Ultrahigh carbon monoxide capture by novel protic cuprous-functionalized dicationic ionic liquids through complexation interactions

•Novel protic cuprous-functionalized dicationic ILs were developed for CO capture.•An unprecedented high CO uptake (1.440 mol/mol at 40 °C and 2.0 bar) was achieved.•The liquid–solid phase transition was responsible for the superior CO solubility.•The formation of Cu(CO)Cl species was confirmed.•The ILs can be reused for ten times with negligible performance loss. CO removal is a very important topic in the scientific and industrial communities. However, the CO capture performance of the currently reported absorbents is still unsatisfactory from an industrial perspective. Described herein have developed a series of novel protic functionalized dicationic ionic liquids (ILs) containing abundant cuprous sites for effective absorption and separation of CO. The physical properties of the prepared ILs were characterized, and the CO solubility was systematically determined. Strikingly, the solubility of CO in the designed IL [HBDMAEE-C6][Cu2Cl3]2 reaches as high as 1.440 mol/mol at 40 °C and 2.0 bar due to the accompanying phase change, which is the highest value reported so far. The interaction mechanism between [HBDMAEE-C6][Cu2Cl3]2 and CO was further elucidated by IR and NMR spectroscopy paired with Gaussian calculation, and the formation of Cu(CO)Cl complexes was confirmed. After ten consecutive absorption–desorption cycles, the CO uptake did not decrease significantly. As far as we know, this series of ILs show excellent CO capture performance and reversible regeneration performance. The strategy of multi-copper sites in this work provides important guidance for the design of novel solvents with promising applications in CO selective separation and storage.