title: Instability of hydrogenated TiO2.
abstract: Hydrogenated TiO2 (H-TiO2) is touted as a viable visible light photocatalyst. We report a systematic study on the thermal stability of H-implanted TiO2 using nuclear reaction analysis (NRA), Rutherford backscattering spectrometry, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy. Protons (40 keV) implanted at a ∼2 atom % level within a ∼120 nm wide profile of rutile TiO2(110) were situated ∼300 nm below the surface. NRA revealed that this H-profile broadened toward the surface after annealing at 373 K, dissipated out of the crystal into vacuum at 473 K, and was absent within the beam sampling depth (∼800 nm) at 523 K. Photoemission showed that the surface was reduced in concert with these changes. Similar anneals had no effect on pristine TiO2(110). The facile bulk diffusivity of H in rutile at low temperatures, as well as its interfacial activity toward reduction, significantly limits the utilization of H-TiO2 as a photocatalyst.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Manjula I
authors.initials: MI
authors.lastname: Nandasiri
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Vaithiyalingam
authors.initials: V
authors.lastname: Shutthanandan
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Manandhar
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Ashleigh M
authors.initials: AM
authors.lastname: Schwarz
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Lucas
authors.initials: L
authors.lastname: Oxenford
authors.affiliation: National Isotope Centre, GNS Science , Lower Hutt 5010, New Zealand.
authors.forename: John V
authors.initials: JV
authors.lastname: Kennedy
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , PO Box 999 MS K8-93, Richland, Washington 99352, United States.
authors.forename: Suntharampillai
authors.initials: S
authors.lastname: Thevuthasan
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory , PO Box 999 MS K8-87, Richland, Washington 99352, United States.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Henderson
keywords: TiO2(110); diffusion; hydrogen; implantation; rutile; surface reduction