Structure of Rutile TiO₂ (110) in Water and 1 Molal Rb+ at pH 12: Interrelationship Among Surface Charge, Interfacial Hydration Structure, and Substrate Structural Displacements

Journal Article · Mon Jan 01 00:00:00 EST 2007 · Surface Science

DOI:https://doi.org/10.1016/j.susc.2006.12.007· OSTI ID:1081585

Zhang, Zhan ^[1]; Fenter, Paul ^[1]; Sturchio, N. C. ^[2]; Bedzyk, Michael J. ^[3]; Machesky, Michael L. ^[4]; Wesolowski, David J ^[5]

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1. Argonne National Laboratory (ANL)
2. University of Illinois, Chicago
3. Northwestern University, Evanston
4. Illinois State Water Survey, Champaign, IL
5. ORNL

The rutile (110)-aqueous solution interface structure was measured in deionized water (DIW) and 1 m RbCl + RbOH solution (pH 12) at 25 C with the X-ray crystal truncation rod method. The rutile surface in both solutions consists of a stoichiometric (1 1) surface unit mesh with the surface terminated by bridging oxygen (BO) and terminal oxygen (TO) sites. An additional hydration layer is observed above the TO site, with three distinct water adsorption sites each having well-defined vertical and lateral locations. Rb+ specifically adsorbs at the tetradentate site between the TO and BO sites, replacing one of the adsorbed water molecules at the interface. There is no further ordered water structure observed above the hydration layer. Structural displacements of atoms at the oxide surface are observed to be sensitive to the solution composition. Ti atom displacements from their bulk lattice positions, as large as 0.05 at the rutile (110)-DIW interface, decay in magnitude into the crystal with significant relaxations that are observable down to the fourth Ti-layer below the surface. A systematic outward shift was observed for Ti atom locations below the BO rows, while a systematic inward displacement was found for Ti atoms below the TO rows. The Ti displacements were mostly reduced in contact with the RbCl solution at pH 12, with no statistically significant relaxations in the fourth layer Ti atoms. The distance between the surface 5-fold Ti atoms and the oxygen atoms of the TO site is 2.13 0.03 in DIW and 2.05 0.03 in the Rb+ solution, suggesting that water adsorbs mainly in molecular form to the rutile (110) surface at the TO site in DIW, while it is primarily in the form of an adsorbed hydroxyl group at pH 12.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1081585
• Journal Information: Surface Science, Vol. 601, Issue 4; ISSN 0039-6028
• Country of Publication: United States
• Language: English