Ji Yuanyuan, Luo Hongxi, Geise Geoffrey M
Department of Chemical Engineering, University of Virginia, 102 Engineers' Way, P. O. Box 400741, Charlottesville, VA 22904, USA.
Phys Chem Chem Phys. 2020 Apr 8;22(14):7283-7293. doi: 10.1039/d0cp00018c.
Understanding the effects of polymer chemistry on membrane ion transport properties is critical for enabling efforts to design advanced highly permselective ion exchange membranes for water purification and energy applications. Here, the effects of fixed charge group type on anion exchange membrane (AEM) apparent permselectivity and ion transport properties were investigated using two crosslinked AEMs. The two AEMs, containing a similar acrylonitrile, styrene and divinyl benzene-based polymer backbone, had either trimethyl ammonium or 1,4-dimethyl imidazolium fixed charge groups. Membrane deswelling, apparent permselectivity and ion transport properties of the two AEMs were characterized using aqueous solutions of lithium chloride, sodium chloride, ammonium chloride, sodium bromide and sodium nitrate. Apparent permselectivity measurements revealed a minor influence of the fixed charge group type on apparent permselectivity. Further analysis of membrane swelling and ion sorption, however, suggests that less hydrophilic fixed charge groups more effectively exclude co-ions compared to more hydrophilic fixed charge groups. Analysis of ion diffusion properties suggest that ion and fixed charge group enthalpy of hydration properties influence ion transport, likely through a counter-ion condensation, ion pairing or binding mechanism. Interactions between fixed charge groups and counter-ions may be stronger if the enthalpy of hydration properties of the ion and fixed charge group are similar, and suppressed counter-ion diffusion was observed in this situation. In general, the hydration properties of the fixed charge group may be important for understanding how fixed charge group chemistry influences ion transport properties in anion exchange membranes.
了解聚合物化学对膜离子传输特性的影响对于设计用于水净化和能源应用的先进高选择性离子交换膜至关重要。在此，使用两种交联阴离子交换膜（AEM）研究了固定电荷基团类型对阴离子交换膜表观选择性和离子传输特性的影响。这两种AEM含有相似的基于丙烯腈、苯乙烯和二乙烯基苯的聚合物主链，分别具有三甲基铵或1,4 - 二甲基咪唑鎓固定电荷基团。使用氯化锂、氯化钠、氯化铵、溴化钠和硝酸钠的水溶液对两种AEM的膜去溶胀、表观选择性和离子传输特性进行了表征。表观选择性测量结果表明固定电荷基团类型对表观选择性影响较小。然而，对膜溶胀和离子吸附的进一步分析表明，与亲水性更强的固定电荷基团相比，亲水性较弱的固定电荷基团能更有效地排斥共离子。对离子扩散特性的分析表明，离子和固定电荷基团的水合焓特性可能通过反离子凝聚、离子配对或结合机制影响离子传输。如果离子和固定电荷基团的水合焓特性相似，固定电荷基团与反离子之间的相互作用可能更强，并且在这种情况下观察到反离子扩散受到抑制。一般来说，固定电荷基团的水合特性对于理解固定电荷基团化学如何影响阴离子交换膜中的离子传输特性可能很重要。
