Surface complexes of acetate on edge surfaces of 2:1 type phyllosilicate: Insights from density functional theory calculation

Liu, Xiandong; Lu, Xiancai; Wang, Rucheng; Zhou, Huiqun; Xu, Shidang

doi:10.1016/j.gca.2008.09.026

Cited by 36 publications

(24 citation statements)

References 67 publications

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“…BLYP has been widely employed in simulation studies of silicates, e.g. in our previous study on phyllosilicates (Liu et al, 2008b), it is shown that the agreement of structures between BLYP and PBE is within 2.0%. For kaolinite, BLYP accurately reproduces the structures (see the Electronic annex).…”

Section: Car-parrinello MDmentioning

confidence: 92%

“…The similar saturation way has been employed in previous simulation studies of 2:1 type phyllosilicates (e.g. Churakov, 2006Churakov, , 2007Liu et al, 2008b).…”

Section: Systemsmentioning

confidence: 99%

“…Cygan, 2001;Bickmore et al, 2003;Cygan et al, 2004Cygan et al, , 2009Boulet et al, 2006;Greenwell et al, 2003Greenwell et al, , 2006Liu and Lu, 2006;Churakov, 2006Churakov, , 2007Kubicki et al, 2007;Rotenberg et al, 2007;Liu et al, 2007Liu et al, , 2008aLiu et al, , 2008bLiu et al, , 2011Liu et al, , 2012 and has proven a powerful complement to experiments. Among various simulation techniques, quantum mechanical method is particularly strong in studying reactive processes.…”

Section: Introductionmentioning

confidence: 99%

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Atomic scale structures of interfaces between kaolinite edges and water

Liu

Wang

et al. 2012

Geochimica et Cosmochimica Acta

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This paper reports the atomic scale structures of kaolinite edge surfaces in contact with water. The commonly occurring edge surfaces are investigated (i.e. (0 1 0) and (1 1 0)) by using first principles molecular dynamics (FPMD) technique. For (1 1 0)-type edge surface, there are two different surface topologies (denoted as (1 1 0)-1 and (1 1 0)-2) and they are considered separately.By using constrained FPMD technique, the free-energy changes for the leaving processes of water ligands of O-sheet Al cations have been calculated and thus, the coordination states of those Al cations are determined. The results show that for (0 1 0) and (1 1 0)-2 edges, both the 5 and 6-fold coordination states are possible whereas for (1 1 0)-1 edges, only the 6-fold states are stable. Based on the analyses of H-bonding structures at the interfaces, the surface acid/base reactive sites are illustrated. (1) T-sheet groups are "Si-OH, behaving as both proton donors and acceptors. (2) Bridging oxygen At (0 1 0) and (1 1 0)-2 edges, these sites are inaccessible from the water and thus, they are not effective reactive sites. At (1 1 0)-1 edges, the bridging oxygen atoms are proton accepting sites. (3) O-sheet groups At (0 1 0) and (1 1 0)-2 edges, for 6-fold Al cases, the active surface groups are "Al-(OH)(OH 2 ) and for the 5-fold Al cases, the active surface groups are "Al-(OH). At (1 1 0)-1 edges, the active site is "Al-OH 2 . This study provides fundamental structural properties for understanding the interface chemistry of widely occurring 1:1 type phyllosilicates.

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Section: Car-parrinello MDmentioning

confidence: 92%

“…The similar saturation way has been employed in previous simulation studies of 2:1 type phyllosilicates (e.g. Churakov, 2006Churakov, , 2007Liu et al, 2008b).…”

Section: Systemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Atomic scale structures of interfaces between kaolinite edges and water

Liu

Wang

et al. 2012

Geochimica et Cosmochimica Acta

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“…1). For the initial surface models, the dangling "SiAO and "AlAO bonds are all saturated by protons; similar edge surface models have been applied in previous simulation studies (Churakov, 2006(Churakov, , 2007Liu et al, 2008b). For the charged frameworks, the most common isomorphic substitutions were explored: one Al for one Si in T-sheets and one Mg for one Al in O-sheets, respectively.…”

