Hydrophobic Side Chains Impart Anion Exchange Membranes with High Monovalent–Divalent Anion Selectivity in Electrodialysis

Abstract

Developing anion exchange membranes that have high anion selectivity and can avoid membrane swelling is a critical, but challenging, target for electrodialysis, which has witnessed great success in a wide range of applications including saline wastewater treatment and resource recovery. We found in this work that by tuning the hydrophobicity of alkyl spacers which connect the positively charged ammonium groups and polymeric backbones of the anion exchange membrane, high anion selectivity, and low membrane swelling of anion exchange membrane can be achieved. The membranes developed here are capable of discriminating monovalent and divalent anions, with a selectivity for Cl–/SO4 2– reaching up to 13.07, and our results suggest the chain length of the spacers determines the anion selectivity of membrane. We attribute such phenomenon to the change in side chain hydrophobicity. This is a particularly interesting finding that could facilitate the development of advanced anion exchange membranes for electrodialysis.

Thermal Stability and Decomposition Pathways in Volatile Molybdenum(VI) Bis-Imides

“…1,10-Phenanthroline (≥99%), was purchased from Sigma-Aldrich and was used as received. 1,4-Di-tert-butyl-1,3-diazabutadiene ( tBu DADH), [67] 1,4-di-isopropyl-2,3dimethyl-1,3-diazabutadiene ( iPr DAD Me ), [68] 1,4-bis(2,6-dimethylphenyl)-1,3-diazabutadiene ( xyl DAD H ), [69] 1,4-dicyclopentyl-1,3-diazabutadiene ( cPe DAD H ), [70] tert-butyl(pyridine-2-yl-methyleneamine) (impy), [71] 2-(N,Ndimethylamino-methylpyridine (dmampy), [72] 1-(tert-butylimino)-N,N,2trimethylpropan-2-amine (imtmpa), [45] 2,5-dimethylhexane-2,5-diamine, [73] ( t BuN)2MoCl2•dme (1a), [34,35] ( t PeN)2MoCl2•dme (1b), [48] (NCMe2(CH2)2CMe2N)MoCl2•dme (1c), [49] (AdN)2MoCl2•dme (1d), [50] MoO2Cl2•dme, [74] MoO2Cl2•( tBu DAD H ), [38] ( t BuN)MoOCl2•dme, [75] ( t BuN)2MoCl2•tmeda (2a), [33] ( t BuN)2MoCl2•bpy (3a), [33] and (xylN)2MoCl2•dme [34] were all prepared following known methods, which are also described in the SI. All solvents (ACS reagent-grade) were Scheme 8.…”

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement

“…This is the main reason for the increase in the flow of coions and a decrease in the selectivity of ion-exchange membranes with high water uptake. These regularities are typical for both cation-exchange and anion-exchange membranes [ 91 , 92 , 93 , 94 ].…”

Angstrom-scale ion channels towards single-ion selectivity

“…Remarkably, the optimized membranes discriminate monovalent and divalent anions with selectivity for Cl À /SO 4 2À of 13.07. 179 The findings demonstrate that increasing membrane hydrophobicity can contribute to the enhancement of monovalent anion selectivity (Fig. 10B).…”