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Published on: May 15, 2017
Hydration-Induced Transition from Site-Controlled to Diffusion-Controlled Ion Transport in Montmorillonite
Irwan Nugraha1,2, Mohammadreza Izadifar3, Katja Emmerich1
1IMB/MPA/CMM Karlsruhe Institute of Technology (KIT), Gotthard-Franz-Str. 3, Karlsruhe 76131, Germany.
ACS Omega
|July 24, 2026
Summary
Hydration fundamentally alters ion transport in clay minerals by changing the energy landscape from localized to diffusion-controlled. This molecular "switch" is crucial for understanding ion mobility in nanoporous materials.
Area of Science:
- Geochemistry
- Materials Science
- Computational Chemistry
Background:
- Ion transport in clay minerals is vital but poorly understood at a molecular level.
- The role of hydration in ion mobility (reducing barriers vs. altering transport nature) is unclear.
Purpose of the Study:
- Investigate Na+ and K+ mobility in montmorillonite as a function of water content.
- Elucidate the molecular mechanisms of hydration on ion transport.
Main Methods:
- Density Functional Theory (DFT) calculations.
- Two-dimensional Potential Energy Surface (PES) mapping.
Main Results:
- Water-free conditions show localized ions with high migration barriers (site-controlled regime).
- Hydration non-linearly decreases barriers and flattens the energy landscape, transitioning to diffusion control.
- Framework topology acts as a sieve, influencing ion localization alongside charge distribution.
- Na+ mobility depends on local vacancies, while K+ transport is spatially averaged due to steric effects.
Conclusions:
- Hydration fundamentally alters the energy landscape topology, not just reducing migration barriers.
- Water acts as a molecular switch, controlling ion behavior between localized and delocalized states in nanoporous materials.
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