Photocatalysis of Dye-Sensitized TiO2 Nanoparticles with Thin Overcoat of Al2O3: Enhanced Activity for H2 Production and Dechlorination of CCl4

Dye-sensitized TiO2 nanoparticles that were loaded simultaneously with Pt and Al2O3 overlayer (Al2O3/TiO2/Pt) were synthesized and investigated for photocatalytic activity under visible light. Introducing a thin AI,03 overlayer (similar to 1 nm thick) on dye-sensitized TiO2 markedly enhanced the visible light activities for the production of hydrogen (in the presence of EDTA as an electron donor) and the dechlorination Of CCl4. The Al2O3/TiO2/Pt powder was characterized by HRTEM, EDX, and XPS. In agreement with the photocatalytic activity data, the photocurrent collected via electron shuttles on a Pt electrode immersed in an aqueous photocatalyst suspension under visible light was also enhanced in the presence of an Al2O3 overlayer, which indicates ail enhanced interfacial electron transfer despite the presence of an insulating surface layer. The initial H, and chloride generation rate increased from 0.4 and 5 mu M min(-1) on TiO2/Pt to 0.9 and 7.5 mu M min(-1) on Al2O3/TiO2/Pt, respectively. The visible light activity of the sensitized photocatalytic reactions highly depended on the thickness of the alumina layer and was optimized at a low level of Al loading (Al/Ti atom ratio similar to 0.01), above which the activity was markedly reduced with thickening of the layer. It is suggested that the alumina layer retards the charge recombination between the electron injected from the excited dye and the oxidized dye. The slower charge recombination in the presence of an alumina overlayer was confirmed by time-resolved diffuse reflectance (TDR) spectroscopy.