Oxygen-containing functional groups in FeO@three-dimensional graphene nanocomposites for enhancing HO production and orientation to O in electro-Fenton.

In electro-Fenton (EF), development of a bifunctional electrocatalyst to realize simultaneous HO generation and activation efficiently for generating reactive species remains a challenge. In particular, a nonradical-mediated EF is more favorable for actual wastewater remediation, and deserves more attention. In this study, three-dimensional graphene loaded with FeO nanoparticles (FeO@3D-GNs) with abundant oxygen-containing functional groups (OFGs) was synchronously synthesized using a NaCl-template method and served as a cathode to establish a highly efficient and selective EF process for contaminant degradation. The amounts of OFGs can be effectively modulated via the pyrolysis temperature to regulate the 2e oxygen reduction reaction activity and reactive oxygen species (ROS) production. The optimized FeO@3D-GNs synthesized at 750 °C (FeO@3D-GNs-750) with the highest -C-O-C and -C꞊O group ratios exhibited the maximum HO and O yields during electrocatalysis, thus showing remarkable versatility for eliminating organic contaminants from surface water bodies. Experiments and theoretical calculations have demonstrated the dominant role of -C-O-C in generating HO and the positive influence of -C꞊O sites on the production of O. Moreover, the surface-bound Fe(II) favors the generation of surface-bound •OH, which steers a more favorable oxidative conversion of HO to O. FeO@3D-GNs were proven to be less pH-dependent, low-energy, stable, and recyclable for practical applications in wastewater purification. This study provides an innovative strategy to engineer active sites to achieve the selective electrocatalysis for eliminating pollution and reveals a novel perspective for O-generation mechanism in the Fenton reaction.