Investigation of hydrogen bonds and temperature effects on the water monolayer adsorption on rutile TiO2 (110) by first-principles molecular dynamics simulations

doi:10.1016/j.susc.2011.04.015

Surface Science

Volume 605, Issues 13–14, July 2011, Pages 1275-1280

https://doi.org/10.1016/j.susc.2011.04.015 Get rights and content

Abstract

Density Functional Theory (DFT), based on both static and Born–Oppenheimer Molecular Dynamics approaches, has been used to investigate the effect of hydrogen bonds and temperature on the water monolayer adsorption on the rutile TiO₂ (110) face. It was demonstrated that the difference between some previous theoretical results and experimental data is due to too slim slab thickness model and/or too small surface area. According to the present static calculations, water monolayer adsorbs molecularly on the five-fold titanium atoms of an optimised five-layer slab thickness, due to the stabilising lateral hydrogen bonds between molecules. From the molecular dynamics simulations, two adsorption mechanisms were described as a function of temperature. Finally, it was pointed out that the dynamics of water adsorption is strongly influenced by the structural model used. When temperature increases, the monolayer dissociates gradually. However, because of the periodic boundary conditions, the 1 × 1 surface unit needs to be extended to at least 2 × 5 to get an accurate representation of the monolayer dissociation ratio. In these conditions, this ratio is around 20%, 25% and 33% at 270, 350 and 425 K, respectively.

Research highlights

► Ab initio Molecular Dynamics approach has been used to investigate hydrogen bonds and temperature effects on H₂O adsorption on TiO₂. ► From static calculations, water monolayer adsorbs molecularly on titanium atoms due to the stabilizing lateral hydrogen bonds. ► Two adsorption mechanisms were described as a function of temperature. ► When temperature increases, the monolayer dissociates gradually. ► The monolyer dissociation ratio is around 20 %, 25 % and 33 % at 270, 350 and 425 K, respectively.

Introduction

Water/metal oxide interfaces take a great place in many industrial applications such as heterogeneous catalysis, photochemistry, electrochemistry and gas sensors [1]. The investigation of water interaction with oxide surface is of high level of interest for the improvement of these technologies. However, if we consider the interface as an area in which water/metal and water/water interactions are in competition, the interpretation of the involved mechanism becomes rather complex [2], [3]. Indeed, water may activate metal surface atom [4], but at the same time hinder the adsorption of ions on the activated site [5]. Consequently, the use of model system can be very helpful to understand such interfaces. The water/TiO₂ interface is considered as a probe system in liquid/metal oxide interface science [6], [7], [8]. For this reason, both experimental and theoretical works have investigated adsorption of water molecules on the rutile TiO₂ (110) face. However, it remains a subject of controversy between some theoretical studies relative to experimental results. Therefore, both understanding and clarification of these discrepancies should be elucidated.

On one hand, some experimental studies concluded on a molecular adsorption for the first hydration layer at low temperature (~ 120 K), whereas dissociation may occur at lower coverage on a perfect surface, at high temperature and/or on surface oxygen vacancies [9], [10], [11], [12], [13], [14]. Kurtz et al. [15] showed by ultraviolet photoemission spectroscopy that water remained on molecular form up to 160 K, then partly dissociated while the temperature increased. Coupling this result with X-ray photoemission spectroscopy, Hugenschmidt et al. [16] determined a temperature programmed desorption peak at 275 K attributed to the molecularly adsorbed water according to a O(1s) peak position at 532.9 eV and a work function decrease of 1.1 eV, while a tail of this peak which extends to 375 K was attributed to the dissociative form according to ultraviolet photoemission spectroscopy results [15]. Henderson [10] completed these investigations and concluded that dissociation should occur at 130 K on defective site.

On the other hand, some theoretical studies (e.g. Hartree Fock [17], semi-empirical [8], static DFT [2], [7], [18], [19], [20], [22] and DFT based on molecular dynamics using three layer slab thickness as surface model [2], [18], [19], [20]) showed dissociation at all coverage on the perfect (110) face, with however a small dissociation ratio. The same behaviour was also found on the rutile TiO₂ (011) [6] and (100) faces [8]. On the contrary, Schaub et al. [21] showed that dissociation can only occurr on defect surfaces by coupling DFT calculations with high resolution STM images. From DFT calculations, using a three-layer slab thickness model, Harris et al. [7] found a maximum difference of about 0.17 eV per water molecule in favour of the dissociative adsorption at low coverage. However by increasing the coverage, they showed that the adsorption is preferentially led by a mixed mode with adsorption energies of 1.30 eV per water molecule, against 1.27 and 1.18 eV for the full molecular and dissociative modes, respectively. This stabilisation was explained thanks to the lateral hydrogen bonds (HB) between neighbouring adsorbed water molecules on a titanium row of the (110) surface [2], [18], [19]. However by using a five layer slab, Harris et al. [7] showed that the molecular adsorption overtook the mixed and full dissociative mode by 0.02 and 0.14 eV per water molecule, respectively. This relative stability order change has been explained by Perron et al. DFT calculations [23] which is due to the parity of the slab. In this study, it has been demonstrated that the three-layer slab is too thin to correctly model water interaction. Finally, Lindan et al. [18] indicated, using DFT molecular dynamics, that the usual surface size 2 × 1, which represents the monolayer by two independent water molecules, cannot provide reliable information on the dissociated molecules fraction.

