Metal-free 2D/2D VdW heterojunction fabricated by amorphous covalent triazine frameworks with nitrogen-defect on polymeric carbon nitride towards enhanced photocatalytic performance

Abstract

The structural design of Van der Waals (VdW) heterojunction photocatalysts has still been a challenging issue, because it usually plays a decisive role in improving photocatalytic performance. Herein, a unique metal-free 2D/2D VdW heterojunction is fabricated by decoration of amorphous covalent triazine frameworks with nitrogen defect (VN-CTFs) on the surface of polymeric carbon nitride (PCN) via a simple acid stripping, self-assembly and heat-treatment process, which demonstrates high-efficiency and stable photocatalytic performance for hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR). The results of experiments reveal that the synergy produced by strong electron-withdrawing effect from cyano groups in VN-CTFs induces charge redistribution at the interface with PCN through π-π interaction of 2D/2D VdW heterojunction, resulting in the formation of built-in electric field, which effectively drives the transfer and separation of photogenerated carriers to enhance the photocatalytic performance. The optimal PCN/VN-CTFs-10 sample exhibits that the average HER rate reaches up to 75.1 and 3.7 times higher than that of onefold VN-CTFs and PCN, respectively, as well as achieves apparent quantum yield (AQY) of 21.5 % at 420 nm and stable operation of 10 cycles totaling 40 h. Meanwhile, CO yields of 28.3 and 2.5 times as high as that of pristine VN-CTFs and PCN, respectively, are also obtained over the optimal PCN/VN-CTFs-10 sample for CO2RR. This work exploits a new structural unit design strategy for developing the metal-free PCN-based VdW heterojunction photocatalysts to boost the photocatalytic performance.