title: Characterization of photocatalytic TiO2powder under varied environments using near ambient pressure X-ray photoelectron spectroscopy.
abstract: Consecutive eight study phases under the successive presence and absence of UV irradiation, water vapor, and oxygen were conducted to characterize surface changes in the photocatalytic TiO2powder using near-ambient-pressure X-ray photoelectron spectroscopy (XPS). Both Ti 2p and O 1s spectra show hysteresis through the experimental course. Under all the study environments, the bridging hydroxyl (OHbr) and terminal hydroxyl (OHt) are identified at 1.1-1.3 eV and 2.1-2.3 eV above lattice oxygen, respectively. This enables novel and complementary approach to characterize reactivity of TiO2powder. The dynamic behavior of surface-bound water molecules under each study environment is identified, while maintaining a constant distance of 1.3 eV from the position of water vapor. In the dark, the continual supply of both water vapor and oxygen is the key factor retaining the activated state of the TiO2powder for a time period. Two new surface peaks at 1.7-1.8 and 4.0-4.2 eV above lattice oxygen are designated as peroxides (OOH/H2O2) and H2O2dissolved in water, respectively. The persistent peroxides on the powder further explain previously observed prolonged oxidation capability of TiO2powder without light irradiation.
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119260, Singapore.
authors.forename: Padmaja
authors.initials: P
authors.lastname: Krishnan
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119260, Singapore.
authors.forename: Minghui
authors.initials: M
authors.lastname: Liu
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Itty
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119260, Singapore.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Rheinheimer
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119260, Singapore.
authors.forename: Min-Hong
authors.initials: MH
authors.lastname: Zhang
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Paulo J M
authors.initials: PJ
authors.lastname: Monteiro
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119260, Singapore.
authors.forename: Liya E
authors.initials: LE
authors.lastname: Yu