The Formation Time of Ti–O• and Ti–O•–Ti Radicals at the n-SrTiO3/Aqueous Interface during Photocatalytic Water Oxidation
- 20 December 2016
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 139 (5), 1830-1841
- https://doi.org/10.1021/jacs.6b09550
Abstract
The initial step of photo-catalytic water oxidation reaction at the metal oxide/aqueous interface involves intermediates formed by trapping photo-generated, valence band holes on different reactive sites of the oxide surface. In SrTiO3, these one-electron intermediates are radicals located in Ti-O• (oxyl) and Ti-O•-Ti (bridge) groups arranged perpendicular and parallel to the surface respectively, and form electronic states in the band gap of SrTiO3. Using an ultrafast sub band-gap probe of 400 nm and white light, we excited transitions between these radical states and the conduction band. By measuring the time evolution of surface reflectivity following the pump pulse of 266 nm light we determined an initial radical formation time of 1.3 ± 0.2 ps, which is identical to the time to populate the surface with titanium oxyl (Ti-O•) radicals. The oxyl is separately observed by a subsurface vibration near 800 cm-1 from Ti-O located in the plane right below Ti-O•. Secondly, a polarized transition optical dipole allows us to assign the 1.3 ps time constant to the production of both O-site radicals. After a 4.5 ps delay, another distinct surface species forms with a time constant of 36 ± 10 ps with a yet undetermined structure. As would be expected, the radicals’ decay, specifically probed by the oxyl’s subsurface vibration, parallels that of the photocurrent. Our results led us to propose a non-adiabatic kinetic mechanism for generating radicals of the type Ti-O• and Ti-O•-Ti from valence band holes based on their solvation at aqueous interfaces.Keywords
Funding Information
- Office of Science (DE-AC02-05CH11231, KC030102)
This publication has 51 references indexed in Scilit:
- Accuracy of exchange-correlation functionals and effect of solvation on the surface energy of copperPhysical Review B, 2013
- Charge carrier trapping, recombination and transfer in hematite (α-Fe2O3) water splitting photoanodesChemical Science, 2013
- Photocarrier recombination dynamics in highly excited SrTiO3 studied by transient absorption and photoluminescence spectroscopyApplied Physics Letters, 2009
- Photoluminescence and reversible photo-induced spectral change of SrTiO3Journal of Physics: Condensed Matter, 2005
- Local hydrogen bonding dynamics and collective reorganization in water: Ultrafast infrared spectroscopy of HOD/D2OThe Journal of Chemical Physics, 2005
- Watching Hydrogen Bonds Break: A Transient Absorption Study of WaterThe Journal of Physical Chemistry A, 2004
- Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U studyPhysical Review B, 1998
- Evidence for a surface dual hole-radical mechanism in the titanium dioxide photocatalytic oxidation of 2,4-D.Environmental Science & Technology, 1995
- Projector augmented-wave methodPhysical Review B, 1994
- Effects of the Helmholtz Layer Capacitance on the Potential Distribution at Semiconductor/Electrolyte Interface and the Linearity of the Mott-Schottky PlotJournal of the Electrochemical Society, 1983