PREPARATION AND STUDY OF DECAVANADATE-PILLARED HYDROTALCITE-LIKE ANIONIC CLAYS CONTAINING TRANSITION-METAL CATIONS IN THE LAYERS .2. SAMPLES CONTAINING MAGNESIUM-CHROMIUM AND NICKEL-CHROMIUM

Mg-Cr and Ni-Cr layered double hydroxides (LDHs) with carbonate anions in the interlayer were used as precursors to synthetize pillared derivatives with decavanadate (V10O28)(6-) anions without the use of any preswelling agent. Characterization was carried out by powder X-ray diffraction, chemical analysis, FT-infrared spectroscopy, thermal analysis, and transmission electron microscopy. The influence of the wetness degree of the starting Mg-Cr and Ni-Cr LDHs and of the pH conditions on the anionic-exchange rate of carbonate was studied. The pillared materials were constituted by a well crystalline phase, together with a coproduct with a lower degree of crystallinity, characterized by a broad X-ray diffraction peak close to 10 Angstrom. Anion-exchange was neither achieved without prewetting of the carbonate-containing LDH nor at pH values larger than 6.5. The thermal stability of the pillared materials and their surface properties are also presented.