Integrated electro-Fenton process enabled by a rotating Fe3O4/gas diffusion cathode for simultaneous generation and activation of H2O2

In this study, we developed an electro-Fenton (EF) system with a Fe3O4/gas diffusion electrode (Fe3O4/GDE) as the rotating cathode, realizing the simultaneous processes of O2 diffusion, H2O2 generation and activation at the cathode for the first time. In this system, H2O2 was effectively electro-generated on the rotating cathode without external aeration, and then in suit activated to hydroxyl radical by the immobilized Fe3O4. Experimental results showed that 50 mg L−1 of tetracycline was completely degraded in 120 min, with the total organic carbon removal efficiency of 56.7%, which was accelerated by 1.7 times compared with the mobilized Fe3O4 as catalyst. This enhancement was ascribed to the increased catalytic ability of immobilized Fe3O4 in the presence of electric field. The effects of some important parameters such as Fe3O4 loading, initial pH, applied potential and the rotation speed were evaluated. Computational fluid dynamics simulation suggested that the rotating disk mode greatly enhanced the mass transfer. Further investigation indicated that the immobilized Fe3O4 contributed to the decomposition of H2O2 predominately, while the effects of leaching iron could be ignored. The hydroxyl radical was considered as the primary reactive oxidants, and the degradation mechanism of tetracycline was proposed combined with the analysis of intermediates by ion chromatograph technology. These findings demonstrated the feasibility of establishing an efficient EF system with a simple and cost-effective integrated cathode based on iron immobilization and rotating GDE for environmental remediation.

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