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Mono-valent selective ion-exchange membrane, as the core component of selective electrodialysis (SED), has received extensive attention. In this work, we report a mono-valent selective anion-exchange membrane (AEM), which was fabricated with distorted poly(aryl ether sulfone) and decorated with bifunctional side-chains providing anion exchange groups and hydrophobic segments. By tuning the length of the hydrophobic side-chains, the nanophase separation within AEMs was finely tuned, evidenced by an ionic cluster size of about 0.47 nm from SAXS analysis. The optimized AEM (PAES-TA-7 AEM) shows a very low water swelling ratio of 6.4 %, signaling good dimensional stability. The perm-selectivity (P S O 4 2 – C l – ) of PAES-TA-7 AEM during ED reached 107 at 2.5 mA∙cm−2 (ion flux: 2.69 × 10−8 mol cm−2 s−1 at 90 min) significantly exceeding that of the commercial Neosepta ACS (11; 2.08 × 10−8 mol cm−2 s−1). It is inferred that the ion channels, resulting from nanophase separation between the side-chains and the backbone, as well as the free volume cavity created by the distorted backbone, significantly contribute to the smooth transport of the Cl− ions through the AEM with less resistance. As a result, it is believed that this work offers a useful strategy to advance the monovalent anion-selective membranes. [Display omitted] • A monovalent selective AEM based on distorted PAES decorated by bifunctional side-chains has been prepared. • The optimized AEM shows low water absorption and swelling ratio with the values of 12.4 % and 6.4 %, respectively. • The P S O 4 2 – C l – of the PAES-TA-7 AEM reaches 107 at mA∙cm−2, significantly exceeding that of Neosepta ACS (11). • The bifunctional side-chains and the distorted backbone significantly contribute to the transport of Cl− through the AEM matrix. [ABSTRACT FROM AUTHOR]

• Two series of side-chain-type polysulfone-based AEMs were prepared via menshutkin reaction. • The optimized AEM exhibits the low area resistance, and good alkaline stability in ED process. • The optimized AEM show the better NaOH enrichment performance than commercial AEM. • The investigation on AEM of this type suggests its potential ED application for alkali enrichment. To meet the need of efficient resource utilization, developing stable and efficient anion exchange membranes (AEMs) for alkaline enrichment application is of significance. In this work, we designed four polysulfone-based side-chain-type AEMs with several cations and different length of spacers per chain, to explore the structure-property relationship and obtained AEMs with high performance for alkaline enrichment via electrodialysis (ED). Our investigation demonstrates that, the optimized AEM (CM-TQ6Q6Q-1, 1.38 mmol·g−1) exhibits low swelling ratio of 8.9%, low area resistance of 2.48 Ω·cm2, acceptable OH– conductivity of 13.7 mS·cm−1. In addition, this AEM also shows relatively good alkaline stability with the IEC retention of 96.7% relative to the original IEC, suggesting the potential application of alkaline enrichment via electrodialysis (ED). After 5-times NaOH enrichment tests in ED, CM-TQ6Q6Q-1 AEM shows an efficient ED performance with alkaline concentration times of ~1.8 (current efficiency: ~90.0%; energy consumption: 8.47 kWh·kg−1), and maintains 96.4% of its original IEC, which are even comparable to those from commercial AEM (Neosepta AHA). The results demonstrate that the as-prepared AEM shows the promising potential ED application for alkali enrichment from the alkaline waste water. [ABSTRACT FROM AUTHOR]

