Efficient degradation of norfloxacin by carbonized polydopamine-decorated g-C3N4 activated peroxymonosulfate: Performance and mechanism

The use of metal-free graphite carbon nitride (CN) to activate peroxymonosulfate (PMS) has attracted extensive attention for organic pollutants degradation. In this work, we prepared carbonized polydopamine-decorated g-C3N4 (CP-700) for activation of PMS to degrade norfloxacin (NOR). The CP-700 composite was obtained by using CN as a base material on which dopamine underwent an autopolymerization reaction to form a CN-PDA complex, followed by pyrolysis. The apparent porous structure and graphitization provided a large number of active sites for catalytic degradation, enabling CP-700 to exhibit excellent catalytic performance during PMS activation. The degradation of NOR was not hindered by sulfate radical (SO4•–) and hydroxyl radical (•OH). Singlet oxygen (1O2) and mediated electron transfer were ultimately identified as the primary mechanisms. According to the linear positive correlation (R2 = 0.9922) between the semi-quantitative carbonyl group (CO) and the reaction rate constant, it was determined that the carbonyl group served as the important active site. The excellent electron transfer ability of CP-700 was evidenced by electrochemical techniques and the electron transfer pathway in the system was that PMS was adsorbed on the CP-700 surface to form metastable complex, and then the electron transfer between NOR and metastable complex was achieved. Based on the non-radical pathway, CP-700/PMS system showed a high tolerance to solution pH (3.0–11.0) and inorganic anions. The cyclic degradation experiments indicated that the system maintained a high degradation capability without the addition of additional CP-700, elucidating its potential application in the degradation of organic pollutants in the water.