Interfacial Processes
The production and use of energy is central to modern society, but ultimately
has deleterious impacts on Earth’s near-surface environment. It is becoming
increasingly clear that the use of engineered geological repositories for carbon
dioxide sequestration and high-level nuclear waste will be necessary to minimize
the impact of energy use on Earth’s near-surface environment. The successful
implementation of geological repositories requires that we have a robust
understanding of the geophysical and geochemical processes to predict repository
performance. The ultimate fate of repository contents, however, is often
controlled by the reactions occurring at mineral surfaces, which are generally
poorly understood.
The Interfacial Processes Group seeks to achieve a fundamental understanding
of mineral/water interface reactivity through direct in-situ observations of
molecular-scale structures and processes at well-defined mineral/water
interfaces. Recent studies have explored the molecular structure of mineral
surfaces, the ordering of fluids adjacent to these surfaces (e.g., interfacial
hydration layers), and the distribution of adsorbed ions at charged mineral
surfaces (e.g., electrical double-layer structure), as well as dynamical
processes such as dissolution and heterogeneous growth processes through
real-time observations. These observations lead to new insights into the specific
reaction mechanisms at mineral/fluid interfaces, define the kinetics and
reaction mechanisms at the atomic scale in key mineral/fluid systems, and
provide critical tests of our understanding of mineral/water reactivity though
comparison with predictions of high-level theoretical studies.
See highlights of our recent results and
a list of publications. This research is funded by the
Geoscience Research program of the Department of Energy’s Office of Basic Energy
Sciences.
The ability to make robust observations of these processes relies on the
application and development of advanced synchrotron-based interfacial x-ray
tools for in-situ studies of mineral/fluid interfaces. These approaches
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 facilitates spectroscopic sensitivities, leading to fundamentally
new types of in situ experiments. We primarily use high (<1 Å) resolution x-ray scattering
techniques, including surface x-ray scattering (e.g., x-ray reflectivity, XR),
resonant anomalous x-ray reflectivity (RAXR), x-ray standing waves (XSW), and
x-ray reflection interface microscopy (XRIM). The relatively high complexity of
mineral/water interfaces has led us also to develop and extend various
model-independent data analysis techniques, including the ability to image
directly: element-specific sub-profiles (e.g., from
phase-sensitive XSW and RAXR data) and interfacial density profiles from XR data
(e.g., using error correction algorithms). (See
Technical Approaches for more detailed descriptions.) The x-ray standing wave and x-ray
reflection interface microscopy measurements are performed on a spectrometer
that we built and is located at station 33-ID at the APS. In many cases, we
perform complementary studies using atomic force microscopy (AFM) and/or x-ray
absorption spectroscopy. This program has ongoing collaborations with scientists
at many organizations, including the University of Illinois at Chicago,
Northwestern University, the Illinois State Water Survey, and Oak Ridge National
Laboratory.
Contact
Paul A. Fenter, Group Leader
Interfacial Processes
Chemical Sciences and Engineering Division
Argonne National Laboratory, Bldg. 200
9700 South Cass Avenue
Argonne, IL 60439 USA
phone: 630/252-7053
e-mail: Fenter@anl.gov
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