O-doped Graphitic Granular Biochar Enables Pollutants Removal via Simultaneous HO Generation and Activation in Neutral Fe-free Electro-Fenton Process.

HO generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the HO electrogeneration, is regarded as an important environmental application of HO generation by 2eORR. However, its application is hindered by the relatively expensive electrode materials. Proposing cathode materials with low cost and facile synthetic procedures are the priority to advance the EF process. In this work, a composite cathode structure that uses graphitic granular bamboo-based biochar (GB) and stainless steel (SS) mesh (GBSS) is proposed, where SS mesh functions as current distributor and GB supports synergistic HO electrogeneration and activation. The graphitic carbon makes GB conductive and the oxygen-containing groups serve as active sites for HO production. 11.3 mg/L HO was produced from 2.0 g GB at 50 mA after 50 min under neutral pH without external O/air supply. The O-doped biochar further increased the HO yield to 18.3 mg/L under same conditions. The GBSS electrode is also effective for HO activation to generate ·OH, especially under neutral pH. Ultimately, a neutral Fe-free EF process enabled by GBSS cathode is effective for removal of various model organic pollutants (reactive blue 19, orange II, 4-nitrophenol) within 120 min, and for their partial mineralization (48.4% to 63.5%). Long-term stability of the GBSS electrode for HO electrogeneration, HO activation, and pollutants degradation were also examined and analyzed. This work offers a promising application for biomass waste for removals of organic pollutants in neutral Fe-free EF process.