N,P co-doped carbon quantum dots bridge g-C₃N₄ and SnO₂: Accelerating charge transport in S-scheme heterojunction for enhanced photocatalytic hydrogen production

The preparation of photocatalysts with efficient electron-hole separation efficiency is the key to achieving sustainable utilization of solar energy. Herein, a three-phase composite of N,P co-doped carbon dots (NPCDs), SnO₂ nanowires, and g-C₃N₄ nanotubes (CNNT) is synthesized, forming an S-scheme SnO₂/NPCDs/CNNT heterojunction. The construction of S-scheme heterojunction not only improves the reduction ability due to band bending, but also promotes the separation of carriers. The conductive NPCDs are located between SnO₂ and CNNT and formed as a unique charge transfer channel that accelerates carriers transfer between S-scheme heterojunction interfaces. Additionally, NPCDs serves as electron acceptors to receive electrons from the conduction band of CNNT, thereby further facilitating the carrier separation. This synergistically boosts the photocatalytic hydrogen production activity of SnO₂/NPCDs/CNNT three-phase catalysts, leading to a high H₂ yield (10.73 mmol·g⁻¹·h⁻¹) and outstanding cyclic stability. This study offers a strategy for designing heterostructure photocatalysts that enhanced charge separation through interface engineering.