Spatiotemporally optimized dual-stage electro-Fenton system with etched Fe⁰-Fe3O4/CF cathode for efficient sulfadiazine degradation

Abstract

Sulfadiazine (SDZ), a potent antibiotic resistant to conventional biological treatment, presents considerable environmental risks if discharged untreated. Electro-Fenton (EF) is a promising technology in SDZ removal. However, oxygen reduction reaction (ORR) performance deterioration caused by iron deposition and the diverse optimal operating conditions for ORR and ferric reduction reaction (FRR) significantly affect the durability and the SDZ removal efficiency in EF system. In this study, a dual-stage spatiotemporal separation heterogeneous EF system was constructed, employing an air-breathing cathode (ABC) in the first stage and a Fe⁰-Fe₃O₄/CF cathode in the second stage, which effectively addresses the inherent limitations of EF systems by separating the ORR, H₂O₂ activation, and FRR spatiotemporally. A novel K₂FeO₄ etching method was employed to fabricate the Fe⁰-Fe₃O₄/CF cathode, ensuring uniformly dispersed active sites within pores. Under optimal operating conditions, the system achieved complete SDZ degradation in 10 min and 80.42 % total organic carbon (TOC) removal. High Fe(II) retention (55.12 %) on Fe⁰-Fe₃O₄/CF₂₅ after reaction was observed due to effective FRR. Mechanism studies confirmed that ·OH generated from heterogeneous Fenton dominated SDZ degradation, with DFT analysis confirming electron transfer from SDZ to ·OH. The system demonstrated high durability and low energy consumption, maintaining the ability to completely degrade SDZ in 30 min after six uses, with an energy consumption of 8.48 kWh (kg SDZ)^-1 and 0.26 kWh (g TOC)^-1. These findings provide ideas for constructing EF systems with higher SDZ removal efficiency and durability.