Letter pubs.acs.org/JPCL
Water Chain Formation on TiO2(110) Junseok Lee,*,†,‡ Dan C. Sorescu,† Xingyi Deng,†,‡ and Kenneth D. Jordan†,§ †
National Energy Technology Laboratory, Department of Energy, Pittsburgh, Pennsylvania 15236, United States URS, P.O. Box 618, South Park, Pennsylvania 15129, United States § Department of Chemistry, University of Pittsburgh, Pennsylvania 15260, United States ‡
S Supporting Information *
ABSTRACT: The adsorption of water on a reduced rutile TiO2(110)-(1×1) surface has been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM measurements show that at a temperature of 50 K, an isolated water monomer adsorbs on top of a Ti(5f) atom on the Ti row in agreement with earlier studies. As the coverage increases, water molecules start to form one-dimensional chain structures along the Ti row direction. Supporting DFT calculations show that the formation of an H-bonded one-dimensional water chain is energetically favorable compared to monomer adsorption. In the chain, there are H-bonds between adjacent water molecules, and the water molecules also form H-bonds to neighboring bridging oxygens of TiO2(110). Thermal annealing at T = 190 K leads to the formation of longer chains facilitated by the diffusion of water on the surface. The results provide insight into the nature of the hydrogen bonding in the initial stage of wetting of TiO2. SECTION: Surfaces, Interfaces, Porous Materials, and Catalysis
T
of water on TiO2 involves hole-induced oxidation rather than electron-induced reduction.18 In spite of these advances, atomic scale information on the interaction between water molecules adsorbed on TiO2 is scarce. While studying the dissociation of water at the VO sites on TiO2(110), Brookes et al.8 observed the growth of linear water chain structures at high water coverage after annealing the surface to T = 150 K. However, no analysis was presented as to the relative importance of water−water and water−surface interactions in forming the chains. A recent study using polarization- and azimuth-resolved infrared reflection−absorption spectroscopy (IRAS) and ab initio molecular dynamics (AIMD) calculations has found strong anisotropy in the bonding of water (D2O) layers grown up to four monolayers on the TiO2(110) surface.19 It was argued that the anisotropy originates from the two different types of H-bonds in which the water molecules on the TiO2(110) surface are engaged, i.e., weak H-bonds between adjacent water molecules along the [001] azimuth and stronger H-bonds between water molecules and bridging oxygen (Ob) atoms along the [11̅0] azimuth. An STM study of water on the TiO2(011)-(2×1) surface showed that one-dimensional H-bonded water chains can grow from hydroxyl species produced by water dissociation at VO sites.20 In the current work, we show using STM measurements that one-dimensional water chains longer than dimers can be formed along the [001] direction on the TiO2(110) surface.
he interaction of water with solid surfaces has been studied intensively due to its importance in electrochemistry, environment science, and heterogeneous catalysis.1,2 Since the discovery of photochemical hydrogen production from water at a TiO2 electrode,3 the surface chemistry of water on TiO2 has been a major area of research.4,5 Most of the fundamental surface science results on water on TiO2 have been obtained using the rutile TiO2(110)-(1×1) surface, which is thermodynamically the most stable facet.6 Temperature-programmed desorption (TPD), vibrational spectroscopy, photoelectron diffraction, scanning tunneling microscopy (STM), and density functional theory (DFT) calculations have all been used to study water on the TiO2(110)-(1×1) surface. Water molecules have been found to adsorb molecularly at Ti(5f) sites on the nearly perfect TiO2(110) surface7 and to dissociate at oxygen vacancy (VO) sites.8−11 The adsorption of water at Ti(5f) sites has also been confirmed by a photoelectron diffraction study where the Ti− Owater bond length was obtained experimentally. 12 The formation of stable water dimers on the TiO2(110) surface and faster diffusion of the dimers compared to the monomer along the Ti rows have been reported.13 In addition, the interactions of water with other adsorbates such as O2,14 atomic oxygen (Oa),15,16 and terminal hydroxyl (OHt)17 species have been studied in great detail using the STM technique. A recent STM study showed that tip-induced reduction of water does not produce bridging hydroxyl (OHb) species, while photoinduced oxidation of water can produce both OHb and OHt species, suggesting that the initial step in the photodissociation © XXXX American Chemical Society
