PREPARATION AND STUDY OF DECAVANADATE-PILLARED HYDROTALCITE-LIKE ANIONIC CLAYS CONTAINING TRANSITION-METAL CATIONS IN THE LAYERS .1. SAMPLES CONTAINING NICKEL-ALUMINUM PREPARED BY ANIONIC-EXCHANGE AND RECONSTRUCTION

For the first time, the nickel-aluminum layered double hydroxide (LDH) [Ni1-xAlx(OH2] (CO3)(x/2). mH(2)O containing carbonate anions in the interlayer, has been pillared with polyvanadate in aqueous solution at pH = 4.5 by anionic exchange without the assistance of any swelling agent. Making use of the so-called memory effect of these materials, synthesis of similarly pillared compounds through recovery of the structure from calcined LDH in contact with an aqueous solution of sodium metavanadate was also achieved. Characterization of the materials obtained so far has been carried out by chemical analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermal analysis. The influence of experimental conditions during the calcination-reconstruction process of the pillared-layered structure, such as calcination temperature and pH during the reaction, as well as the temperature during hydrothermal treatment (to improve crystallinity), is reported; purity of the product depends on the calcination temperature of the starting precursor, and at pH values higher than 4.5, a (VO3)(n) polyvanadate chainlike pillared material is obtained. Exchange of carbonate anions depends on the pH of the solution, total exchange being only attained at pH = 4.5-5.5. Thermal stability of the pillared materials and the microstructure properties are also reported.