Quasi-cubic hematite with exposed high-energy facets for ethanol gas detection

Facet engineering is a surface optimization strategy to improve the physical and chemical properties of metal oxide semiconductors. To exploit a facile method to fabricate high-performance ethanol sensing material and study the sensing mechanism, a quasi-cubic α-Fe₂O₃ was investigated, which with high-energy facets exposed. Cetyl trimethyl ammonium bromide (CTAB) surfactant was employed in the preparation of α-Fe₂O₃ to control the shape and size. The resulting Fe₂O₃ particles exhibited a mean size of 1.10 µm with high uniformity in size and shape. Additionally, the cubic structure can also optimize the electronic transmission path. Charge carriers are conducting between the cubes required to pass through the electron depletion layer on the surface, as the Fe₂O₃ particles are separated. Thus, the resistance change of the electron depletion layer significantly affected the overall conductivity. The DFT calculation also confirmed that the exposed facets had high adsorption energy to ethanol molecules, which validated the experimental results. The resulting α-Fe₂O₃ exhibited an excellent selectivity towards ethanol vapor with a response of 35.14–500 ppm ethanol gas, and the response and recovery times were 12 s and 41 s, respectively. Additionally, the sensing materials exhibited good long-term stability which maintained 92% of its initial response after 60 days, potential using in practical ethanol gas detection.