Synthesis of CoIICoIII2-xAlxO4-Al2O3 nanocomposites via decomposition of CoII0.73CoIII 0.27(OH)2.00(NO3)0.23(CO3)0.02-0.5H2O in a sol-gel-derived γ-Al2O3 matrix

Nanocomposite materials Of (CoCo2-xAlxO4)-Co-II-Al-III-Al2O3 (0 less than or equal to x < 1.63) have been prepared from biphasic xerogels that contain the cobalt hydrotalcite-like compound (Co0.73Co0.27III)-Co-II(OH)(2.00)(NO3)(0.23)(CO3)(0.02).0.5H(2)O and sol-gel-derived Al2O3. With XRD/FTIR/XPS/DSC/TGA methods, an investigation has been carried out to understand the formation processes of the composites and chemical reactivity of the embedded cobalt hydrotalcite-like compound with alumina gel matrixes at various heating temperatures. It has been found that cubic spinels Of Co3O4 and (CoCo2-xAlxO4)-Co-II-Al-III are generated sequentially inside alumina matrixes upon decomposition of the hydrotalcite-like compound in static air. The average spinel crystallite size is in the range of 9-13 nm at 350 degreesC to 31-38 nm at 800 degreesC, whereas the specific surface area of the composites is reduced gradually from 277-363 m(2) g(-1) at 350 degreesC to 184-224 m(2) g(-1) at 800 degreesC. On one hand, the catalytic effect of cobalt on combustion reactions of organics trapped within the amorphous alumina gel matrixes is elucidated by varying the cobalt content and synthesis conditions. On the other hand, the retardation effect of gamma -Al2O3 matrixes on the growth of the crystallite is also revealed, It has been indicated that the content of aluminum (x) in (CoCo2-xAlxO4)-Co-II-Al-III-Al2O3 is indeed a function of the heating temperature. After thermal decomposition of the cobalt hydrotalcite-like compound, the Co3O4 phase starts to form at a temperature as low as 200 degreesC and is fully developed at 350 degreesC. At 500-800 degreesC, the formed Co3O4 is converted to the (CoCo2-xAlxO4)-Co-II-Al-III phase due to the reaction between the included phase and alumina matrixes.