Hydrothermal synthesis of CoAl2O4 spinel: effect of reaction conditions on the characteristic and morphological features

Abstract

The spinel form of cobalt aluminate (CoAl2O4) was synthesized by a hydrothermal method in moderate conditions. The synthesized phases were qualitatively and quantitively identified by means of different characterization techniques. The effects of reaction conditions of Co/Al ratio, pH, stirring time, reaction temperature, reaction time and capping agent addition on the color performance and morphology were studied. The capping agents of n-cetyl-n, n, n trimethylammonium bromide (CTAB), 2-pyrrolidinone (PVP), triethylamine (TEA) and oleic acid (OA) were used. The probable reaction mechanism can be explained with the steps of (i) formation of Co-Al-O complexes and (ii) conversion to Co-spinel. In the reaction mechanism, the addition of capping agents improved the conversion of complexes to Co-spinel. The characteristic band values were observed at 550, 595 and 650 nm in the ultraviolet-visible wavelength range, in UV analyses. The lowest b* and the highest BET surface area were determined in the TEA added sample with values of - 37.4 and 16.02, respectively. Layer shaped particles were obtained in CTAB added samples whereas the angled cubic particles were seen in the TEA and OA added samples. The smallest particles were observed in the use of PVP addition to spinel, and the particle size was around 100 nm. The experimental results proved that characteristic properties of prepared samples can be enhanced by the selection of a suitable capping agent.