Levofloxacin degradation performance and mechanism in the novel electro-Fenton system constructed with vanadium oxide electrodes under neutral pH

Abstract

• A novel VO-EF system was proposed for levofloxacin degradation under neutral pH. • The redox of VO x on cathode and oxygen vacancies on anode ensured good performance. • Complete mineralization of levofloxacin and low H 2 O 2 residue were achieved. • Degradation pathways and mechanism of levofloxacin were proposed. • Great bioavailability in the effluent was observed. Heterogenous ferrum-based materials usually suffer from large overpotential between the redox of Fe 3+ /Fe 2+ and two-electron oxygen reduction reaction (2e − ORR), leading to less desired performance in electro-Fenton (EF) process. Herein, heterogeneous vanadium oxide EF system (VO-EF) was proposed by electrodepositing VO on carbon paper cathode (VO x @CP) and anode (V 3 O 7 @CP) for levofloxacin degradation. The VO x @CP cathode showed the optimal potential of 2e − ORR at −0.90 V (vs. SCE) with H 2 O 2 generation rate of 1.44 × 10 −4 mmol·L −1 ·cm −2 ·s −1 . Though overpotential disparity of 0.35 V was exhibited between the redox of VO x and 2e − ORR, rapid H 2 O 2 consumption rate was still achieved and facilitated ·OH generation. The oxygen vacancies existed in V 3 O 7 @CP anode reduced oxygen evolution reaction potential, leading to the cell voltage decrease of 0.36 V. Levofloxacin (30 mg·L −1 ) degradation efficiency of 97.67% was achieved in the VO-EF system within 120 min, and 19.19 mg·L −1 TOC was mineralized with energy consumption of 12.3 J·mg·L −1 TOC under neutral pH condition. Complete mineralization and low H 2 O 2 residue allowed good bioavailability in the effluent. Levofloxacin degradation pathways and mechanism were proposed based on identified intermediates and theoretical calculation. This study provides inspiration for developing novel EF systems for efficient pollutants degradation.