8 research outputs found
Interfacial polymerization of covalent organic frameworks (COFs) on polymeric substrates for molecular separations
Covalent organic frameworks (COFs) represent a new family of porous polymers with highly ordered two or three-dimensional channels. Although numerous studies have been focused on the design and synthesis of COF in the form of powders, the development of COF-based separation membranes is still hampered by the challenges of COF particles agglomeration and harsh synthetic conditions. In this work, interfacial polymerization (IP) directly performed on polymeric substrates as employed in the traditional IP process of polyamide (PA) membranes is developed for the synthesis of COF-based membranes. With the moderate reaction rate between monomer pairs in corresponding aqueous and organic solutions, a conformal growth of COF crystallites directly composited with the polysulfone (PSF) ultrafiltration substrates can be realized within 1 min. The synthesis parameters including reaction time and precursor concentrations are optimized, and thus-synthesized COF/PSF membrane presents a stable rejection to dye (Congo red) of 99.5% with a high water permeance of up to 50 L m h bar, which is 2–10 times higher than that of many other membranes with similar rejection. This convenient IP process is expected to facilitate the up-scaling and real-world applications of COF-based membranes
Selective Swelling of Electrospun Block Copolymers: From Perforated Nanofibers to High Flux and Responsive Ultrafiltration Membranes
This work is devoted
to the development of high-flux ultrafiltration
membranes using electrospun nanofibers of amphiphilic block copolymers
(BCPs) of polystyrene-<i>block</i>-poly(2-vinylpyridine)
(PS-<i>b</i>-P2VP) as building blocks. When soaked in hot
ethanol, the solid as-spun BCP fibers are progressively transformed
into three-dimensionally perforated fibers with increasing porosities
with rising degrees of swelling, which ended up with the equilibrated
morphology of spherical micelles. The BCP nanofibers are collected
on macroporous substrates and subjected to heating to convert loosely
stacked fibers to dense and continuous films. Subsequent swelling
in hot ethanol leads to robust composite membranes with nanoporous
BCP selective layers tightly adhered to the substrates. Filtration
performances of the composite membranes can be conveniently modulated
by electrospinning durations. The water permeabilities are as high
as 6100 L m<sup>–2</sup> h<sup>–1</sup> bar<sup>–1</sup>, which is ∼10–35 times higher than that of commercial
membranes with similar rejections. Moreover, with the surface enrichment
of P2VP chains the membranes exhibit a strikingly sharp pH-dependent
water permeability switchable in the largest amplitude ever reported
for multiple cycles. Electrospun fibers can be promising building
materials to produce a wide range of membranes with 3D interconnected
nanoporosities which also show great potential in separation and biomedical
applications
Homoporous Membranes with Tailored Pores by Soaking Block Copolymer/Homopolymer Blends in Selective Solvents: Dissolution versus Swelling
Extraction
homopolymers premixed in aligned films of block copolymers
by rinsing with selective solvents has long been used for the preparation
of membranes with uniform straight pores (homoporous membranes). It
is frequently assumed that only the dissolution of homopolymers contributes
to the pore formation. However, in this work, we demonstrate that
the effect of swelling plays a significant role in determining the
pore sizes. We prepare blended films of block copolymers of polystyrene-<i>block</i>-poly(2-vinylpyridine) (PS-<i>b</i>-P2VP) and P2VP homopolymers with low molecular weight and anneal
the films to perpendicularly align the P2VP microdomains. Rinsing
the aligned films in ethanol results in homoporous membranes, and
the pore sizes can be tuned by the dosages of P2VP homopolymers. Interestingly,
the pore sizes can also be effectively tailored by changing the rinsing
temperatures and/or durations because of the significant contribution
of the selective swelling of P2VP blocks under strong rinsing conditions
in addition to the contribution of the dissolution of P2VP homopolymers.
We identify the portion of the contribution from dissolution and from
swelling and demonstrate that the pore sizes can be flexibly tuned
within a wider range at no expense of pore ordering and uniformity
by balancing the effect of dissolution and swelling
Temperature-dependent rearrangement of gas molecules in ultramicroporous materials for tunable adsorption of CO2 and C2H2
Temperature-dependent rearrangement of gas molecules in ultramicroporous materials for tunable adsorption of CO2 and C2H2
Abstract The interactions between adsorbed gas molecules within porous metal-organic frameworks are crucial to gas selectivity but remain poorly explored. Here, we report the modulation of packing geometries of CO2 and C2H2 clusters within the ultramicroporous CUK-1 material as a function of temperature. In-situ synchrotron X-ray diffraction reveals a unique temperature-dependent reversal of CO2 and C2H2 adsorption affinities on CUK-1, which is validated by gas sorption and dynamic breakthrough experiments, affording high-purity C2H2 (99.95%) from the equimolar mixture of C2H2/CO2 via a one-step purification process. At low temperatures (10) and capacity (170 cm3 g−1) owing to the formation of CO2 tetramers that simultaneously maximize the guest-guest and host-guest interactions. At room temperature, conventionally selective adsorption of C2H2 is observed. The selectivity reversal, structural robustness, and facile regeneration of CUK-1 suggest its potential for producing high-purity C2H2 by temperature-swing sorption