Tunable gas-phase etching enables few-layer carbon nitride with site-selective nitrogen vacancies and record photocatalytic activity

Abstract

Photocatalytic water splitting offers a sustainable pathway for H2 evolution, yet the efficiency of polymeric carbon nitride (PCN) is severely limited by its low surface area, insufficient active sites, and rapid charge recombination. Herein, we report a general approach using triethylamine as a gas-phase etching agent to simultaneously exfoliate bulk PCN into few-layer nanosheets and introduce site-selective N vacancies. The resulting PCN-M (PCN derived from melamine) nanosheets exhibit an ultralow thickness of ~0.68 nm (about two stacked heptazine layers) and a markedly increased specific surface area of 186.6 m 2 •g -1 (15.2 times that of bulk PCN-M). Mechanistic studies reveal that the triethylamine treatment preferentially cleaves the N-(C)3 bridging sites, generating N vacancies with positional selectivity, which in turn induces a broadened visible absorption tail and prolongs carrier lifetime. Benefiting from these synergistic features, the PCN-M nanosheets achieve a photocatalytic H2 evolution rate of 240.2 μmol•h -1 , approximately 13.6 times that of bulk PCN-M, with an apparent quantum yield (AQY) of 33.1% at 400 nm, alongside enhanced H2O2 production via oxygen reduction. The strategy is further validated on PCN derived from dicyandiamide and trithiocyanuric acid, confirming its universality. Notably, the PCN-T (PCN derived from trithiocyanuric acid) nanosheets achieve an AQY of 45.5% at 400 nm, which represents one of the highest AQYs among PCN-based photocatalysts reported to date. This work establishes triethylamine as a previously unexplored etching agent that enables simultaneous exfoliation and site-selective defect engineering, offering a new paradigm for designing high-performance PCN photocatalysts.