Modulate the Strong Exciton Effect by Na⁺ Coordination-Induced Trap States: Efficient Photocatalytic H₂O₂ Production

Due to the strong Coulomb interaction, in most polymer photocatalysts, electron-hole pairs exist in the form of excitons rather than free charge carriers. The giant excitonic effect is a key obstacle to generating free charge carriers. Therefore, effectively regulating the exciton effect is the first step to achieving optimized carrier separation. Here, we used C-ring/g-C₃N₄ as the prototypical model system to design a photocatalyst with a Na-coordination-induced trap state. We demonstrate that the excitons can be effectively dissociated into charge carriers by combining with the trap state formed by Na doping sites. Encouragingly, signals from the dissociation of excitons into carriers were observed by ultrafast transient spectroscopy. Benefiting from the enhanced exciton dissociation, Na-C/CN displayed a H₂O₂ production rate of 17.4 mmol·L^-1·h^-1 with an apparent quantum efficiency up to 26.9% at 380 nm, which is much higher than many other g-C₃N₄-based photocatalysts. This work explains the effect of cation doping on the exciton-carrier behavior in polymers. Also, it provides a new way to regulate the exciton effect.