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

Abstract

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 Ca-In2O3 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 °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.