Construction of intramolecular donor–acceptor type carbon nitride for photocatalytic hydrogen production

High-efficiency photocatalysts based on organic polymeric semiconductor are often limited by slow charge separation kinetics and sluggish redox reaction dynamics. Herein, the donor-acceptor conjugated polymeric carbon nitride (D/A-CN) was synthesized by grafting benzene ring and pyridine moiety into the backbone of CN through a flexible pyrolysis strategy. The D/A-CN shows a high photocatalytic H2 evolution rate of 4795 µmol·h-1·g-1, which is ≈6.08 times higher than that of pristine CN (787.5 µmol·h-1·g-1). Both experimental and theoretical results confirm that the robust internal electric field is established in the D/A-CN framework due to the enhanced molecular dipole, which apply a kinetic force to facilitate the separation and mobility of photogenerated carriers. Meanwhile, the deeper conduction band potential caused by the elevated orbital energy level of D/A-CN contributes to the enhanced reduction ability of photoinduced electron. Consequently, the faster carrier transfer kinetics and the stronger thermodynamic reduction driving force synergistically lead to efficient photocatalytic H2 production of D/A-CN. This work reinforces the comprehension of the structure-performance relationship of donor-acceptor structural photocatalysts and provides an insight for enhancing the photocatalytic activity of polymeric photocatalysts at the molecular level.