Defect-rich ultrathin poly-heptazine-imide-framework nanosheets with alkali-ion doping for photocatalytic solar hydrogen and selective benzylamine oxidation

Polymeric carbon nitride (CN) as a metal-free photocatalyst holds great promise to produce high-value chemicals and H₂ fuel utilizing clean solar energy. However, the wider deployment of pristine CN is critically hampered by the poor charge carrier transport and high recombination. Herein, we develop a facile salt template-assisted interfacial polymerization strategy that in-situ introduces alkali ions (Na⁺, K⁺) and nitrogen defects in CN (denoted as v-CN-KNa) to simultaneously promote charge separation and transportation and steer photoexcited holes and electrons to their oxidation and reduction sites. The photocatalyst exhibits an impressive photocatalytic H₂ evolution rate of 8641.5 μmol·g⁻¹·h⁻¹ (33-fold higher than pristine CN) and also works readily in real seawater (10752.0 μmol·g⁻¹·h⁻¹) with a high apparent quantum efficiency up to 18.5% at 420 nm. In addition, we further demonstrate that the v-CN-KNa can simultaneously produce H₂ and N-benzylidenebenzylamine without using any other sacrificial reagent. In situ characterizations and DFT calculations reveal that the alkali ions notably promote charge transport, while the nitrogen defects generate abundant edge active sites, which further contribute to efficient electron excitation to trigger photoredox reactions.