Selective electrochemical H₂O₂ generation on the graphene aerogel for efficient electro-Fenton degradation of ciprofloxacin

A novel cathode of macroporous graphene aerogel (GA) with high specific surface area was proposed for the electro-Fenton (E-Fenton) system. The GA was prepared by reduction self-assembly method. The physicochemical properties were characterized in details. The GA displayed a low electrochemical resistance and exhibited an excellent electrocatalytic activity. Comparing with the traditional carbon fiber and graphite felt cathodes, the GA cathode showed more positive oxygen reduction potential of 0.07 V (versus saturated calomel electrode). In E-Fenton system, H₂O₂ could be in situ electro-generated efficiently and continuously via a two-electron oxygen reduction reaction on the GA cathode. The electron transfer number n was calculated to be 1.0–2.0 for GA. The production of H₂O₂ of 107.6 mg L⁻¹ was obtained for GA in 90 min. Good performance was exhibited to degrade antibiotic ciprofloxacin. Results showed that nearly 100% ciprofloxacin degradation ratio and 91% TOC removal were achieved in 90 min and 120 min, respectively, which were much higher than control groups. The mineralization current efficiency was 12.75% in 30 min. It was attributed to the plenty of macro-pores of GA acted as reaction trap to accelerate electro-generated H₂O₂ decomposing by Fe²⁺ to form ·OH efficiently, which was verified by probe molecule trapping experiments and electron paramagnetic resonance analysis. Simultaneously, the strong charge transfer ability of GA was beneficial to the conversion of Fe³⁺/Fe²⁺. The GA also presented distinguished reusability and stability. Therefore, GA is a promising candidate material for E-Fenton cathode due to low cost, high efficient and corrosion resistance.