Polarization of the ion-selective systems results in the formation of ion-depleted and ion-concentrated zones in the electrolyte layers adjacent to the system. One can employ ion-concentration polarization for the removal of charged large molecules and small ions from the flowing liquid. Removal of large molecules from the flowing solution and their local accumulation is often referred to as preconcentration, removal of small ions as desalination. Here, we study the effect of the channel geometry on the removal of charged species from their water solutions experimentally. Straight, converging, and diverging channels equipped with a pair of heterogeneous cation-exchange membranes are compared in terms of their effect on preconcentration of an observable fluorescein dye and on desalination of water solution of potassium chloride. Our results show that preconcentration of the dye is not significantly affected by the channel geometry. The distance of the preconcentration band from one of the membranes was approximately the same in all tested channel geometries. The major difference was in the location of the band within the channel, when the conical channels localized the band at one of the channel walls. The straight channel showed a slightly broader range of applicable flow rates. The semibatch desalination of 0.01M KCl solution turned out to be more efficient in conical channels, which was associated with a larger volume of the channel available for the accumulation of the concentrated solution. Our results suggest that conical channels can be advantageously used in transforming the ion-concentration-polarization-based semibatch desalination into a fully continuous one.

中文翻译：

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通道几何形状对基于离子浓度极化的预浓缩和脱盐的影响。

离子选择系统的极化导致在与系统相邻的电解质层中形成离子耗尽和离子集中的区域。可以采用离子浓差极化从流动的液体中去除带电的大分子和小离子。从流动溶液中去除大分子及其局部积累通常被称为预浓缩，将小离子去除称为脱盐。在这里，我们通过实验研究了通道几何形状对带电物种从其水溶液中去除的影响。比较了配备有一对异质阳离子交换膜的直通道，会聚通道和发散通道，它们对可观察到的荧光素染料的预浓缩和对氯化钾水溶液的脱盐效果均佳。我们的结果表明，染料的预浓缩不受通道几何形状的显着影响。在所有测试的通道几何结构中，预浓缩带与其中一个膜的距离大致相同。主要区别在于，当锥形通道将通道定位在通道壁之一处时，通道内通道的位置不同。直通道显示的适用流速范围稍宽一些。结果证明，在锥形通道中对0.01M KCl溶液进行半批量脱盐更有效，这与可用于浓缩溶液积累的较大通道通道有关。我们的结果表明，锥形通道可有利地用于将基于离子浓度极化的半间歇式脱盐转变为完全连续的脱盐。