First-principles study of water desorption from montmorillonite surface

Area of Science:

• Materials Science
• Physical Chemistry
• Geochemistry

Background:

• Water diffusion in montmorillonites (MMT) is crucial for understanding MMT swelling.
• Describing water desorption provides a complete picture of water diffusion dynamics.

Purpose of the Study:

• To investigate water molecule desorption paths and energetics from MMT surfaces with Li+, Na+, or K+ counterions.
• To compare surface and vacuum desorption pathways and their energetic favorability.
• To determine the influence of counterions on water desorption energy barriers.

Main Methods:

• Utilized periodic density functional theory (DFT) calculations.
• Designed and analyzed two desorption paths: surface and vacuum.
• Calculated energy barriers and activation energies for water desorption.

Main Results:

• Surface desorption is energetically more favorable than vacuum desorption due to stabilizing water-surface hydrogen bonds.
• Water desorption energy barriers follow the order Li+ > Na+ > K+, correlating with ionic radius and binding strength.
• Water desorption mechanisms differ from adsorption mechanisms due to surface effects stabilizing water conformers.

Conclusions:

• Surface interactions significantly influence water desorption energetics and mechanisms in MMT.
• Counterion type critically affects the energy required for water desorption.
• DFT calculations provide valuable insights into water diffusion and MMT swelling processes.