Charged Nanochannels in Covalent Organic Framework Membranes Enabling Efficient Ion Exclusion

Abstract

Controllable ion transport through nanochannels is crucial for biological and artificial membrane systems. Covalent organic frameworks (COFs) with regular and tunable nanochannels are emerging as an ideal material platform to develop synthetic membranes for ion transport. However, ion exclusion by COF membranes remains challenging because most COF materials have large-sized nanochannels leading to nonselective transport of small ions. Here we develop ionic COF membranes (iCOFMs) to control ion transport through charged framework nanochannels, the interior surfaces of which are covered with arrayed sulfonate groups to render superior charge density. The overlap of an electrical double layer in charged nanochannels blocks the entry of co-ions, narrows their passageways, and concomitantly restrains the permeation of counterions via the charge balance. These highly charged large-sized nanochannels within the iCOFM enable ion exclusion while maintaining intrinsically high water permeability. Our results reveal possibilities for controllable ion transport based on COF membranes for water purification, ionic separation, sensing, and energy conversion.

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

“…The specific area of membranes based on Brunauer–Emmett–Teller (BET) gave the value of ~ 24 m 2 g −1 , which was much lower than that of COF powders. This result was similar to those of other COF membranes [ 2 , 40 , 41 ] and was primarily due to the lamellar structures of COF units within membranes. The high aspect ratio of COF units restricted effective adsorption of N 2 molecule inside frameworks, leading to the lower surface areas of membranes.…”

[2,1,3]-Benzothiadiazole-Spaced Co-Porphyrin-Based Covalent Organic Frameworks for O2 Reduction

“…Reticular chemistry offers the opportunity to tailor the spacing between atomic sites precisely by using various ligands, which has a significant impact on the electro- kinetics. 9,10 Covalent organic frameworks (COFs) 11−19 and metal−organic frameworks (MOFs) 20−23 are materials that possess high porosity with atomically well-defined chemical environments and have a wide range of applications including gas separations/storage, 24−27 catalysis, 28,29 optoelectronics, 30,31 and energy storage. 32,33 Single atom-based COFs could address existing challenges for developing ideal SAECs based on their diverse reticular designs.…”

“…These are crucial parameters to control the activation barriers and mass transport kinetics. Reticular chemistry offers the opportunity to tailor the spacing between atomic sites precisely by using various ligands, which has a significant impact on the electro-kinetics. , Covalent organic frameworks (COFs) − and metal–organic frameworks (MOFs) − are materials that possess high porosity with atomically well-defined chemical environments and have a wide range of applications including gas separations/storage, − catalysis, , optoelectronics, , and energy storage. , Single atom-based COFs could address existing challenges for developing ideal SAECs based on their diverse reticular designs. The ability to define the spacing between atomic sites using different synthetic building units (SBUs) as spacers also makes the strategy attractive. , The in-plane extensive π delocalization and out-of-plane π–π alignment of COF monolayers can potentially enhance charge transport inside crystals. , The emergence since 2015 of redox-active porphyrinic COFs and MOFs as SAECs has advanced the fields of CO 2 reduction reaction (CO 2 RR), − hydrogen evolution reaction (HER) , oxygen evolution reaction (OER), , ORR, , and Li-ion battery .…”

Hyperlooping Carbon Nanotube-Graphene Oxide Nanoarchitectonics as Membranes for Ultrafast Organic Solvent Nanofiltration

“…For this reason, there is a need for new membrane materials with strong solvent resistance and fast transport properties. − Two-dimensional (2D) graphene-based materials have shown enormous potential for OSN process, given their monatomic thickness, which offers lowest theoretical transport resistance and good chemical stability. − Furthermore, solution processable derivatives such as graphene oxide (GO) nanosheets with basal plane oxygen-containing functional groups can be assembled into laminar microstructures with 2D nanochannels of tunable interlayer spacing for precise molecular sieving. − It is known that 2D nanochannels can facilitate solvent transport. , However, GO membranes suffer from an ubiquitous poor stability in polar solvents as the oxygen-containing functional groups dehydrogenate when solvated and formed negative charges that lead to easy swelling and disintegration of the laminar microstructure . One way to address this instability is to chemically convert GO to reduced GO (rGO) membranes, where the oxygen functionalities are partially removed to induce stronger van der Waals forces and more compact restacking, leading to greater stability toward polar solvents .…”