Degradation of organic pollutants by Fe/N co-doped biochar via peroxymonosulfate activation: Synthesis, performance, mechanism and its potential for practical application

This study shows that the simple pyrolysis of mixed sawdust, FeCl₃ and dicyandiamide can produce Fe/N co-doped biochar (Fe-N-C) with great catalytic and separation performances. Fe-N-C had a larger specific surface area (215.25 m²/g), higher defective degree (I_D/I_G = 0.98) and more active species for PMS activation because of the synergy between Fe and N doping. Furthermore, graphitic N, pyridinic N, Fe-N_x, Fe₂O₃ and Fe⁰ were identified as the dominant reactive species contributing to the activation of PMS. As a result, the production of reactive oxidizing species (ROS), including both sulfate radical (SO₄^•−), hydroxyl radical (•OH) and singlet oxygen (¹O₂), in the Fe-N-C/PMS system was significantly promoted. As a result, Fe-N-C exhibited 37.07 and 6.04-fold higher reaction rates for activating peroxymonosulfate (PMS) to degrade bisphenol A (BPA) relative to the rates achieved by pristine biochar and nitrogen doped biochar, respectively. Moreover, the mineralization rate of BPA by the Fe-N-C/PMS system was 68.9%, which was much higher than that achieved by the pristine biochar/PMS and N-biochar/PMS systems. Chemical-quenching tests further suggested that SO₄^•− and •OH played dominant roles in the degradation of BPA under acidic and neutral conditions, while ¹O₂ played a dominant role under alkaline conditions. Furthermore, the potential of Fe-N-C to be used in practical applications was systematically evaluated in terms of its stability, separability and selectivity to organics; the effect of operating parameters was also studied. Generally, our study highlighted the great potential of Fe/N co-doped biochar and provided valuable insight into the synthesis of highly efficient carbon-based catalysts for environmental applications.