Layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)(36) (W7O24). 4H(2)O was prepared via anion exchange reaction of the synthetic precursor, Mg4Al2(OH)(12)TA . xH(2)O (TA(2-) = terephthalate), and [W7O24](6-) ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO2 and HCl by irradiating a Mg12Al6(OH)36 (W7O24). 4H(2)O suspension in the near UV area. Disappearance of trace HCH follows Langmuir-Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg12Al6(OH)(36)(W7O24). 4H(2)O 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 B.V. All rights reserved.