Porous carbon monoliths for electrochemical removal of aqueous herbicides by "one-stop" catalysis of oxygen reduction and H2O2 activation

Highlights: • PCM-HDA had a 310% higher H₂O₂ production at circum-neutral condition than CB. • The generated H₂O₂ was catalytically decomposed over PCM-HDA to produce • OH. • More O content and sp3 defects along with mesoporosity enhanced PCM-HDA activity. • The PCM-HDA electrode obtained an ~80% degradation of napropamide in 60 min • Efficient removal of napropamide was achieved by PCM-HDA in the pH range of 4–10_. The overuse of herbicides has posed a threat to human health and the aquatic environment via DNA mutations and antibiotic gene resistance. Carbon-based cathodic electrochemical advanced oxidation has evolved as a promising technology for herbicide degradation by generating hydroxyl radicals (• OH). However, conventional electro-Fenton process relies on interaction of multiple species that adds to the system complexity and cost and narrows the working pH range. Herein, a series of porous carbon monoliths (PCMs) were developed as a "one-stop" platform for catalysis of the 2-electron ORR coupled with further catalytic reductive cleavage of H₂O₂ to produce • OH. A PCM prepared using 1,6-hexamethylene diamine (denoted as PCM-HDA) produced H₂O₂ at a level that was 374% higher than that obtained using commercially available carbon black at circum-neutral pH. Meanwhile, the generated H₂O₂ was catalytically decomposed to produce • OH. Based on these results, the PCM-HDA electrode achieved an 80 ± 2% degradation of napropamide in 60 min over the pH range of 4–10 at a mildly reducing potential, with a 69 ± 2% TOC reduction at circum-neutral condition in 2 h. This simplified system overcomes the system complexity and pH limitation of the conventional electron-Fenton processes.