Modeling adsorption of the uranyl dication on the hydroxylated α-Al ₂O ₃(0001) surface in an aqueous medium. Density functional study

As a first step toward modeling the interaction of dissolved actinide contaminants with mineral surfaces, we studied low-coverage adsorption of aqueous uranyl, UO ₂ ²⁺, on the hydroxylated α-Al ₂O ₃(0001) surface. We carried out density functional periodic slab model calculations and modeled solvation effects by explicit aqua ligands. We explored the formation of both inner- and outer-sphere complexes and estimated the corresponding adsorption energies. Effects of solvation were accounted for by explicit consideration of the first hydration shell of uranyl and by means of a posteriori corrections for long-range solvent effect. With energetics described at the GGA-PW91 level and under the assumption of a fully protonated ideal surface, we predict a weakly bound outer-sphere adsorption complex.