Interfacial Processes Group

In situ studies of mineral-fluid interfaces are performed using high resolution X-ray scattering and spectroscopic techniques to achieve a fundamental understanding of mineral-water interface structure and reactivity. The atomic-scale structure of both the substrate and near-surface fluid provides new insight into the equilibrium structure of this interface as a function of solution composition. Compositional changes are also observed directly in real-time during reactions to reveal dynamic processes. Direct observation of these structural changes leads to new insights into specific reaction mechanisms at mineral-fluid interfaces.

Recent work includes direct in situ measurements of the of hydration layer structure at mineral-water interfaces, ion adsorption, silicate dissolution, and more. See examples of our recent results, and a complete list of publications. For more information contact Paul Fenter.

Ongoing collaborations, including Neil Sturchio (Univ. of Illinois at Chicago/ANL), Michael Bedzyk (Northwestern University/ANL), Kathryn Nagy (Univ. of Illinois at Chicago), Michael Machesky (Illinois State Water Survey), David Wesolowski (Oak Ridge National Laboratory), Steve Sutton (GSE-CARS, Univ. of Chicago) and others.

Synchrotron Radiation Studies at the Advanced Photon Source

We have been making measurements at the Advanced Photon Source (APS) since 1997, using beamlines at the BESSRC and other sectors. We primarily use X-ray scattering techniques, including surface X-ray scattering (including X-ray reflectivity and grazing incidence X-ray scattering), resonant anomalous X-ray reflectivity, and X-ray standing waves, and X-ray standing wave imaging. X-ray standing wave measurements are performed on a spectrometer that we built and operate at end-station 12-ID-D. In many cases, we perform complimentary studies using atomic force microscopy (AFM) and/or X-ray absorption spectroscopy.

The development and application of synchrotron X-ray scattering techniques for in situ studies of mineral-fluid interfaces is an important part of our research program. These developments take advantage of the unique characteristics of synchrotron radiation at the Advanced Photon Source (APS), including temporal and spatial resolution afforded by the high APS beam brilliance as well as the tunability of the X-ray photon energy that allows for spectroscopic sensitivities. Fundamentally new types of in situ experiments are possible for mineral-fluid interfaces, especially microbeam and time-resolved scattering studies. These experiments will further define kinetics and reaction mechanisms at the atomic scale in key mineral-fluid systems, and will constrain the continued development of theory pertinent to mineral-fluid interface processes.

This research is funded by the Geosciences Research Program of the DOE's Office of Basic Energy Sciences.

	Recent Highlights: Resonant Anomolous X-ray Reflectivity				Recent Hightlights: Mineral-Water Interface Structures
	Probing Adsorbates with Resonant Anomalous X-ray Reflectivity Resonant anomalous X-ray reflectivity (RAXR) can directly and simultaneously probe the geometric and spectroscopic structures of weakly bound adsorbates at the mineral-water interface. Measurements of platinum tetraamine adsorbed at the quartz(100)-water interface revealed that the PTA complex adsorbs above the surface hydration layer (i.e., as an outer-sphere species). (More...)				Mineral-Water Interface Structures Revealed by X-ray Scattering The reactivity and properties of the mineral-water interface ultimately derive from the properties of water in the immediate vicinity of the mineral surface (i.e., “interfacial water”). Numerous recent X-ray scattering studies have revealed the structure of water at interfaces. (More...)