- Xihan Chen,听Stephanie N. Choing, Daniel J. Aschaffenburg,听C. D. Pemmaraju,听David Prendergast, and听Tanja Cuk听
- J. Am. Chem. Soc.,听2017,听139听(5), pp 1830鈥�1841.听顿翱滨:听10.1021/jacs.6b09550. Download
The initial step of photocatalytic water oxidation reaction at the metal oxide/aqueous interface involves intermediates formed by trapping photogenerated, valence band holes on different reactive sites of the oxide surface. In SrTiO3,听these one-electron intermediates are radicals located in Ti鈥揙鈥�听(oxyl) and Ti鈥揙鈥�鈥揟i (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 卤 0.2 ps, which is identical to the time to populate the surface with titanium oxyl (Ti鈥揙鈥�) radicals. The oxyl was separately observed by a subsurface vibration near 800 cm鈥�1听from Ti鈥揙 located in the plane right below Ti鈥揙鈥�. Second, 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 卤 10 ps with a yet undetermined structure. As would be expected, the radicals鈥� decay, specifically probed by the oxyl鈥檚 subsurface vibration, parallels that of the photocurrent. Our results led us to propose a nonadiabatic kinetic mechanism for generating radicals of the type Ti鈥揙鈥�听and Ti鈥揙鈥�鈥揟i from valence band holes based on their solvation at aqueous interfaces.