Koyu Aoki

Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping

TiO2-based powder, including 0.1 at% of N doped in the rutile lattice, has been synthesized by oxidation of TiN. As a result, a significant shift of the absorption edge to a lower energy in the visible-light region has been observed. The substitutional doping of N into the TiO2 lattice is found to be effective; its 2p states contribute to the band-gap narrowing by mixing with O 2p as shown in ab initio electronic structure calculations.

Photodegradation of toluene over TiO2−xNx under visible light irradiation

We report the photooxidation of toluene over nitrogen doped TiO(2) (TiO(2-x)N(x)) under visible light irradiation. The photocatalytic oxidation of toluene in air over TiO(2-x)N(x) powders was studied using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), gas chromatography (GC), ion chromatography (IC), and gas chromatography mass spectrometry (GC-MS), focusing on the photocatalytic decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO(2-x)N(x) surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. No gaseous intermediates were detected during the photooxidation. Major intermediates adsorbed at the catalyst surface were oxalic acid, (COOH)(2), acetic acid, CH(3)COOH, formic acid, HCOOH, and pyruvic acid, CH(3)COCOOH, whereas more complicated carboxylic species, including propionic acid, CH(3)CH(2)COOH, isovaleric acid, (CH(3))(2)CHCH(2)COOH, and succinic acid, (CH(2)COOH)(2), were also found in the early stage of the photooxidation. These intermediate products were gradually photodegraded to CO(2) and H(2)O under visible light irradiation.

Evaluation of photocatalytic activities and characteristics of Cu- or Fe-modified nitrogen-doped titanium dioxides for applications in environmental purification

Photocatalytic activities, as manifested in gas decomposition rates of volatile organic compounds under visible light irradiation, are well known to be enhanced by Cu or Fe compounds loaded onto the surface of nitrogen-doped titanium dioxide (N-TiO2). Antimicrobial properties are also known to be improved by Cu compounds loaded onto N-TiO2. In this study, the acetaldehyde gas decomposition rates and antimicrobial properties achieved by loading Cu or Fe compounds onto N-TiO2 have been investigated from a practical viewpoint. Enhancements of the photocatalytic activities have been confirmed, and the durability of the Cu- or Fe-modified N-TiO2 in acetaldehyde gas decomposition has been demonstrated. The enhancements have been rationalized by considering the valence states of the loaded material. The enhancements were inferred to be a result of increased amounts of oxidative species arising from the photo-Fenton reaction at the surface of the loaded metal compounds. With a view to expanding the range of indoor applications of such visible-light-sensitive photocatalysts, preparation processes, i.e., nanosizing of the powder and improvement of the immobilization on various substrates, are also discussed.