Nanofiber Based Organic Solvent Anion Exchange Membranes for Selective Separation of Monovalent anions

Abstract

Present anion exchange membranes are generally constructed by simple and positively charged polymers with insufficient organic solvent resistance, and exhibit a low selectivity in the separation of anions. Here, dissolving poly­(paraphenylene terephthalamide) nanofibers into small nanofibers and performing a reaction with quaternary ammonium groups in the one-dimensional small nanofibers, high-performance anion exchange membranes were successfully fabricated. By increasing the 2,3-epoxypropyl trimethylammonium chloride content, the synthesized amide nanofiber quaternary ammonium membranes (ANF#QA) exhibited a higher anion exchange capacity (as high as 1.75 mmol·g–1) and achieved a high electrochemical performance. In electrodialysis, the ANF#QA-10 membrane showed an exceptional Cl– selectivity in dilute and concentrated cells. Due to the dense structure and presence of carboxyl groups on the nanofibers, the ANF#QA membranes exhibited a selective separation of monovalent anions. After 48 h of immersion in aqueous acetone solutions, the final ANF#QA-10 membrane exhibited high desalination and concentration efficiency as the initial membrane. This work highlights the promising use of positive charges on small nanofibers, and proposes the design of a special anion exchange membrane, which can be used for electrodialysis in organic solvent solutions, and to selectively separate monovalent anions.

De Novo Ion-Exchange Membranes Based on Nanofibers

“…For applications such as dialysis membranes and BPMs, a hot-pressing process is necessary to obtain dense membranes [ 31 ]. In addition, the KANF-based IEMs are usually prepared by casting Kevlar NF solutions, which are obtained by dissolution of Kevlar aramid fiber [ 32 , 33 , 34 ]. The dense NF composite membranes are usually prepared by casting polymer solutions on NF networks, followed by a drying process [ 35 ].…”

“…The prepared aramid NF quaternary ammonium membranes (ANF#QA) reached a high IEC of 1.75 mmol·g −1 . Furthermore, the membranes exhibited a high desalination and concentration efficiency with selective separation of Cl - /SO 4 2- during ED [ 32 ]. Shen et al fabricated a series of organic solvent-resistant CEMs by splitting Kevlar fabrics into small and short NFs, followed by modification with 4-amino-benzenesulfonic acid monosodium salt and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) via amide condensation.…”

Angstrom-scale ion channels towards single-ion selectivity

“…) was realized by anion exchange membranes [175][176][177] with excellent monovalent anion perm-selectivity. Hydrated Cl À and SO 4 2À ions have very close ion diameters, making them difficult to be separated based on size-sieving.…”

A review on ion-exchange nanofiber membranes: properties, structure and application in electrochemical (waste)water treatment

“…While most applications of ED occur in aqueous media, more attention is being given to organic media as well [264]. Zhao et al expanded the development of ED membranes to the treatment of waste organic streams [239,240,244,246]. Their ED membranes are based on poly (paraphenylene terephthalamide) nanofibers, which are characterized by their organic solvent resistance, high strength and outstanding thermal stability.…”