Adsorption of Uranyl Species onto the Rutile (110) Surface: A Periodic DFT Study

Abstract

To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO(2) rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta- or hexa-coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H(2)O, OH(-), and CO(3)(2-) ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface-[UO(2)(H(2)O)(3)](2+) system were well reproduced by our calculations. With respect to adsorbates, [UO(2)(L1)(x)(L2)(y)(L3)(z)](n) (L1=H(2)O, L2=OH(-), L3=CO(3)(2-), x≤3, y≤3, z≤2, x+y+2z≤4), on the ideal surface, the variation of ligands from H(2)O to OH(-) and CO(3)(2-) lengthens the U-O(surf) and U-Ti distances. As a result, the uranyl-surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO(2) decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U=O distances that are longer than those of aquouranyl species by 0.1-0.3 Å. Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U=O bond lengths, shorter uranyl-surface separations in most cases, and stronger sorption interactions.

A combined DFT and molecular dynamics study of U(VI)/calcite interaction in aqueous solution

“…Therefore, the binding energy definition in Eq. (2) was found to provide relatively reasonable results [13] for highly charged adsorption systems.…”

“…The probable ion exchange reactions with the first-layer surface Ca atoms have also been studied for the first time. The surface solvation energy of minerals was either neglected [13,15] or assumed to be unchanged [20,21] in previous DFT investigations. This approximation simplified the difficulty in modeling periodic boundary systems, but left an open question: to what degree does uranyl adsorption influence the surface solvation energy of minerals.…”

“…It is worth mentioning that novel functional materials such as metal organic materials exhibit excellent extraction ability towards actinides, which makes them promising candidates in a variety of application fields in the future [11,12]. Up to date, only a few of quantum chemistry investigations have been performed to probe the U(VI)/minerals interaction mechanisms [13][14][15][16][17][18][19] owing to the big challenges in treating large or charged adsorption systems as well as solvation effect. There are several popular strategies in solving these problems in previous periodic density functional theory (DFT) studies.…”

Pore-Scale Process Coupling and Effective Surface Reaction Rates in Heterogeneous Subsurface Materials

“…Mineral surfaces have included silica (Greathouse et al 2002;Patsahan and Holovko 2007;Boily and Rosso 2011), alumina (Moskaleva et al 2004;Glezakou and deJong 2011;Tan et al 2013), iron and titanium oxides (Steele et al 2002;Perron et al 2006aPerron et al ,b, 2008Drot et al 2007;Sherman et al 2008;Roques et al 2009;Skomurski et al 2011;Pan et al 2012;Sebbari et al 2012) , phyllosilicates (Zaidan et al 2003;Cygan 2005, 2006;Kremleva et al 2008Kremleva et al , 2011Kremleva et al , 2012Veilly et al 2008;Hattori et al 2009;Martorell et al 2010;Lectez et al 2012;Liu et al 2013b;Yang and Zaoui 2013a,b;Teich-McGoldrick et al 2014); feldspars Liu 2012, 2014), and carbonates (Doudou et al 2012). The majority of these studies focused on energy minimizations of adsorbed uranyl complexes at various mineral surfaces.…”

Preparation of magnetic calcium silicate hydrate for the efficient removal of uranium from aqueous systems

“…[1] Therefore, it is extremely important to choose a suitable and 25 effective method to remove uranium from aqueous systems. [1] Therefore, it is extremely important to choose a suitable and 25 effective method to remove uranium from aqueous systems.…”