Simultaneously optimizing optical response and exciton dissociation of amino-rich red poly(heptazine imide) nanoparticles with tunable n–π* electronic transition for improved photocatalytic hydrogen evolution

Crystalline carbon nitride, poly(heptazine imide) (PHI), demonstrates high photocatalytic activity and shows promise as a photocatalytic material. However, it still suffers from limitations in optical absorption and exciton dissociation efficiency. In this study, we successfully synthesized an amino-rich red poly(heptazine imide) nanoparticle (RPHINP) with tunable n–π* electronic transitions by controlling the calcination temperature (550–610 ℃) in a precursor-molten salt system comprising melamine, KSCN, and NH 4 Cl. At elevated temperatures of 600 ℃ and 610 ℃, the formation of nanoparticles and the enhanced n–π* electronic transition rendered RPHINP600 and RPHINP610 red in color. The synergistic effects of the n–π* electronic transition and nanoparticle structure extended the optical response range up to 800 nm and promoted exciton dissociation. As a result, the photocatalytic H 2 evolution reaction (HER) rates of the RPHINP samples improved significantly, especially under λ > 510 nm light irradiation. Notably, RPHINP600 exhibited HER rates of 10.4 and 19.8 times higher than pristine carbon nitride (PCN) under visible light exceeding 420 and 510 nm, respectively. This work presents a novel strategy for the simultaneous optimization of light absorption and exciton dissociation in PHI-based materials.