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 Fe 3 O 4 /gas diffusion electrode (Fe 3 O 4 /GDE) as the rotating cathode, realizing the simultaneous processes of O 2 diffusion, H 2 O 2 generation and activation at the cathode for the first time. In this system, H 2 O 2 was effectively electro-generated on the rotating cathode without external aeration, and then in suit activated to hydroxyl radical by the immobilized Fe 3 O 4 . 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 Fe 3 O 4 as catalyst. This enhancement was ascribed to the increased catalytic ability of immobilized Fe 3 O 4 in the presence of electric field. The effects of some important parameters such as Fe 3 O 4 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 Fe 3 O 4 contributed to the decomposition of H 2 O 2 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.