  On the way to advance the sensing technology, various strategies based on the
nano-materials have been introduced to improve the performance of the gas
sensors. In this study, we have introduced a facile fabrication procedure for
annealing hematite to monitor ethanol gas. Due to large specific area of this
conductive platform, more available target molecules (ethanol gas) are
detected. To construct this platform, initially, a large scale well-separated
iron oxide (hematite) nanostructures are created via an annealing process. The
morphology of the nanostructure is optimized through annealing temperature and
operating temperature for ethanol gas. The best response for the gas sensor is
achieved for hematite nanostructures fabricated through the annealing
temperature of 500{\deg}C and the operating temperature of 225$^\circ$C. The
fabricated nanostructures is tested in air ambient conditions for various
ethanol gas concentrations from 50 to 1000 ppm. The modified sensor exhibited
acceptable reproducibility and good selectivity with no interference-effect. To
examine the X-ray diffraction patterns of hematite nanostructures at three
annealed temperatures, the Rietveld method and FullProf software are used in
which the average crystal size has been obtained. Obviously, with increasing
the annealing temperature, the average size of the crystals has been increased.
The results of ultraviolet-visible spectroscopy show that the energy gap
decreased with increasing annealing temperature. The maximum sensing response
of hematite flower-like nanostructures is obtained at a concentration of 1000
ppm. Also, the shortest response time is estimated at about 27 seconds for
ethanol at a concentration of 200 ppm. The detection limit of this sensor is
obtained at 50 ppm.
