Achieving efficient incorporation of electron-withdrawing sites into carbon nitride nanosheets for boosting hydrogen generation

Abstract

There is an acute demand for the development of high-performance photocatalysts for large-scale green H2 production using solar energy. To address this challenge, a novel approach has been proposed for the fabrication of high-performance 0D/2D carbon quantum dot/C3N4 nanosheet heterojunction (CQD/CNN) photocatalytic materials using a tandem synthesis strategy of carboxylated CQD-induced hydrothermal-pyrolysis. The incorporation of CQD into the synthesis of CNN significantly reduces its thickness, making the CQD/CNN low to 2.5 nm, which is a noteworthy one thirty-sixth in height of bulk CNN. The carboxylated CQD play a crucial role in regulating the proportion of oxygen-containing surface functional groups of CQD/CNN. The CQD/CNN heterojunction shows exceptional H2 production rates and demonstrated the ability to convert O2 into H2O2. The H2 production rate of CQD/CNN is gained to be 54.50 mmol g−1 under continuous 3.5 h visible light irradiation, which is a remarkable seven-fold enhancement in performance over bulk CNN. Moreover, the CQD/CNN photocatalyst achieves a maximum H2O2 concentration of 0.763 mmol/L, which is sixteen times higher than that of pure CNN (0.0475 mmol/L). Through elucidating the relationships between morphological/structural modulation and photocatalytic capability, the CO/C–O ratio is found to have the greatest impact on performance, indicating that the electron-withdrawing sites of CQD/CNN can be augmented by incorporating carboxylated CQD, and the electron-withdrawing group can enhance electron conduction and make electron transfer easier to occur, thereby improving the performance of the heterojunctions. Our findings provide a comprehensive framework for achieving desirable photocatalytic properties of C3N4 materials through electron-withdrawing functional group regulation.