Preparation and photocatalytic performance of nano-TiO2-coated beads for methylene blue decomposition

Fluidized bed chemical vapor deposition (FB-CVD) method using tetra iso-propoxide as a precursor of TiO₂ was applied to achieve TiO₂ coating onto various types of beads. The substrates of the beads included alumina, silica-gel, and glass, and these beads were of small diameter (ca. 1–2 mm). From our investigation of TiO₂-coated surfaces of these beads, we observed formation of TiO₂ coating down to ～35 nm in thickness. In addition, we found that both the type of the substrate and condition of coating process had effect on the surface morphology of coated beads. From combined studies of the surface morphology and the photocatalytic decomposition of methylene blue, we detected characteristic features of coated surface which were associated with high photocatalytic performance. Provided are the explanations to account for the high photocatalytic performance found for TiO₂-coated beads of silica-gel substrate.