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Preferential Adsorption in Mixed Electrolytes Confined by Charged Amorphous Silica

Abstract : Preferential ion adsorption in mixed electrolytes plays a crucial role in many practical applications, such as ion sensing and separation and in colloid science. Using all-atom molecular dynamics simulations of aqueous NaCl, CaCl2, and NaCl–CaCl2 solutions confined by charged amorphous silica, we show that Na+ ions can adsorb preferentially over Ca2+ ions, depending on the surface structure. We propose that this occurs when the local surface structure sterically hinders the first hydration shell of the Ca2+ ion. Introducing a protrusion metric as a function of protrusion of deprotonated silanols, ion-specificity is successfully predicted on isolated, vicinal, and geminal silanols alike, provided that no other deprotonated silanols are found nearby. Furthermore, we introduce a new strategy to analyze the results as a function of distance from the surface. This approach effectively removes surface roughness effects allowing for direct comparison with classical electric double layer theory and distinction of specifically adsorbed ions and electrostatically adsorbed ions.
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Soumis le : lundi 25 novembre 2019 - 15:36:03
Dernière modification le : lundi 11 octobre 2021 - 13:24:59

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Max Döpke, Johannes Lützenkirchen, Othonas Moultos, Bertrand Siboulet, Jean-François Dufrêche, et al.. Preferential Adsorption in Mixed Electrolytes Confined by Charged Amorphous Silica. Journal of Physical Chemistry C, American Chemical Society, 2019, 123 (27), pp.16711-16720. ⟨10.1021/acs.jpcc.9b02975⟩. ⟨hal-02379210⟩



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