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

Abstract

• A novel OCNTs/FeOCl natural air diffusion electrode (NADE) was developed. • OCNTs/FeOCl NADE was applied in a heterogeneous electro-Fenton (hetero-EF) system. • H 2 O 2 was electro-generated without external aeration and activated in situ. • Efficient ciprofloxacin removal was achieved at a wide range of pH (3–9). • The possible mechanism in hetero-EF process with OCNTs/FeOCl NADE was proposed. 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 O 2 diffusion, H 2 O 2 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, ·O 2 – and 1 O 2 were all involved in the process, with 1 O 2 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.