Comparing Quasiparticle H<sub>2</sub>O Level Alignment on Anatase and Rutile TiO<sub>2</sub>

ACS Catalysis 5, 4242 - 4254 (2015)

Comparing Quasiparticle H2O Level Alignment on Anatase and Rutile TiO2

Huijuan Sun, Duncan J. Mowbray, Annapaola Migani, Jin Zhao, Hrvoje Petek, Angel Rubio

Knowledge of the molecular frontier levels' alignment in the ground state can be used to predict the photocatalytic activity of an interface. The position of the adsorbate's highest occupied molecular orbital (HOMO) levels relative to the substrate's valence band maximum (VBM) in the interface describes the favorability of photogenerated hole transfer from the VBM to the adsorbed molecule. This is a key quantity for assessing and comparing H2O photooxidation activities on two prototypical photocatalytic TiO2 surfaces: anatase (A)-TiO2(101) and rutile (R)-TiO2(110). Using the projected density of states (DOS) from state-of-the-art quasiparticle QP G0W0 calculations, we assess the relative photocatalytic activity of intact and dissociated H2O on coordinately unsaturated (Ticus) sites of idealized stoichiometric (A-TiO2(101)/R-TiO2(110)) and bridging O vacancies (Obrvac) of defective (A-TiO2-x(101)/R-TiO2-x(110)) surfaces (x=1/4,1/8) for various coverages. Such a many-body treatment is necessary to correctly describe the anisotropic screening of electron-electron interactions at a photocatalytic interface. Our results suggest that (1) hole trapping is more favored on A-TiO2(101) than R-TiO2(110) and (2) HO@Ticus is more photocatalytically active than intact H2O@Ticus. The more favorable ground state HOMO level alignment for A-TiO2(101) may explain why the anatase polymorph shows higher photocatalytic activies than the rutile polymorph.

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