CO(2)/N(2) Separation Properties of Polyimide-Based Mixed-Matrix Membranes Comprising UiO-66 with Various Functionalities

Nanocrystalline UiO-66 and its derivatives (containing -NH(2), -Br, -(OH)(2)) were developed via pre-synthetic functionalization and incorporated into a polyimide membrane to develop a mixed-matrix membrane (MMM) for CO(2)/N(2) separation. Incorporation of the non-functionalized UiO-66 nanocrystals into the polyimide membrane successfully improved CO(2) permeability, with a slight decrease in CO(2)/N(2) selectivity, owing to its large accessible surface area. The addition of other functional groups further improved the CO(2)/N(2) selectivity of the polymeric membrane, with UiO-66-NH(2), UiO-66-Br, and UiO-66-(OH)(2) 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(2) diffusivity while suppressing N(2) sorption, thus, resulting in improved CO(2)/N(2) 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(2) separation performance of MMMs.