Modulation of Charge-Ordered Carriers Within 3D Fe3S4 Polyurethane Foam (Fe3S4-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 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.