Enhanced electro-Fenton degradation of sulfonamides using the N, S co-doped cathode: Mechanism for H2O2 formation and pollutants decay

Facing low reactivity/selectivity of oxygen reduction reaction (ORR) in electro-Fenton (EF), N, S atoms were introduced into carbon-based cathode. “End-on” O 2 adsorption was achieved by adjusting electronic nature via N doping, while *OOH binding capability was tuned by spin density variation via S doping. Results showed the optimized N, S co-doped cathode presented a 42.47% improvement of H 2 O 2 accumulation (7.95 ± 0.02 mg L −1 cm −2 ). According to density functional theory (DFT), N, S co-doped structure favored the “end-on” O 2 adsorption as adsorption energy dropped to − 2.24 eV. Moreover, O-O/C-O bond lengths variation proved a possibility for *OOH desorption. The elaborated cathode was used in EF for sulfonamides (SAs) decay. A 100% removal rate of sulfadiazine (SDZ), sulfathiazole (STZ) and sulfadimethoxine (SDM) was achieved within 60 min, among which SDZ tended to be degraded easily. Because the absolute hardness ( η ) of those pollutants is ranked as follows: η SDM >  η STZ >  η SDZ . Degradation pathways were proposed based on the detected byproducts, along with toxicity was evaluated by ecological structure-activity relationship (ECOSAR) program. Results showed that toxic intermediates generated were reduced or even disappeared. EF with N, S co-doped cathode provides a promising process for antibiotics wastewater treatment .