Received: October 25, 2012 Accepted: December 11, 2012
53
dx.doi.org/10.1021/jz301727n | J. Phys. Chem. Lett. 2013, 4, 53−57
The Journal of Physical Chemistry Letters
Letter
STM features such as bright Ti rows and dark bridging oxygen (Ob) rows are visible.21 In addition, oxygen vacancies (VO) are visible as bright features on the dark Ob rows. Water was dosed onto the clean TiO2(110) surface at T = 50 K (Figure 1b). An increased number of bright features on the Ti rows as well as a slightly increased number of OHb features on the Ob rows are observed. We assign the bright features on the Ti rows to water monomers adsorbed on Ti(5f) atoms, consistent with previous findings.13,18 The adsorption site was determined from a highresolution STM image by superimposing a TiO2(110) surface lattice grid as shown in Figure 1c. The center of the water feature is positioned at an intersection of grid lines indicating that the Ti(5f) atom is the adsorption site of water on TiO2(110). DFT calculations at 1/16 ML (1/8 ML) coverage show that the most stable adsorption configuration of water is at the Ti(5f) atom with the formation of a Ti(5f)−Owater bond with a binding energy of 23.7 (23.4) kcal/mol as shown in Figure 1d. This value is slightly larger than the theoretical result of Sebbari et al.22 due to the inclusion of dispersion correction in our calculations. In the optimized structure, the Ti(5f)− Owater bond axis is slightly tilted away from the surface normal. One of the H−Owater groups in the adsorbed water molecule points to a nearby Ob atom forming a H-bond. The other H− Owater group is free and tilted by 53° with respect to the surface normal. An isolated water molecule at a Ti(5f) site can bind to the Ob atom on either side of the Ti atom, and the calculated barrier for interconversion between the two minimum energy configurations via the symmetrical transition state is only 0.5 kcal/mol. Thus, the streaky nature of the STM feature associated with an isolated water molecule at the Ti(5f) site may be due to wide amplitude motion of the water molecule at this site. By use of the voltage pulsing technique, we confirmed that the species adsorbed on the Ti(5f) atom is indeed a water molecule. Figure 1e shows an STM image where five adsorbed water molecules are observed. Electrons were injected by applying positive voltage pulses (+2.8 V, 500 ms) to four water species marked with squares and a circle while recording the current traces. Out of four water species, three (in the squares) turn into oxygen adatoms (Oa) as shown in Figure 1f. One water feature shows streakiness after the pulse, and it is assigned to a terminal hydroxyl species as shown in a previous study.18 The STM image of the OHt species produced in this manner looks quite different from that observed at room temperature in previous studies.17,23 Application of a voltage pulse to an OHt species produces an Oa species (Figures S1a and S1b, Supporting Information). Voltage pulsing with negative bias (hole injection) is found to lead to the formation of a OHb species in a nearby Ob row as shown in Figures S1c and S1d. We did not find adsorbed OHt species nearby after the pulse, which agrees with a recent postirradiation STM study.18 It is likely that the •OH species produced from holeinduced dissociation desorbs from the reaction site. One-dimensional clusters (chains) are formed when the water coverage is increased on the TiO2(110) surface. Figure 2a shows an STM image resulting from dosing of ∼0.04 ML of water on TiO2(110) at T = 50 K. The onset of the development of a one-dimensional water chain along a Ti row is observed along with some isolated water monomers. The chain appears streaky, similar to the water monomer case. The exact number of water molecules in the chain observed in Figure 2a could not be determined. At a higher coverage (0.13 ML), longer chains are formed as shown in Figure 2b.
