Tailored Linker Defects in UiO-67 with High Ligand-to-Metal Charge Transfer toward Efficient Photoreduction of CO₂

Defect engineering can be used as a potential tool to activate metal-organic frameworks by regulating the pore structure, electronic properties, and catalytic activity. Herein, linker defects were effectively controlled by adjusting the amount of formic acid, and UiO-67 with different CO₂ reduction capabilities was obtained. Among them, UiO-67-200 had the highest ability to selectively reduce CO₂ to CO (12.29 μmol g^-1 h^-1). On the one hand, the results based on time-resolved photoluminescence decay curves and photochemical experiments revealed that UiO-67-200 had the highest charge separation efficiency. On the other hand, the linker defects affected the band structure of UiO-67 by changing the lowest unoccupied molecular orbital (LUMO) based on the density functional theory and UV-vis spectra. Hence, the proper linker defects enhanced the ligand-to-metal charge transfer process by promoting the transfer of electrons between the highest occupied molecular orbital and LUMO. Additionally, in situ Fourier transform infrared spectra and ¹³CO₂ labeling experiments also indicated that COOH* was an important intermediate for CO formation and that CO originated from the photoreduction of CO₂.