Ionic Liquid-Modified Porous Organometallic Polymers as Efficient and Selective Photocatalysts for Visible-Light-Driven CO Reduction.

In the photoreduction of CO to CO, the competitive H evolution is always inevitable due to the approximate reduction potentials of H/H and CO/CO, which results in poor selectivity for CO production. Herein, imidazolium-type ionic liquid- (IL-) modified rhenium bipyridine-based porous organometallic polymers (Re-POMP-IL) were designed as efficient and selective photocatalysts for visible-light CO photoreduction to CO based on the affinity of IL with CO. Photoreduction studies demonstrated that CO photoreduction promoted by Re-POMP-IL functioning as the catalyst exhibits excellent CO selectivity up to 95.5% and generate 40.1 mmol CO/g of Re-POMP-IL1.0 (obtained by providing equivalent [(5,5'-divinyl-2,2'-bipyridine)Re(CO)Cl] and 3-ethyl-1-vinyl-1-imidazol-3-ium bromide) at 12 h, outperforming that attained with the corresponding Re-POMP analogue without IL, which highlights the crucial role of IL. Notably, CO adsorption, light harvesting, and transfer of photogenerated charges as key steps for CORR were studied by employing POMPs modified with different amounts of IL as photocatalysts, among which the CO affinity as an important factor for POMPs catalyzed CO reduction is revealed. Overall, this work provides a practical pathway to improve the CO photoreduction efficiency and CO selectivity by employing IL as a regulator.