Our DFT calculations show that the H-bonding is responsible for the water chain formation and that chains longer than dimers are favored by comparing per-monomer adsorption energies of water chains of different lengths. Figure 1a shows an STM image of the clean reduced TiO2(110)-(1×1) surface at T = 50 K. Typical empty-state
Figure 1. (a) A typical empty state STM image (1.5 V, 10 pA, 15 × 15 nm2) of a clean TiO2(110)-(1×1) surface. Alternating bright Ti rows and dark bridging oxygen rows are observed along the [001] direction. A few bridging hydroxyls (OHb) and oxygen vacancies (VO) are also shown. (b) STM image (1.5 V, 10 pA, 15 × 15 nm2) after dosing water on the TiO2(110)-(1×1) surface at T = 50 K. The new bright features that appear on the Ti rows are assigned to water monomers. The coverage of water is estimated to be about 0.015 ML based on counting the number of water features in the STM images from different surface areas. OHb and (OHb)pair species are also indicated. (c) A TiO2(110)-(1×1) lattice grid is superimposed on a STM image (1.5 V, 5 pA, 4.3 × 4.3 nm2). The intersections of the grid lines mark the positions of the surface Ti atoms. The water features in the STM image show streakiness. (d) Side and top view of the most stable adsorption configuration of a water monomer on TiO2(110) from DFT calculations. The Ti(5f)−Owater bond is slightly off normal. Only the topmost layer of TiO2(110) is shown. (Gray ball: Ti; red ball: O; yellow ball: H; and blue dotted line: H-bonding.) (e,f) STM images (1.5 V, 5 pA, 10 × 10 nm2) at T = 50 K before and after applying +2.8 V (500 ms) pulses to the adsorbed water molecules marked with squares and a circle in panel e. The three water molecules indicated by squares dissociated into Oa species, while the water molecule in the circle dissociated into OHt species. 54
dx.doi.org/10.1021/jz301727n | J. Phys. Chem. Lett. 2013, 4, 53−57
The Journal of Physical Chemistry Letters
Letter
measurements show that there are water chains longer than the tetramer on the Ti rows. In addition, our DFT calculations indicate that the tetramer is slightly more stable than the two separate dimers, which will be shown below. No two-dimensional growth of water layers on TiO2(110) was observed at 0.5 ML coverage unlike the situation for various metal surfaces where two-dimensional water layers are known to form,24−27 with Cu(110) being an exception.28,29 This is due to the fact that on TiO2(110) intermolecular Hbonding between water molecules along the [11̅0] direction is hindered because of the presence of Ob atoms acting as hydrogen acceptors. In addition, the distance between the water molecules adsorbed on the opposite sides of an Ob row is too large to form H-bonds across the Ob row, further hindering the two-dimensional growth of a water layer. In this regard, the Ob rows on TiO2(110) act as guiding walls for one-dimensional water chain growth along the [001] direction. Our DFT calculations show that one-dimensional water chains with both intermolecular H-bonding and H-bonding between water molecules and Ob atoms are quite stable on the surface. Two different types of one-dimensional water chains (WC1 and WC2) on a stoichiometric TiO2(110) surface at 0.5 ML coverage are considered in Figure 3. In the WC1 structure, all H-bonds between water molecules and Ob sites are on the same side (Figure 3a). The oxygen atoms of the water (Owater) molecules in the WC1 structure are displaced slightly off the Ti(5f) atoms toward the Ob atoms. Repeating intermolecular H-bonds form the backbone of the water chain. The calculated binding energy (per monomer) of the WC1 structure is 25.9
Figure 2. (a) STM image (1.5 V, 10 pA, 9 × 9 nm2) of water molecules on TiO2(110) at T = 50 K and 0.04 ML. A short, streaky water chain can be seen. Isolated water monomers, VO sites, and OHb species are also indicated. (b) STM image (1.5 V, 10 pA, 12 × 12 nm2) of water molecules on TiO2(110) at T = 50 K at 0.13 ML. Longer onedimensional water chains are observed. (c) STM image (1.5 V, 10 pA, 9 × 9 nm2) of water molecules on TiO2(110) at T = 50 K after annealing the sample in panel b to T = 190 K for 5 min. The chain appears streaky at the sides. (d) STM image (1.5 V, 10 pA, 14 × 14 nm2) of water molecules on TiO2(110) at an initial coverage of 0.5 ML imaged at T = 50 K after annealing to T = 190 K for 5 min.
