Achieving long-lived shallow trapping states in carbon nitride through the n-π*electronic transition for enhanced photocatalytic hydrogen generation

The presence of short-lived shallow trapping states in semiconductor-based photocatalysts hinders efficient utilization of charge carrier, which compromises the solar-to-hydrogen efficiency. Here, we presented an engineered graphitic carbon nitride (g-CN) nanosheets with long-lived shallow trapping states achieved through an n-π * electronic transition. This transition induces a significant red-shifted absorption edge at 600 nm, effectively extending the range of light absorption compared to pristine g-CN. Moreover, the engineered g-CN nanosheets exhibit lower exciton binding energies (36 meV) compared to pristine counterparts (50.1 meV), as revealed by temperature-dependent photoluminescence (PL) spectra. Femtosecond transient absorption spectroscopy (fs-TAS) confirms the presence of long-lived shallow trapping states (lifetime: 565.8 ps) in the engineered g-CN nanosheets. These states enable a greater participation of photoinduced electrons in photocatalytic reactions, resulting in significantly enhanced photoactivity. Notably, the g-CN sample with the n-π * transition achieves a remarkable photocatalytic H2 production rate of 61.8 µmol h−1, which is a fivefold enhancement over pristine g-CN nanosheets. These findings highlight the crucial role of the n-π * transition in g-CN for prolonging shallow electron trapping and ultimately leading to superior photocatalytic performance.