Thermal decomposition of hydrotalcite with molybdate and vanadate anions in the interlayer |
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Authors: | Sara J Palmer R L Frost T Nguyen |
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Institution: | (1) Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane Queensland, 4001, Australia |
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Abstract: | Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were
characterized by XRD, and TG/DTA to determine the stability of the hydrotalcites synthesized. The thermal decomposition of
carbonate hydrotalcites consist of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation
and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where
the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting
with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding
metal oxides, including MgO, Al2O3, MgAl2O4, NaMg4(VO4)3 and Na2Mg4(MoO4)5. The presence of oxy-anions proved to be beneficial in the stability of the hydrotalcite structure, shown by the delay in
dehydroxylation of oxy-anion containing hydrotalcites compared to the carbonate hydrotalcite. This is due to the substantial
amount of hydroxyl groups involved in a network of hydrogen bonds involving the intercalated anions. Therefore, the stability
of the hydrotalcite structure appears to be dependent on the type of anion present in the interlayer. The order of thermal
stability for the synthesized hydrotalcites in this study is Syn-HT-V>Syn-HT-Mo> Syn-HT-CO3-V>Syn-HT-CO3-Mo>Syn-HT-CO3. Carbonate containing hydrotalcites prove to be less stable than oxy-anion only hydrotalcites. |
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Keywords: | carbonate hydrotalcite iowaite molybdate pyroaurite stitchtite thermogravimetry vanadate |
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