Sludge-Derived Hercynite–Carbon as a Low-Cost Catalyst for Efficient Degradation of Refractory Pollutants in Wastewater

Developing a robust Fenton-like catalyst through a feasible method is a significant challenge and is crucial for sustainability in wastewater treatment. Herein, we report a novel dual-phase H2O2 activation for •OH generation via both heterogeneous surface-mediated reactions and homogeneous radical propagation pathways. Mechanistic investigations revealed that the surface Fe2+/Fe3+ redox cycle was the primary driver of catalysis at pH 5. Notably, the catalyst produced fewer secondary pollutants than Fenton reactions and was effective in treating pollutants with high concentrations. The oxidative performance of the PAS-ISe was comparable to that of commercial FeSO4·7H2O in terms of chemical oxygen demand (COD) removal efficiency and reaction kinetics. Besides, the utility of the catalyst was 2-75-fold greater than that of state-of-the-art Fenton or photo-Fenton-like catalysts. A detailed techno-economic analysis confirmed the feasibility of this strategy and significant cost advantages over existing heterogeneous catalyst synthesis methods. This study concurrently proposes a low-cost approach to valorizing hazardous sludge and effectively treating industrial wastewater, which may support circular economic principles.