Effect of iron on photocatalytic properties of titanium dioxide

Technological advancements and population growth are placing enhanced stress on global energy resources. At the same time, the increasingly apparent negative effects of climate change indicate the need to generate clean energy, such as solar energy. This thesis is an attempt in making a contribution towards the development of materials for solar energy conversion. The present technology of solar devices is focused on silicon-based solar cells. Awareness is growing, however, that titanium dioxide, TiO2, is a promising candidate as a raw material for processing a new generation of solar materials that can be applied for solar-to-chemical energy conversion. The pioneering work of Fujishima and Honda [1] indicates that TiO2 may be used as photo-electrode for the generation of hydrogen fuel by water oxidation. The report of Fujishima and Honda resulted in intensive studies on processing TiO2 with enhanced performance in solar energy conversion. TiO2 exhibits an outstanding stability in water and, at the same time, strong reactivity with water upon UV irradiation leading to its oxidation. The main shortcoming of TiO2 for sunlight absorption is its relatively large band gap, which is 3.0 eV and 3.2 eV for rutile and anatase, respectively, while the maximum efficiency of solar energy conversion can be achieved at 1.5 eV. Therefore, the most commonly reported research aims at reduction of the band gap of TiO2 by incorporation of extrinsic ions The recent progress in photocatalysis indicates that the efficiency of solar-to chemical energy conversion by TiO2-based semiconductors is determined by a range of key performance-related properties (KPPs), including the concentration of surface active sites, Fermi level, charge transport, and charge transfer, in addition to the band gap [4, 5]. All these KPPs are defect-related. Therefore, processing the TiO2-based photocatalysts with enhanced performance imposes the need to better understand the effect of defect disorder on the reactivity of TiO2 and its solid solutions with water. When considering the effect of extrinsic ions on properties of TiO2, it is important to realize that the surface composition, which is mainly responsible for photocatalytic activity, is entirely different from that of the bulk phase as a result of segregation [6]. Recognition of this effect imposes the need to understand the effect of segregation on surface vs. bulk composition of TiO2-based solid solutions. The present work aims at understanding the effect of extrinsic ions, specifically iron ions, on electronic structure, surface vs. bulk composition, and photocatalytic activity of TiO2