Accelerated Fe²⁺ Regeneration in an Effective Electro-Fenton Process by Boosting Internal Electron Transfer to a Nitrogen-Conjugated Fe(III) Complex

The regeneration rate of Fe 2+ from Fe 3+ dictates the performance of the electro-Fenton (EF) process, represented by the amount of produced hydroxyl radicals (·OH). Current strategies for the acceleration of Fe 2+ regeneration normally require additional chemical reagents, to vary the redox potential of Fe 2+ /Fe 3+ . Here, we report an attempt at using the intrinsic property of the electrode to our advantage, i.e., nitrogen-doped carbon aerogel (NDCA), as a reducing agent for the regeneration of Fe 2+ without using foreign reagents. Moreover, the pyrrolic N in NDCA provides unpaired electrons through the carbon framework to reduce Fe 3+, while the graphitic and pyridinic N coordinate with Fe 3+ to form a C–O–Fe–N 2 bond, facilitating electron transfer from both the external circuit and pyrrolic N to Fe 3+ . Our Fe 2+ /NDCA-EF system exhibits a 5.8 ± 0.3 times higher performance, in terms of the amount of generated ·OH, than a traditional Fenton system using the same Fe 2+ concentration. In the subsequent reaction, the Fe 2+ /NDCA-EF system demonstrates 100.0% removal of dimethyl phthalate, 3-chlorophenol, bisphenol A, and sulfamethoxazole with a low specific energy consumption of 0.17–0.36 kW·h·g –1 . Furthermore, 90.1 ± 0.6% removal of dissolved organic carbon and 83.3 ± 0.9% removal of NH 3 -N are achieved in the treatment of domestic sewage. The purpose of this work is to present a novel strategy for the regeneration of Fe 2+ in the EF process and also to elucidate the role of different N species of the carbonaceous electrode in contributing to the redox cycle of Fe 2+ /Fe 3+ .