Impacts of Metal-organic Frameworks on Structure and Performance of Polyamide Thin-film Nanocomposite Membranes.

Metal-organic frameworks (MOFs), a class of hybrid organic-inorganic materials, have recently attracted tremendous interests in the fabrication of thin-film nanocomposite (TFN) membranes with exceptional permselectivity. However, the structure-performance relationship of such membranes, which is a function of both MOF type and membrane fabrication procedure, has not been elucidated in the literature. In this study, three types of hydro-stable MOFs, namely MIL-53(Al), NH2-UiO-66 and ZIF-8, were used to fabricate TFN nanofiltration (NF) membranes via both blending (BL) and preloading (PL) interfacial polymerization (IP) methods. Results show that the incorporation of MOFs could enhance water permeability of TFN membranes to 7.2 L/m2·h·bar at most (TFNNH2-UiO-66-BL-0.10%), about 1.3 times of corresponding TFC membranes, without sacrificing their selectivity to reject NaCl (> 40%) and xylose (> 65%). Membrane characterization revealed that MOFs decreased the cross-linking degree while increasing the membrane thickness, surface negative charge and roughness of polyamide active layer. MIL-53(Al) were found to bind with polyamide via reacting with piperazine, while weaker polyamide-MOF interactions were observed for NH2-UiO-66 and ZIF-8. This difference, along with the hydrophilicity of MOF particles, explained the varied permselectivity of different TFN membranes. Compared to pristine polyamide membrane, the TFN membranes demonstrated higher or comparable efficiencies in removing a set of six pharmaceuticals (PhACs), which were determined by the molecular properties of PhACs and membrane structure. The findings of this study deepens our understanding of the roles that MOFs plays in regulating membrane performance, promoting molecular design of MOF-incorporated TFN membranes via precise control of MOF-polymer interactions.