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

Abstract 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 Fe ₃ S ₄ ‐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 Fe ₃ S ₄ ‐PUF during 130 h of continuous operation, benefiting from the charge‐ordered 3D Fe ₃ S ₄ ‐PUF framework and the TCCR design. Mechanism investigations reveal that the abundant Lewis basic ≡SH site and light‐induced sustainable Fe ²⁺ /Fe ³⁺ redox cycling within Fe ₃ S ₄ facilitates the production of H ₂ O ₂ and ROS. Density functional theory (DFT) calculations indicate that Fe ²⁺ acts as an active site for capturing and activating O ₂ , leading to either one‐electron (O ₂ →O ₂ ^•− →H ₂ O ₂ →•OH) or two‐electron transfer (O ₂ →H ₂ O ₂ ) pathways. Meanwhile, photogenerated electron and the oxygen atoms in H ₂ O ₂ provide electrons to Fe ³⁺ , facilitating the reduction of Fe ³⁺ to Fe ²⁺ , thus elucidating the Fe ²⁺ /Fe ³⁺ 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 Fe ₃ S ₄ ‐PUF composite, suggesting its potential for implementation in large‐scale antibiotic wastewater treatment systems.