However, the length of the water chains formed by dosing at T = 50 K was limited probably due to a sizable diffusion barrier of water monomers along the Ti row (Figure S2). To produce longer water chains, we annealed the sample to T = 190 K to facilitate the diffusion of water along the Ti rows and the resulting STM image is shown in Figure 2c. Three distinct changes are observed: (1) longer water chains than shown in Figure 2b are formed due to the diffusion of water molecules and their subsequent clustering, (2) features on Ti rows that are slightly larger than the monomer are observed, and (3) the effective coverage of water is much lower than that in Figure 2b and all VO sites have been converted to OHb. The features that are slightly larger than the monomers are expected to be due to immobilized water dimers that are known to exist during the annealing process. In a previous work, it was reported that water tetramers were formed but quickly split into dimers at T = ∼161 K.13 The lower effective coverage at thermal annealing is caused by the dissociation of water molecules at VO sites during the diffusion process. Our DFT calculations give a barrier for diffusion of a water monomer along the Ti row of 10.9 kcal/mol and a barrier for dissociation of water at the VO site of 11.6 kcal/mol (Figure S3). Thus the diffusion and dissociation of water compete during the annealing process. At an initial coverage of 0.5 ML, water chains as long as 6.9 nm (estimated to be ∼24 water molecules long with a lattice constant of 2.96 Å) are observed after thermal annealing to T = 190 K and then cooling back to T = 50 K for imaging (Figure 2d). Contrary to a previous report that the tetramer and longer chains are unstable and split into dimers at T > 160 K,13 our
Figure 3. Calculated structure of one-dimensional water chains on the stoichiometric TiO2(110) surface at 0.5 ML water. (Gray: Ti atom; red: oxygen atom; yellow: hydrogen atom; blue dotted line: Hbonding) (a) Side view and top view of a one-dimensional water chain (WC1), with the H-bonds between water and Ob (Hwater−Ob) occurring only on the right-hand side of the chain. Intermolecular Hbonds between water molecules can be seen in addition to the Hwater− Ob bonds. (b) Side view and top view of a one-dimensional water chain (WC2), with the H-bonds between water and Ob occurring in a zigzag manner. The average H-bond length (RO−H) and the average O−O bond length (RO−O) are indicated for both structures. 55
dx.doi.org/10.1021/jz301727n | J. Phys. Chem. Lett. 2013, 4, 53−57
The Journal of Physical Chemistry Letters
Letter
structure to the W5 structure, suggesting that convergence has essentially been reached at that chain length. It should be noted that the increased adsorption energy of the W6 structure compared to that of the W5 structure is due to the additional H-bonding resulting from the use of a (6 × 2) supercell with periodic boundary conditions. We also note that the adsorption energy (per monomer) of the “W2 + W2” structure is smaller than that of the W2 and W4 structures. Thus, our DFT calculations indicate a preference for formation of water chains longer than the dimer, which is also supported by previous studies.8,19 However, due to the small energy difference between W4 and 2W2 species, the lengths of the water chains observed on the surface may depend on temperature and coverage as well as the relative stabilities of the different length chains. Further studies are required to elucidate the role of VO sites and OHb species in the formation of water chains and the extent to which the photochemistry of water molecules in the chains differ from that of isolated water molecules on the surface. In summary, we have studied the adsorption of water on the TiO2(110)-(1×1) surface at low temperatures and found the formation of one-dimensional H-bonded water chains along the Ti rows by using STM measurements. At low coverage, water monomers adsorb at the Ti(5f) atoms at T = 50 K. At higher water coverage, linear water chains are formed. The growth of longer chains is achieved via the thermal diffusion of water molecules at elevated temperatures. DFT calculations were carried out and confirm the stability of the one-dimensional chains.
kcal/mol, which is larger than that of the isolated adsorbed monomer (23.7 kcal/mol). (All binding energies reported in this work are on a per monomer basis.) The average Owater− Owater intermolecular bond length (ROw−Ow) is 2.96 Å and the average Owater−Ob bond length (ROw−Ob) is 2.74 Å. For comparison, the values of RO−O in ice Ih is 2.75 Å from a neutron diffraction study at T = 60 K.30 In the WC2 structure, the H-bonds between the water molecules and the Ob atoms alternate on opposite sides of the chain, forming a zigzag arrangement (Figure 3b). The WC2 structure is that proposed by Kimmel et al.19 at 1 ML coverage. The calculated binding energy of the water monomers in the WC2 chain is 26.0 kcal/ mol, which is slightly greater than that for WC1. The average ROw−Ow is 3.07 Å and the ROw−Ob is 2.83 Å in the WC2 structure. The WC1 and W2 structures represent two limiting cases, and, in fact, structures with more random orientations of the water monomers are comparable in stability and are expected to coexist on the surface. The intermolecular distances, ROw‑Ow, in the one-dimensional water chains are close to the distance between the adjacent Ti(5f) atoms on a Ti row (2.96 Å). Since stronger H-bonds are usually formed in the systems with smaller ROw−Ow,31 the Hbonds in the one-dimensional water chain on TiO2(110) (ROw−Ow = 2.96 Å) are weaker than that found, for example, in the network of ice (ROw−Ow = 2.75 Å).1 To gain further insight into the stability of the water chains on TiO2(110), we report in Figure 4 the calculated adsorption energies of the finite chains with the WC2 configuration. It is seen that the calculated adsorption energy per molecule increases monotonically from the monomer (W1) up to the tetramer (W4) structure, suggesting a favorable formation of water chains. There is no stability gain going from the W4
■
ASSOCIATED CONTENT
S Supporting Information *
Experimental methods, theoretical methods, and supporting figures are included. This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. The authors declare no competing financial interest.
