Tailoring local conjugation in heptazine-based polymers through donor unit engineering for photocatalytic water splitting

Abstract

Photocatalysis has emerged as a green technology for addressing global energy and environmental challenges. Although g-C₃N₄ exhibits potential as a photocatalyst, its efficiency is hindered by poor charge separation and exciton dissociation. In this study, a donor–acceptor (D–A) engineered carbon nitride (CN-UC_x) was synthesized by incorporating UC monomers into heptazine. Combined theoretical and experimental analyses reveal that the introduced donor units create two new donor levels, facilitating spatial charge separation and exciton dissociation while preserving strong reducibility. KPFM, surface photovoltage analysis, and photoelectrochemical characterization studies confirm the presence of an intrinsic potential difference within CN-UC_x. As a result, the optimized CN-UC_0.02 sample demonstrates exceptional photocatalytic performance, achieving a hydrogen evolution rate of 171.2 μmol h⁻¹ (normalized to 10 mg catalyst) under visible light (λ > 420 nm), which is 74.4 times higher than that of g-C₃N₄. Remarkably, even in the absence of cocatalysts or sacrificial agents, CN-UC_0.02 maintains hydrogen evolution rates of 18.3 and 2.6 μmol h⁻¹, respectively. Furthermore, CN-UC_0.02 achieves complete (100%) conversion in the photocatalytic oxidation of methyl phenyl sulfide. This work presents an effective strategy for designing high-performance D–A polymeric photocatalysts through the rational integration of donor units.