Optimizing the Optical Absorption of Poly(heptazine imide) by the n → π* Electron Transition for Improved...

Poly(heptazine imide) (abbreviated as PHI), a heptazine-based crystalline carbon nitride photocatalyst, has attracted widespread attention in the photocatalytic H₂ evolution benefiting from its high crystallinity. Nevertheless, the optical absorption range of the directly synthesized PHI is generally narrow, which severely hinders the utilization of visible light. Much research aimed to extend the optical absorption range of PHI; however, either the optimization degree was insufficient or the synthesis process was cumbersome. Herein, red PHI (RPHI) for improving the photocatalytic H₂ evolution was facilely synthesized by the one step method. The optimal RPHI sample possesses an obvious new absorption band of the n → π* electron transition and exhibits a significantly enhanced photocatalytic H₂ evolution rate of 169 μmol h^-1 (λ > 510 nm) and 46 μmol h^-1 (λ > 600 nm), which is about 5 times (λ > 510 nm) and 7.7 times (λ > 600 nm) that of pristine PHI and surpasses most reported RPHIs. This work may promote the development of the PHI photocatalyst for near-infrared photocatalytic H₂ production.