Mesoporous NiCo2O4 Spinel: Influence of Calcination Temperature over Phase Purity and Thermal Stability

Mesoporous NiCo2O4 spinel has been synthesized by nanocasting, using SBA-15 and KIT-6 silica its hard templates. Two temperatures of calcination were applied for the conversion of the spinel precursors (metal nitrates) into NiCo2O4. At 375 degrees C the pure spinel was obtained, whereas at 550 degrees C NiO impurities were detected. The mesoporous powders obtained were characterized by transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, and magnetic measurements. In addition. their thermal stability was assessed by post heat-treating the materials at 550 degrees C: the mesostructure of the pure spinel (calcined at 375 degrees C) collapsed, leading to the disruption of the porous network, while the mesoporosity of the powders calcined at 550 degrees C was preserved. In all cases, the post-thermal treatment induced the segregation of NiO; the final NiO amount was found to be in the 7-10 wt % range.