Metal ion and N co-doped TiO₂ 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.