Efficient roxarsone degradation via in-situ H₂O₂ generation through 2e^-ORR over a Pd-Fe₂O₃ catalyst system

Despite its efficacy in mineralizing pollutants, the Fenton reaction's requirement for continuous H₂O₂ addition entails high cost and safety drawbacks. This paper focuses on "substituting iron-based materials for ferrous salts in the Fenton reaction while simultaneously accelerating the two-electron oxygen reduction reaction (2e^-ORR) to boost H₂O₂ production". At normal temperature and pressure, H₂ was adsorbed and activated on Pd⁰ sites to form H∗, which was transferred to the catalyst surface through the hydrogen spillover effect to form [H]. Finally, H₂O₂ is generated in situ via the 2e^-ORR. The H₂O₂ was further decomposed at the iron site into ·OH, O₂^-·, ¹O₂, and Fe (II), facilitating the degradation of the target pollutant ROX. Within 120 min, the degradation rates of 50 mg L^-1 roxarsone in the Pd-on-Fe₂O₃+H₂ and Pd-in-Fe₂O₃+H₂ reaction systems were 96.0% and 69.5%, respectively. The quenching experiments and electron spin resonance (ESR) analysis demonstrated that ¹O₂ plays a dominant role in the system. The degradation efficiency of roxarsone was affected by the catalyst dosing, initial pH, H₂ flow rates, and initial concentration of roxarsone. Furthermore, excellent stability of the Pd-Fe₂O₃ system was confirmed over six consecutive cycling experiments.