• A new type of monovalent anion-selective amphoteric membrane was fabricated. • The blend AIEMs show the good miscibility between the two polymer components. • The swelling ratio of the optimized blending AIEM is as low as 10.9% at 25 °C. • The Cl–/SO 4 2– selectivity of the most optimized AIEM in ED is 21.8 at 2.5 mA cm−2. It is of significant importance to develop highly monovalent anion-selective membranes (MASM) having stable structure for a wide range of applications. To realize the efficient monovalent/bivalent anion separation, in this work, three amphoteric ion-exchange membranes (AIEMs) through blending were fabricated for use in electrodialysis (ED). The three membranes were prepared by blending amino-containing poly(arylene ether sulfone) (PAES-NH 2) with 10, 15, and 20 wt% of sulfonated polysulfone (SPSf), respectively, followed by grafting imidazolium salt-terminated side alkyl chains on PAES backbone. Our investigations demonstrate that each transparent AIEM shows good miscibility between the two components, which has been verified by a homogeneous structure via SEM observation and by an even distribution of N element via EDX mapping. In the ED process at a current density of 2.5 mA cm−2, AIEM with 15 wt% of SPSf shows the superior perm-selectivity (Cl–/SO 4 2–) of 21.8, relative to many reported MASMs having modified surfaces (<6.0), which is synergistically contributed by (i) electrostatic repulsion difference from the negatively-charged sulfonate groups against monovalent Cl– ions and bivalent SO 4 2– ions and (ii) hydrated energy difference of hydrated Cl–/SO 4 2– ions. This work thus presents a strategy to guide the architectural design of advanced MASMs. [ABSTRACT FROM AUTHOR]

Ion-conductive polymers having highly ordered and well-defined phase-separated structures are potential materials for use as monovalent anion-selective membranes (MASMs). In this work, to investigate the effect of hydrophobic spacers, four side-chain-type imidazolium salt-tethered poly(arylene ether sulfone) anion-exchange membranes (AEMs) with different alkyl spacer lengths (–CH 2 – number: 3, 6, 9, and 12) were fabricated for use in electrodialysis (ED). Our investigations using atomic force microscopy, small angle X-ray scattering and X-ray diffraction demonstrate that the extended alkyl spacers change the nano-phase-separated structures, with an increased ion cluster space ranging from 3.29 nm to 7.76 nm, resulting from increased immiscibility between the additional hydrophobic alkyl spacers and (i) the hydrophobic aromatic backbones and (ii) the hydrophilic ion-conductive groups. In addition, with the extension of the alkyl spacer, chloride (Cl−) ion conductivity at 25 °C decreases from 16.4 mS cm−1 to 11.4 mS cm−1 and water uptake is reduced to 12.8% (20 °C). It is found that the as-prepared AEM with a hexyl alkyl spacer shows the superior perm-selectivity (Cl−/SO 4 2−) of 7.10 (separation efficiency: 70.3%), as compared with three others (3.48, 6.81, and 4.26). This work thus presents an efficient strategy to guide the architectural design of novel MASMs. Image 1 • Four side-chain-type AEMs with different alkyl spacer lengths were fabricated. • Pronounced phase-separated morphologies verified by AFM and SAXS are obtained. • Extended alkyl spacer decreases the ion conductivity and lowers the water uptake. • Perm-selectivity of PAES-6C-IM AEM attains a maximum of 7.10 at 5.0 mA cm−2. [ABSTRACT FROM AUTHOR]

Ion selective separations play crucial roles in the fields of energy storage, pollution management, and industrial processes, etc. Ion exchange membranes (IEMs) offer promise for these separations but often lacking the required selectivity. In this work, we have developed a kind of IEM based on metal-organic frameworks (MOFs) to enhance membrane separation performance for electrodialysis (ED). Specifically, for poly(arylene ether sulfone)-based anion exchange membranes (AEMs), we introduced the modified MOFs through doping to create a transport pathway for target ions, leveraging their precise size-based separation effects. This approach significantly improves ion selectivity. Remarkably, at a current density of 2.5 mA·cm−2, the monovalent ion selectivity (Cl−/SO 4 2−) of PAES-UIO-66-Pyr could reach 54.26, while the monovalent ion selectivity (NO 3 −/SO 4 2−) could reach 55.90. These enhancements may stem from the incorporation of MOF particles, which facilitate the formation of fixed-size channel structures within membrane matrix. These fixed-size channels, coupled with the hydrophobic differences between the original poly(arylene ether sulfone) polymer, created a composite channel system that significantly improved the separation performance for monovalent ions, including Cl−/SO 4 2− and NO 3 −/SO 4 2−. [Display omitted] • A kind of MOF-modified cross-linked poly(arylene ether sulfone) AEM has been prepared. • The introduced cross-linked structure increases the density of AIEM. • The perm-selectivities of Cl−/SO 4 2− and NO 3 −/SO 4 2− reached 54.26 and 55.90, respectively. • The incorporation of MOFs could facilitate the formation of fixed-size channel structures. [ABSTRACT FROM AUTHOR]

