Tuesday, November 10, 2015: 1:30 PM
355A (Salt Palace Convention Center)
Titanium dioxide TiO2 is a benchmark photocatalyst which, however, suffers from a low activity under near-UV and visible light. TiO2 is not very effective in the photocatalytic water reduction, since electrochemical potential of its conduction band minimum (CBM) is only slightly more negative than the potential of water reduction half-reaction. Certain alkaline earth titanates MTiO3 (M=Ca, Sr) feature the more negative potentials of the CBM vs. that in TiO2, while their band gaps are about the same. Plasmonic photocatalysis utilizes the phenomenon of surface plasmon resonance (SPR) in supported metal nanoparticles (NPs) for “sensitization” of semiconductors towards near-UV/visible light. We prepared nanocrystalline and mesoporous perovskites MTiO3 (M=Ca, Sr) and characterized them by the BET, XRD, UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS), ATR-FTIR, Raman spectroscopy, and TEM. Then, we prepared composite photocatalysts Ag/MTiO3 (M=Ca, Sr) by the in-situ deposition, and characterized them by UV-Vis DRS, X-ray fluorescence, and photoluminescence (PL) spectroscopy. The UV-Vis DRS show optical absorption due to the SPR in supported silver NPs. We have tested Ag/MTiO3 in hydrogen generation from water with and without organic sacrificial donor under near-UV/visible light. Activity of Ag/MTiO3 was optimized against experimental conditions, and it follows a bell shape vs. amount of noble metal at 0.1-10 %. Composite photocatalysts Ag/MTiO3 are more active in hydrogen generation than the respective MTiO3 under UV/visible light (λ>254 nm), near-UV light (λ>365 nm), and visible light (λ>400 nm); an enhancement of hydrogen generation rate is >4-fold, up to 340 μmol/g*h. Further, we have utilized defect states in perovskites as intrinsic spectroscopic probe, in order to determine the direction of the photoinduced charge transfer in the Ag/MTiO3 photocatalysts. As shown by the front-face photoluminescence spectroscopy (FF-PL), under photoexcitation of MTiO3 with near-UV light, electron transfer proceeds to supported metal; work is in progress to determine the direction of charge transfer under visible light. Acknowledgments: A.S. thanks Research Corporation for Science Advancement (RCSA) for his Cottrell College Science grant, and Rutgers University for his Research Council Award.