Boosting n→π∗ electronic transition via reducing interlayer stacking distance in red Poly(heptazine imide) towards efficient photocatalytic H2 production

Poly(heptazine imide) (PHI) exhibits exceptional photocatalytic performance due to its unique structural advantages. However, its effectiveness is limited by a narrow light response range and inefficiencies in charge carrier separation and transfer. Herein, we introduce an innovative approach to synthesize red PHI (RPHIx) with a reduced interlayer distance and a highly in-plane ordered structure by calcining melon-based carbon nitride with KSCN at varying target calcination temperature. The compact interlayer π-π stacking facilitates n→π∗ electronic transition, thereby broadening the range of light absorption and enhancing the separation of photo-induced carriers. The resulting RPHI600 reveals a remarkable photocatalytic H 2 evolution reaction (HER) rate that is 85 times higher than that of pristine PHI under 510< λ < 780 nm irradiation. Moreover, the improved in-plane integrity and reduced interlayer distance facilitate the transfer of charge carriers in both horizontal and vertical directions, leading to an HER rate 2.3 times greater than that of PHI under 420< λ < 780 nm illumination. This work offers valuable insights for enhancing the light-harvesting capability and crystallinity of PHI-based photocatalyst. Red poly(heptazine imide) (RPHI) with activated n→π∗ electronic transition, reduced interlayer distance and a highly in-plane ordered structure was synthesized by calcining melon with KSCN, resulting in broadened photoresponse range and promoted charge carriers separation and transfer. • Red PHI (RPHIx) with boosted n.→π∗ electronic transition was synthesized. • A reduced interlayer spacing and an enhanced in-plane integrity were achieved. • The HER rate of RPHI600 is 85 times higher than pristine PHI under 510< λ < 780 nm. • It roots in the refining of light response, horizontal and vertical carrier dynamics.