Influence of synthesis methods (combustion and precipitation) on the formation of nanocrystalline CeO2, MgO, and NiO phase materials

Attempts were made to prepare CeO2, MgO, and NiO nanomaterials by combustion and precipitation methods using aniline as a fuel and KOH as a precipitating agent (with the aid of PEG as a surfactant). The formation of CeO2, Mg(OH)2, and NiO as combustion products, and CeO2, Mg(OH)2, and Ni(OH)2 as precipitated products were obtained in a single step. In a single-step process, both combustion and precipitation methods yield CeO2 materials with the significant differences in XRD structural features. The annealing (500 °C/4h) treatment enhances the nanocrystalline nature with the formation of pure MgO, NiO, and CeO2 phases. Variation in refined lattice parameters is noted for the present different materials. The color appearance of the as-prepared and annealed materials obtained by these methods is differentiated. The as-prepared Ni(OH)2 phase materials produced via precipitation with PEG and without PEG as surfactant show a quite major difference in the structural (a, c, and D values) and thermal (TG/DTA) features. The phase pure as-prepared combustion product of CeO2 materials shows a relatively minimum weight loss of 1.4%. A maximum weight loss of 33.9% was noted for the precipitated product of Mg(OH)2 phase materials reduced to 28.2% despite the formation of pure MgO phase materials upon annealing at 500 °C/4h at the end temperature, 1000 °C. The UV–Vis diffuse reflectance measurements exhibit a difference in the absorbance peak intensity and the Eg values calculated from the Tauc relation ranging from 1.65 to 5.42 eV for annealed MgO, NiO, and CeO2 phase materials. Significant changes in the NIR reflectance (<10 – 80%) values are seen in the 750–2500 nm regions for these nanomaterials owing to the difference in the color appearance of powder samples. From the NIR reflectance spectral study, we found that the MgO and CeO2 nanomaterials are suitable for NIR reflecting solar and color pigmentation applications owing to their higher (∼80%) NIR reflectance values in the NIR region.