Sequestration of Radionuclides in Metal-Organic Frameworks from Density Functional Theory Calculations

The high porosity, modularity, and synthetic diversity of metal-organic frameworks (MOFs) make them attractive candidate materials for selective sensing, separation, and sequestration of the radionuclides present in the nuclear wastes. We use density functional theory (DFT) calculations to determine the favorability of ion exchange at the metal node of Tc, U, Th, Am, and Cm in Zr-, U-, and Th-based MOF clusters. A range of DFT methods, including several exchange-correlation functionals, the DFT+U technique, relativistic effects, and magnetic effects, are employed to establish robustness in the results. We also explore various reference states of ions including the vacuum, continuum water medium, and explicit water molecules surrounding ions. Substitution of Tc, Am, Cm, and Th is found to be energetically favorable in all the MOFs using ions surrounded by explicit water molecules as a reference.