Morphological and structural evolution of mesoporous calcium aluminate nanocomposites by microwave-assisted synthesis

Novel special dual-structure calcium aluminate nanocomposites consisting of mesoporous Ca-containing Al₂O₃ nanonetworks with Ca ₁₂Al₁₄O₃₃ polycrystalline nanorods have been successfully synthesized using the microwave-hydrothermal (M-H) process in an alcohol solution consisting of calcium nitrate and mesoporous alumina, followed by calcination at a lower temperature (e.g., less than 600 C). The mesoporous Ca-containing aluminate nanocomposites possessed a specific surface area of 51 m² g^-1 and a broad pore size distribution of 4-12 nm in diameter, as observed from N₂ adsorption/desorption measurements. The results showed that highly dispersed Ca₁₂Al₁₄O ₃₃ nanorods grown on the mesoporous nanostructure were obtained by varying the molar ratio of Ca/Al or by controlling microwave heating time, as characterized by scanning electron microscopy (SEM), transmission electron microscopy/electronic energy loss spectroscopy (TEM/EELS) and powder X-ray diffraction (PXRD). The Ca₁₂Al₁₄O₃₃ nanorods with diameters of 50-100 nm and lengths of 200-400 nm were grown in and on the one-dimensional mesochannels. A formation mechanism of the mesoporous Ca-containing aluminate nanocomposites involving amorphous mesoporous hydrated-Al₂O₃ was also proposed.