Simple preparation of monolithic N-doped electrode for efficient EF remediation of petrochemical wastewater: Performance, degradation pathways, and mechanism of different N-doped positions

Developing metal-free N-doped electrode for efficient electro-Fenton (EF) application is significant for petrochemical wastewater treatment considering the serious water pollution problem that caused by petrochemical industry. Herein, a robust monolithic N-doped electrode was fabricated by simple physical mixing and heating methods using accessible raw materials, and applied in EF system for wastewater treatment. The prepared 3D NC-650 electrode was used as cathode, showing excellent catalytic activity and stability for degradation of typical p-nitrophenol (PNP) pollutant and remediation of petrochemical wastewater. During the EF process, the PNP was completely decomposed via the substitution, oxidation, and ring-opening reactions under the attack of center dot OH. The degradation pathways of organics in real wastewater matrix were also revealed based on liquid chromatography-mass spectrometry and three-dimensional fluorescence analysis. According to the degradation experiments, microstructure analysis, and theoretical calculation (molecular electrostatic potential, bond length, and adsorption energy), the possible mechanism of different N-doped positions on the monolithic 3D NC-650 electrode was revealed, in which the graphitic N, edge pyridinic N, and edge pyrrolic N all contribute to enhance the EF activity by accelerating the O-2 adsorption, facilitating the H2O2 formation by promotion of *-OOH bond breaking, and promoting the adsorption of organics on electrode surface, respectively. This work illustrates insights into the EF reaction mechanism with the monolithic N-doped electrode, and thus accelerates its application for actual wastewater remediation.