Oxygen functionalized graphitic carbon nitride as an efficient metal-free ozonation catalyst for atrazine removal: Performance and mechanism

The oxygen functionalized graphitic carbon nitride (O@g-C3N4) composite was synthesized by a facile hydrogen peroxide hydrothermal approach in this study. It is the first report about the investigation and application of O@g-C3N4 as the metal-free catalyst for catalytic ozonation of atrazine (ATZ) in aqueous solution. The composition, structure, and morphology of obtained O@g-C3N4 were characterized by BET, XRD, FT-IR, SEM, TEM, and XPS, respectively. It was noted that O@g-C3N4 appeared as flower cluster or short rod-like structures with hierarchical edges, which was remarkably different from the laminated g-C3N4. The characterization results revealed that the doping O atoms into g-C3N4 framework via C=O, C-O, or/and N-O bonds would modulate the configuration and physicochemical properties of g-C3N4, and meanwhile create nitrogen vacancies and new active sites to enhance the catalytic performance. The O@g-C3N4 exhibited superior catalytic ozonation activity with an improvement of 29.76% on ATZ degradation efficiency and more than 3.36 times of pseudo-first-order rate constant (0.6279 min(-1)) was achieved in O-3/O@g-C3N4 process compared to single ozonation. Meanwhile, the feasibility of O@g-C3N4 for practical application was further evaluated at different catalyst dosages, initial ATZ concentrations, solution pHs, and natural organic matters. According to electron spin resonance and radical scavenger experiments, both superoxide radical and center dot OH were identified as the major reactive oxygen species in O-3/@g-C3N4 process. Moreover, the O@g-C3N4 showed excellent stability and reusability over multiple reaction cycles without obvious activity loss. The results indicated that O@g-C3N4 was demonstrated to be a highly efficient, stable, and recoverable catalyst, presenting the great potential in contributing to a new paradigm for designing environmental-friendly and highly efficient ozonation catalysts for water treatment.