Role in photocatalysis and coordination structure of metal ions adsorbed on titanium dioxide particles: a comparison between lanthanide and iron ions

The effect of simply adsorbed Sm, Eu, and Yb ions on TiO2 (Ln/TiO2) and Fe ions adsorbed onto TiO2 (Fe/TiO2) was examined from the photocatalytic decomposition of adenosine 50-triphosphate (ATP) as an anionic substance, 2-propanol as a neutral substance, and methylene blue (MB) as a cationic substance. The amount ofATP disappearing in 40 min of reaction in the presence of Ln/TiO2 increases in the order Ln ¼ Sm < Eu < Yb. For 2-propanol, the photocatalytic activities of Ln/TiO2 catalysts were similar to that of unmodifiedTiO2 (u-TiO2) catalyst. ForMB, the photocatalytic activities ofLn/TiO2 catalystswere less than that of u-TiO2 catalyst. By contrast, Fe/TiO2 catalyst was excellent in photocatalytic decomposition of ATP, 2-propanol, and MB. The photocatalytic activity of Yb/TiO2-C calcined at 500 8C for 1 h was reduced for ATP, a reduced slightly for 2-propanol, and increased forMBcompared withYb/TiO2. Photocatalytic activities of Fe/TiO2-C forATP, 2-propanol, andMBwere all less than for Fe/TiO2. The local structure around the lanthanide ions on TiO2 particles was revealed by EXAFS measurement. The structure of the Yb atom in Yb/TiO2-C was composed of the Yb–O bonds as in Yb2O3, rather than Yb–Cl bonds in Yb/TiO2. # 2004 Elsevier B.V. All rights reserved.