Chemistry Weekly Seminar-Ardalan Hayatifar, Postdoctoral Research, Geological Sciences.

Title

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

Abstract

Interfacial processes involving metal (oxyhydr)oxide phases play a crucial role in the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. These processes significantly impact ecosystem health and functioning, and have influenced the biological and environmental co-evolution of Earth over geologic time. In this talk, we present a study that employs reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy, to explore the molecular-scale interfacial processes affecting surface complexation in ferrihydrite-water systems containing aqueous MoO₄²⁻. The effectiveness of this approach is demonstrated by directly calculating surface complexation models from simulations. The reactive force field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. Upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. This restructuring leads to a unique interfacial hydrogen bond network compared to bulk water, which is monitored through water dynamics. By employing umbrella sampling, we construct the free energy landscape of aqueous MoO₄²⁻ adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with values reported by experimental surface complexation models.These findings show how reactive molecular dynamics can provide new insights into mineral-water interfaces, enriching and refining surface complexation models beyond their traditional assumptions.