In summary, it appears that previous theoretical DFT results are not consistent. From these previous static studies, it seems that the surface model used to represent the TiO₂ surface, in terms of slab thickness and surface area, can have a significant influence on the water monolayer behaviour. Moreover, the temperature should also affect the adsorption process, the repartition between the different adsorption modes and the associated proton transfer dynamic, as well. Therefore, the aim of this work is to clarify the discrepancy of these previous theoretical works by using the DFT in both, static and Born Oppenheimer Molecular Dynamics (MD) approaches. In the first part, the limitation of the three-layer slab (S3) will be compared to the five-layer slab (S5) in terms of adsorption energies and temperature behaviour. This part will confirm the choice of S5 as a good surface model. Then, coverage (up to the saturation of the first hydration layer) and temperature effects on the water adsorption modes will be investigated with the optimised S5 model. Finally, some insights of dissociation mechanism in terms of energy profile will be proposed.

Section snippets

Computational background

All calculations were performed using DFT based on plane wave basis sets generated with the Projector Augmented Wave method (PAW) [24] as implemented in the Vienna ab initio Simulation Package code (VASP) [25], [26], [27]. The Generalised Gradient Approximation (GGA) as defined by Perdew and Wang PW91 [28] has been used. Titanium atoms were described with four valence electrons (4s² 3d²) and oxygen ones with six (2s² 2p⁴). The Kohn–Sham equations were resolved with an optimised plane wave

Slab thickness effect

According to the DFT-static calculations of Perron et al. [23], the S5 model corresponds to an accurate surface model with a surface energy of 0.60 ± 0.02 J/m² (about 0.75 J/m² for the S3 model) relative to 0.50 ± 0.02 J/m² for the unconstrained 12 layers surface used as reference. Adsorption energies were compared with the S3 and S5 models using static calculations, while their behaviours in temperature were studied by MD. The 2 × 3 surface model was used which corresponds, for a full coverage (θ = 1 ML)

Conclusion

Density Functional Theory, in both static and Born Oppenheimer Molecular Dynamics approaches, was used to clarify the difference of the theoretical results about the water monolayer adsorption on the rutile TiO₂ (110) face. In this work, it has been showed that the choice of the structural model is essential for the representation of water adsorption versus temperature. In agreement with Perron et al. [23], it has been demonstrated that the three layer slab is unable to correctly describe the

Acknowledgements

The CCRT supercomputer within the framework of an EDF–CEA contract has been used. Parts of the calculations have been performed on the IBM BG/L and BG/P EDF R&D supercomputers.

References (40)

R. Long et al.
Phys. Lett. A
(2010)
C.D. Taylor et al.
Curr. Opin. Solid State Mater. Sci.
(2005)
T.J. Beck et al.
Surf. Sci.
(2005)
K. Jug et al.
Surf. Sci.
(2005)
M.A. Henderson
Surf. Sci.
(1996)
M.A. Henderson
Surf. Sci. Rep.
(2002)
D. Brinkley et al.
Surf. Sci.
(1998)
T. Bezrodna et al.
J. Mol. Struct.
(2004)
R.L. Kurtz et al.
Surf. Sci.
(1989)
M.B. Hugenschmidt et al.
Surf. Sci.
(1994)

A. Fahmi et al.

Surf. Sci.

(1994)

P.J.D. Lindan et al.

Chem. Phys. Lett.

(1996)

J. Goniakowski et al.

Surf. Sci.

(1996)

H. Perron et al.

Surf. Sci.

(2007)

C. Zhang et al.

J. Chem. Phys.

(2003)

C.D. Taylor et al.

J. Electrochem. Soc.

(2006)

A. Tilocca et al.

J. Phys. Chem. B

(2004)

L.A. Harris et al.

Phys. Rev. Lett.

