Controllable synthesis of Ho-doped In2O3 porous nanotubes by electrospinning and their application as an ethanol gas sensor

Pure and Ho-doped In 2 O 3 nanotubes (NTs) and porous nanotubes (PNTs) were successfully synthesized by conventional electrospinning process and the following calcination at different temperatures. X-ray diffractometry (XRD), thermogravimetric analysis (TGA), Raman spectrometer, energy-dispersive spectroscopy, scanning and transmission electron microscopy were carefully used to investigate the morphologies, structures and chemical compositions of these samples. Their sensing properties toward ethanol gas were studied. Compared with pure In 2 O 3 NTs (response value is 17), pure In 2 O 3 PNTs (response value is 20) demonstrated enhanced sensing characteristics. What’s more, the response of Ho-doped In 2 O 3 PNTs sensors to 100 ppm ethanol was up to 60 at 240 °C, which increased three times more than that of the pure In 2 O 3 PNTs. Additionally, the minimum concentration for ethanol was 200 ppb (response value is 2). The increased gas-sensing ability was attributed not only to the hollow and porous structure, but to the Ho dopant. Furthermore, Ho-doped In 2 O 3 PNTs enable sensor to discriminate between ethanol and the other gas distinctly, particularly acetone that is usually indistinguishable from ethanol. Also, by analyzing XRD, TGA and Raman spectrometer, a possible formation mechanism of porous nanotubes and sensing mechanism were put forward.