Complete antihistamine degradation in wastewater matrix using a metal-free N-doped carbon with superior electrocatalytic performance for in-situ $$H_2O_2$ production

Abstract

A new gas-diffusion electrode (GDE) has been developed and optimized to apply the heterogeneous electro-Fenton (EF) process to the degradation of the antihistamine diphenhydramine. The complete removal of this hazardous drug pollutant was achieved within only 120 min in actual urban wastewater at pH 5.9. Nitrogendoped carbon electrocatalysts were first synthesized by direct pyrolysis of blends of commercial Vulcan carbon and melamine as nitrogen dopant. A radar chart was proposed to correlate the tested physicochemical and electrochemical properties. A well-balanced surface area, mesopores volume and defective carbon content were critical to ensure the highest activity (<em>E</em>_onset = 0.38 V vs. RHE) and selectivity (<em>n</em> ~ 2, <em>y</em>_H2O2 ~ 95.3%) for twoelectron oxygen reduction reaction (ORR), which allowed the efficient in-situ production of H₂O₂ as ^•OH precursor. N-doping (10.5 wt%), along with the presence of pyrrolic N (3.5%), are also key factors to explain the enhancement. GDEs fabricated with the optimal electrocatalyst (71.4 wt% melamine content) were capable of accumulating up to ~35 mM H₂O₂ within 5 h, outperforming the commercial GDEs. This work evidences theinterplay of physicochemical and electrocatalytic parameters in H₂O₂-based advanced water treatment, demonstrating that it is possible to envisage a more efficient and greener tertiary wastewater treatment.