In-situ cathode induction of HKUST-1-derived polyvalent copper oxides in electro-Fenton systems for effective sulfamethoxazole degradation

In this study, a graphite felt (GF) electrode material supporting a Cu-based catalyst (CuHDC-400/GF) was prepared by a hydrothermal process and subsequent heat treatment. A heterogeneous electro-Fenton (EF) system was built to investigate the degradation of sulfamethoxazole (SMX) by the composite cathode. Scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the physical and chemical properties of the composite cathode. The results show that the composite cathode CuHDC-400/GF has excellent catalytic performance, achieving 100 % removal of SMX (10 mg/L) within 45 min (aeration rate = 0.6 L min−1, current density = 5 mA cm−2, initial pH = 5.6). Furthermore, efficient removal of SMX can be achieved over a wide pH range (pH = 3–9). The electrode material can still efficiently degrade SMX after eight cycles. Compared with a heterogeneous EF system, in which the Cu catalyst was directly added to the reaction solution, using CuHDC-400/GF as the cathode realizes the in-situ catalysis of H2O2, leading to reduced catalyst consumption and enhanced electrode stability. The investigation of potential SMX degradation pathways and mechanisms revealed that the continuous production of active free radicals is facilitated by the redox cycle between CuⅠ and CuⅡ on the electrode surface, which can enable SMX degradation. Unlike the Fe-based Fenton reaction, the active superoxide radical O2– was identified as the major contributor to SMX degradation in this system, followed by the hydroxyl radical OH. The active sites for SMX degradation were predicted by density functional theory calculations. Combined with the measured mass/charge ratios, the possible degradation paths and intermediates of SMX were predicted. Furthermore, toxicity analysis shows that toxicity significantly declines after degradation. This work is expected to inspire subsequent research on heterogeneous EF cathode materials with high catalytic performance.