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ION ADSORPTION AT THE RUTILE-WATER INTERFACE: LINKING MOLECULAR AND MACROSCOPIC PROPERTIES

ION ADSORPTION AT THE RUTILE-WATER INTERFACE: LINKING MOLECULAR AND MACROSCOPIC PROPERTIES,10.1021/la0353834,Langmuir,Z. ZHANG,P. FENTER,L. CHENG,N. C

ION ADSORPTION AT THE RUTILE-WATER INTERFACE: LINKING MOLECULAR AND MACROSCOPIC PROPERTIES   (Citations: 36)
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Z. ZHANG, P. FENTER, L. CHENG, N. C. Sturchio, M. J. Bedzyk, M. PREDOTA, A. BANDURA, J. KUBICKI, S. N. Lvov, P. T. Cummings, A. A. Chialvo, M. K. Ridleyhttp://academic.research.microsoft.com/io.ashx?type=5&id=10955753&selfId1=0&selfId2=0&maxNumber=12&query=
A comprehensive picture of the interface between aqueous solutions and the (110) surface of rutile (R-TiO2) is being developed by combining molecular-scale and macroscopic approaches, including experimental measurements, quantum calculations, molecular simulations, and Gouy-Chapman-Stern models. In situ X-ray reflectivity and X-ray standing-wave measurements are used to define the atomic arrangement of adsorbed ions, the coordination of interfacial water molecules, and substrate surface termination and structure. Ab initio calculations and molecular dynamics simulations, validated through direct comparison with the X-ray results, are used to predict ion distributions not measured experimentally. Potentiometric titration and ion adsorption results for rutile powders having predominant (110) surface expression provide macroscopic constraints of electrical double layer (EDL) properties (e.g., proton release) which are evaluated by comparison with a three-layer EDL model including surface oxygen proton affinities calculated using ab initio bond lengths and partial charges. These results allow a direct correlation of the three-dimensional, crystallographically controlled arrangements of various species (H2O, Na+ ,R b + ,C a2+, Sr2+ ,Z n 2+ ,Y 3+ ,N d 3+) with macroscopic observables (H+ release, metal uptake, zeta potential) and thermodynamic/electrostatic constraints. All cations are found to be adsorbed as "inner sphere" species bonded directly to surface oxygen atoms, while the specific binding geometries and reaction stoichiometries are dependent on ionic radius. Ternary surface complexes of sorbed cations with electrolyte anions are not observed. Finally, surface oxygen proton affinities computed using the MUSIC model are improved by incorporation of ab initio bond lengths and hydrogen bonding information derived from MD simulations. This multitechnique and multiscale approach demonstrates the compatibility of bond-valence models of surface oxygen proton affinities and Stern-based models of the EDL structure, with the actual molecular interfacial distributions observed experimentally, revealing new insight into EDL properties including specific binding sites and hydration states of sorbed ions, interfacial solvent properties (structure, diffusivity, dielectric constant), surface protonation and hydrolysis, and the effect of solution ionic strength.
Journal: Langmuir , vol. 20, no. 12, pp. 4954-4969, 2004
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    • ...backscattering spectroscopy [9], quasi-elastic neutron scattering [10], attenuated total reflectance infrared spectroscopy [11], X-ray reflectivity measurements [12] and ultrafast infrared spectroscopy [13]...

    Tuan A. Hoet al. Interfacial water on crystalline silica: a comparative molecular dynam...

    • ...There is also agreement between the simulations and X-ray experiments [37] (table <0005" ref-type="table">5)...

    A. A. Skeltonet al. Interaction of liquid water with the rutile TiO2 (110) surface

    • ...The electrostatic adsorption is mainly related to the deposition of alkaline ions on the surface of catalytic supports 180 181 though it has been reported recently that Rb+ hydrated ions form inner sphere complex on the rutile surface 185...

    Kyriakos Bourikaset al. The Role of the Liquid‐Solid Interface in the Preparation of Supported...

