Decomposition processes of organic-anion-pillared clays CoaMgbAl(OH)c(TA)d·nH 2O

Abstract

CoMgAl-hydrotalcite-like compounds (CoaMgbAl(OH)c(TA)d·nH 2O) intercalated with terephthalate anions ([C6H4(COO)2]2- or TA2-) have been prepared. By using XRD, FTIR, ICP/CHN, DTA, TGA, combined TGA-FTIR, HRTEM, and XPS methods, it has been found that the as-prepared samples undergo different decomposition pathways when they are heated, respectively, in air and in nitrogen atmospheres. In particular, the collapse of the layered structure, i.e., dehydroxylation and the thermal decomposition of TA2- are overlapped within a narrow temperature range (20-30 °C) in air, showing a vigorously exothermic effect. However, the two thermal processes are distinctly separated in N2; each lasts over a rather wide temperature range (100-200 °C). Carbon nanoparticles and short tubules have been produced in the solid state from the intercalated TA2- anions during the decomposition of the hydrotalcite-like compounds in N2. These carbon nanomaterials are multiwalled and close-ended with a diameter of 10-35 nm and a length of 20-200 nm. Pathways of the nanocarbon formation as well as catalytic function of cobalt oxides generated from the above thermal processes have been further investigated with various instrumental methods. © 2000 American Chemical Society.