Proton blocking anion exchange membrane (AEMs) can be used to treat various of acidic wastewater (i.e., enrich the recovered acid from acidic wastewater). In this work, four AEMs based on aliphatic chain segment imbedding poly(arylene ether sulfone)s bearing salt-terminated side-chains have been prepared for acid enrichment by electrodialysis (ED). In particular, the length of flexible aliphatic chain segments (methylenes of –(CH 2) 3 –), –(CH 2) 6 –, –(CH 2) 9 –, and –(CH 2) 12 –) in aromatic poly(arylene ether sulfone) was tuned to tailor the micro-structure. Our investigation demonstrates that the AEM with aliphatic chain segments of –(CH 2) 12 – shows the strongest surface hydrophobicity (water contact angle: 107°) and has the smallest ion clusters (0.75 nm, relative to the other three AEMs with 0.78 nm, 0.80 nm, and 0.81 nm). In ED process, at the current densities of 10 mA cm−2, the maximum concentration of H+ enriched by the AEM is 2.06 M (initial concentration: 1.0 M). The investigations demonstrate that the optimized AEM with stronger hydrophobicity and smaller ion clusters shows the superior capacity of acid concentration relative to commercial AEM (AMX, Astom Japan). This work should be certain guiding significance for designing advanced proton blocking AEMs. [Display omitted] • Four aliphatic chain segment imbedding PAES AEMs bearing side-chains were prepared. • The length of aliphatic segments in aromatic PAES was tuned to tailor the micro-structure. • Acid blocking performance of as-prepared AEM outperforms the commercial AEM. • The maximum concentration of H+ enriched by the optimized AEM is achived to 2.06 M. [ABSTRACT FROM AUTHOR]

• A strategy for the preparation of crosslinked AEMs with 3D network structure was reported. • The ultraviolet cross-linking method makes the reaction simpler and more controllable. • The as-prepared AEMs with 3D structure show the enhanced mechanical and thermal stabilities. • The optimized AEM shows NaCl removal rate of 75.0% and current efficiency of 92.7%. A series of trimethylamine quaternized crosslinked anion-exchange membranes (AEMs) based on polysulfone has been prepared by using an ultraviolet cross-linking method, which avoids the uneven reaction and undesirable aggregation of the basic functional groups (trimethylamine) by heterogeneous quaternization. The ultraviolet cross-linking method makes the reaction simpler and more controllable, compared with traditional method. By crosslinking, at 40 °C, the water uptakes of as-prepared AEMs decrease from 62.6% to 36.9%, while the linear expansion ratios reducing from 26.3% to 13.4% without significantly sacrificing the surface area resistance (increased 2.32 Ω cm2 to 2.98 Ω cm2). In addition, the introduced crosslinking yields the more robust AEMs with increased tensile strength from 4.32 to 11.89 MPa and increased elongation at break in a range of 13.8–30.9%. The significantly reduced water absorption, enhanced (dimensional and mechanical) stabilities suggest crosslinkers with more acrylate groups could promote high crosslinking within AEMs. For electrodialysis (ED) application, the optimized AEM exhibits an enhanced NaCl removal ratio of 75.0%, current efficiency of 92.7% and energy consumption of 6.06 kWh Kg−1, compared with AEM without cross-linking (61.4%; 75.9%; 6.20 kWh Kg−1). This investigation demonstrates that the as-proposed strategy has certain guiding significance for the development of advanced AEMs. [ABSTRACT FROM AUTHOR]