COMPARATIVE-STUDY OF THE SYNTHESIS AND PROPERTIES OF VANADATE-EXCHANGED LAYERED DOUBLE HYDROXIDES

The synthesis and characterization of polyoxovanadate-intercalated MgA l hydrotalcite-like layered double hydroxides (LDH) is described. Seve n different methods have been used to intercalate the vanadate anion. These include exchange of the initial carbonate or terephthalate anion s, as well as reconstruction of the layered structure from the carbona te form previously calcined at 550-degrees-C-the reconstruction being either directly to the vanadate or indirectly via a terephthalate inte rmediate. Preswelling with glycerol was also used in some cases. Chara cterization has been carried out by elemental chemical analysis, powde r X-ray diffraction, differential thermal and thermogravimetric analys es, Fourier-transform infrared spectroscopy, transmission electron mic roscopy, and specific surface area and porosity assessment by nitrogen adsorption at -196-degrees-C. In all cases a layered material contain ing the [V10O28]6- anion in the interlayer is formed. Direct reconstru ction from calcined MgAl LDH with vanadate at pH = 4.5 leads, in addit ion, to a fibrous material and partial dissolution of magnesium. Exper imental results indicate total CO32-/C6H4(COO)22- exchange as well as the absence of glycerol in those cases where it had been used as a pre swelling agent. The principal difference between the samples is found within the pore size distribution-a narrow distribution is present in samples prepared via a terephthalate intermediate, while for others th e pore size distribution is broader.