Membranes are widely used for liquid separations such as removing solute components from solvents or liquid/liquid separations. Due to negligible vapor pressure, adjustable physical properties, and thermal stability, the application of ionic liquids (ILs) has been extended to fabricating a myriad of membranes for liquid separations. A comprehensive overview of the recent developments in ILs in fabricating membranes for liquid separations is highlighted in this review article. Four major functions of ILs are discussed in detail, including their usage as (i) raw membrane materials, (ii) physical additives, (iii) chemical modifiers, and (iv) solvents. Meanwhile, the applications of IL assisted membranes are discussed, highlighting the issues, challenges, and future perspectives of these IL assisted membranes in liquid separations.
The development of highly permeable and selective thin-film
composite
(TFC) membranes is essential for organic solvent nanofiltration (OSN)
applications. However, overcoming the permeability–selectivity
trade-off in polymer membranes remains highly challenging owing to
the difficulty in controlling the thickness and nanostructures of
the selective layers. In this study, TFC OSN membranes with sandwich-like
structures were developed via interfacial polymerization on Cu-TCPP
nanosheet-modified microporous polyvinylidene fluoride (PVDF) substrate
surface. The interfacial polymerization was done by using mixed amine
(polyethyleneimine and piperazine) in the aqueous phase and the 1,3,5-benzenetricarbonyl
trichloride in the hydrophobic ionic liquid phase as monomers. It
was found that the Cu-TCPP nanosheets of micrometer lateral dimensions
and nanometer thickness (1.5 ± 0.6 nm) can be deposited on the
PVDF substrate as an interlayer to facilitate the following interfacial
polymerization reaction. The Cu-TCPP interlayer also can be served
as a binder between the polyamide selective layer and the microporous
PVDF substrate to enhance their mechanical strength. As compared with
the PVDF/PA membrane, the PVDF/t-Cu-TCPP/PA membrane
exhibited higher elongation (8.0 vs. 4.6%) while ensuring slightly
lower tensile strength (36.0 vs. 48.6 MPa). Under optimal synthetic
conditions, the TFC membranes could achieve 2.7 L m–2 h–1 bar–1, and 98.9% and 95.0%
rejection to Brilliant Blue R (826 Da) and Congo red (697 Da), respectively,
in ethanol. Furthermore, the membranes showed steady performance throughout
the 36 h nanofiltration of the Rose bengal/ethanol mixture and exhibited
good performance in the concentration of lecithin in methanol. Accordingly,
this work highlights the potential of using thin metal–organic
framework nanosheets as interlayers to develop high-performance TFC
membranes for OSN applications.
Herein, thin-film composite membranes consisting of poly(m-phenyleneisophthalamide) substrate and polyamide active layer were constructed by transition metal ionassisted interfacial polymerization method. As compared to the traditional polyamide membranes, a much thinner polyamide layer (33 vs. 200 nm) can be synthesized with higher permeance (3.2 vs. 0.62 L m À2 h À1 bar À1 ) in the organic solvent nanofiltration.
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