Adsorption of organic molecules at the TiO2(110) surface: The effect of van der Waals interactions

Abstract

Abstract. Understanding the interaction of organic molecules with TiO 2 surfaces is important for a wide range of technological applications. While density functional theory (DFT) calculations can provide valuable insight about these interactions, traditional DFT approaches with local exchangecorrelation functionals suffer from a poor description of non-bonding van der Waals (vdW) interactions. We examine here the contribution of vdW forces to the interaction of small organic molecules (methane, methanol, formic acid and glycine) with the TiO 2 (110) surface, based on DFT calculations with the optB88-vdW functional, which incorporate non-local correlation. The adsorption geometries and energies at different configurations were also obtained in the standard generalized gradient approximation (GGA-PBE) for comparison. We find that the optB88-vdW consistently gives shorter surface adsorbate-to-surface distances and slightly stronger interactions than PBE for the weak (physisorbed) modes of adsorption. In the case of strongly adsorbed (chemisorbed) molecules both functionals give similar results for the adsorption geometries, and also similar values of the relative energies between different chemisorption modes for each molecule. In particular both functionals predict that dissociative adsorption is more favourable than molecular adsorption for methanol, formic acid and glycine, in general agreement with experiment. The dissociation energies obtained from both functionals are also very similar, indicating that vdW interactions do not affect the thermodynamics of surface deprotonation. However, the optB88-vdW always predicts stronger adsorption than PBE. The comparison of the methanol adsorption energies with values obtained from a Redhead analysis of temperature programmed desorption data suggests that optB88-vdW significantly overestimates the adsorption strength, although we warn about the uncertainties involved in such comparisons.

Adsorption of Methyl Acetoacetate at Ni{111}: Experiment and Theory

“…Only the two uppermost Ni layers were fully relaxed, while the two bottom layers were fixed in the bulk positions; this procedure is often found to accelerate the convergence of calculated surface properties with respect to the thickness of the simulation slab. 34,35 The positions of the MAA molecule were also allowed to fully relax. In order to compensate for the use of an asymmetric slab, all simulations included a dipole correction as implemented in VASP, based on a method proposed by Makov and Payne.…”

Adsorption and oxidation of oxalic acid on anatase TiO2 (001) surface: A density functional theory study

“…However, the effect of van der Waals interactions can be positive or negative based on the results using current methods [38]. It has been demonstrated that the consideration of vdW interaction with some semi-empirical methods may overestimate the adsorption energies of organic species on surfaces of ionic crystals [39]. To solve this problem, a new Tkatchenko-Scheffler (TS) method based on the atoms-in-molecules (AIM) approach has been developed recently, which has been demonstrated to lead to accurate results for many molecular and solid systems [40].…”

Insights into the adsorption of organic molecules on rutile TiO2 (1 1 0) surface: A theoretical study

“…This surface structure contains the double-bonded and neighbor bridging oxygen atoms and five-fold and six-fold coordinated titanium (Ti 5f , Ti 6f ) atoms with in-plane threefold coordinated O atoms as shown in figure 1. [5,11] The simulated surface in this work is set up at 3 x 2 x 4 supercell with a = 13.24 Å; b = 9.10 Å; c = 25.00 Å. The automatically generated Γcenter k-points grids are used for all of surfacerelated calculations after convergence testing.…”

“…[3] Further, the rutile (1 1 0) face is the most stable surface of rutile phase and commonly studied in surface science. [3][4][5] In recent years, the elementary surface reactions on TiO 2 surfaces have increasingly been investigated but the origin and role of interactions have not been understood clearly. [2,10] Furthermore, this surface has become the prototype for single crystal investigations of photo-induced molecular reactions and adsorbate-surface interactions on TiO 2 .…”

“…[9,10] Recent theoretical results for example indicate that the interactions occurred between the prototype adhesion proteins on bone-cell's surfaces and the oxide layer at the surface of the metal implant is controlled by the strength of the molecular interactions, especially for TiO 2 surface. [5,9,10] Therefore, to have a better control on what really happens, understanding of the surfaceabsorbate interaction at molecular level is crucial. The current understanding of the interactions of organic molecules with TiO 2 -rutile surfaces was summarized in a recent report by Thomas and Syres.…”