Molecular transport in ionic liquid/nanomembrane hybrids

Abstract

Ionic liquids and nanoscale membranes are both considered as promising functional components to design next-generation gas separation technologies. Herein, we combine free-standing carbon nanomembranes (CNMs) with [bmim][Tf₂N] ionic liquid having affinity to carbon dioxide, and explore molecular permeation through such a composite membrane. Gas transport measurements reveal an increase in the transmembrane flux of carbon dioxide as compared to that of bare CNMs, whereas passage of helium is found to be suppressed in accordance with the solubility constants. Upon exposure to water vapor, the behavior of the hybrid membrane appears to differ strikingly as hydrophilic properties of CNMs are camouflaged by the hydrophobic nature of the ionic liquid. Kinetic simulations are conducted to account for the change in permeation mechanism, and the results agree with the experimental data obtained. Our study confirms that molecular transport in two-dimensional membranes can be tailored by imparting chemical functionalities, but at the same time highlights practical challenges in surface modification.