New Information on the Ion-Identity-Dependent Structure of Stern Layer Revealed by Sum Frequency Generation Vibrational Spectroscopy

We observed that the structure of water in the Stern layer depends on the identity of the cation, which cannot be predicted with classical double layer models. The ability of a cation to displace the hydration water on a silica surface is in the order of Mg2+ > Ca2+ > Li+ > Na+, which is co...

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Bibliographic Details
Published in:Journal of physical chemistry. C 2016-08, Vol.120 (32), p.18099-18104
Main Authors: Lovering, Kaitlin A, Bertram, Allan K, Chou, Keng C
Format: Article
Language:English
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Summary:We observed that the structure of water in the Stern layer depends on the identity of the cation, which cannot be predicted with classical double layer models. The ability of a cation to displace the hydration water on a silica surface is in the order of Mg2+ > Ca2+ > Li+ > Na+, which is consistent with the trend of the acid dissociation constant (K a) of the salt. Our data suggest that ions with a high pK a, such as Mg2+ and Ca2+, have a local electrostatic field strong enough to polarize water molecules in the hydration shells of the ions which form linkages with the negative charges on the silica, Si-O–···H+δ···OH–δ···M2+, and displace the hydration water on the silica surface. Ions with a low pK a, such as Na+ and Li+, are unable to displace the hydration water on the silica surface.
ISSN:1932-7447
1932-7455
DOI:10.1021/acs.jpcc.6b05564