Preparation and spectroscopic study of nanosized aluminate spinels Al 2 XO 4 ( X = Cd, Ni and Co) synthesized by solution combustion technique

The aluminate nano-powders Al 2 XO 4 (X = Cd, Ni and Co), crystallizing in a cubic spinel, were prepared by combustion method at 900°C. The effects of cations on the structure, optical properties and distribution of the cations as well as the binding energy of the samples were studied by X-ray diffraction (XRD), UV-Vis diffuse reflectance and FT-IR) spectroscopy. The XRD analysis confirmed the spinel structure of all samples, and showed that the average crystallite size of Al 2 XO 4 increases from 23.89 to 32.72 nm, while the lattice parameter changes from 8.0490 to 8.1066 Å when going from Ni to Co. As expected, the FT-IR spectroscopy of Al 2 XO 4 showed the presence of the fundamental absorption peaks in the region (400–745 cm − 1 ), confirming the formation of the aluminate spinels. The slight shift toward longer wavenumbers is due to the low electronegativity of Cd. The forbidden bands (E g ), determined by diffuse reflectance, were found to be 3.78, 3.82 and 3.75 eV respectively for Al 2 CdO 4 , Al 2 NiO 4 and Al 2 CoO 4 , assigned to the charge transfer O 2− 2p → X 2+ d orbital, making our spinels good candidates for optoelectronic and photocatalytic applications.