Enhancing the Utilization of Visible-Light by Controlling the Electronic and Photonic Band Structures of TiO2-based Materials

Abstract

As industrial development is on going everyday, and the associated research is required for the development of mew materials to be applied for energy or environmental areas. TiO2 is main candidates as photocalyst, photoelectrode materials due to its noticible photostability, low cost and nontoxicity. However, challenging point is still existed for employing TiO2 on practical photocatalytic applications. TiO2 has wide bandgap (3.2 eV for anatase and 3.0 eV for rutile), which can activate under only within ultraviolet light region. This thesis deals with the engineering the energy band strcutrue of TiO2 for absorbing the visible light region and how mateirals are applied to environment and energy areas. <br/> Environmental applications of heterogeneous photocatalysis have been considered among the most effective methods for elimination of many hazardous organic pollutants. Interfacial energy band bending of heterogeneous photocatalyst facilitate the charge transfer, leads to high photocatalytic performance. The modulation the Fermi level of metal change the electric field of photocatalyst without any electron mediator. The amount and rate of whole charge transfer were directly validated to the photocatalytic performance in the acetaldehyde photooxidation reaction. <br/> Photonic nanostructures are currently attracting considerable atteintions due to their property, guiding the light. Structural color has an origin in geometric structures, which differ from the most common color generation associated with the use of pigments or dyes. The hierarchical TiO2 nanobowl arrays were fabricated by a two-step anodization process where the nanobowl structure brought about two different reflection peaks from its flat bottom and inclined plane. The positions of the two reflection peaks as well as their wavelength gap were simply adjusted by changing the diameter of TiO2 nanobowls that depended on the anodizing potential. The reflected wavelength gradually increased with changing the periodicity of the TiO2 nanobowl, as expected from Bragg diffraction theory. This method enabled us to create a broad color distribution with a high contrast and brightness without employing complicated color generation. Combined light trapping in photonic structure and hot electron formation of noble metal provide the design strategy for the visible light responsive photoelectrochemical water splitting.<br/>