Toward a Reliable Energetics of Adsorption at Solvated Mineral Surfaces: A Computational Study of Uranyl(VI) on 2:1 Clay Minerals

We developed an efficient computational protocol for studying adsorption at solvated solid surfaces by a quantum mechanical method. We combine first-principles molecular dynamics at low temperature with simulated annealing and optimization steps to allow relaxation of the solvent structure without strongly perturbing the geometry of adsorption complexes. On the example of uranyl(VI) adsorption at the (110) edge surface of smectite minerals we show by density functional calculations using periodic slab models that our approach yields more reliable energies than direct optimization. In this way we were able to identify the preferred adsorption complex at this smectite surface. By decomposing the complex formation energies into deprotonation energies of the surface and adsorption energies as well as by a charge analysis of the adsorption sites, we rationalize this result as well as the composition and the structures of less stable adsorbed species. Our computational results are compatible with available experimental structural data of uranyl(VI), adsorbed at montmorillonite.