Optimizing microstructure of polymer composite membranes by tailoring different ionic liquids to accelerate CO2 transport

Abstract This study researched a strategy to optimize the microstructure of polymer composite membranes by designing and tailoring different anions and cations for ionic liquids (ILs). A series of ILs containing the 1-alkyl-3-methylimidazolium cation ([CnMIM]+) and anion of tetrafluotoborate ([BF4]−), acetate ([Ac]−) or glycine ([Gly]−) were incorporated into a Pebax® MH 1657 (Pebax) matrix to fabricate polymer composite membranes to accelerate CO2 transport. The [Gly]− anion and [C6MIM]+ cation gave the membranes the optimal microstructure, which had free volume cavities with a favorable radius (0.338 nm) only for CO2 molecule transport, rendering a precise molecular sieving ability. Additionally, the free amino acid anions of IL in the polymer composite membranes contained abundant amino and carboxyl groups, which served as mobile CO2 carriers, facilitating and accelerating highly efficient CO2 transport. The resultant membranes containing 20 wt% [C6MIM][Gly] showed CO2 permeability of 1490 ± 30 Barrer. This study may stimulate research on optimizing polymer microstructures by tailoring the types of ILs.