Characterization of metal ion-implanted titanium oxide photocatalysts operating under visible light irradiation

The metal ion-implantation of titanium oxide with metal ions (Cr+ or V+) at high energy acceleration and the subsequent calcination of these metal ion-implanted TiO2 in oxygen at around 725 K resulted in a large shift in the absorption spectra toward visible light regions. These catalysts exhibited effective and remarkable photocatalytic reactivity for various reactions such as the decomposition of NO into N-2, O-2 and N2O at 275 K not only under UV but also under visible light irradiation. XAFS, ESR and UV-Vis studies have revealed that the implanted metal ions (Cr+ or V+) are located at the lattice positions of Ti4+ in TiO2 and stabilized as Cr3+ or (V3+ V4+) species after the calcination of the sample in O-2 at around 775 K. Thus, these spectroscopic studies show that the presence of these substitutional metal ion species are, in fact, responsible for the large shift in the absorption spectra of these catalysts toward visible light regions.