AbstractsBiology & Animal Science

Titanium dioxide has attracted tremendous research attentions for its excellent photoactivities with low cost, low toxicity, and long-term stability. Despite the advantages of TiO2, only UV light, which accounts for about 4% of the entire solar spectrum, can be used to directly drive the photovoltaic and photochemical effects for the wide band gap of the most common forms of TiO2 (3.0 eV for rutile and 3.2 eV for anatase). Significant efforts have been focused on the improvement of TiO2 photoactivities in visible region. In this thesis, plasmon-enhanced photocurrent generation and water oxidation on TiO2 photoelectrode in visible wavelength region was demonstrated. Two kinds of TiO2 crystalline structure, rutile and anatase, were used for the plasmon-enhanced photocurrent generation. Gold nanoislands with particle size of several tens of nanometer were employed for the TiO2 surface decoration, which enhanced the TiO2 photorespond in visible wavelength region due to the localized surface plasmon resonance. In order to fabricate Au nanoparticles on rutile TiO2 single crystal surface, a 3-nm Au thin film was sputtered on TiO2 surface and then annealed in vary atmosphere. For 800°C annealing, Au nanoislands (Au-NIs) with round shape (top view) were formed on TiO2 surface. The Au-NIs exhibited characteristic plasmon resonance band at around 600 nm. The photocurrent measurement showed Au-NIs decorated TiO2 exhibited an obvious photocurrent enhancement at the Au-NIs localized surface plasmon resonance band with 0.1 mol/dm3 KClO4 supporting electrolyte. Water oxidation was further confirmed on the Au-NIs/TiO2 electrode under the visible light irradiation. The photo-generated electron to oxygen yield was stoichiometrically to be 91.6%(Chapter 2). A further study of the electron transfer between Au-NIs and TiO2 was investigated: one is photoexcited electron transfer from Au-NIs to TiO2 and the other is charge transfer alternatively from TiO2 to Au-NIs by electrochemical control. For the photoexcited electron transfer from Au-NIs to TiO2, a crucial role was the contact between Au-NIs and TiO2 crystal surface, which was controlled by the annealing temperature during the Au-NIs fabrication process. The higher annealing temperature produced a tightly contact between the Au-NIs and the TiO2; the lower annealing temperature induced a several atomic defect layer between the Au-NIs and the TiO2 single crystal surface. The defect layer was further studied by high resolution TEM, which depicted that the defect layer was a reduced TiO2 layer. The surface defect layer suppressed theelectron transfer from the plasmon excited Au-NIs to TiO2 conduction band and/or decreased the hole trapping ability of the TiO2 surface states, and decreased the photocurrent conversion efficiency. For the charge transfer from TiO2 to Au-NIs by electrochemical control, Au-NIs plasmon band blue-shifted when electrons were trapped in Au-NIs. However, the red-shift of plasmon band of Au-NIs cannot be observed when electrons were transferred from Au-NIs to TiO2,…