N-doping enhanced catalytic mechanism of Co-loaded biochar cathode for degrading organic phosphorus flame retardants in heterogeneous electro-Fenton system.

The development of metal catalysts supported on waste biomass-derived biochar for effective removal of emerging contaminants has attracted growing interest. However, the enhancement mechanisms of heteroatom-doped biochar-supported metal catalysts in heterogeneous electrocatalytic processes remain insufficiently explored. In this study, cobalt-loaded nitrogen-doped lignin-derived biochar catalysts were prepared via solvothermal treatment followed by pyrolysis, using aminated lignin and cobalt salt as precursors. The catalysts were employed as cathodes in electrocatalytic degradation systems for organophosphate flame retardants (DOPO) removal, aiming to evaluate the effect of nitrogen doping on the catalytic performance. The results demonstrated that N-doping increased the specific surface area and cobalt loading, leading to enhanced electrochemical activity. Under optimal conditions, the heterogeneous electro-Fenton system with Co-AL3@C (a catalyst prepared by mixing pine wood lignin, anhydrous ethylenediamine, and formaldehyde solution in a mass ratio of 1:1:3) as the cathode and 0.1 mol L-1 NaCl solution as the electrolyte achieved a DOPO removal efficiency of 99.3 ± 0.7 % within 30 min. Quenching experiments confirmed that singlet oxygen (1O2) and chlorine oxide radicals (ClO•) played major roles in DOPO degradation. DFT calculations further revealed that N-doping reduced the energy barrier for H2O2 adsorption and activation, thereby promoting reactive oxygen species generation and facilitating rapid pollutant degradation and mineralization. Moreover, the E-Co-AL3@C system (a heterogeneous electro-Fenton system with Co-AL3@C catalyst as cathode) exhibited good recyclability and strong anti-interference capability, demonstrating its potential for practical wastewater treatment.