Thin Film Composite Membrane Comprising Ionic Liquid/Graphene Oxide in the Selective Layer for Enhanced CO2 Separation

Significant progress has been made in recent years in the fabrication of CO2 separation membranes using thin-film composite membranes (TFCs) prepared by the interfacial polymerization (IP) process. However, more advancement is still required to realize the full potential of IP-TFCs in highly permeable/selective gas separation membranes. Here, nitrogen-doped graphene oxide (N-GO) nanosheets and dicationic imidazolium ionic liquids (ILs) with two different aliphatic linkers (i.e., trimethylene and hexamethylene), C3IL and C6IL, respectively, are added in the polyamide (PA) selective layer of a TFC membrane, and the gas separation performance of the membranes is investigated. With the incorporation of the C3IL/N-GO additive, the CO2 permeance and CO2/CH4 and CO2/N2 selectivities of the TFC membranes are increased by 900, 2, and 6%, respectively. On the other hand, the corresponding increases in the CO2 permeance and CO2/gas selectivities, by introducing the C6IL/N-GO additive are 700, 9, and 16%, respectively. These enhancements are attributed to the role of IL molecules in improving the distribution of N-GO nanosheets in the PA selective layer of TFCs, tuning the N-GO sieving channels in favor of CO2 transport, and creating ultrasmall holes which are highly accessible to CO2 molecules. We believe that the incorporation of IL/GO additives into the selective layer of IP-TFCs will pave the way to improving the gas separation performance of thin-film composite membranes.