Molecular simulation of humic substance–Ca-montmorillonite complexes

Sutton, Rebecca; Sposito, Garrison

doi:10.1016/j.gca.2006.04.032

Cited by 90 publications

(82 citation statements)

References 107 publications

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“…This "patchy" charge inversion contradicts the assumption that EDL ions are uniformly distributed in the xy plane beyond the d-plane, at least at the high ionic strengths studied here. We hypothesize that this patchiness of the EDL could promote the adsorption of molecules that carry different types of functional group, such as those in natural organic matter [118] or, more generally, zwitterions [119].…”

Section: Three Dimensional Structure Of the Electrical Double Layermentioning

confidence: 99%

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

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We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl-CaCl 2 electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO 2 or high-level radioactive waste (0.34 to 1.83 mol c dm -3 ). Our results confirm the existence of three distinct ion adsorption planes (0-, β-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the β-and dplanes are independent of ionic strength or ion type and (2) "indifferent electrolyte" ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl + ion pairs. Therefore, at concentrations ≥ 0.34 mol c dm -3 , properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid "ice-like" structures for water on clay mineral surfaces.

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Section: Three Dimensional Structure Of the Electrical Double Layermentioning

confidence: 99%

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

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248

223

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“…4,5 NOM can also easily adsorb onto mineral surfaces, forming an organic coating which significantly alters the electrostatic properties of the surface and strongly affects the transport and availability of toxic species. [6][7][8][9][10][11] The formation of NOM coatings is also a significant factor controlling the stability of viruses in aquatic systems 12 and the performance characteristics of inorganic and polymeric nanofiltration membranes. 13,14 Common cations such as Na + , Mg 2+ , and Ca 2+ are thought to play an important role in the supramolecular aggregation of NOM molecules into colloidal particles, 2,3,[15][16][17][18][19][20] the formation of NOM surface coatings, [10][11][12][13] and the aggregation of mineral particles.…”

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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“…It could be inferred that some aliphatic hydrocarbon molecules from DOM were intercalated into the interlayer of montmorillonite. Similarly, Sutton and Sposito found that the DOM-montmorillonite complex featured significantly direct hydrophobic and Hbonding interactions between organic and mineral components using molecule simulation [29]. In contrast to the montmorillonite system, kaolinite is a nonexpanding clay mineral.…”

Section: X-ray Diffraction and Ftir Spectra Of Samplesmentioning

confidence: 93%

Sorption of Pyrene by Clay Minerals Coated with Dissolved Organic Matter (DOM) from Landfill Leachate

Wen

Xiang

et al. 2015

Journal of Chemistry

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Interactions of dissolved organic matter (DOM) from landfill leachate with clays could affect significantly the fate of hydrophobic organic compounds (HOCs) in soils. The complexes of montmorillonite (MT) and kaolinite (KL) with DOM extracted from landfill leachate were prepared under controlled conditions, termed CMT and CKL, respectively. The bare clays and their complexes were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Batch experiments were designed to investigate the sorption behavior of pyrene onto the clays in the presence of DOM. The maximum sorption capacities of pyrene on MT, CMT, KL, and CKL were 22.18, 38.96, 42.00, and 44.99 g⋅g −1 , respectively, at the initial concentration of 1000 ± 150 g⋅L −1 . The sorption isotherms of pyrene by the bare clays followed the Henry model well, whereas the Freundlich sorption isotherm provided a better fit to the equilibrium data of the sorption by the complexes. The role of montmorillonite and kaolinite complexes with DOM in the retention of pyrene in soils was different. This may be due to the different crystal structures between montmorillonite and kaolinite.

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Molecular simulation of humic substance–Ca-montmorillonite complexes

Cited by 90 publications

References 107 publications

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

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

Sorption of Pyrene by Clay Minerals Coated with Dissolved Organic Matter (DOM) from Landfill Leachate

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