Wide bandgap mesoporous hematite nanowire bundles as a sensitive and rapid response ethanol sensor

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Abstract
In this study, α -Fe 2 O 3 nanowires were synthesized using mesoporous SBA-15 silica as the hard templates with the nanocasting method, and then mesoporous α -Fe 2 O 3 nanowire bundles (NWBs) were separated from the well-dispersed α -Fe 2 O 3 nanowires (NWs) by the centrifugation technique. Both samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm and UV-vis spectra. All results indicated that the α -Fe 2 O 3 NWBs with mesoporous structure presented a higher BET surface area (95 m 2 g −1 ) and wider bandgap (2.08 eV) than those of α -Fe 2 O 3 NWs (32 m 2 g −1 and 1.91 eV). The bandgap of α -Fe 2 O 3 NWBs was in accordance with the bulk α -Fe 2 O 3 , while the BET surface area was much higher. The results from the gas-sensing measurement revealed that the α -Fe 2 O 3 NWBs based gas sensor exhibited a high sensitivity of 21.7, fast response-recovery of 7.5 s and 1 s, and good selectivity to ethanol at 340 °C. The sensitivity (21.7) for ethanol of α -Fe 2 O 3 NWBs was much better than that of the α -Fe 2 O 3 NWs (12.2), which should be attributed to the higher BET surface area and wider bandgap of α -Fe 2 O 3 NWBs.

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