High-Efficiency and Ground-State Atomic Oxygen-Dominant Photodegradation of Carbamazepine by Coupling Chlorine and g-C3N4

In this study, a solar/chlorine/graphitic carbon nitride (g-C3N4) system for the highly efficient degradation of carbamazepine (CBZ) was constructed, and the degradation mechanism of CBZ in this system was elucidated. The removal rate of CBZ by g-C3N4 combined with solar/chlorine was as high as 97.8%, which was more than twice that of the solar/chlorine combined system (43.8%). Electron spin resonance analysis revealed that the hydroxyl radicals (HO•) in the solar/chlorine/g-C3N4 system were remarkably less than that in the solar/chlorine photocatalytic system, wherein HO• was the dominant participant. However, the former system had higher efficiency than the latter. Scavenging tests confirmed the existence of a synergistic effect between solar/chlorine and g-C3N4 in CBZ degradation, and ground-state atomic oxygen (O(3P)) played a more important role than HO• in the solar/chlorine/g-C3N4 system. A novel O3-related pathway of CBZ degradation was proposed on the basis of the determination of intermediates. The intermediates detected via liquid chromatography quadrupole time of flight mass spectrometry (LC/Q-TOF-MS)/MS analysis indicated that O3 attacked the double bond of CBZ via the Criegee mechanism and produced intermediates with two new aldehydes. This study not only improved the knowledge of the effects of O(3P) and the O(3P)-related degradation mechanism of organic pollutants but also provided a reminder that O(3P) might be overlooked in the photocatalytic processes, especially in processes that occur in the presence of dissolved oxygen or oxygen-containing anions.