Anion exchange membranes with hydrophobic chain modified dications for electrodialytic desalination

Anion exchange membranes (AEMs) directly determine the performance of electrodialytic desalination. In this paper, a series of quaternized polysulfone (PSf) AEMs with dications containing fuorinated side chains were synthesized by grafting PSf backbone with 1,4-diazabicyclo [2.2.2] octane bicationic liquids bearing 1-bromo-5-fluoropentane hydrophobic side chains. The fabricated QPSf-DFx membranes (x being the grafting ratio) were compared with QPSfs membranes of different polar side chains and those without side chains in terms of microphase separation structure and electrodialysis desalination performance. It is found that the QPSf-DF75 % membrane has a hydrophobic-hydrophilic-hydrophobic structure, which can enhance the microphase separation to the greatest extent; when applied to electrodialysis of 0.1 M NaCl solution, the QPSf-DF75 % membrane gave current efficiency, energy consumption and chloride ion permeability of 92.51 %, 3.05 kWh kg⁻¹ and 94.34 % respectively, outperforming its counterparts. This work demonstrates that the hydrophobic-hydrophilic-hydrophobic structure of grafted fluorinated side chains can promote microphase separation and thereby enhance the performance of AEMs in electrodialysis applications.