Layered double hydroxides pillared by tungsten polyoxometalates - Synthesis and photocatalytic activity

Layered double hydroxides pillared by tungsten polyoxometalates were prepar ed by anion exchange reaction of the synthetic precursor. Mg4Al2(OH)(12)TA .H2O, Zn3Cr(OH)(aleph)DS . 3H(2)O or Zn2Al(OH)(6)NO3.H2O with the polyoxome talates. The intercalated polyoxometalates included the Paratungstate A [W7 O24](6-) ion: the monosubstituted or lacunary Keggin [SiW11O39Mn(H2O)](6-), [SiW11O39Ni(H2O)](6-) or [SiW11O39](8-) ion: the monohubstituted Dawson [P 2W17O61Mn(H2O)](8-) ion and the Preyssler [NaP5W30O110](14-) ion, resulting in the gallery heights of the intercalates in the range 0.76 similar to1.7 0 nm. The photocatalytic activities of the intercalates were studied by the degradation reaction of an aqueous organochlorine pesticide, hexachlorocyc lohexane (HCH). The model and mechanism for the photocatalytic degradation of HCH on the polyoxometalate-pillared compounds were proposed, indicating that the interlayer space is the reaction field and that photogeneration of OH radicals are responsible for the degradation pathway. (C) 2001 Elsevier Science Ltd. All rights reserved.