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.