Hironobu Koike

Metal ion and N co-doped TiO 2 as a visible-light photocatalyst

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.

Preparing Titania Fibers and Their Photocatalytic Activity

Continuous titania fibers were prepared by a polytitanoxane precursor method. Polytitanoxane was synthesized through hydrolysis and polymerization reaction between partially chelated titanium isopropoxide and water without acid catalyst. Polytitanoxane, which was precipitated from an isopropanol solution by adding adequate amount of water to titanium isopropoxide, was then dried and dissolved in tetrahydrofuran. The concentrated viscous solution of polytitanoxane was considerably stable to further self-condensation and had good spinnability. The precursor fiber which was obtained by spinning the solution was calcined to form titania fibers. Two types of titania fibers were obtained under different calcination conditions from the same precursor fiber; Dense fiber with high tensile strength of higher than 1 GPa, and porous fiber with high surface area of more than 10 m 2 /g. Photocatalytic activity of those fibers was studied using the phenol mineralization reaction in water. The phenol degradation ability of high-surface-area titania fiber was almost the same as that of commercial titania powder for photocatalyst.