X-RAY SCATTERING AND SPECTROSCOPIC STUDIES OF THE MINERAL-WATER INTERFACE

The chemistry of the mineral-water interface is of central importance to understanding the geochemistry of natural waters. Over the past several decades researchers have strived to develop and apply tools that allow the development of a molecular scale picture of the factors that control interface reactivity. Synchrotron based x-ray scattering and spectroscopy in particular have resulted in numerous advances in our understanding of the mineral-water interface structure, and the increasing number of researchers utilizing these methods will result in new insights for many years to come. In particular, the application of synchrotron based surface x-ray scattering provides has provided a unique approach for developing detailed models of interface structure, and understanding structural modifications that result from changes in (bio)geochemical conditions. Such models are critical to furthering the development of a structure based understanding of environmental interface systems and improving both conceptual and quantitative models of environmental chemical pathways.

We will present an overview of recent work focused on determining the structure of low index faces of common iron-(hydr)oxide phases. Iron-oxides are of particular interest due to their widespread occurrence, typically high specific surface area, and high surface reactivity, making them important scavengers of aqueous trace metals, and substrates that support the heterogeneous transformation of aqueous contaminants. Specifically, we will focus on the changes in surface structure associated with variations in primary variables such as temperature, and redox potential, and utilize the results of density functional theory calculations to provide a thermodynamic framework for interpretation of the experimental results.