Doping of Nb5+ Species at the Au-TiO2 Interface for Plasmonic Photocatalysis Enhancement

Au nanoparticles loaded on semiconductor TiO2 absorb visible light due to their surface plasmon resonance (SPR) and inject the photogenerated hot electrons (e(hot)(-)) into the conduction band of TiO2. The separated charges promote oxidation and reduction reactions. The step that determines the rate of the plasmonic photocatalysis on the Au/TiO2 system is the e(hot)(-) injection through the Schottky barrier created at the Au-TiO2 interface. In the present work, niobium (Nb5+) oxide species were doped at the Au-TiO2 interface by loading Nb5+ onto the TiO2 surface followed by deposition of Au particles (2 wt % of TiO2). Visible light irradiation of the Au/Nb5+/TiO2 catalysts promotes aerobic oxidation of alcohols with much higher efficiency than that of undoped Au/TiO2. Lewis acidity of the Nb5+ species located at the interface cancels the negative charges of Au and creates a barrier with a narrower depletion layer, promoting tunneling e(hot)(-) injection. Efficiency of the e(hot)(-) injection depends on the amount of Nb5+ doped. Loading small amounts of Nb5+ (similar to 0.1 wt % of TiO2) creates mononuclear NbO4 species and shows large activity enhancement. In contrast, loading larger amounts of Nb5+ creates aggregated polynuclear Nb2O5 species. They decrease the electron density of Au particles and weaken their SPR absorption. This suppresses the e(hot)(-) generation on the Au particles and decreases the activity of plasmonic photocatalysis.