(2004)

M.A. Henderson

Langmuir

(1996)

M. Primet et al.

J. Phys. Chem.

(1971)

Cited by (25)

Dynamical and structural properties of adsorbed water molecules at the TiO<inf>2</inf> anatase-(1 0 1) surface: Importance of interfacial hydrogen-bond rearrangements
2020, Chemical Physics Letters
Citation Excerpt :
To render H2 competitive as a fuel with fossil fuels, the United-States DOE stipulates that its production costs should be lower than $ 4 per kg of H2, and PEC approaches are promising to the end for industrial scale-up if appropriate water-splitting catalysts can be improved substantially in terms of solar-to-hydrogen (STH) performance [3]. The hydrogen-bond (HB) between protons in water molecules and the bridging oxygen atoms at the surface, as well as the variation in bond stretch and bond-angle bending modes in the water molecules are a sensitive probe of the water-TiO2 interfacial interactions [11,12]. These interfacial hydrogen bonds stand out for their critical role in catalytic reactions: for hydrogen-evolution modifiers of TiO2, metal sulphides and selenides can be used as spatially-controlled oxidation and reduction co-catalysts/modifiers on titania surfaces, which serve to modify hydrogen-bonding arrangements [13].
Dynamical and structural properties of physically- and chemically-adsorbed water molecules on partially hydroxylated anatase-(1 0 1) surfaces have been studied via Born-Oppenheimer molecular dynamics. Most molecules adopt surface-parallel orientations. Two main types of water-splitting modes were: at a Ti₅ site, rupturing the neighbouring oxygen-atom bridge featuring two surface OH-groups connected with a hydrogen bond, and a co-catalytic molecule in the hydration layer forming an intermediate hydronium ion donating a proton to a bridging oxygen atom. A 1155 cm⁻¹ vibrational mode arises from ‘deformation’ in OH-groups, bound to surface-adsorbed water molecules by weak hydrogen bonds – a key ‘signature’ of covalently-shared protons.
Application of density functional theory in studying CO<inf>2</inf> capture with TiO<inf>2</inf>-supported K<inf>2</inf>CO<inf>3</inf> being an example
2018, Applied Energy
Citation Excerpt :
In addition, the adsorption of H2O on pure K2CO3 up to 126.4 kJ·mol−1 [14] is stronger than that at the interface of K2CO3/TiO2 and support of TiO2. In recent studies, it was found that H2O molecules not only remain intact when adsorbed at low temperature at monolayer coverage, but also that a small portion of H2O monomers can dissociate, with the fraction of such dissociated monomers increasing with increased temperature [55,56]. Accordingly, we also investigated the dissociative adsorption of H2O on K2CO3/TiO2.
Solid sorbents based CO₂ capture has become increasingly important. Great progress has been achieved with experimental studies in this area. However, the density functional theory based capture study on the function of H₂O in CO₂ capture is lacking. This research was designed to make progress in this important area with TiO₂-supported K₂CO₃ being an example. Due to its high cost-effectiveness, dry K₂CO₃ is a promising sorbent for capturing CO₂. Yet challenges remain in accelerating the rate of the absorption process. The study of mechanism of the effect of H₂O on CO₂ adsorption as well as the carbonation reaction can help select and design better support for the sorbent. Up to now, it is open. In this work, the adsorption and reaction of CO₂ over K₂CO₃ loaded on a rutile (1 1 0) surface have been studied using theoretical calculations. The results show that the CO₂ adsorption is increased when H₂O appears, and carbonation reaction mainly occurs at the interfaces of K₂CO₃/TiO₂ includes bicarbonate formation resulting from the reactions of CO₂ with OH via H₂O dissociation and CO₃ anion with transferred H via H₂O dissociation combining. In addition, H transfer step appears when support TiO₂ exists compared to that on pure K₂CO₃ sorbent. The kinetic modeling indicates that the H₂O dissociation may limit the carbonation reaction. Therefore, H₂O-dissociative or high OH coverage TiO₂ support material can assist CO₂ sorption with the solid K₂CO₃ based CO₂ capture technology. It is expected that the theoretical study sheds light on the preparation of cost-effective CO₂ sorbents in the future.
Photoemission studies of water dissociation on rutile TiO <inf>2</inf> (1 1 0): Aspects on experimental procedures and the influence of steps
2014, Applied Surface Science
Citation Excerpt :
Dissociation on stoichiometric TiO2 (1 1 0) has been a very controversial topic [17,18]. However, the most recent experimental and theoretical efforts are consistent in that the first water layer on a defect-free surface is partially dissociated [19–26]. Specifically, using surface-sensitive O 1s photoelectron spectra in conjunction with DFT calculations and Monte Carlo simulations we have proposed a mechanism for the OH and H2O speciation, which is found to vary with the coverage [22].
