Efficient degradation of levofloxacin using a g-C3N4@glucose-derived carbon catalyst with adjustable N content via peroxymonosulfate activation

Abstract

Metal-free carbon-based catalysts hold great promise for the degradation of organic pollutants by peroxymonosulfate (PMS) activation because they avoid the negative effects of metal catalysts such as harmful metal ions leaching. However, these carbon-based catalysts are limited by their high cost and complex synthesis, and the mechanisms for the activation of PMS are unclear. Herein, the N-rich carbon catalysts (GCN-x) derived from glucose and g-C3N4 were facilely synthesized by hydrothermal treatment and carbonization to explore the mechanism of PMS activation. The nitrogen content of catalysts could be adjusted by simply altering the ratio of glucose and g-C3N4. GCN-2.4 with a ratio of glucose and g-C3N4 of 2.4 displayed the highest efficiency for the degradation of pollutants represented by Levofloxacin. The electron paramagnetic resonance and quenching experiments demonstrated that the non-radical pathway was dominant in Levofloxacin degradation and singlet oxygen (1O2) was the main active specie. Further, we found 1O2 was generated from superoxide radical (• O2−) which has rarely been studied. Levofloxacin degradation rate was shown to be positively correlated with both the amount of graphitic N and pyridinic N. Graphitic N and pyridinic N were identified as the catalytic sites. The GCN-2.4/PMS system could also remove multifarious contaminants effectively. Overall, this research advances understanding of the role of N species in PMS activation and has potential practical application in wastewater treatment.