Unveiling the activation mechanism: The role of nitrogen-doped biochar in enhancing Fe(VI) catalysis

Despite the widespread use of biochar as a heterogeneous catalyst in AOPs, there is still a need to clarify the activation mechanism of nitrogen-doped biochar on ferrate (Fe(VI)). The Fe(VI) activation was significantly enhanced by the nitrogen-doped biochar synthesized at 800 °C (BCN-800) in this research, resulting in improved degradation of carbamazepine. Characterizations showed that a honeycomb-like pore and channel structure was formed on the inner layer of modified biochar and the SSA and pore volume were increased five and two times respectively as the temperature raised to 800 °C. Numerous indications indicated that the main active oxidizers in the BCN-800/Fe(VI) system were the high Fe species, and subsequent examination unveiled that the incorporation of nitrogen resulted in decreased resistance to charge transfer and enhanced efficiency of electron transfer for the production of high Fe species. DFT calculation illustrated that the SET path in the BCN-800/Fe(VI) system was spontaneous and single-electron oxygen atom transfer was the primary path for generating more highly reactive Fe(V) species. Notably, the BCN-800 remains stable after the organic degradation reaction and the toxicity of the intermediates produced during degradation decreases. This research will not only establish a theoretical foundation for designing eco-friendly catalysts based on biochar but also boost the investigation of biochar's ecological impacts.