Argonne National Laboratory
Knowledge of ion adsorption behavior at mineral-water interfaces is fundamental to understand the mobility of elements in the environment, but relatively little is directly known about the structures and distributions of ions at mineral-water interfaces. Here I discuss our recent efforts to determine the distribution of Sr2+, Zn2+, and Y3+ ions near the rutile(110)-water interface. The surface charge evolution of rutile (TiO2) surfaces is typical of oxide surfaces and is determined by surface protonation reactions. I describe how X-ray standing waves (XSW) is a powerful method to determine ion distributions at mineral-water interfaces. Here I describe both traditional approaches to determining ion adsorption sites (e.g. XSW triangulation) and recent efforts whereby ion distributions are directly revealed through a model-independent approach. These results reveal substantial (and some unexpected) differences in the ion adsorption geometries for Sr2+, Zn2+ and Y3+ ions.
This work is done in collaboration with Z. Zhang, L. Cheng, C. Park, D. J.
Wesolowski, M. Machesky, M. J. Bedzyk, and N. C. Sturchio