Green degradation of ofloxacin in electric Fenton based on Fe3+/Fe2+ internal cycling within Fe3O4 under neutral condition

Abstract

To break the drawbacks of the traditional electro-Fenton (EF) such as narrow pH, low utilization of ·OH, Fe2+ loss, and low Fe3+ reduction rate, a new strategy that the ·OH generation in EF is based on the internal cycling of Fe2+/Fe3+ within Fe3O4 is proposed. A new-type homogeneous EF system (EF-Fe3O4@CF) where the Fe3O4-modified carbon felt box with clinoptilolite addition was used as the cathode, was established. The experimental results indicate that the system has 100 % removal efficiency for ofloxacin (OFL) and 86.4 ± 2.4 % removal efficiency for TOC at 120 min at pH = 7, and in multi-cycle operation the efficiency of OFL and TOC degradation did not decrease. Fe2+ (within Fe3O4) can activate H2O2 to generate ·OH and Fe3+ (within Fe3O4) is simultaneously reduced to Fe2+ on the cathode, so the internal cycling of Fe3+/Fe2+ within Fe3O4 achieve the green regeneration of ·OH. The conversion range of Fe3+/Fe2+ within Fe3O4 crystal is 4.43:1–1.46:1. The EF-Fe3O4@CF with multi-functions of adsorption, catalysis, and green degradation showed good stability and reusability. Our work provides fundamental research for Fe3O4 as a promising heterogeneous EF catalyst in advanced wastewater treatment.