title: Evolution of anatase surface active sites probed by in situ sum-frequency phonon spectroscopy.
abstract: Surface active sites of crystals often govern their relevant surface chemistry, yet to monitor them in situ in real atmosphere remains a challenge. Using surface-specific sum-frequency spectroscopy, we identified the surface phonon mode associated with the active sites of undercoordinated titanium ions and conjoint oxygen vacancies, and used it to monitor them on anatase (TiO2) (101) under ambient conditions. In conjunction with theory, we determined related surface structure around the active sites and tracked the evolution of oxygen vacancies under ultraviolet irradiation. We further found that unlike in vacuum, the surface oxygen vacancies, which dominate the surface reactivity, are strongly regulated by ambient gas molecules, including methanol and water, as well as weakly associated species, such as nitrogen and hydrogen. The result revealed a rich interplay between prevailing ambient species and surface reactivity, which can be omnipresent in environmental and catalytic applications of titanium dioxides.
authors.affiliation: Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China.; Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Key Laboratory of Polar Materials and Devices (MOE), East China Normal University, Shanghai 200241, China.; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China.
authors.forename: Shiyou
authors.identifier: 0000-0002-4039-8549
authors.initials: S
authors.lastname: Chen
authors.affiliation: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Yadong
authors.initials: Y
authors.lastname: Li
authors.affiliation: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China.; Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Deheng
authors.identifier: 0000-0002-2604-7216
authors.initials: D
authors.lastname: Yang
authors.affiliation: Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China.; Physics Department, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Yuen Ron
authors.initials: YR
authors.lastname: Shen
authors.affiliation: Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China.; Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Wei-Tao
authors.identifier: 0000-0003-0566-671X
authors.initials: WT
authors.lastname: Liu
mesh_terms: D002384:Catalysis; D020134:Catalytic Domain; D006859:Hydrogen / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D060739:Phonons; D013057:Spectrum Analysis; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; C009495:titanium dioxide; D006859:Hydrogen; D014025:Titanium; D010100:Oxygen; D000432:Methanol
keywords: Anatase surface; in situ surface spectroscopy; sum-frequency phonon spectroscopy; surface active sites; surface oxygen vacancies; surface photochemistry