Research on photocatalytic performance and mechanism of nitrogen–sulfur co-doped carbon quantum dots and C3N4 co-modified BiOBr

In this study, nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were prepared by hydrothermal method, carbon nitride (C₃N₄) was fired in a muffle furnace in an air atmosphere, and finally, the ternary heterostructure of NSCQDs, C₃N₄ and bismuth oxide bromide (BiOBr) was synthesized by a hydrothermal method (NSCQDs/C₃N₄/BiOBr). The morphology of the catalyst was observed through SEM and TEM. The chemical bonds were analyzed by XPS and FT-IR to further confirm that NSCQDs and C₃N₄ were successfully attached to BiOBr. The photocatalytic activity of the synthesized catalysts was studied by degrading RhB under simulated light source. The experiment results showed that under optimal conditions, the degradation rate of RhB by NSCQDs/C₃N₄/BiOBr within 20 min was as high as 99.9%, which was much higher than that of pure BiOBr (33.5%). The degradation curve was combined with a pseudo-first-order kinetic model with a kinetic constant of 0.32578 min⁻¹, which was 17.7 times that of BiOBr (0.01837 min⁻¹). Catalyst recycling tests showed that NSCQDs/C3N4/BiOBr had extremely high stability. The active species quenching test showed that \({\text{O}}_{2}^{ \cdot - }\) ${\text{O}}_2^{·-}$ and ¹O₂ were the main active species during the photocatalytic process. The inhibition effect of NSCQDs and C₃N₄ on BiOBr photogenerated carrier recombination was analyzed by photoluminescence and transient photocurrent tests. This study is expected to provide an attractive strategy for constructing efficient and environmentally friendly photocatalysts for environmental remediation.