Enhanced photocatalytic tetracycline degradation using N-CQDs/OV-BiOBr composites: Unraveling the complementary effects between N-CQDs and oxygen vacancy

Complementary effect of components in a hybrid photocatalyst is an essential factor for improving solar energy-conversion efficiency, yet the underlying correlation between nitrogen-doped carbon quantum dots (N-CQDs) and oxygen vacancy (OV) is still ambiguous. Herein, using BiOBr nanosheets as model photocatalyst, we studied the specific roles of N-CQDs and OV in antibiotic photodegradation over full-spectrum. Electrons were overwhelmingly collected on N-CQDs rather than OV, achieving prominent separation of photo-excitons. However, OV could extend the congenitally optical absorption boundary of BiOBr to maximum utilizing the up-converted photons by N-CQDs. Moreover, active radical tests revealed that N-CQDs mainly regulated the single-electron reduction of dissolved oxygen to produce superoxide radicals (O2−) and OV mainly drove the robust H2O2 generation via two-electron reduction of the chemisorbed oxygen molecules. Although partial O2− were consumed as the raw of H2O2, a Photo-Fenton like reaction could transform H2O2 into hydroxyl radicals (OH) to provide more powerful oxidizing force. This work provides an in-depth understanding on the complementary roles of N-CQDs and OV and is helpful for designing highly efficient metallic oxide catalysts for photocatalytic pollutant removal.