Section: Systemsmentioning

confidence: 99%

Atomic-scale structures of interfaces between phyllosilicate edges and water

Liu

Meijer

et al. 2012

Geochimica et Cosmochimica Acta

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We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral and charged silicate frameworks are considered, and for charged cases, the octahedral (Mg for Al) and tetrahedral (Al for Si) substitutions are taken into account. For all frameworks, we focus on the commonly occurring (0 1 0)-and (1 1 0)-type edge surfaces.With constrained FPMD, we calculated the free energy of the leaving processes of coordinated water of octahedral cations; therefore, the coordination states of those edge cations are determined. For (0 1 0)-type edges, both the 5-and 6-fold coordination states of Al are stable and occur with a similar probability, whereas only the 5-fold coordination is stable for Mg cations. For (1 1 0)-type edges, only the 6-fold states of Al cations are stable. However, for Mg cations, both coordination states are stable. In the 5-fold case, the solvent water molecules form H-bonds with the bridging oxygen atoms (i.e., "MgAOASi"). The free energy results indicate that there should be a considerable number of 5-fold coordinated octahedral sites (i.e., "MgAOH/ "AlAOH) at the interfaces. The interfacial structures and acid/base groups were determined by detailed H-bonding analyses.(1) Bridging oxygen sites. For (0 1 0) edges, the bridging oxygen atoms are not effective proton-accepting sites because they are inaccessible from the solvent. For (1 1 0) edges, the oxygen atoms of neutral and octahedrally substituted frameworks (i.e., "MAOASi" for M@Al/Mg) are proton-accepting sites. For T-sheet substituted cases, the bridging oxygen site becomes a proton-donating group (i.e., "AlAOHASi") through the capture of a proton. (2) T-sheet groups. All T-sheet edge groups are "MAOH (M@Si/Al) and act as both proton donors and acceptors. (3)O-sheet groups. For (0 1 0) edges with 6-fold Al, the active surface groups include "AlA(OH)(H 2 O) and "AlA(OH) 2 , whereas for Mg cations, the edge group is "MgA(OH 2 ) 2 . For 5-fold coordination, the active groups are "AlAOH. At (1 1 0) edges, proton-donating sites include "AlAOH, "AlAOH 2 and "MgAOH 2 groups. Overall, our results reveal the significant effects of isomorphic substitutions on the interfacial structures, and the models provide a molecular-level basis for understanding relevant interfacial processes.

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“…[43][44][45] Carboxylic groups are the most important interaction sites for metal binding to these molecules, as they are for many other organic and bioorganic molecules. Experimental and theoretical studies of the hydration of metal ions [48][49][50][51][52][53] and carboxylic functional groups [54][55][56][57] show that carboxylic groups are sites of strong association of divalent ions with NOM 24,[58][59][60] and that increasing the cation charge density increases the tendency to form a contact ion pair. 44,47 Here we present a computational molecular dynamics (MD) study of the interaction of Na + , Ca 2+ , and Mg 2+ with the carboxylic groups of a TNB NOM fragment and with acetate anion that provides an improved quantitative understanding of the structure and energetics of these interactions.…”

Section: Introductionmentioning

confidence: 99%

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

Iskrenova-Tchoukova¹,

Kalinichev²,

2010

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Natural organic matter (NOM, or humic substance) has a known tendency to form colloidal aggregates in aqueous environments, with the composition and concentration of cationic species in solution, pH, temperature, and the composition of the NOM itself playing important roles. Strong interaction of carboxylic groups of NOM with dissolved metal cations is thought to be the leading chemical interaction in NOM supramolecular aggregation.Computational molecular dynamics (MD) study of the interactions of Na + , Mg 2+ , and Ca 2+ with the carboxylic groups of a model NOM fragment and acetate anions in aqueous solutions provides new quantitative insight into the structure, energetics, and dynamics of the interactions of carboxylic groups with metal cations, their association and the effects of cations on the colloidal aggregation of NOM molecules. Potentials of mean force and the equilibrium constants describing overall ion association and the distribution of metal cations between contact ion pairs and solvent separated ions pairs were computed from free MD simulations and restrained umbrella sampling calculations. The results provide insight into the local structural environments of metal-carboxylate association and the dynamics of exchange among these sites. All three cations prefer contact ion pair to solvent separated ion pair coordination, and Na + and Ca 2+ show a strong preference for bidentate contact ion pair formation. The average residence time of a Ca 2+ ion in a contact ion pair with the carboxylic groups is of the order of 0.5 ns, whereas the corresponding residence time of a Na + ion is only between 0.02 and 0.05 ns. The average residence times of a Ca 2+ ion in a bidentate coordinated contact ion pair vs. a monodentate coordinated contact ion pair are about 0.5 ns and about 0.08 ns, respectively. On the 10-ns time scale of our simulations, aggregation of the NOM molecules occurs in the presence of Ca 2+ but not Na + or Mg 2+ . These results agree with previous experimental observations and are explained 3 by both Ca 2+ ion-bridging between NOM molecules and decreased repulsion between the NOM molecules due to the reduced net charge of the NOM-metal complexes. Simulations on a larger scale are needed to further explore the relative importance of the different aggregation mechanisms and the stability of NOM aggregates.4

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Surface complexes of acetate on edge surfaces of 2:1 type phyllosilicate: Insights from density functional theory calculation

Cited by 36 publications

References 67 publications

Atomic scale structures of interfaces between kaolinite edges and water

Atomic scale structures of interfaces between kaolinite edges and water

Atomic-scale structures of interfaces between phyllosilicate edges and water

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

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