Sulfite activation by Fe-doped g-C3N4 for metronidazole degradation

The shortcomings of homogeneous activation for metal/sulfite such as narrow pH range, recovery and potential secondary contamination seriously limit the application of metal/sulfite systems in practical conditions. To overcome these drawbacks, we tested the degradation of metronidazole using an iron-doped graphite carbonitride (5%Fe-g-C3N4) as the catalyst to activate sulfite. The mechanism of the reaction was studied by X-ray photoelectron spectroscopy, radical quenching and chemical probe experiment. The effects of pH, Fe-g-C3N4, sulfite dosages and common anions were assessed and the degradation pathway of MNZ was also proposed. The results showed that 5%Fe-g-C3N4 was an effective catalyst for sulfite activation in the heterogeneous system and SO4 center dot- and (OH)-O-center dot were the main radicals leading to the degradation of metronidazole. After five times of recycle, Feg-C3N4 still had a good catalytic activity. Moreover, the Fe-g-C3N4/sulfite system could degrade metronidazole at a wide pH range of 4-9.