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

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 N-2 single gas permeation performance was tested at temperatures in the range of 25-50 degrees C, to compare with the previously reported IL-CS hybrid membranes. The best CO2 permeability and CO2/N-2 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.