A novel route for the preparation of CoCr2O4/SiO2 nanocomposite starting from Co(II)–Cr(III) carboxylate complex combinations

Abstract

This study reports the preparation and characterization of the spinel CoCr2O4. In order to obtain 20% CoCr2O4/80% SiO2 and 50% CoCr2O4/50% SiO2 (mol%) nanocomposites, we have used a versatile pathway based on the thermal decomposition of some particular precursors, Co(II) and Co(III) carboxylate-type complex combinations, inside the SiO2 matrix. The ligands of these coordination compounds result in the redox reaction between Co(II) and Cr(III) nitrates and 1,3-propylene glycol by heating at 150 °C of the gels (tetraethylorthosilicate–metal nitrates–1,3-propylene glycol). The as-obtained precursors, embedded in silica gels, were characterized by FT-IR spectrometry and thermal analysis. Both precursors decompose up to 350 °C, leading to the corresponding metal oxides inside the silica matrix. X-ray diffraction of the powders annealed at different temperatures has evidenced the formation of CoCr2O4 starting with 400 °C for 20% CoCr2O4/SiO2 and 300 °C for 50% CoCr2O4/SiO2. This behaviour can be explained by the fact that, by thermal decomposition of the chromium carboxylates, a nonstoichiometric chromium oxide Cr2O3+x is formed. At ~ 400 °C, Cr2O3+x turns to α-Cr2O3, which interacts with CoO leading to cobalt chromite nuclei inside the pores of the silica matrix. CoCr2O4 has been obtained as nanocrystallites homogenously dispersed within the silica matrix as resulted from XRD, TEM and EDX mapping, with mean particle size in the range 5–20 nm.