Fe3+-substituted aluminium oxide nano-flakes: Structural, morphological, optical, and gas sensing properties

Abstract

Mixed metal oxides with chemical formula FexAl2-xO3 (where x = 0.2–1.0) (FANF) was synthesized via sol-gel auto combustion process. X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy were employed to characterize produced oxide materials. The final product FANF was sintered for 5 h at 1100 °C. The TG-DTA validated the mixed metal oxides phase evolution and steady-state temperature. The replacement of aluminium ions results in orthorhombohedral structure in mixed metal oxides (MMO). The bandgap decreased from 3.72 eV to 3.21 eV and the crystallite size decreased from 28 nm to 14 nm as the iron content increased in the sample FexAl2-xO3 (where x = 0.2–1.0). The FT-IR confirmed no impurity peaks and the single phase with iron oxide band is near 432 cm−1, while the aluminium oxide band is 565–600 cm−1. Microstructural investigation shows flake-like growth, and EDS confirmed a stoichiometric ratio of MMO. Iron-substituted aluminate gas sensors detected CO, H2S, and NO2 at temperature ranging from 25 to 300 °C. Fe0.6Al1.4O4 (F3ANF) sensor responded 46.69% towards 100 ppm H2S at 200 °C. Overall, the results showed that a flake-like FANF sensor can be used effectively as a H2S gas sensor.