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

• Published in: Langmuir Vol. 35; no. 16; pp. 5455 - 5462
• Main Authors: Shiraishi, Yasuhiro, Imai, Jun, Yasumoto, Naoki, Sakamoto, Hirokatsu, Tanaka, Shunsuke, Ichikawa, Satoshi, Hirai, Takayuki
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23-04-2019
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.8b04075

Au nanoparticles loaded on semiconductor TiO2 absorb visible light due to their surface plasmon resonance (SPR) and inject the photogenerated hot electrons (ehot –) 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 ehot – 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 ehot – injection. Efficiency of the ehot – injection depends on the amount of Nb5+ doped. Loading small amounts of Nb5+ (∼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 ehot – generation on the Au particles and decreases the activity of plasmonic photocatalysis.