In situ monitoring of NiO-Al2O3 nanoparticles synthesis by thermo-Raman spectroscopy

Simultaneous thermogravimetric analysis and thermo-Raman spectroscopy (TRS) measurements for in situ monitoring of wet chemical reaction of Ni(OH)2.4H2O and Al(OH)3 forming NiO-Al2O3 nanoparticles is studied and compared with the solid-state reaction. Herein, a different approach of synthesis and monitoring of NiO-Al2O3 by TRS is presented, in which, in situ thermo-Raman spectra are recorded at every degree interval from 25 to 800 deg. C to understand the structural and compositional changes in NiO-Al2O3 as a function of temperature. Slow controlled heating of the sample as in TRS, enables better control over morphology and particle size distribution (∼10-20 nm diameter). The X-ray diffraction (XRD) shows that smaller particle size is obtained using wet chemical reaction than the solid-state reaction (∼25 nm diameter). TRS studies also reveal that, the bulk NiAl2O4 forms at temperatures above 800 deg. C, although, the onset of formation is around 600 deg. C. Condensation of Al(OH)3 forming Al2O3 is also monitored, wherein, presence of hydrocarbon is found to contribute to the observed fluorescence background. Based on the TRS and complementary characterizations using XRD, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis, the formation of supported NiO-Al2O3 is discussed.