This work reports a novel, effective, soft template strategy that can fabricate good-performance anion exchange membranes (AEMs) for electrodialysis application. Specifically, 1,2-ethanedisulfonic acid (EDA) is used as a small-molecule, soft template to promote microphase separation in multi-cation functionalized poly (2,6-dimethyl-1,4-phenylene oxide) membranes through electrostatic interaction between quaternary ammonium groups and sulfonic acid groups. The enhanced microphase separation has been confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering studies. The prepared TPPO-2S-x membranes (where x represents the mass percent of EDA) were tested in the electrodialysis device for desalinating 0.1 M NaCl solution. Among them, the TPPO-2S-1 membrane gave the highest ED current efficiency (92.90 %), the lowest energy consumption (4.08 kWh kg −1 ), and the largest Cl − transport number (0.98); these performance results are better compared with those of the TPPO-2S-0 membrane (89.29 %, 4.39 kWh kg −1 , and 0.98), which is not processed by soft template strategy. Although the TPPO-2S-4 and TPPO-2S-7 membrane show more obvious microphase separation than TPPO-2S-1, the current efficiencies of their ED devices are lower and the energy consumptions are higher due to their undesirable surface area resistance and chloride ion transport number. The investigation demonstrates that the soft template strategy is effective to improve membrane performance in ED devices.
The present study describes the synthesis of new nanofiltration membranes inspired by asymmetric porous membranes used as monovalent anion selective membranes for electro-membrane separation. The membrane surface was firstly modified, by deposition of a mussel-inspired “bio-glue” polydopamine (PDA) layer, and subsequently a compact polyamide layer was polymerized on the surface of the membrane's active layer. The chemical constitution and structure of these modified porous membranes were explored by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The surface roughness and hydrophilicity of the membranes were explored by atomic force microscopy (AFM) and water contact angle measurements, respectively. In addition, the electrochemical properties of the surface of the modified membranes were analyzed in terms of membrane surface resistance and zeta potential values. As for the performance of these modified porous membranes, this was investigated by measuring the permselectivity of a Cl−/SO42− system. The obtained results show that the new membranes exhibit an enhanced monovalent anion permselectivity, which is in agreement with the improved membrane surface properties. Furthermore, membranes modified by the addition of a PDA layer and a dense polyamide active layer lead to a significant improvement in selectivity , compared with a conventional interfacial polymerization modified membrane . The excellent performance can be ascribed to the synergistic effect of the compact PDA layer and negatively charged interfacial polymerization layer, dependent on the sieving and electrostatic repulsion, respectively. Thus, this process is promising for the further development of porous monovalent selective anion exchange membranes.
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