Design and Synthesis of Eosin Y-Sensitized MOF-on-MOF Heterojunction Photocatalysts for Enhancing Water Splitting

Constructing metal-organic framework (MOF) heterojunctions with effective photocatalytic activity, outstanding stability, and integrated redox centers remains challenging. Herein, a chiral [Cu^I(IPEA)] 1) and an achiral [Cu^II(IPEA)]·(H₂O) 2) (IPEA = (E)-3-[4-(imidazol-1-ylmethyl)phenyl]prop-2-enoic acid) were hydrothermally self-assembled. Notably, [Cu^II(IPEA)]·(H₂O) vertically grew on the surface of [Cu^I(IPEA)] to form a MOF-on-MOF S-scheme heterojunction [Cu^ICu^II(IPEA)] 3). Structural and interfacial charge transfer analyses (SEM/TEM/XRD/IR, XPS/UPS/KPFM, DFT) confirmed a built-in electric field at the heterojunction interface, efficiently separating electrons/holes at redox terminals. Furthermore, Eosin Y (EY) chemical adsorption on [Cu^ICu^II(IPEA)] sensitized it for photocatalytic H₂ evolution, achieving a high efficiency of 4800 µmol·g^-1·h^-1. This work offers new insights for solar energy utilization and dye-containing wastewater reutilization.