Ferrihydrite is a widespread iron oxide in natural systems. As a nanocrystalline material, ferrihydrite plays a critical role in a variety of important environmental processes, including the biogeochemical cycling of iron and other elements, adsorption of environmental contaminants, and the myriad reactions and chemical transformations involving its high density of reactive surface sites. Molecular-scale detail of water-ferrihydrite interactions is necessary for understanding and modeling the stability of ferrihydrite suspensions and aggregation processes, the protonation of reactive surface sites, the development of surface charge and the electric double layer, dissolution and mineral growth, ion adsorption, surface-mediated chemical reactions involving water such as proton-transfer, and the diffusive mass-transport of near-surface ions. <br/><br/>This talk presents results from molecular dynamics simulations of 2.5 nm ferrihydrite nanoparticles in contact with water ~10,000 single-point charge water molecules.Trajectories from 10-ns simulations were analyzed to quantify important dynamic properties of the ferrihydrite surface. Specifically, from mean-squared displacements and autocorrelation functions, we calculated diffusion coefficients, residence times, rotational relaxation times, and hydrogen-bond lifetimes of water in radial hydration shells surrounding the nanoparticles. In addition, we characterized the hydrogen-bonding network at the immediate surface to quantify surface-site reactivity within the framework of the MUSIC model, The results provide detail on the structure of the ferrihydrite-interface, estimates of proton affinity constants, and a modeling framework for future molecular studies of this important nanoparticle.

Water structure and dynamics at the aqueous interface of ferrihydrite nanoparticles

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.