Nitrogen-doped carbon dots decorated on g-C3N4/Ag3PO4 photocatalyst with improved visible light photocatalytic activity and mechanism insight

In this work, an all solid Z-scheme g-C3N4/Ag3PO4/NCDs photocatalyst has been prepared through decorating the direct Z-scheme g-C3N4/Ag3PO4 photocatalyst with nitrogen-doped carbon dots (NCDs). The g-C3N4/Ag3PO4/NCDs photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene blue (MB), rhodamine B (RhB) and phenol under visible light irradiation. The solutions of MB (10 mg L−1) and RhB (10 mg L−1) can be efficiently degraded within 20 min and 15 min, respectively, and the phenol (50 mg L−1) can be degraded to 36% within 80 min, which are much better than those of Ag3PO4 and g-C3N4/Ag3PO4, indicating that the introduction of NCDs into g-C3N4/Ag3PO4 can effectively improve the photocatalytic activity. Moreover, the photocatalytic performance of g-C3N4/Ag3PO4/NCDs shows just a slight decrease after four degradation cycles, indicating a high stability of the g-C3N4/Ag3PO4/NCDs photocatalyst. A possible photocatalytic mechanism based on the experimental results is proposed. It is revealed that NCDs on the ternary g-C3N4/Ag3PO4/NCDs can enhance the light harvesting capacity and molecular oxygen activation ability of the photocatalyst, and serve as excellent electronic transmission medium to promote the transfer and separation of photo-generated electron-hole pairs. This study demonstrates that NCDs decorated photocatalysts are very promising for environment and related applications.