Fluorenone-based covalent triazine frameworks/crystalline carbon nitride S-scheme heterojunction for efficient photocatalytic H2 evolution

Covalent triazine frameworks (CTFs) possess high conjugation and tunable structures for photocatalysis, but low electron-hole separation and poor stability limit their hydrogen evolution from water splitting. Herein, a new S-scheme heterojunction was effectively created through electrostatic self-assembly of a fluorenone-based covalent triazine framework (FOCTF) with heptazine crystalline carbon nitride (HCN). Staggered band structures were confirmed via Mott-Schottky measurements and UPS characterization, and electron spin resonance (ESR) analysis validated the S-scheme electron transfer pathway. The optimal HCN@FOCTF sample exhibited the highest photocatalytic hydrogen production rate (80.79 μmol h −1 ) at 405 nm, with an apparent quantum yield of 32.51%. Experimental studies confirm that HCN@FOCTF exhibits outstanding photocatalytic performance and stability. The constructed S-scheme heterojunction generates a favorable intrinsic electric field, accelerating directional S-scheme charge carrier transport and thereby enhancing carrier separation and utilization rate. This work proposes a novel idea for constructing an S-scheme heterojunction to regulate electron transfer pathways, towards efficient photocatalytic hydrogen production.