Concerted Metal Cation Desorption and Proton Transfer on Deprotonated Silica Surfaces

Abstract

The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption-desorption is often proposed to occur in concert with proton transfer on hydroxyl-covered mineral surfaces, but to date this cooperative effect has been inferred indirectly. This work applies density functional theory-based molecular dynamics simulations of explicit liquid water/mineral interfaces to calculate metal ion desorption free energies. Monodentate adsorption of Na, Mg, and Cu on partially deprotonated silica surfaces are considered. Na is predicted to be unbound, while Cu exhibits binding free energies to surface SiO groups that are larger than those of Mg. The predicted trends agree with competitive adsorption measurements on fumed silica surfaces. As desorption proceeds, Cu dissociates one of the HO molecules in its first solvation shell, turning into Cu(OH)(HO), while Mg remains Mg(HO). The protonation state of the SiO group at the initial binding site does not vary monotonically with cation desorption.

Edge-Propagation Discharge Mechanism in CFx Batteries—A First-Principles and Experimental Study

“…This periodically replicated cell is charge neutral but exhibits a signficant dipole moment which can lead to electrostatic energy artifacts. 78 Using larger, 1 × 2 × 1 and 2 × 2 × 1 surface supercells, the energy costs are ΔE = 2.14 and 2.21 eV, respectively, suggesting that this energy has converged to within ∼0.1 eV. During recharge, this energy cost needs to be provided by changing the applied electronic voltage e .…”

Influence of Muscovite (001) Surface Nanotopography on Radionuclide Adsorption Studied by Kinetic Monte Carlo Simulations

“…Deprotonation of any edge sites creates a negative surface charge that attracts cations from the solution and leads to an increased inner-sphere adsorption at deprotonated oxygen atoms [32]. Another adsorption mechanism is a proton exchange during the inner-sphere adsorption reaction, e.g., leading to the formation of an inner-sphere tridentate complex and three hydronium (H 3 O + ) ions or water molecules if radionuclide hydroxide complexes are involved [30,31,33]. Due to the different coordination of surface oxygen atoms, it can be expected that the adsorption mechanism differs between basal and edge surfaces on muscovite.…”

First Principles, Explicit Interface Studies of Oxygen Vacancy and Chloride in Alumina Films for Corrosion Applications

“…The lateral images of the dipole moment repel one another. 103 O should occur at constant V e in the limit of infinite A (Eq. 6).…”

“…Potential-of-mean-force simu-lations for desorption of Cl − from the surface in liquid water conditions may be applied to to re-examine the desorption free energy in the future. 103…”