Highly efficient metal-free electro-Fenton degradation of organic contaminants on a bifunctional catalyst.

Heterogeneous electro-Fenton (e-Fenton) is a promising technology for the treatment of persistent organic pollutants, in which HO is produced via 2e oxygen reduction and is simultaneously activated into •OH by the iron-based catalyst. This system often suffers from the inevitable metal dissolution in the acidic or even neutral environment, leading to poor pH adaptation and low stability. In this work, we designed a metal-free e-Fenton system, using O-doped carbon nanotubes (OCNTs) as the bifunctional metal-free cathode for the degradation of organic pollutants. The system showed the excellent e-Fenton performance under neutral conditions with the phenol degradation kinetic constant of 0.071 min, and the corresponding TOC removal was 76.6% within 300 min. It also exhibited excellent performance for actual coking wastewater treatment with the specific energy consumption of 7.4 kW h kg COD, which was lower than that reported heterogeneous electro-Fenton system (9.2-14.4 kW h kg COD). The in-situ metal-free e-Fenton system could be regarded as a promising strategy for actual wastewater treatment.