Synthesis of bifunctional α-Bi 2 O 3 nanostructured fibres for UV light and gas sensing applications

α-Bi2O3 was synthesised by the coprecipitation method using bismuth nitrate and concentrated formic acid. The precursor formed at room temperature was identified as bismuth formate, which transforms to β-Bi2O3 by heating at 250 °C. The subsequent annealing at 400 °C produced α-Bi2O3, which has monoclinic crystalline structure. The particle morphology corresponds to nanostructured fibres with a length between 0.2 and 3.2 µm, and a cross-section in the range 0.05–0.18 µm. The optical bandgap energy was obtained by the Tauc approach giving 2.88 eV. UV light detection at room temperature shows a linear response of the photocurrent with optical irradiance, and a responsivity of 1.7 × 10−4 A/W. Gas sensing properties measured at 300 °C revealed excellent detection of ethanol, with a linear variation of electrical resistance with gas concentration. In contrast, for CO and CO2 it was significantly lower and almost zero for excess O2 in air.