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

The effect of simply adsorbed Sin, Eu, and Yb ions on TiO2(Ln/TiO2) and Fe ions adsorbed onto TiO2(Fe/TiO2) was examined from the photocatalytic decomposition of adenosine 5'-triphosphate (ATP) as an anionic substance, 2-propanol as a neutral substance, and methylene blue (NIB) as a cationic substance. The amount of ATP disappearing in 40 min of reaction in the presence of Ln/TiO2, increases in the order Ln = Sin < Eu < Yb. For 2-propanol, the photocatalytic activities of Ln/TiO2 catalysts were similar to that of unmodified TiO2 (u-TiO2) catalyst. For MB, the photocatalytic activities of Ln/TiO2 catalysts were 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 degreesC for 1 h was reduced for ATP, a reduced slightly for 2-propanol, and increased for MB compared with Yb/TiO2. Photocatalytic activities of Fe/TiO2-C for ATP, 2-propanol, and MB were 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. (C) 2004 Elsevier B.V All rights reserved.