CO/N Separation Properties of Polyimide-Based Mixed-Matrix Membranes Comprising UiO-66 with Various Functionalities.

Nanocrystalline UiO-66 and its derivatives (containing -NH, -Br, -(OH)) were developed via pre-synthetic functionalization and incorporated into a polyimide membrane to develop a mixed-matrix membrane (MMM) for CO/N separation. Incorporation of the non-functionalized UiO-66 nanocrystals into the polyimide membrane successfully improved CO permeability, with a slight decrease in CO/N selectivity, owing to its large accessible surface area. The addition of other functional groups further improved the CO/N selectivity of the polymeric membrane, with UiO-66-NH, UiO-66-Br, and UiO-66-(OH) demonstrating improvements of 12%, 4%, and 17%, respectively. Further evaluation by solubility-diffusivity analysis revealed that the functionalized UiO-66 in MMMs can effectively increase CO diffusivity while suppressing N sorption, thus, resulting in improved CO/N selectivity. Such results imply that the structural tuning of UiO-66 by the incorporation of various functional groups is an effective strategy to improve the CO separation performance of MMMs.