Synthesis of highly soluble zirconium organic cages by iodine substitution toward a CO/N separation membrane.

Metal organic cages (MOCs) show promise as fillers in mixed-matrix membranes (MMMs) for gas separation; highly soluble MOCs are desirable for fabrication of high-compatibility membranes. Herein, we report an iodine substitution strategy to substantially increase the MOC solubility. The synthesized MOC of ZrT-NH-I possesses over 10-fold higher solubility than the parent ZrT-NH in organic solvents whilst retaining the original molecular structure and permanent porosity. Such enhanced solubility allows for the effective integration of ZrT-NH-I with an amidoxime polymer of intrinsic microporosity (PIM-PAO), resulting in a compatible MMM with a uniform distribution of MOC. The ZrT-NH-I@PIM-PAO MMM demonstrates a CO permeability of 1377 barrer and a CO/N gas selectivity of 45 which is 45 times that of the membrane made from ZrT-NH. The permeability-selectivity performance not only surpasses the 2008 upper bound, but also exceeds those of currently available MMMs.