Characterization of the Active Surface Species Responsible for UV-Induced Desorption of O2 from the Rutile TiO2(110) Surface

• Published in: Journal of physical chemistry. C 2013-03, Vol.117 (11), p.5774-5784
• Main Authors: Henderson, Michael A, Shen, Mingmin, Wang, Zhi-Tao, Lyubinetsky, Igor
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; Impact phenomena (including electron spectra and sputtering); Photon- and electron-stimulated desorption; Physics
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp312161y

We have examined the chemical and photochemical properties of molecular oxygen on the (110) surface of rutile TiO2 at 100 K using electron energy loss spectroscopy (EELS), photon stimulated desorption (PSD), and scanning tunneling microscopy (STM). Oxygen chemisorbs on the TiO2(110) surface at 100 K through charge transfer from surface Ti3+ sites. The charge-transfer process is evident in EELS by a decrease in the intensity of the Ti3+ d-to-d transition at ∼0.9 eV and formation of a new loss at ∼2.8 eV. On the basis of comparisons with the available homogeneous and heterogeneous literature for complexed/adsorbed O2, the species responsible for the 2.8 eV peak can be assigned to a surface peroxo (O2 2–) state of O2. This species was identified as the active form of adsorbed O2 on TiO2(110) for PSD. The adsorption site of this peroxo species was assigned to that of a regular five-coordinated Ti4+ (Ti5c) site based on comparisons between the UV exposure-dependent behavior of O2 in STM, PSD, and EELS data. Assignment of the active form of adsorbed O2 to a peroxo species at normal Ti5c sites necessitates reevaluation of the simple mechanism in which a single valence band hole neutralizes a singly charged O2 species (superoxo or O2 –), leading to desorption of O2 from a physisorbed potential energy surface.