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Separating Hofmeister Trends in Stern and Diffuse Layers at a Charged Interface.
Nathaniel Tetteh1, Shyam Parshotam1, Julianne M Gibbs1
1Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
The Journal of Physical Chemistry Letters
|August 29, 2024
Summary
Specific ion effects (SIEs) and pH significantly alter the electrical double layer (EDL) at mineral interfaces. Ions impact water structure differently in the Stern and diffuse layers, revealing complex ion-water interactions.
Area of Science:
- Surface Chemistry
- Colloid Science
- Environmental Science
Background:
- The electrical double layer (EDL) governs interfacial phenomena in environmental and industrial settings.
- Simultaneous impacts of pH and specific ion effects (SIEs) on EDL structure are not well understood.
Purpose of the Study:
- To elucidate the detailed structure of the Stern and diffuse regions of the EDL.
- To investigate the combined influence of pH and SIEs on the silica/water interface.
Main Methods:
- Zeta potential measurements
- Vibrational sum frequency generation spectroscopy
- Maximum entropy method
Main Results:
- Alkali metal cations (Li+, Na+, Cs+) differentially affect water structure in the Stern layer at varying pH.
- Opposing SIE trends observed in diffuse and Stern layers at pH 2 and pH 12.
- Hofmeister trends inverted at low and high pH, influencing diffuse layer structure.
Conclusions:
- SIEs play critical and distinct roles in both electrostatic and water-structuring properties of the EDL.
- Understanding these roles is vital for accurate modeling of interfacial processes.
- Ion-specific interactions significantly modulate EDL behavior across a wide pH range.
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