Mimic metalloenzymes with atomically dispersed Fe sites in covalent organic framework membranes for enhanced CO photoreduction.

The massive CO emissions from continuous increases in fossil fuel consumption have caused disastrous environmental and ecological crises. Covalent organic frameworks (COFs) hold the potential to convert CO and water into value-added chemicals and O to mitigate this crisis. However, their activity and selectivity are very low under conditions close to natural photosynthesis. In this work, inspired by the photosynthesis process in natural leaves, we successfully anchored atomically dispersed Fe sites into interlayers of the photoactive triazine-based COF (Fe-COF) membrane to serve as a mimic metalloenzyme for the first time. It is found that under gas-solid conditions and no addition of any photosensitizer and sacrificial reagent, the highly crystalline Fe-COF membrane shows a record high CO photoreduction performance with a CO production of 3972 μmol g in a 4 h reaction, ∼100% selectivity of CO, and excellent cycling stability (at least 10 cycles). In such a remarkable photocatalytic CO conversion, the atomically dispersed Fe sites with high catalytic activity significantly reduce the formation energy barrier of key *CO and *COOH intermediates, the high-density triazine moieties supply more electrons to the iron catalytic center to promote CO reduction, and the homogeneous COF membrane greatly improves the electron/mass transport. Thus, this work opens a new window for the design of highly efficient photocatalysts and provides new insights into their structure-activity relationship in CO photocatalytic reduction.