Mimic Metalloenzymes with Atomically Dispersed Fe Sites into Covalent Organic Framework Membranes for Enhanced CO2 Photoreduction

Abstract

The massive CO2 emissions from continuous increases in fossil fuel consumption have caused disastrous environmental and ecological crises. Covalent organic frameworks (COFs) hold the potential to convert CO2 and water into value-added chemicals and O2 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 the conditions of gas-solid and no addition of any photosensitizer and sacrificial reagent, the highly crystalline Fe-COF membrane shows a record high CO2 photoreduction performance with the CO production of 3972 μmol g-1 in a 4 h reaction, ~100% selectivity of CO, and excellent cycling stability (at least 10 cycles). In such a remarkable photocatalytic CO2 conversion, the atomically dispersed Fe sites with high catalytic activity significantly reduce the formation energy barrier of key *CO2 and *COOH intermediates, the high-density triazine moieties supply more electrons to the iron catalytic center to promote CO2 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 CO2 photocatalytic reduction.