Enhancing photocatalytic CO2 reduction activity of ZnIn2S4/MOF-808 microsphere with S-scheme heterojunction by in situ synthesis method

The design of a heterogeneous structure for photocatalysts has attracted significant attention. In this study, a step-scheme (S-scheme) heterojunction was designed using an in-situ synthesis method. The resulting heterojunction comprised 3D microspheres of ZnIn2S4 and octahedral MOF-808 (ZnIn2S4/MOF-808). During this process, we investigated the impact of the scale of the ZnIn2S4 microspheres on performance by controlling the growth of the ZnIn2S4 microspheres with various scales. The maximum catalytic activity was discovered to be achieved with ZnIn2S4 microspheres of 6 µm when coupled with MOF-808. Compared to pure ZnIn2S4 and MOF-808, the fabricated S-scheme ZnIn2S4/MOF-808 heterojunction exhibited notably improved photocatalytic CO2 reduction performance. The performance of the CO yield of the optimized sample could reach 8.21 μmol g−1 h−1, which was approximately 10 and 8 times higher than those of ZnIn2S4 (0.84 μmol g−1 h−1) and MOF-808 (1.03 μmol g−1 h−1), respectively. Moreover, ultraviolet photoelectron spectroscopy, ESR, in situ X-ray photoelectron spectroscopy, and density functional theory calculations were used to study the charge transfer mechanism of the S-scheme heterojunction. In-situ FT-IR investigation established the Carbene pathway as the source of CO production (CO2 → CO2* → COOH* → CO* → CO). This study provides an efficient method for designing an S-scheme heterojunction for photocatalytic CO2 reduction.