Efficient removal of ciprofloxacin by heterogeneous electro-Fenton using natural air–cathode

In this study, we developed a Heterogeneous Electro-Fenton (Hetero-EF) system using an oxidized carbon nanotubes/iron oxychloride natural air diffusion electrode (OCNTs/FeOCl NADE) as the cathode, enabling simultaneous processes of O2 diffusion, H2O2 electro-generation and the activation in liquid–gas-solid three-phase interfaces on the cathode. Experimental results showed that rapid ciprofloxacin (CIP) degradation was realized over a wide pH range (3–9). CIP was completely degraded in 90 min, with the total organic carbon (TOC) removal efficiency of 46.8% ± 1.9% under the condition of current 75 mA and initial pH 7. The electron paramagnetic resonance and radical quenching experiments revealed that the reactive species of ·OH, ·O2– and 1O2 were all involved in the process, with 1O2 being the dominant contributor in CIP degradation. From the Fukui function based on the theoretical calculation and the degradation intermediates detected by LC-MS, the possible CIP degradation pathways were deduced. The toxicities of CIP degradation products were also predicted. This study demonstrated the feasibility of a simple and cost-effective integrated cathode combining the OCNTs/FeOCl catalyst exhibiting dual Fenton-like and oxygen reduction reaction (ORR) activity with the natural air diffusion electrode in a Hetero-EF system for efficient wastewater treatment.