Electrospun Ca-doped In2O3 nanotubes for ethanol detection with enhanced sensitivity and selectivity

Sensitivity and selectivity of metal oxide semiconductor-based gas sensors are two crucial criteria. In this work, a highly sensitive and selective ethanol sensor has been prepared based on Ca-doped In2O3 nanotubes (Ca-In2O3 NTs). The products were synthesized by a simple electrospinning method with subsequent annealing in air. The crystal structure and morphology of as-obtained products are obviously affected by Ca-doping levels (1-10 mol %). X-ray diffraction and electron paramagnetic resonance results reveal that some Ca dopants (<= 3 mol%) can enter the lattice of In2O3 with the decreasing grain size, and an enrichment of the oxygen vacancies. In contrast, the grain size of Ca-In2O3 NTs increases dramatically with further increase of Ca concentration (7-10 mol%), and the excessive Ca dopants tend to form a new CaIn2O4 phase. Gas-sensing measurements demonstrate that the CaIn2O3 sensors exhibit enhanced ethanol sensing properties with respect to the pure In2O3 sensor. Especially, the 3% Ca-In2O3 sensor shows the highest response (183.3, at 100 ppm) with the excellent selectivity for ethanol detection at 240 degrees C. Such sensitive and selective ethanol detection is mainly based on the doping effect of Ca2+ ions, suggesting an effective route to develop the ability of In2O3 based gas sensors.