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Chemical Sciences and Engineering Division |
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Interfacial ProcessesThe 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 |
