Synthesis of Fe₃O₄/CNT/ACF cathode-based electro-fenton system for efficient mineralization of methylene blue dye: Kinetics and mechanism

Electro-Fenton (EF) is an innovative process to use in situ generated H2O2 and •OH to destruct organic contaminants in wastewater. In this study, methylene blue (MB) was degraded using activated-carbon-felt (ACF) composite cathodes (CNT/ACF, Fe3O4/ACF, and Fe3O4/CNT/ACF). Magnetite (Fe3O4) nanoparticles (MNPs) and carbon nanotubes (CNTs) were used as surface modifiers, i.e., Fe3O4, to facilitate easy charge-transfer by forming multilayered channels and CNTs to enhance the thermal and structural strength of the electrode. When Fe3O4/CNT/ACF was used as cathode, the removal efficiency of 93.7% for MB could be obtained within 1 h; the MB degradation followed the pseudo-second-order kinetics with the rate constant of 2.73 × 10-2 M-1 min-1. Based on total organic carbon (TOC) analysis, 57.8% of MB could be mineralized by the cathode system, which was also confirmed by evaluating the mineralization current efficiency (MCE, kWh m-3). When the EF oxidation time was raised to 2.5 h, MB could be completely degraded while mineralization efficiency was 87%. At 2.5-h degradation time, Fe3O4/CNT/ACF exhibited the highest removal efficiency for color and TOC among the three synthesized electrodes, proving that the cathode has an outstanding catalytic oxidation power for MB degradation with high stability. Thus, the overall study provides an insight for an innovative mechanism of integrating well-performing and easily recyclable electrode composites in an EF system for treating recalcitrant organic pollutants existing in wastewater.