Although ion dehydration in confined water is ubiquitous in many important processes concerning ion adsorption, transport and separation, and so forth, few theoretical models have been developed to unravel the mechanism of dehydration in confined space. Herein, a molecular model is proposed by weighing the molecular orientation of surrounding water within the first hydration shell, and then this model is applied to predict the hydration numbers and hydrated radii of simple ions with the help of molecular density functional theory. The predictions are rationalized not only with parallel simulations but also with relevant experimental measurements. We find that the ion hydration in confined water is depressed owing to the confinement, and thus the multilayer hydration shell is disturbed, which results in the decline of hydration number and hydrated radius, favoring the ion dehydration. This work provides an insightful route toward the quantitative understanding and prediction of ion dehydration in confined water.

中文翻译：

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承压水中离子脱水的分子模型

尽管在许多有关离子吸附，传输和分离等重要过程中，密闭水中的离子脱水普遍存在，但很少有理论模型可以揭示密闭空间中的脱水机理。在此，通过权衡第一水合壳内周围水的分子取向来提出分子模型，然后借助分子密度泛函理论将该模型用于预测简单离子的水合数和水合半径。这些预测不仅可以通过并行仿真得到合理化，而且可以通过相关的实验测量得到合理化。我们发现由于封闭作用，封闭水中的离子水合作用受到抑制，因此多层水合壳受到干扰，这导致水合数和水合半径的降低，有利于离子脱水。这项工作为定量了解和预测承压水中的离子脱水提供了有见地的途径。