Photocatalysis has recently become a common word and various products using photocatalytic functions have been commercialized. Among many candidates for photocatalysts, TiO2 is almost the only material suitable for industrial use at present and also probably in the future. This is because TiO2 has the most efficient photoactivity, the highest stability and the lowest cost. More significantly, it has been used as a white pigment from ancient times, and thus, its safety to humans and the environment is guaranteed by history. There are two types of photochemical reaction proceeding on a TiO2 surface when irradiated with ultraviolet light. One includes the photo-induced redox reactions of adsorbed substances, and the other is the photo-induced hydrophilic conversion of TiO2 itself. The former type has been known since the early part of the 20th century, but the latter was found only at the end of the century. The combination of these two functions has opened up various novel applications of TiO2, particularly in the field of building materials. Here, we review the progress of the scientific research on TiO2 photocatalysis as well as its industrial applications, and describe future prospects of this field mainly based on the present authors' work.

The oxidation power of the TiO2 - x N x powders with low nitrogen concentrations (<0.02) was evaluated by the decomposition of gaseous 2-propanol (IPA) under the same absorbed photon number, 1.4 × 1014 quanta·cm-2·s-1, of visible (Vis) or ultraviolet (UV) light. Regardless of the x value, the quantum yield values from irradiating with Vis light was lower than with UV light, which suggests that the isolated narrow band formed above the valence band is responsible for the Vis light response in the present nitrogen doped TiO2. In addition, increasing the nitrogen concentration when irradiating with UV light lowered the quantum yields, indicating that the doping sites could also serve as recombination sites.

Introduction 9824 2. Materials Design for Visible-Light-Sensitive Photocatalyst 9825 2.1. Electronic Structure of TiO 2 9825 2.2. Photoelectrochemistry of TiO 2 and Conditions for Visible-Light Sensitization 9826 2.3. Metal Doping of TiO 2 9827 2.4. Design of Nonmetal Doping for Visible-Sensitization 9828 3. Synthesis and Properties of N-Doped TiO 2 9830 3.1. Synthesis 9830 3.1.1. Powder 9830 3.

Carbon-doped TiO2 powders in an anatase phase colored yellow were fabricated by oxidative annealing of TiC. Carbons were located at oxygen sites. The carbon substitution caused the absorbance edge of TiO2 to be shifted to the higher wavelength region. Carbon-doped TiO2 showed photocatalytic activities for the decomposition of IPA to CO2 via acetone under visible light (400–530 nm) irradiation.

We investigated the role of Cu(II) ions and their associated structural features, such as chemical state and environment, in the Cu(II)-grafted TiO2 photocatalyst by means of 2-propanol oxidative decomposition under visible light and X-ray absorption fine structure (XAFS) measurements. The 2-propanol decomposition activity under visible light (1 mW cm−2, 450−580 nm) was highly reproducible (three repetitions). The XAFS results indicated that the Cu(II) is incorporated in a distorted amorphous CuO-like structure, having a five-coordinated square pyramidal form. The distorted CuO formed clusters and attached to the TiO2 surface. The chemical state and environment of the Cu(II) ions were not changed, even after the photocatalytic oxidative reaction. Thus, Cu(II)-grafted TiO2 can be regarded as a stable photocatalyst. In addition, in situ XAFS measurements were performed under visible light in the presence of 2-propanol and absence of oxygen. Under these conditions, Cu(I) was generated. However, the latter converted back to Cu(II) when it was exposed to oxygen, indicating the oxygen reduction activity of Cu(I).