Synthesis and characterisation of MOF/ionic liquid/chitosan mixed matrix membranes for CO2/N2 separation

Abstract

Mixed matrix membranes (MMMs) have been prepared by combining a small amount of highly absorbing non-toxic ionic liquid, [emim][Ac] (IL) (5 wt%), a biopolymer from renewable abundant natural resources, chitosan (CS), and nanometre-sized metal–organic framework (MOF) ZIF-8 or HKUST-1 particles to improve the selectivity of the IL–CS hybrid continuous polymer matrix. The TGA revealed that the thermal stability has been enhanced by the influence of both IL and ZIF-8 or HKUST-1 fillers, while keeping a water content of around 20 wt%, which suggests the potential of such materials for developing high temperature water resistant membranes for CO₂ separation. The CO₂ and N₂ single gas permeation performance was tested at temperatures in the range of 25–50 °C, to compare with the previously reported IL–CS hybrid membranes. The best CO₂ permeability and CO₂/N₂ selectivity performance is obtained for 10 wt% ZIF-8 and 5 wt% HKUST-1/IL–CS membranes, as high as 5413 ± 191 Barrer and 11.5, and 4754 ± 1388 Barrer and 19.3, respectively. This is attributed to a better adhesion and smaller particle size of ZIF-8 than HKUST-1 nanoparticles with respect to the IL–CS continuous matrix, as interpreted by Hansen solubility parameters and Maxwell-based models, modified to account for rigidification, pore blockage and crystallinity of the CS matrix, with very accurate predictions.