K–Na co-doping in crystalline polymeric carbon nitride for highly improved photocatalytic hydrogen evolution

Integrated modification of polymeric carbon nitride (PCN) by crystallinity-improving and multi-element-doping was realized to advance the photocatalytic activity of PCN in this work. Specifically, K–Na co-doped crystalline PCN (K–Na–CCN) was facilely synthesized by calcining melon with NaCl and subsequent with KOH solution. It owned well-defined poly (heptazine imide) framework doped with both Na+ and K+. K–Na–CCN realized enhanced visible light absorption and reduced recombination of photogenerated electron-hole pairs, leading to favorable photocatalytic hydrogen evolution activity much superior to the melon-based bulk PCN and Na-doped crystalline PCN. The co-doping of K+ and Na+ in the crystalline carbon nitride framework was highlighted for this improvement. This work owns reference significance to the microstructure optimization of crystalline PCN.