Tunable Oxygen Activation for Catalytic Organic Oxidation: Schottky Junction versus Plasmonic Effects

The charge state of the Pd surface is a critical parameter in terms of the ability of Pd nanocrystals to activate O 2 to generate a species that behaves like singlet O 2 both chemically and physically. Motivated by this finding, we designed a metal–semiconductor hybrid system in which Pd nanocrystals enclosed by {100} facets are deposited on TiO 2 supports. Driven by the Schottky junction, the TiO 2 supports can provide electrons for metal catalysts under illumination by appropriate light. Further examination by ultrafast spectroscopy revealed that the plasmonics of Pd may force a large number of electrons to undergo reverse migration from Pd to the conduction band of TiO 2 under strong illumination, thus lowering the electron density of the Pd surface as a side effect. We were therefore able to rationally tailor the charge state of the metal surface and thus modulate the function of Pd nanocrystals in O 2 activation and organic oxidation reactions by simply altering the intensity of light shed on Pd–TiO 2 hybrid structures.