Influence of the Mg2+ or Mn2+ contents on the structure of NiMnAl and CoMgAl hydrotalcite materials with high aluminum contents

In this work, layered double hydroxides with high aluminum content (aluminum atom fractions 0.3 and 0.5, relative to total metal cations) were successfully synthesized in the systems Co Al, Co Mg Al, Ni Al and Ni Mn Al, using a co-precipitation method with controlled pH. Terephthalate was used as the charge compensation anion. Different characterization techniques (XRD, FTIR,ICP, AAS, TGA, CHN and E)(AFS) showed that for these high-aluminum LDHs, the terephthalate ions are vertically placed within the interlayer galleries and the cations were effectively included in the layers. The unusually large limiting value for the intralayer aluminum proportion is possibly associated with the larger length and polarizability of the terephthalate anion as compared to the usual small inorganic anions (as carbonate, nitrate or hydroxyl). However, in the trimetallic samples (Co-Mg-Al and Ni-Mn-Al) a segregated aluminum phase was found for higher Mg or Mn contents. With high Mn content a manganese terephthalate phase was also observed. (C) 2014 Elsevier B.V. All rights reserved.