Effect of annealing temperature on a highly sensitive nickel oxide-based LPG sensor operated at room temperature

Abstract

In the present work, nanostructured nickel oxide (NiO) powder has been synthesized using the sol–gel method and is annealed at different temperatures to study the impact of annealing temperature on its structural, optical, morphological, and LPG sensing properties. The obtained powder was analyzed by several characterization techniques such as field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), particle analyzer, and Fourier-transform infrared spectroscopy. XRD patterns show that NiO nanoparticles have a cubic unit cell structure. The average crystallite size for each of the samples was calculated to be 27–77 nm using the Debye–Scherrer formula and Williamson-Hall uniform deformation model plot. FESEM images revealed the mesoporous morphology of prepared NiO nanoparticles and found that the particle size increases with an increase in annealing temperature. The UV–Vis absorption spectrum shows that the energy band gap decreases with an increase in annealing temperature for NiO nanoparticles. Liquefied petroleum gas (LPG) sensing properties of the prepared pellets were also examined at room temperature (300 K) in the range of 0.5–2.0 vol% concentration of LPG. The gas sensing response of the NiO:500 sample is 244.4% which is the highest among all the samples due to the combined effect of nanocrystal defects and specific surface area. The sensing response of the synthesized material increased significantly as the concentration of the test gas rose.