Preparation, Characterization, and Reactivities of Highly Functional Titanium Oxide-Based Photocatalysts Able to Operate under UV–Visible Light Irradiation: Approaches in Realizing High Efficiency in the Use of Visible Light

Abstract

A review of the research advances made in the design and development of highly reactive and functional titanium oxide photocatalysts, which can utilize not only UV but also visible or solar light, and a clarification of the active sites as well as the detection of the reaction intermediates at the molecular level have been presented here. The potential for the effective utilization and conversion of solar energy into useful and safe chemical energy by the modification of the electronic properties of such TiO2 photocatalysts is great when one considers their myriad applications as well as their non-polluting qualities. Such a modification process by methods such as ion-implantation can be applied not only for semiconducting bulk TiO2 photocatalysts but also for TiO2 thin film photocatalysts and titanium oxide photocatalysts highly dispersed within zeolite frameworks. Moreover, the photocatalytic reactivity of semiconducting TiO2 nano-powders was found to be dramatically enhanced by the loading of small amounts of Pt. This worked to enhance the reduction reaction, resulting in the charge separation of the electrons and holes generated by light irradiation. In addition, highly dispersed titanium oxide species prepared within zeolite frameworks as well as SiO2 or Al2O3 matrices showed much higher and unique photocatalytic performances as compared to semiconducting bulk TiO2 photocatalysts. Significantly, a new alternative method to directly prepare such visible light-responsive TiO2 thin film photocatalysts on various substrates has been successfully developed by applying a RF magnetron sputtering deposition method.