Boosting charge carrier separation efficiency by constructing an intramolecular DA system towards efficient photoreduction of CO2

Carbon nitride (CN) has attracted increasing attention in the field of photocatalysis due to its special properties such as visible light response, high stability, and low cost. However, the low separation efficiency of photogenerated electrons and holes limits its catalytic activity. Herein, a novel kind of CN based intramolecular donor–acceptor (DA) system was prepared to facilitate the separation efficiency of photoinduced charge carriers. The catalysts were prepared from CN and 4,7-dibromo-2,1,3-benzothiadiazole (Dbbt) by a simple calcination method. A series of characterization results confirmed that Dbbt is successfully introduced into the framework of CN (CN–Dbbt-x). It was found that the formation of the DA structure leads to the spatial separation of electrons and holes which significantly accelerate the separation efficiency of charge carriers. Moreover, the DA structure played an important role in regulating the bandgap structure, which can increase the optical absorption ability of the catalysts. Also, the DA system led to the formation of a built-in electric field, which remarkably accelerates the migration speed of electrons. CN–Dbbt-0.01 displayed the best photocatalytic CO2 reduction performance, and the CO evolution rate was 4.9 times higher than that of CN. Moreover, the reaction was carried out in water without any sacrificial agents, which makes it a green and environmentally friendly reaction. DFT simulation and experimental results showed that Dbbt and CN respectively serve as the donor and acceptor in CN–Dbbt-0.01.