A diketimine-linked metal covalent organic framework for efficient photocatalytic CO2 reduction
Metal covalent organic frameworks (MCOFs) are promising photocatalysts for carbon dioxide reduction reaction (CO2RR). However, the synthesis of ketimine-linked COFs remains challenging due to the low reactivity of ketones. Here, we report a straightforward strategy to construct diketimine-linked MCOFs via the condensation of acenaphthenequinone (Ace) with 1,3,6,8-tetra(4-aminophenyl)pyrene (TAPPy). The metal-free COF (TACOF-AA) exhibits AA stacking, while the addition of NiCl2·6H2O under identical conditions yields an AB-stacked Ni-based MCOF (Ni-TACOF-AB). The coordinated Ni species serve as active sites for CO2RR and enhance electron-hole separation. Photocatalytic tests demonstrate that Ni-TACOF-AB achieves a CO evolution rate of 11.71 mmol g−1 h−1 with 99.9% selectivity, which is 7.6 times higher than that of TACOF-AA. Density functional theory (DFT) calculations reveal that Ni-TACOF-AB lowers the activation energy barrier of the rate-determining step by regulating local charge distribution, facilitating electron transfer to adsorbed CO2. This work provides a novel approach for synthesizing ketimine-based COFs and highlights the importance of interlayer stacking in modulating photocatalytic performance.