N/B co-doped polymeric carbon nitride with boosted charge transfer property and enhanced photocatalytic degradation of tetracycline

Polymeric carbon nitride (PCN) is an excellent metal-free photocatalyst. Nevertheless, its application has been seriously limited due to its inherent shortcomings such as the rapid recombination of charge carriers, insufficient light absorption capacity and slow reaction kinetics. The hetero/homo-atom doping was believed as an effective method to improve the photocatalytic performance of PCN. Herein, N/B co-doped PCN (NBCN) was synthesized by a facile one-step thermal condensation method with the assistant of recrystallization. The characterization results of XPS and NMR verified that N and B were successfully doped into the tri-s-triazine units of PCN. According to the calculation of density functional theory, N/B co-doping significantly varied the electronic structure of PCN and resulted in the spatial split of HOMO and LUMO in NBCN. This facilitated the transfer and separation of charge carriers, consequently, leading to a better photocatalytic performance. The photocatalytic degradation rate of tetracycline over NBCN was 2.5 times that over PCN. Additionally, the vulnerably attacked sites in the tetracycline molecular were predicted by Frontier Electron Densities. The possible degradation intermediates and pathways were proposed with the help of HPLC-MS analysis. Furthermore, the acute toxicity testing revealed that the global toxicity of the treated solution decreased gradually during photocatalysis.