Self-Assembled Ultrathin H-terminated Si Nanosheet/g-C3N4 Heterojunction for Photocatalytic Hydrogen Evolution

Two-dimensional silicon (Si) nanosheets are becoming increasingly exciting for photocatalytic applications. Their unique morphology and physiochemical properties make it attractive in heterojunction engineering. In this work, we report the construction of 2D H–Si/g-C3N4 hybrid as a heterojunction photocatalyst for solar photocatalytic hydrogen evolution. The exfoliated silicon nanosheets etched by hydrofluoric acid exhibit a hydrogen-terminated surface with an inverse charging state, which can thus be easily anchored onto g-C3N4 nanosheets by self-assembly. The optimized H–Si/g-C3N4 heterojunction photocatalyst with Pt as the cocatalyst achieved an improved photocatalytic hydrogen production rate which is about 2 times that of g-C3N4 nanosheets under simulated sunlight irradiation using methanol as the sacrificial agent. Density functional theory calculations revealed that the built-in electric field (BIEF) at the H–Si/g-C3N4 interface contributes to the spatial charge separation of the heterojunction. The BIEF leads to an S-scheme carrier transfer mechanism at the H–Si/g-C3N4 interface that benefits the carrier separation on g-C3N4 nanosheets, resulting in uniform deposition of the Pt cocatalyst at the heterojunction interface and improved photocatalytic performance. This work not only expands the application of silicon nanosheets by supporting the potential of 2D H–Si/g-C3N4 heterojunction in photocatalytic reactions but also provides valuable insights to the interface behavior of the H–Si/g-C3N4 heterostructure.