Fabrication of an Organic/Inorganic Hybrid TpPa-1-COF/ZnIn₂S₄ S‑Scheme Heterojunction for Boosted Photocatalytic Hydrogen Production

Covalent organic frameworks (COFs) exhibit significant prospects in photocatalytic H₂ evolution because of their periodic pore structure, large surface area, and outstanding chemical stability. Nevertheless, a bare COF always suffers from poor photogenerated charge separation efficiency. Hence, it is crucial to design highly effective COF-based heterojunction photocatalysts. In this work, we have successfully prepared an organic/inorganic hybrid TpPa-1-COF/ZnIn₂S₄ (ZIS) heterojunction with well-matched S-scheme interfacial charge-transfer channels. The results demonstrate that COF/ZIS-20% has an optimal photocatalytic H₂ evolution rate, which can reach 853 μmol g^–1 h^–1 in the absence of any cocatalyst, 6.2 times that of the bare TpPa-1-COF when exposed to visible light. Moreover, the apparent quantum efficiency (AQE) of COF/ZIS-20% at 420 nm is up to 2.08%. Density functional theory (DFT) calculations have demonstrated the presence of interfacial charge transfers from TpPa-1-COF to the surface of ZnIn₂S₄ spontaneously and the formation of an electric field at the area of the COF/ZIS heterojunction under the ground-state condition. Furthermore, the creation of a tuned built-in electric field drives the directional S-scheme charge transfer, while the photogenerated electron has a high reduction, thus synergistically promoting photocatalytic H₂ evolution, which has been demonstrated by experiments and theoretical calculation results. This work provides an advanced method for the preparation of S-scheme high-efficiency heterojunction photocatalysts based on COF by matching the band structures.