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

Abstract

The effect of simply adsorbed Sm, Eu, and Yb ions on TiO 2 (Ln/TiO 2) and Fe ions adsorbed onto TiO 2 (Fe/TiO 2) was examined from the photocatalytic decomposition of adenosine 5′-triphosphate (ATP) as an anionic substance, 2-propanol as a neutral substance, and methylene blue (MB) as a cationic substance. The amount of ATP disappearing in 40 min of reaction in the presence of Ln/TiO 2 increases in the order Ln=Sm<Eu<Yb. For 2-propanol, the photocatalytic activities of Ln/TiO 2 catalysts were similar to that of unmodified TiO 2 (u-TiO 2) catalyst. For MB, the photocatalytic activities of Ln/TiO 2 catalysts were less than that of u-TiO 2 catalyst. By contrast, Fe/TiO 2 catalyst was excellent in photocatalytic decomposition of ATP, 2-propanol, and MB. The photocatalytic activity of Yb/TiO 2-C calcined at 500 °C for 1 h was reduced for ATP, a reduced slightly for 2-propanol, and increased for MB compared with Yb/TiO 2. Photocatalytic activities of Fe/TiO 2-C for ATP, 2-propanol, and MB were all less than for Fe/TiO 2. The local structure around the lanthanide ions on TiO 2 particles was revealed by EXAFS measurement. The structure of the Yb atom in Yb/TiO 2-C was composed of the YbO bonds as in Yb 2O 3, rather than YbCl bonds in Yb/TiO 2.