The composition of the first water layer on the stoichiometric rutile TiO₂ (1 1 0) surface was studied with the use of synchrotron radiation photoelectron spectroscopy. The same H₂O–OH balance was reached using different preparation procedures and there was no difference between H₂O and D₂O. On this basis, we rule out the possibility that the partially dissociated layer is an artifact caused by photon irradiation during measurements. Pre-deposition of Au at room temperature, primarily decorating step edges [e.g. S.A. Tenney et al. J. Phys. Chem. C 115 (2011) 11112] decreases the water uptake but does not change the relative amount that dissociates. This implies that the observed H₂O–OH balance is not controlled by dissociation at steps and subsequent out-diffusion of hydrogens on the terraces. That is, the formation of a partially dissociated water layer is an inherent property of stoichiometric terraces.
Competing water dissociation channels on rutile TiO<inf>2</inf>(110)
2014, Surface Science
Citation Excerpt :
Very recently, it was also shown that the r-TiO2 surface presents oxygen vacancies at steps that are active towards water dissociation [8]. The adsorption state of water on the defect-free stoichiometric TiO2(110) surface (s-TiO2) has been much more controversial [1–4,9–17]. On the perfect surface, dissociation occurs through H2O adsorption on a Ti ion followed by proton donation to a neighboring Obr ion.
The interplay between two different water dissociation channels on rutile TiO₂(110) was studied with the use of synchrotron radiation photoelectron spectroscopy. It was found that water dissociation at oxygen vacancies competes with water dissociation on defect-free regions such that one vacancy assisted dissociation event cancels one dissociation event on defect-free regions. The quenching affects the thermally most stable dissociated species that form at low coverage on the defect free surface but does not affect the stability of molecular water. As a result, molecular adsorption becomes favored at low coverage on a surface where all vacancies have been hydroxylated. The presence of competitive dissociation channels rationalizes the difficulties in identifying dissociated species on defect-free regions in previous studies.
First-principles molecular dynamics simulations of uranyl ion interaction at the water/rutile TiO <inf>2</inf>(110) interface
2012, Surface Science
Citation Excerpt :
The surface area was set to 2a √ 2 × 4c = 156.24 Å2 which corresponds to eight elementary surface areas of a √ 2 × c = 19.53 Å2 containing each one fivefold – Ti(5) and one sixfold – Ti(6) coordinated titanium atoms with surface Os and bridging Ob oxygen atoms (Fig. 1a). The bulk parameters were calculated according to a DFT static study of Perron et al. [44] with a = b = 4.65 Å (4.59 Å), c = 2.97 Å (2.95 Å), internal parameter x = 0.30 (0.30) and c/a = 0.64 (0.64) (in parentheses are experimental values from [45–47]). According to a vacuum thickness of 21 Å between slabs, the liquid phase was represented with 111 water molecules with water density close to 1 g.cc− 1.
The effects of temperature and solvation on uranyl ion adsorption at the water/rutile TiO₂(110) interface are investigated by Density Functional Theory (DFT) in both static and Born–Oppenheimer molecular dynamics approaches. According to experimental observations, uranyl ion can form two surface complexes in a pH range from 1.5 to 4.5. Based on these observations, the structures of the complexes at 293 K are first calculated in agreement with vacuum static calculations. Then, an increase in temperature (293 to 425 K) induces the reinforcement of uranyl ion adsorption due to the release of water molecules from the solvation shell of uranyl ion. Finally, temperature can modify the nature of the surface species.
Water adsorption on rutile titanium dioxide (110): Theoretical study of the effect of surface oxygen vacancies and water flux in the steady state case
2023, Revista Mexicana de Fisica

View all citing articles on Scopus

View full text

Investigation of hydrogen bonds and temperature effects on the water monolayer adsorption on rutile TiO2 (110) by first-principles molecular dynamics simulations

Abstract

Research highlights

Introduction

Section snippets

Computational background

Slab thickness effect

Conclusion

Acknowledgements

Phys. Lett. A

Curr. Opin. Solid State Mater. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci. Rep.

Surf. Sci.

J. Mol. Struct.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Chem. Phys. Lett.

Surf. Sci.

Surf. Sci.

J. Chem. Phys.

J. Electrochem. Soc.

J. Phys. Chem. B

Phys. Rev. Lett.

Langmuir

J. Phys. Chem.

Investigation of hydrogen bonds and temperature effects on the water monolayer adsorption on rutile TiO₂ (110) by first-principles molecular dynamics simulations