The enhanced photocatalytic performance toward carbamazepine by nitrogen-doped carbon dots decorated on BiOBr/CeO2: Mechanism insight and degradation pathways

Novel nitrogen-doped carbon dots (NCDs) modified BiOBr/CeO2 was constructed successfully via a facile method. The morphology, structure, optical and photo-electrochemical properties of the photocatalysts were characterized by various technologies. The photocatalytic performance was evaluated by the degradation of carbamazepine (CBZ) under simulated solar light irradiation. The CBZ degradation by NCDs/BiOBr/CeO2 could achieve 98% within 120 min illumination, which was much higher than BiOBr or BiOBr/CeO2. The enhanced degradation of CBZ was due to the fact that the introduction of NCDs significantly accelerated the migration and separation of the photoinduced charge carries at the tightly contacted interface. The effects of some key operating parameters were further investigated, including photocatalyst dosage, initial CBZ concentration, initial pH, coexisting inorganic anions (Cl-, NO3-, SO42-) and natural organic matters (NOM), light irradiation conditions and water matrix. Basing on the scavenging experiments and electron spin resonance (ESR), the photocatalytic mechanism was proposed for the charge separation. Furthermore, the transformation intermediates and possible degradation pathway of CBZ were investigated by liquid chromatography coupled with mass spectrometry (LC/MS) and three-dimensional excitation-emission matrix fluorescence spectra (3D EEMs). Finally, the composite showed excellent recyclability and stability. This study created new opportunities for the design of photocatalysts and degradation of recalcitrant organic contaminants in aquatic environment.