Probing atomic-scale processes at the ferrihydrite-water interface with reactive molecular dynamics

Area of Science:

• Environmental Science
• Geochemistry
• Computational Chemistry

Background:

• Mineral-water interfaces govern nutrient and contaminant behavior in natural systems.
• Understanding these interfaces is crucial for ecosystem health and Earth's co-evolution.
• Ferrihydrite is a key metal (oxyhydr)oxide phase in soils and sediments.

Purpose of the Study:

• To investigate molecular-scale interfacial processes in ferrihydrite-water systems.
• To study surface complexation dynamics using reactive molecular dynamics simulations.
• To validate simulation methods by comparing with experimental surface complexation models.

Main Methods:

• Reactive molecular dynamics simulations were employed.
• Synchrotron X-ray spectroscopy and high-resolution X-ray diffraction were used for validation.
• Umbrella sampling was utilized to calculate free energy landscapes.

Main Results:

• Ferrihydrite restructures into a more disordered phase upon hydration and adsorption.
• Surface charge equilibration and interfacial water dynamics were observed.
• Simulated adsorption free energies and deprotonation values agreed well with experimental data.

Conclusions:

• Reactive molecular dynamics accurately captures mineral-water interface dynamics.
• This approach refines surface complexation models beyond static assumptions.
• Findings enhance understanding of contaminant and nutrient mobility at interfaces.