Oxygen-doped biochar for the activation of ferrate for the highly efficient degradation of sulfadiazine with a distinct pathway

Oxygen-containing functional groups in functionalized biochar (BC) play an important role in its environmental applications. Herein, we introduced oxygen atoms into BC by copyrolysis of sawdust and magnesium carbonate basic pentahydrate (MgCO3)4·Mg(OH)2·5 H2O for the preparation of O-enriched porous BC (OPBC). OPBC800 (OPBC pyrolyzed at 800 °C) exhibited ultrahigh activity to activate ferrate (K2FeO4) for the oxidation of sulfadiazine (SDZ, 100% removal of SDZ in 2 min at pH = 5). We found that SDZ molecules can be rapidly adsorbed by the hierarchical porous structure of OPBC and were expediently oxidized by in situ generated Fe(IV) and Fe(V) active species on the surface of OPBC. The degradation mechanism of SDZ involved is quite different from the well-confirmed mechanism in which only active species in the solution play a role. Electrochemical impedance spectroscopy showed that O-doping in OPBC improved the electron-donating ability and expedited the electron transfer to ferrate, thus enhancing the catalytic activity of OPBC. This provides a new functionalization method for BC and provides more information about the activation of ferrate.