Photocatalytic oxidation of acetaldehyde with oxygen on TiO 2/ZSM-5 photocatalysts: Effect of hydrophobicity of zeolites

Abstract

TiO 2 photocatalysts hybridized with ZSM-5 were prepared by the impregnation of (NH 4) 2[TiO(C 2O 4) 2] aqueous solution. This is one of the most ideal green processes in establishing TiO 2 photocatalysts because of an organic solvent-free preparation method. The highly hydrophobic H-ZSM-5 with low Al 2O 3 content was effective as an adsorbent for acetaldehyde molecules. These results suggest the close relationship between the hydrophobicity of the zeolite and the high photocatalytic reactivity of TiO 2 prepared on zeolites compared with unloaded TiO 2 catalysts. However, acetaldehyde molecules were strongly trapped on the Na + sites of ZSM-5 and their efficient diffusion onto the TiO 2 sites was inhibited, resulting in low photocatalytic reactivity. The photocatalytic oxidation of acetaldehyde over TiO 2/ZSM-5 was improved in the coexistence of H 2O vapor. The role of the H 2O molecules was estimated to be the efficient formation of OH radicals and the prevention of strong adsorption of acetaldehyde on the TiO 2 sites.