Oxygen Photochemistry on TiO₂(110): Recyclable, Photoactive Oxygen Produced by Annealing Adsorbed O₂

Abstract

The photochemistry of oxygen adsorbed on TiO2(110) at 30 K and annealed up to 600 K is investigated. UV irradiation results in exchange of atoms between chemisorbed and physisorbed oxygen. Annealing chemisorbed oxygen to 350 K maximizes these exchange reactions, while such reactions are not observed for oxygen that is dissociatively adsorbed on TiO2(110) at 300 K. For oxygen annealed to 350 K, the exchange products photodesorb in the plane perpendicular to the bridge-bonded oxygen rows at an angle of 45°. In contrast, chemisorbed O2 photodesorbs normal to the surface. Remarkably, the chemisorbed species is stable under multiple cycles of UV irradiation. Atoms in the chemisorbed species can be changed from 18O to 16O and then back to 18O via the exchange reactions. The results show that annealing oxygen on TiO2(110) to ∼350 K produces a stable chemical species with novel photochemical properties. Possible forms for the photoactive species include O2 adsorbed in a bridging oxygen vacancy or tetraoxygen.