Tuning Ion-Pair Interaction in Cuprous-Based Protic Ionic Liquids for Significantly Improved CO Capture

Because of the high bond dissociation energy of CO, achieving efficient absorption of CO in liquid solvents is still a significant challenge in gas separation. Herein, it is unprecedently found that cuprous-based protic ionic liquid (PIL) [EimH][CuCl2] exhibits ultrahigh absorption capacity for CO, with the value of 0.157 mol.mol(-1) at 293.2 K and 1 bar, being 100 times that of a commonly used IL [Bmim] [Tf2N] (0.0015 mol.mol(-1)). The IR and Raman spectroscopies coupled with theoretical calculation demonstrated that the protonated imidazolium cation ([EimH](+)) played an essential role in strengthening the ion-pair interaction between CO and dinuclear cuprous species, contributing to an obvious red shift for the system [EimH][CuCl2] + CO and thereby to such superior CO capacity. Furthermore, the PIL [EimH][CuCl2] displayed very large absorption selectivities for CO/CO2, CO/N-2, and CO/H-2, and the absorption of CO was completely reversible. The present work thus triggers important guidance for the design of new solvents with promising application in selective separation of CO.