Fe3C-Biochar hybrid cathode boosts in situ production of singlet oxygen for efficient heterogeneous electro-Fenton abatement of nitenpyram

Heterogeneous Electro-Fenton (HEF) technology, which requires only oxygen and electric energy, holds significant potential for organic wastewater treatment due to its high efficiency. In this study, an iron-carbon composite cathode catalyst (Fe 3 C/BC) featuring highly dispersed Fe 3 C active sites on biochar (BC) was designed and synthesized to degrade nitenpyram (NTP), a representative neonicotinoid pesticide. The optimized Fe 3 C/BC-HEF system exhibited remarkable catalytic activity for NTP degradation, along with strong pH tolerance (3.0–9.0) and adaptability to various water matrices. This excellent performance can be attributed not only to its enhanced H 2 O 2 generation capability but also to the obviously faster H 2 O 2 activation efficiency to produce reactive oxygen species (ROS) for NTP degradation. Reactive species quenching experiments and electron paramagnetic resonance (EPR) spectroscopy confirmed that singlet oxygen (¹O 2 ) was the dominant reactive species responsible for NTP degradation. Furthermore, combined with HPLC-MS/MS analysis and Fukui index calculation, the intermediate products and degradation pathway of NTP were verified. The excellent reusability and stability of the cathode could be due to the protective role of BC, which minimized direct contact between Fe₃C active sites and the reaction solution, and thus reducing Fe 3 C corrosion during the HEF process. This study offers important insights into the design of superior metal-carbon hybrid cathode for electrochemical water remediation technologies.