Hexyl-modified series-connected bipyridine and DABCO di-cations functionalized anion exchange membranes for electrodialysis desalination
Hexyl-modified series-connected bipyridine and 1,4-diazabicyclo[2.2.2]octane (DABCO) di-cations functionalized anion exchange membranes (QPPO-DP and QPPO-DABCO respectively) for electrodialysis (ED) were prepared via reactions of brominated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and the self-designed quaternization agents containing mono-ionic bipyridine and DABCO moieties. These agents are precursors to the combinations of different di-cations and hydrophobic side chains. QPPO-DP (thickness: 95 μm) and QPPO-DABCO (thickness: 70 μm) with similar functionalization degrees were characterized in terms of ion exchange capacity (IEC), water uptake (WU), swelling ratio (SR), thermal and mechanical stabilities, morphology, area resistance ( R m ), transport number ( t - ) and limiting current density. QPPO-DP and QPPO-DABCO give IECs of 2.27 and 2.63 mmol g −1 respectively owing to the different unit masses of the di-cations. The conjugated aromatic bicyclic structure of bipyridine di-cations offers QPPO-DP higher WU than that of QPPO-DABCO. The relatively weaker hydrophilicity of DABCO di-cations ensures QPPO-DABCO moderate WU, superior R m and t - (2.77 Ω cm 2 and 0.949). Thus, QPPO-DABCO displays more excellent ED performances than those of commercial AMX under the same ED conditions, including current efficiency of 89.58%, salt flux of 81.39 mg m −2 s −1 and reasonable energy consumption of 1.76 kWh kg −1 NaCl, revealing its potential in ED application.
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