Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst

The photocatalytic degradation of a highly hydrophobic and stable organic pollutant, gamma-hexachlorocyclohexane (gamma-HCH), was performed in aqueous suspended mixture of TiO2-containing catalysts. Unlike most of the organic pollutants, gamma-HCH was very stable under the conventional photocatalytic condition with TiO2 (P25). Among various catalysts, TiO2 pillared fluorine mica (Ti-mica) showed highest activity. The effect of preparation method of Ti-mica was also examined. The hydrothermal treatment increased the crystallinity of anatase pillar of Ti-mica, though the treatment at high temperature resulted in a decrease in the surface area and an increase in the pore size. Consequently, Ti-mica treated at lowest temperature (373 K), Ti-mica-373, was the most effective photocatalyst. The catalytic activity of TiO2 and Ti-mica-373 was compared for 13 kinds of organic compounds with various hydrophobicity. Ti-mica-373 showed 5-66 times higher rate than TiO2 for the degradation of hydrophobic organic pollutants (alpha, beta, gamma and delta-HCH, trans- and cis-chlordane, DDE, DDD and DDT) of low concentration (10 ppb). In contrast, TiO2 Showed higher rate than Ti-mica-373 for the degradations of less hydrophobic compounds (benzonitrile, chlorobenzene, 4-chloroacetophenone and 4-chloronitrobenzene). Over TiO2-mica-373, organic compounds with higher log P-OW value, i.e. more hydrophobic compounds, were decomposed with higher rate. A positive effect of the fluorine mica support is suggested to be caused by the interaction of hydrophobic reactant with the hydrophobic interlayer surface of pillared-clay. (C) 2004 Elsevier B.V. All rights reserved.