Synthesis of NiAl layered double hydroxides intercalated with aliphatic dibasic anions and their exchange with heptamolybdate

Layered double hydroxides (LDH) of general formula Ni1-x Al-x(OH)(2)(A)(x/2)center dot mH(2)O were obtained by a co-precipitation method at constant pH, using succinate (C4H4O42-), adipate (C6H8O42-) and sebacate (C10H16O42-) as compensation anions and two x values, 0.3 and 0.5. The formation of NiAl LDH was evidenced, although in the Al-richer samples carbon analysis and solid-state Al-27 NMR spectroscopy indicated the segregation of a small amount of an aluminum-containing phase. To prepare NiAlMo LDH, the original compensation anions were replaced by heptamolybdate ion using an anion exchange method. The results showed almost complete anion exchange in most samples, with small amounts of residual organic material, evidencing easy removal of the aliphatic dibasic anions as compared with terephthalate. The samples were characterized by FTIR, XRD, ICP-OES, CHN and Raman and Al-27 MAS solid-state NMR spectroscopies.