Preparation of 3D/2D ZnIn₂S₄/Porphyrin(Cu)-COF Type II Heterojunction: An In-Depth Insight into Interfacial Charge Transfer for Efficient Light-to-Hydrogen Conversion

Semiconductor heterojunctions could accelerate carrier separation and transfer for improving light-to-hydrogen (LTH) conversion efficiency. However, the lack of tight and efficient interfacial charge cross in three-dimensional semiconductor-based heterojunctions limits their practical application and the relevant profound understanding of the interfacial charge delivery. In this work, porphyrin (Cu)-based COF with a highly conjugated structure was deposited onto three-dimensional (3D) ZnIn2S4 by a facile solvothermal method to prepare a 3D/2D ZnIn2S4@CuP–Ph COF heterojunction. The content-optimized ZnIn2S4@CuP–Ph COF composite showed an excellent LTH conversion rate of up to 2667.94 μmol g–1 h–1, about 13.5 times higher than that of pristine ZnIn2S4. The significantly meliorated photocatalytic performance is attributed to the synergistically functioning contributors, that is, the fast interfacial charge transfer and the augmented light capturing capability after integration. Also, the work function results by DFT calculation reveals that the electrons of CuP–Ph COF (Φ = 4.41 eV) transfer from the interface electron delivery channels of the two components to ZIS (Φ = 7.03 eV) until the Fermi level of the two components reaches equilibrium. This moment, the work function of ZnIn2S4@CuP–Ph COF (Φ = 6.50 eV) lies between the two components, and an electron accumulation region is formed on the side of ZIS. Additionally, the free-energy barriers of hydrogen evolution dominated by ZnIn2S4@CuP–Ph COF (0.0955 eV) is much lower than that of ZnIn2S4 (0.1256 eV). This study possesses certain guiding significance for the design of organic–inorganic heterojunction photocatalysts for efficient LTH conversion.