Photodesorption of H₂O from Anatase-TiO₂(101): A Combined Quantum Chemical and Quantum Dynamical Study

Abstract

A theoretical study to clarify the photodesorption process of water on anatase-TiO 2 (101) was pursued in this study using a combined approach based on quantum chemical calculations and quantum dynamical simulations assisted by machine learning of artificial neural networks. First, an embedded cluster model was used to assess three-dimensional potential energy surfaces of ground and excited state of molecular water adsorption. The excited state addressed herein consists of a photogenerated hole which oxidizes the adsorbed water molecule. Next, the approximately 23 000 data points for each surface were fitted using artificial neural networks to generate a dense grid of the data. These fits are a prerequisite for our subsequent quantum dynamical simulations based on the propagation of wavepackets. Eventually, the photodesorption process of water on anatase-TiO 2 (101) was found to consist of a multidimensional mechanism involving a lateral translation of the water molecule toward the bridging oxygen row. Upon relaxation to the ground state, the maximum possible photodesorption probability of 85% was calculated through analyzing specific resonance lifetimes of the chargetransfer state. By comparison with experimental velocity distributions, long resonance lifetimes of over 60 fs can be ascribed to the studied system. Moreover, temperature effects by studying the population of vibronically excited states were included, which turned out to play a minor role in the photodesorption process.

Quantum Chemical Investigation of Photocatalytical Sulfoxidation of Hydrocarbons on TiO2

“…In total, six characteristic atomic sites appear for both structures. Titanium is present in two coordinated states: the six-coordinated 6f-Ti (6f = six-folded), which is less relevant for adsorption, and the five-coordinated 5f-Ti (5f = five-folded), which serves as an adsorption center for many molecules such as H 2 O due to its unsaturated coordination. , For oxygen, four relevant atomic positions need to be considered: on the direct surface, the bridging oxygens br-O (br = bridge), which are also important in several adsorption processes, and the pl-O (pl = plane) atoms which are situated in the 5f-Ti plane. The lower-lying oxygen atoms us1-O and us2-O (us = under surface) play an important role in terms of defects and doping. , A widely used approach to compute these surfaces with periodic boundary conditions is to cut the bulk structure along the plane specified by Miller indices and using multiple layers (1 layer = 6 atoms [Ti 2 O 4 ] for anatase and rutile) to generate a stoichiometric surface with enough atoms so that the surface energy converges (slab model). , For this purpose, only the first layers of the surface are relaxed in a geometry optimization process, and the lower-lying layers are frozen to simulate the underlying bulk structure.…”

“…Titanium is present in two coordinated states: the six-coordinated 6f-Ti (6f = six-folded), which is less relevant for adsorption, and the five-coordinated 5f-Ti (5f = fivefolded), which serves as an adsorption center for many molecules such as H 2 O due to its unsaturated coordination. 26,27 For oxygen, four relevant atomic positions need to be considered: on the direct surface, the bridging oxygens br-O (br = bridge), which are also important in several adsorption processes, and the pl-O (pl = plane) atoms which are situated in the 5f-Ti plane. The lower-lying oxygen atoms us1-O and us2-O (us = under surface) play an important role in terms of defects and doping.…”

Understanding the prototype catalyst TiO2 surface with the help of density functional theory calculation

“…Petersen et al have investigated the photodesorption process of water on anatase TiO 2 (101) in detail. 154 An embedded cluster model was used to assess the potential energy surfaces of the ground and excited state. Each surface was then fitted using artificial neural networks and used for subsequent quantum dynamical simulations based on the propagation of wavepackets.…”

Adiabatic models for the quantum dynamics of surface scattering with lattice effects

“…Over recent decades, reaction (77) has been studied widely but more attention has still been paid by researchers across disciplines to the photo-dissociation on the TiO 2 surfaces. [240][241][242][243][244][245][246][247][248][249][250][251][252][253][254][255][256][257] It was found [253][254][255] that TiO 2 has the ability to use both as a catalyst and photo-catalyst and thus has a wide range of applications as purifications of water and air, selfcleaning glass, anti-fogging, solar cells, and so forth, while water is often present as a critical reactant or an unavoidable contamination in these applications.…”