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Please use this identifier to cite or link to this item: http://hdl.handle.net/1942/25709

Title: Anion Layering and Steric Hydration Repulsion on Positively Charged Surfaces in Aqueous Electrolytes
Authors: Hu, Qingyun
Weber, Christian
Cheng, Hsiu-Wei
Renner, Frank Uwe
Valtiner, Markus
Issue Date: 2017
Citation: CHEMPHYSCHEM, 18(21), p. 3056-3065
Abstract: The molecular structure at charged solid/liquid interfaces is vital for many chemical or electrochemical processes, such as adhesion, catalysis, or the stability of colloidal dispersions. How cations influence structural hydration forces and interactions across negatively charged surfaces has been studied in great detail. However, how anions influence structural hydration forces on positively charged surfaces is much less understood. Herein we report force versus distance profiles on freshly cleaved mica using atomic force microscopy with silicon tips. We characterize steric anion hydration forces for a set of common anions (Cl-, ClO4-, NO3-, SO42- and PO43-) in pure acids at pH approximate to 1, where protons are the co-ions. Solutions containing anions with low hydration energies exhibit repulsive structural hydration forces, indicating significant ion and/or water structuring within the first 1-2nm on a positively charged surface. We attribute this to specific adsorption effects within the Stern layer. In contrast, ions with high hydration energies show exponentially repulsive hydration forces, indicating a lower degree of structuring within the Stern layer. The presented data demonstrates that anion hydration forces in the inner double layer are comparable to cation hydration forces, and that they qualitatively correlate with hydration free energies. This work contributes to understanding interaction processes in which positive charge is screened by anions within an electrolyte.
Notes: [Hu, Qingyun; Cheng, Hsiu-Wei; Valtiner, Markus] Max Planck Inst Eisenforsch GmbH, Dept Interface Chem & Surface Engn, D-40237 Dusseldorf, Germany. [Renner, Frank Uwe] Hasselt Univ, Inst Mat Res IMO, Wetenschapspk 1, B-3590 Diepenbeek, Belgium. [Weber, Christian; Cheng, Hsiu-Wei; Valtiner, Markus] TU Bergakad Freiberg, Inst Phys Chem, D-09599 Freiberg, Germany.
URI: http://hdl.handle.net/1942/25709
DOI: 10.1002/cphc.201700865
ISI #: 000414406400014
ISSN: 1439-4235
Category: A1
Type: Journal Contribution
Appears in Collections: Research publications

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