Upcycling Iron Oxide Scale Slag into a High‐Performance, Sustainable Ozone Catalyst

Upcycling iron slag into a monolithic catalyst has led to low-cost heterogeneous catalytic ozonation (HCO) strategies for water treatment. The primary industrial challenges are the low chemical oxygen demand (COD) reduction rate in treating authentic wastewater and difficulties sustaining close-loop reaction cycles. In this study, we present a monolithic catalyst transformed from low-cost iron oxide scale slag (IOS_M) for highly efficient, sustainable ozone catalysis. The IOS_M, constituted of 59.70 % Fe₂O₃ and 40.30 % Fe₃O₄, effectively decomposes ozone into superoxide radicals (⋅O₂ ^-) through a close-loop cyclic reaction facilitated by interfacial charge transfer. This mechanism enables super-fast degradation of 100 mg L^-1 tetracycline at ozone concentrations below 1.00 mg L^-1 in just four minutes, with the iron leaching merely at 59 μg L^-1 after 10 cycles. In tests with authentic antibiotic wastewater, the IOS_M-based HCO system achieves a record-breaking 81.70 % COD reduction within two hours. This research underscores the potential of upcycling industrial waste into highly effective ozone catalysts for sustainable practices in wastewater treatment.