A comparative study of optical absorption and photocatalytic properties of nanocrystalline single-phase anatase and rutile TiO2 doped with transition metal cations

The effect of nanocrystalline TiO₂ doping with transition metal cations (Cu²⁺, Fe³⁺, Co²⁺, Cr³⁺) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO₂ samples were characterized by X-ray diffraction, scanning electron microscopy, and UV-vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: A<A/Co<A/Cu<A/Fe. On the contrary, photocatalytic activity of rutile samples decreases upon doping in the series R>R/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88 eV.