Powders of TiO2 doped with a metal ion and N species were prepared by a polymerized complex method and the visible-light photocatalytic activities of the products are investigated. Of the metal ions studied (K+, Ca2+, Sr2+, Ba2+, Nb5+, Fe3+, Zn2+, and Al3+), the photocatalyst prepared with Sr2+ exhibits the highest activity for acetaldehyde decomposition under visible-light irradiation. Results obtained from x-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) analyses suggest that the doped N species reside at interstitial lattice positions in the catalyst. It was also found by XPS and ESR measurements that the doped N species combine with lattice oxygen to give rise to a paramagnetic property. The visible-light response of the catalyst is driven by the formation of paramagnetic N species at interstitial positions in the TiO2 lattice.

A thin film composed of an ion-exchangeable layered oxide HxTi(2-x/4)⃞x/4O4 (HTiO) (where the open square, ⃞, is vacancy) is studied as an electrode material. The thin film prepared on an indium tin oxide substrate functions as an electrode for the redox reaction of Ru(bpy)32+/Ru(bpy)33+ without noticeable degradation. Lack of reaction in the presence of Fe(CN)64−/Fe(CN)63− indicates that reaction on this electrode occurs in the interlayers between titanate sheets. A Ru(bpy)32+-intercalated form of the electrode generates photocurrent under visible light irradiation.

The interlayer space of a thin film of layered titanate, Cs0.68Ti1.83‪0.17O4, was successfully expanded by SiO2 pillaring. Ion exchange of the Cs ions in the interlayer to alkylammoniuim cations, n-CnH2n+1NH3+ (n = 8, 12, 18), expanded the interlayer space, and enabled intercalation of tetraethylorthosilicate. X-ray diffraction and the cross section of transmission electron microscopy images revealed that tetraethylorthosilicate-treated thin film maintained the expansion of interlayer space by SiO2 pillaring after calcination at 773 K. X-ray photoelectron spectroscopy after etching the thin film about 100 nm from the surface further confirmed the existence of SiO2 in the interlayer space.

A layered perovskite type oxide, K2La2Ti3O10, was prepared by a gel technique using the polymerized complex (PC) method. A single phase K2La2Ti3O10 was obtained by adding twice the potassium required for stoichiometry. The Ni–K2La2Ti3O10 catalyst prepared by the PC method exhibited a higher photocatalytic activity for decomposition of H2O into H2 and O2 than that prepared by a conventional solid state reaction.

A new porous material was prepared from a layered compound, K4Nb6O17, through the exfoliation of its layers. A composite of the niobate sheets and MgO particles were obtained by precipitating the exfoliated two-dimensional niobate sheets with MgO fine particles. Porous niobium oxide was obtained by removal of the MgO particles from the composite after thermal treatment. It had a large surface area and showed higher photocatalytic activity than the original H+/K4Nb6O17 for H2 evolution from various aqueous alcohol solutions.