Charge Separation on Titanium Dioxide Nanocrystals

The fervent search for alternative and renewable energy sources on one hand and the catalytic treatment of hazardous wastes and contaminations in groundwater and air, on the other, are two prominent incentives for current research and addressed by the photo-electrochemisty and photocatalysis on titanium dioxide TiO2 materials, respectively. Conventional TiO2 electrodes can be used for the photogeneration of electricity and for electrolytic cells for hydrogen production. A variety of different TiO2 coatings are employed for photocatalytic applications. In this context, the morphology and texture of the respective TiO2 surfaces is of particular interest, since the surface mediated recombination of photogenerated charge carriers is a major limitation for all photochemical applications. However, little is known about the nature and location of sites which are capable of charge trapping and those which mediate charge carrier recombination. The present research project aims at the identification of certain surface structures as trapping sites as well as detrimental recombination centers for photogenerated charges. For this purpose uniformly sized anatase nanocrystals with well-defined facets and a controlled degree of surface corrugation will be synthesized by advanced wet chemical techniques. The most characteristic candidates will be selected by high resolution transmission electron microscopy and subjected to studies which focus on light-induced charge separation in the semiconducting nanocrystal. Charge trapping associated with localized states will be investigated by dynamic electron paramagnetic resonance measurements and the presence of delocalized conduction band electrons will be monitored by infrared absorption spectroscopy. The characterization of photoluminescence properties, i.e. the radiative recombination of photogenerated charges, will be included and repective results related to charge trapping effects. In this regard, the proposed project combines for the first time the synthesis of shape-controlled TiO2 nanocrystals with spectroscopy studies directed to the explanation of the photocatalyst`s surface reactivity. Only the detailed understanding of how morphology and surface structure of the TiO2 particles affect charge separation and interfacial charge transfer processes, will provide a base for the engineering of nanostructured surfaces with enhanced photochemical efficiencies.

The fervent search for alternative and renewable energy sources on one hand and the catalytic treatment of hazardous wastes and contaminations in groundwater and air, on the other, are two prominent incentives for current research and addressed by the photo-electrochemisty and photocatalysis on titanium dioxide TiO2 materials, respectively. Conventional TiO2 electrodes can be used for the photogeneration of electricity and for electrolytic cells for hydrogen production. A variety of different TiO2 coatings are employed for photocatalytic applications. In this context, the morphology and texture of the respective TiO2 surfaces is of particular interest, since the surface mediated recombination of photogenerated charge carriers is a major limitation for all photochemical applications. However, little is known about the nature and location of sites which are capable of charge trapping and those which mediate charge carrier recombination. The present research project aims at the identification of certain surface structures as trapping sites as well as detrimental recombination centers for photogenerated charges. For this purpose uniformly sized anatase nanocrystals with well-defined facets and a controlled degree of surface corrugation will be synthesized by advanced wet chemical techniques. The most characteristic candidates will be selected by high resolution transmission electron microscopy and subjected to studies which focus on light-induced charge separation in the semiconducting nanocrystal. Charge trapping associated with localized states will be investigated by dynamic electron paramagnetic resonance measurements and the presence of delocalized conduction band electrons will be monitored by infrared absorption spectroscopy. The characterization of photoluminescence properties, i.e. the radiative recombination of photogenerated charges, will be included and repective results related to charge trapping effects. In this regard, the proposed project combines for the first time the synthesis of shape-controlled TiO2 nanocrystals with spectroscopy studies directed to the explanation of the photocatalyst`s surface reactivity. Only the detailed understanding of how morphology and surface structure of the TiO2 particles affect charge separation and interfacial charge transfer processes, will provide a base for the engineering of nanostructured surfaces with enhanced photochemical efficiencies.