Ik Ji Kim  Hyuk Taek Kwon

Vol. 29,  No. 1, pp. 71-75, Mar.  2023
10.7464/ksct.2023.29.1.71

Polycrystalline membrane Intercrystalline defect plugging Polymer coating Metal-organic Framework UiO-66

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In general, the presence of non-selective intercrystalline (grain boundary) defects in polycrystalline metal-organic framework (MOF) or zeolite membranes, which are known to be ca. 1 nm in size, causes lower membrane performance (selectivity) than the intrinsically expected. In this study we show that applying a thin polymeric coating of polydimethylsiloxane (PDMS) on a polycrystalline MOF membrane is effective to cap the non-selective intercrystalline defects and therefore improve membrane performance. To demonstrate the concept, first, polycrystalline UiO-66, one of Zr-based MOFs, membranes were prepared by an in-situ solvothermal growth. By controlling membrane growth condition with respect to growth temperature, we were able to obtain polycrystalline UiO-66 membranes at 150 oC with intercrystalline defects of which the quantity is not significant, so it can be plugged by the suggested PDMS deposition. Second, their performances were compared before and after the PDMS deposition. As expected, the PDMS deposition ended up with a noticeable increase in CO2/N2 ideal selectivity from 6 to 14, indicating successful intercrystalline defect plugging. However, the enhancement in CO2/N2 selectivity was accompanied by a significant reduction in CO2 permeance from 5700 to 33 GPU because the PDMS deposition not only plugs defects but also forms a continuous coating on membrane surface, adding an additional transport resistance.