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

Abstract

The aluminate nano-powders Al2XO4 (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 Al2XO4 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 Al2XO4 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 (Eg), determined by diffuse reflectance, were found to be 3.78, 3.82 and 3.75 eV respectively for Al2CdO4, Al2NiO4 and Al2CoO4, assigned to the charge transfer O2−: 2p → X2+: d orbital, making our spinels good candidates for optoelectronic and photocatalytic applications.