Figure 4. Calculated per monomer adsorption energies (solid black bar) and vibrational zero-point energy corrected (ZPEC) adsorption energies (solid red bar) of finite water chain structures. The corresponding calculated structures (W1−W6) are also shown. A stoichiometric TiO2(110) surface with a (6 × 2) slab was used in the calculation. The highest coverage structure, W6, corresponds to 0.5 ML, and with the periodic boundary conditions, corresponds to the infinite WC2 chain. (W2 + W2) corresponds to two water dimers on a Ti row, separated by a lattice spacing.
■
ACKNOWLEDGMENTS We acknowledge a grant of computer time at the Pittsburgh Supercomputer Center. The research was performed in support of the National Energy Technology Laboratory’s ongoing research under the RES contract DE-FE0004000. 56
dx.doi.org/10.1021/jz301727n | J. Phys. Chem. Lett. 2013, 4, 53−57
The Journal of Physical Chemistry Letters
■
Letter
(23) Du, Y.; Deskins, N. A.; Zhang, Z. R.; Dohnálek, Z.; Dupuis, M.; Lyubinetsky, I. Imaging Consecutive Steps of O2 Reaction with Hydroxylated TiO2(110): Identification of HO2 and Terminal OH Intermediates. J. Phys. Chem. C 2009, 113, 666−671. (24) Michaelides, A.; Morgenstern, K. Ice Nanoclusters at Hydrophobic Metal Surfaces. Nat. Mater. 2007, 6, 597−601. (25) Haq, S.; Clay, C.; Darling, G. R.; Zimbitas, G.; Hodgson, A. Growth of Intact Water Ice on Ru(0001) between 140 and 160K: Experiment and Density-Functional Theory Calculations. Phys. Rev. B 2006, 73, 115414. (26) Cerdá, J.; Michaelides, A.; Bocquet, M. L.; Feibelman, P. J.; Mitsui, T.; Rose, M.; Fomin, E.; Salmeron, M. Novel Water Overlayer Growth on Pd(111) Characterized with Scanning Tunneling Microscopy and Density Functional Theory. Phys. Rev. Lett. 2004, 93, 116101. (27) Nie, S.; Feibelman, P. J.; Bartelt, N. C.; Thürmer, K. Pentagons and Heptagons in the First Water Layer on Pt(111). Phys. Rev. Lett. 2010, 105, 026102. (28) Yamada, T.; Tamamori, S.; Okuyama, H.; Aruga, T. Anisotropic Water Chain Growth on Cu(110) Observed with Scanning Tunneling Microscopy. Phys. Rev. Lett. 2006, 96, 036105. (29) Carrasco, J.; Michaelides, A.; Forster, M.; Haq, S.; Raval, R.; Hodgson, A. A One-Dimensional Ice Structure Built from Pentagons. Nat. Mater. 2009, 8, 427−431. (30) Kuhs, W. F.; Lehmann, M. S. The Structure of the Ice Ih by Neutron Diffraction. J. Phys. Chem. 1983, 87, 4312−4313. (31) Pimentel, G. C.; McClellan, A. L. Hydrogen Bonding. Annu. Rev. Phys. Chem. 1971, 22, 347−385.
