Continuous‐Flow Photocatalytic Antibiotics Degradation

Photocatalytic antibiotic degradation is an energy-efficient and environmentally friendly approach with the potential for large-scale application but is severely constrained by the lack of efficient and stable catalysts to produce reactive oxygen species (ROS). This research introduces a charge-ordered 3D Fe₃S₄-PUF composite integrated into a custom-built photocatalytic tandem continuous-flow cylinder reactor (TCCR) for antibiotic degradation. The system consistently achieves 100% tetracycline (TC) degradation efficiency with Fe₃S₄-PUF during 130 h of continuous operation, benefiting from the charge-ordered 3D Fe₃S₄-PUF framework and the TCCR design. Mechanism investigations reveal that the abundant Lewis basic ≡SH site and light-induced sustainable Fe²⁺/Fe³⁺ redox cycling within Fe₃S₄ facilitates the production of H₂O₂ and ROS. Density functional theory (DFT) calculations indicate that Fe²⁺ acts as an active site for capturing and activating O₂, leading to either one-electron (O₂→O₂ ^•-→H₂O₂→•OH) or two-electron transfer (O₂→H₂O₂) pathways. Meanwhile, photogenerated electron and the oxygen atoms in H₂O₂ provide electrons to Fe³⁺, facilitating the reduction of Fe³⁺ to Fe²⁺, thus elucidating the Fe²⁺/Fe³⁺ redox cycling mechanism. Moreover, the 3D PUF structure enhances the mass transfer and pollutant-ROS interactions. The continuous-flow photocatalytic reaction validate the efficient antibiotic degradation of Fe₃S₄-PUF composite, suggesting its potential for implementation in large-scale antibiotic wastewater treatment systems.