Exploring the Molecular Driving Forces for Lanthanide and Actinide Complexation and Partitioning to Mineral Interfaces
EMSL Project ID
47944
Abstract
In this project, we will use a combination of optical spectroscopy techniques (time-resolved fluorescence and sum-frequency generation) and computational methods (molecular dynamics, density functional theory and mixed methods-- QM/MM) to study the hydration of f-elements in mixed solvent systems. Our overall objective is to integrate experimental and computational methods to directly probe the hydration and covalency of the f-element cations in aqueous and mixed solvent electrolyte systems, and to develop modeling and simulation tools that reflect changes in hydration and covalency as a function of changes in solvent properties. TRLFS and fluorescence lifetime measurements will be used to directly probe the solvation change and complexation in solution. Sum-frequency generation-vibrational spectroscopy (SFG) will be used to characterize solvent bonding and arrangement at surface and interfaces. State-of-the art simulations that cross length and timescales will incorporate the most realistic possible chemical components for enhanced predictability of experimental complexation data. Where possible, we will correlate our resulting molecular descriptions with observed geochemical observations in radiologically contaminated subsurface systems. The impact of the proposed studies will be to provide a molecular foundation for understanding complex environmental systems and the fate of radionuclides within such systems. This basic knowledge is essential for designing effective remediation strategies for contaminated DOE legacy sites. Our proposed studies will also provide a foundation for advancing our understanding of actinide biogeochemistry. Our studies are designed to quantify the impact of increased covalency for the 5f period of elements compared to the 4f period on complexation in mixed solvent systems. In addition, our work build upon the recent computational contributions of A. E. Clark, who has been working to integrate new mixed quantum mechanical/molecular mechanics simulations of ions in mixed electrolyte systems and at interfaces.
The facilities and infrastructure at EMSL are essential for success in this project because of the integration of experimental and computational tools necessary to address the problem. Conducting the work under the EMSL umbrella provides a collaborative environment that will be essential for this project, as described. In our prior work, we have shown that integration of the experiment and computational studies occurs seamlessly via a feedback loop wherein the computational studies help define the spectroscopic approaches, and similarly, the experimental results aid in refining the computational models employed. This avoids the common problem where experimental studies alone don't provide unequivocal results, and computational studies may not be benchmarked to experimental and/or molecular reality. In addition, the proposed studies using laser fluorescence spectroscopy and SFG will build on completed experimental work from Washington State University involving other experimental tools, such as nuclear magnetic resonance, absorption spectroscopy, and calorimetry. This integration of information from multiple spectroscopic and computational tools will enable us to more fully define the role of f-element solvation in lanthanide and actinide biogeochemistry.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2013-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members