Extended light absorption and accelerated charge migration in ultrathin twisted carbon nitride nanoplates for efficient solar hydrogen production

Polymeric carbon nitride has been widely developed as a promising photocatalyst for solar hydrogen production via photocatalytic water splitting. However, pristine carbon nitride prepared by traditional solid-state polymerization usually encounters issues such as rapid carrier recombination and insufficient absorption of visible light below 460 nm. Herein, poly(heptazine imide) with a distinctive nanoplate structure was synthesized in a binary molten salt of NaCl–CaCl₂. The salt template allows the formation of the thin nanoplate structure, which promotes the charge separation and migration. Besides, the intercalation of Ca²⁺ ions between the conjugated layers endows the activation of n–π* electron transition due to the distortion of in-plane heptazine layers. Accordingly, the optimized poly(heptazine imide) nanoplates achieve an apparent quantum efficiency of up to 17.3% at 500 nm for photocatalytic hydrogen production from water. This work shares new idea for rational control of the optical absorption and charge carrier dynamics of poly(heptazine imide).