This review article is devoted to bridging the conventional and newly-developed NF membranes with the potential environmental applications by systematically discussing the synthesis–property–performance relationships.
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 membranes via both
blending (BL) and preloading interfacial polymerization 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 the corresponding thin-film composite 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 the polyamide active layer. MIL-53(Al) were found
to bind with polyamide via reacting with piperazine, whereas 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 membranes, 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
deepen our understanding of the roles that MOFs play in regulating
membrane performance, promoting molecular design of MOF-incorporated
TFN membranes via precise control of MOF–polymer interactions.
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