Undoped and n-type doped TiO2 Anatase Surface Structures and Reactivity with Water.
EMSL Project ID
25626
Abstract
Of all the crystallographic forms of TiO2, anatase is technologically the most interesting. N-type doped TiO2 is useful for photocatalytic reactions, and in particular N-doped TiO2 has been successfully prepared by the PNNL group, which was chosen to enhance visible solar light absorption, and to promote H20 splitting to produce H2. In order to gain a better understanding of such TiO2 -based devices, it is important to obtain atomic-scale information on carefully prepared anatase surfaces. While there are currently hundreds of studies being reported on anatase, few have been devoted to structural determinations of the surface, and most of these are theoretical. There is presently little corresponding experimental data.A goal of the present studies is to determine the surface structure of thin-film anatase TiO2(001), a crystal morphology that as large crystals are necessary for this investigation, but not readily found and difficult to grow. In addition, surface structures of thin-film n-type doped anatase TiO2(001) will be determined. Thirdly, we will attempt to identify the fate of water molecules interacting with these varying surfaces. The overarching motivation for this work is that TiO2 nanocrystals, exhibiting the anatase structure, are commonly encountered in many applications (sensors, photocatalysis) where water or water vapor is frequently present.
The group, led by Scott Chambers at PNNL, has pioneered efforts to grow these films using oxygen plasmas assisted molecular beam epitaxy, and will be invaluable collaborators in the growth and structural studies at PNNL. In addition, Michael Henderson, well known for his extensive and thorough review of water-surface interactions, and extensive experiments at water/substrate interfaces, will collaborate on thermal desorption spectroscopy of water from the undoped TiO2, leading to a initial understanding of these water desorption conditions. (Due to limited time, this will be carried out only on the undoped films). Subsequent experiments at the UW-Milwaukee Low Energy Electron Diffraction-Infrared Laboratory for Oxide Studies will refine the structural parameters for the clean substrates, examine structures of water covered surfaces and identify whether or not water dissociates upon adsorption under controlled conditions. The series of undoped and doped TiO2 samples has been chosen to provide a predictable series of changing conditions to help elucidate how the n-type doping will have an impact on water/substrate reactivity.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-05-29
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members