REFERENCES
(1) Thiel, P. A.; Madey, T. E. The Interaction of Water with Solid Surfaces: Fundamental Aspects. Surf. Sci. Rep. 1987, 7, 211−385. (2) Henderson, M. A. The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited. Surf. Sci. Rep. 2002, 46, 1−308. (3) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37−38. (4) Henderson, M. A. A Surface Science Perspective on Photocatalysis. Surf. Sci. Rep. 2011, 66, 185−297. (5) Fujishima, A.; Zhang, X.; Tryk, D. A. TiO2 Photocatalysis and Related Surface Phenomena. Surf. Sci. Rep. 2008, 63, 515−582. (6) Diebold, U. The Surface Science of Titanium Dioxide. Surf. Sci. Rep. 2003, 48, 53−229. (7) Hugenschmidt, M. B.; Gamble, L.; Campbell, C. T. The Interaction of H2O with a TiO2(110) Surface. Surf. Sci. 1994, 302, 329−340. (8) Brookes, I. M.; Muryn, C. A.; Thornton, G. Imaging Water Dissociation on TiO2(110). Phys. Rev. Lett. 2001, 87, 266103. (9) Schaub, R.; Thostrup, P.; Lopez, N.; Lægsgaard, E.; Stensgaard, I.; Nørskov, J. K.; Besenbacher, F. Oxygen Vacancies as Active Sites for Water Dissociation on Rutile TiO2(110). Phys. Rev. Lett. 2001, 87, 266104. (10) Bikondoa, O.; Pang, C. L.; Ithnin, R.; Muryn, C. A.; Onishi, H.; Thornton, G. Direct Visualization of Defect-Mediated Dissociation of Water on TiO2(110). Nat. Mater. 2006, 5, 189−192. (11) Zhang, Z.; Bondarchuk, O.; Kay, B. D.; White, J. M.; Dohnálek, Z. Imaging Water Dissociation on TiO2(110): Evidence for Inequivalent Geminate OH Groups. J. Phys. Chem. B 2006, 110, 21840−21845. (12) Allegretti, F.; O’Brien, S.; Polcik, M.; Sayago, D. I.; Woodruff, D. P. Adsorption Bond Length for H2O on TiO2(110): A Key Parameter for Theoretical Understanding. Phys. Rev. Lett. 2005, 95, 226104. (13) Matthiesen, J.; Hansen, J. Ø.; Wendt, S.; Lira, E.; Schaub, R.; Lægsgaard, E.; Besenbacher, F.; Hammer, B. Formation and Diffusion of Water Dimers on Rutile TiO2(110). Phys. Rev. Lett. 2009, 102, 226101. (14) Zhang, Z.; Du, Y.; Petrik, N. G.; Kimmel, G. A.; Lyubinetsky, I.; Dohnálek, Z. Water as a Catalyst: Imaging Reactions of O2 with Partially and Fully Hydroxylated TiO2(110) Surfaces. J. Phys. Chem. C 2009, 113, 1908−1916. (15) Epling, W. S.; Peden, C. H. F.; Henderson, M. A.; Diebold, U. Evidence for Oxygen Adatoms on TiO2(110) Resulting from O2 Dissociation at Vacancy Sites. Surf. Sci. 1998, 412−13, 333−343. (16) Du, Y.; Deskins, N. A.; Zhang, Z.; Dohnálek, Z.; Dupuis, M.; Lyubinetsky, I. Two Pathways for Water Interaction with Oxygen Adatoms on TiO2(110). Phys. Rev. Lett. 2009, 102, 096102. (17) Du, Y.; Deskins, N. A.; Zhang, Z.; Dohnálek, Z.; Dupuis, M.; Lyubinetsky, I. Water Interactions with Terminal Hydroxyls on TiO2(110). J. Phys. Chem. C 2010, 114, 17080−17084. (18) Tan, S.; Feng, H.; Ji, Y.; Wang, Y.; Zhao, J.; Zhao, A.; Wang, B.; Luo, Y.; Yang, J.; Hou, J. G. Observation of Photocatalytic Dissociation of Water on Terminal Ti Sites of TiO2(110)-1×1 Surface. J. Am. Chem. Soc. 2012, 134, 9978−9985. (19) Kimmel, G. A.; Baer, M.; Petrik, N. G.; VandeVondele, J.; Rousseau, R.; Mundy, C. J. Polarization- and Azimuth-Resolved Infrared Spectroscopy of Water on TiO2(110): Anisotropy and the Hydrogen-Bonding Network. J. Phys. Chem. Lett. 2012, 3, 778−784. (20) He, Y.; Li, W.-K.; Gong, X.-Q.; Dulub, O.; Selloni, A.; Diebold, U. Nucleation and Growth of 1D Water Clusters on Rutile TiO2 (011)-2×1. J. Phys. Chem. C 2009, 113, 10329−10332. (21) Diebold, U.; Anderson, J. F.; Ng, K. O.; Vanderbilt, D. Evidence for the Tunneling Site on Transition-metal Oxides: TiO2(110). Phys. Rev. Lett. 1996, 77, 1322−1325. (22) Sebbari, K.; Domain, C.; Roques, J.; Perron, H.; Simoni, E.; Catalette, H. Investigation of Hydrogen Bonds and Temperature Effects on the Water Monolayer Adsorption on Rutile TiO2(110) by First-Principles Molecular Dynamics Simulations. Surf. Sci. 2011, 605, 1275−1280. 57
dx.doi.org/10.1021/jz301727n | J. Phys. Chem. Lett. 2013, 4, 53−57
