When Ions Defy Electrostatics: The Case of Superchaotropic Nanoion Adsorption - Université de Montpellier
Article Dans Une Revue Journal of Physical Chemistry Letters Année : 2023

When Ions Defy Electrostatics: The Case of Superchaotropic Nanoion Adsorption

Max Hohenschutz
Olivier Diat

Résumé

Nanometer-sized anions, like polyoxometalates and borate clusters, bind to nonionic hydrated matter driven by the chaotropic effect, which arises from the favorable dehydration of the ions. Herein, we evaluate the adsorption and activity coefficient of the superchaotropic Keggin polyoxometalate SiW12O404– (SiW) on nonionic surfactant (C8E4) micelles by modeling small-angle X-ray and neutron-scattering spectra. Neither hard sphere nor electrostatic repulsion models reproduce the experimental activity coefficient of adsorbed SiW ions on the micelles. However, the activity and binding of SiW on the micelles is well-described by a Langmuir adsorption isotherm. These results imply that adsorbed SiW ions are non-interacting and “create” around themselves adsorption sites on the micelle. The temperature dependence of the adsorption constant showed that the SiW adsorption is enthalpically driven and entropically unfavorable, in line with the typical chaotropic thermochemical signature. The adsorption enthalpy can be split into an electrostatic term and a water-recovery term to evaluate and qualitatively predict the superchaotropicity of a nanoion.
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Dates et versions

hal-04156138 , version 1 (07-07-2023)

Identifiants

Citer

Max Hohenschutz, Jean-François Dufrêche, Olivier Diat, Pierre Bauduin. When Ions Defy Electrostatics: The Case of Superchaotropic Nanoion Adsorption. Journal of Physical Chemistry Letters, 2023, 14 (15), pp.3602-3608. ⟨10.1021/acs.jpclett.3c00095⟩. ⟨hal-04156138⟩
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