    • ...8: nominally above the BO site (Fig. 1c, site A1), and between two TO sites (Fig. 1c, site A2), with the majority of Zn2+ in the A1 site (Zhang et al., 2004b)...
    • ...hydroxylated TiO2 (110) surface also yielded two adsorption sites around A1 and A2, respectively (Predota et al., 2004b; Zhang et al., 2004b), there were substantial disagreements between the density functional theory (DFT) calculations, the MD simulations and X-ray measurement at site A2, including a discrepancy of � 0.7 A ˚ in the predicted heights above the basal plane...
    • ...We speculated (Zhang et al., 2004b) that the disagreement might be due to: (1) uncertainties of the XSW measurements or, (2) an implicit assumption in the DFT and MD studies that the surface adsorbed Zn2+ species remained sixfold coordinated, as found for aqueous Zn2+ (Marcus, 1997; Zhang et al., 2004b) and suggested from EXAFS studies of Co2+ adsorption on rutile powder and single-crystal surfaces (O’Day et al., 1996; Towle et al., 1999)...
    • ...We speculated (Zhang et al., 2004b) that the disagreement might be due to: (1) uncertainties of the XSW measurements or, (2) an implicit assumption in the DFT and MD studies that the surface adsorbed Zn2+ species remained sixfold coordinated, as found for aqueous Zn2+ (Marcus, 1997; Zhang et al., 2004b) and suggested from EXAFS studies of Co2+ adsorption on rutile powder and single-crystal surfaces (O’Day et al., 1996; Towle et al., 1999)...
    • ...solution interface at pHs lower than the aqueous hydrolysis constants of Zn2+ (Zhang et al., 2004b)...
    • ...1a and b), as supported by X-ray scattering measurements (Zhang et al., 2004b), DFT calculations (Lindan et al., 1998; Bandura and Kubicki, 2003; Bandura et al., 2004; Zhang et al., 2004b), and MD simulations (Predota et al., 2004a)...
    • ...1a and b), as supported by X-ray scattering measurements (Zhang et al., 2004b), DFT calculations (Lindan et al., 1998; Bandura and Kubicki, 2003; Bandura et al., 2004; Zhang et al., 2004b), and MD simulations (Predota et al., 2004a)...
    • ...Comparison of ion adsorption behavior revealed that the surface is best described as having both the BO and TO sites protonated at neutral or acidic pH, corresponding to the dissociatively adsorbed water molecules at the TiO2 (110) surface (Zhang et al., 2004b)...
    • ... surface lattice parameters are a ¼ c ¼ ffiffiffi 2 p a0 = 6.497 A ˚ ,a ndb = c0 = 2.959 A ˚ . The coordinate system is defined with the origin (x = y = z = 0) located on the basal plane directly underneath the BO site of an unrelaxed bulk lattice, as shown in Fig. 1. Previous X-ray crystal truncation rod (CTR) measurements and DFT calculations indicate minimal displacements of the basal plane ions from their bulk structural positions ...
    • ...To satisfy the neutrality condition, terminal hydroxyl groups were attached to the fivefold Ti atoms on each surface (Zhang et al., 2004b)...
    • ...The A1 site (directly above the BO) is the dominant site for adsorption of Zn2+ as seen by the XSW data (Zhang et al., 2004b)...
    • ...modeled (Zhang et al., 2004b) with octahedrally coordinated Zn2+ at A1 site (Fig. 4a) because Zn 2+ is commonly...
    • ...The energy of the final structure was � 59 kJ/mol lower than that of structure A. Therefore, this tetrahedral configuration is predicted to be more stable based on potential energies than the octahedrally coordinated Zn2+ species calculated previously (Zhang et al., 2004b)...
    • ...investigated by this group (Predota et al., 2004b; Zhang et al., 2004b)...
    • ...enhanced hydrolysis was also found beneficial in fitting pH-titration and sampling studies of rutile powder suspensions using a Guoy–Chapman–Stern site complexation model (Zhang et al., 2004b)...
    • ...The dielectric constant may be lower near the oxide-aqueous solution interface than that in the bulk solution (Brown et al., 1999; Zhang et al., 2004b), although the magnitude of the interfacial dielectric constant and its spatial extent into solution are not well understood...
    • ...about 50 (Machesky et al., 2001; Zhang et al., 2004b)...
    • ...With the atomic level knowledge from the XSW measurements, a Gouy– Chapman–Stern surface complexation model predicted that the surface induced hydrolysis would happen at the rutile (110)-aqueous solution interface upon Zn2+ adsorp- tion, (Zhang et al., 2004b)...

    Zhan Zhanget al. Structure of hydrated Zn 2+ at the rutile TiO 2 (110)-aqueous solution...

    • ...However, when electrokinetic measurements are made on the same samples, the IEP defined by the lowest ionic strength is different to the pHPZSE (Huang and Stumm, 1973; Yates, 1975; Fokkink, 1987; Zeltner and Anderson, 1988; Gibb and Koopal, 1990; Kallay et al., 1994; Trivedi and Axe, 2001; Rosenqvist et al., 2002)...

    Dimitri A. Sverjensky. Prediction of surface charge on oxides in salt solutions: Revisions fo...

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