Fundamental Water and Ion Transport through ZIF-8/Polymer Nanocomposite Membranes

Abstract

This dissertation describes fundamental water and ion transport properties of metal organic framework (MOF)/polymer nanocomposite membranes based on uncharged amorphous rubbery polymer, cross-linked poly(ethylene glycol) diacrylate (XLPEGDA). The flexible polymer chain was selected as a suitable polymeric matrix. Due to the ultrathin nature of polyamide layer within thin-film nanocomposite membranes, the experimental design capable of revealing the in-depth water/ion transport properties of MOF embedded nanocomposite membrane, is not straightforward. Among the MOFs, zeolitic imidazole framework-8 (ZIF-8) was chosen due to its appropriate pore size for separation of water and ions. The ZIF-8/XLPEGDA nanocomposite membranes were successfully prepared by varying the ZIF-8 content. No interfacial change between ZIF-8 and XLPEGDA was confirmed by density and crosslinking degree measurements. For water and ion transport properties, the water permeability was considerably increased, whereas NaCl permeability was nearly unchanged despite the increase in ZIF-8 loading, and water/NaCl permselectivity was consistently increased with the increase of ZIF-8 content. Based on the characterizations of water and salt permeability, the water/salt properties of ZIF-8 incorporated nanocomposite membranes differ from that of polymeric membrane. Overall, we revealed that the ZIF-8 enables the ions to transport inside the pore and provides the highly water permselective pathway in polymeric matrix. Furthermore, this approach of water and ion transport study would contribute to the practical guideline in fabricating optimal nanocomposite membranes.