Constructing interconnected ionic cluster network in polyelectrolyte membranes for enhanced CO2 permeation

Membranes with fast CO2 transport pathways have attracted intense attention due to their outstanding CO2 permeability, showing potential for industrial application. Regulating the spatial distribution of CO2 philic groups in polymer-based membranes is expected to be a promising strategy to achieve the fast CO2 transport pathways. In membrane matrix, the interconnected network of concentrated domains of CO2 facilitated transport groups provides membranes with specific CO2 transport pathways and finally leads to their high separation performance. In this study, a novel kind of polyelectrolyte membrane, quaternary ammonium polysulfone with interconnected ionic clusters, is prepared to enhance the CO2 permeability. The hydrophilic quaternary ammonium groups tend to aggregate spontaneously to create ionic clusters. Furthermore, under humidified conditions, these ionic clusters are connected by water to form an ionic cluster network in the membrane matrix. The ionic cluster network plays the crucial role in accelerating the selective transport for CO2 molecules over CH4 by the reversible interaction between CO2 and ion pairs. By tuning the quaternization degree of polysulfone, a series of polyelectrolyte membranes with different size of ionic clusters were developed. Membranes with hydrated ionic clusters (5-9 nm) show dramatic enhancement in CO2 separation performance, especially in CO2 permeability. The as-prepared quaternary ammonium polysulfone membrane with 8.98 nm ionic clusters exhibited the high CO2 permeability of 1109.44 Barrer and a high CO2/CH4 selectivity of 29.70, which exceeds 2008 Robeson upper bound limit. The optimized separation performance of QA-PSf membranes is attractive for potential application such as CO2 capture from flue gas and natural gas. (C) 2019 Elsevier Ltd. All rights reserved.