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

Abstract

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.

Keywords: Carbonyl groups; Electron transfer process; Graphitic N; Polydopamine; Singlet oxygen.