Porous covalent organic framework liquid for boosting CO2 adsorption and catalysis via dynamically expanding effect

ABSTRACT The features of intrinsic porosity and fluidity endow porous liquids (PLs) with unique properties and performance but the preparation of PLs remains challenging due to the difficulty in liquefying and keeping porous features at the same time. Herein, we develop a stepwise surface functionalization and ion exchange strategy to achieve a rare example of flexible covalent organic framework (COF)-based PL (COF-PLs). By coating the outer surface of the judiciously selected three-dimensional flexible COF-301 with an imidazolium salt corona, followed by liquefaction using the anion canopy potassium poly(ethylene glycol) sulfonate (PEGS) via electrostatic interactions, a flexible PL, COF-301-PL, can be obtained. Theoretical calculations and CO2 adsorption experiments reveal that the cavities of COF-301-PL undergo dynamic adjustments in response to changes in CO2 pressure. The dynamic expansion effect can not only provide additional gas adsorption capacity (7.04 mmol/g at 40 bar) but also facilitate the mass transfer of gas molecules during the catalytic process. Consequently, COF-301-PL exhibits superior catalytic efficiency for the conversion of CO2 into cyclic carbonate by a factor of 24 and 17 compared to those of PEGS and COF-301 solid counterpart, respectively. The optimization of substrate adsorption and mass transfer conditions consequently improves the overall efficiency of catalytic reactions. This work offers a new perspective on the preparation of PLs and their great potential application for gas adsorption and catalysis.