The impact of solvents on obtaining nanocrystalline Cr 2 O 3 materials - structural, thermal, and optical features

Abstract A series of nanocrystalline Cr 2 O 3 phase materials was prepared via a combustion route by varying the solvents, including deionized water (DIW), ethanol (EtOH), and ethylene glycol (EG) and a mixture of DIW + EtOH, DIW + EG, and EtOH + EG. Hexamine was used as fuel with efficiency values of ϕ e x 0 and of ϕ e x 2. The resulting as-obtained nanomaterials were thoroughly characterized to assess their structural, microstructural, thermal, and optical properties. The average crystalline size of the Cr 2 O 3 rhombohedral phase ranged from 12.8 and 25.1 nm, showing rice grain-like and spherical-like shapes. The average particle size of 43.5 nm and 17.7 nm is observed by FESEM analysis for the use of EtOH and EG as solvents which shows the polycrystalline nature of the material. The thermal analysis (TGA) indicates a maximum weight loss of 20.5% for the Cr 2 O 3 phase materials obtained with EtOH ( ϕ e x 0) and a minimum of 6.3% obtained with EG ( ϕ e x 2). In FTIR transmittance spectra, the species (Cr–O/Cr=O) are found between 1000 and 400 cm −1 confirming the presence of Cr 2 O 3 phase. Four E g bands and one A g band are seen in Raman spectra which indicates the Cr 2 O 3 phase. The bandgap energy values range from 2.2 to 2.6 eV, with high reflectance (68%) suggesting their prospective application as an eco-friendly green NIR reflecting Cr 2 O 3 pigments.