Fabrication and excellent formaldehyde Gas sensing properties of Yb-doped In2O3 nanotubes

Pure and Yb-doped In2O3 nanotubes have been successfully fabricated by using the single-capillary electrospinning method, followed by calcination. The morphological and structural characteristics of the as-synthesized nanotubes are investigated by scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The SEM images reveal that all the pure and Yb-doped In2O3 nanotubes are distributed evenly, and the average diameter of the as-synthesized nanotubes is about 200 nm. The XRD analysis results show that the as-prepared samples are well-crystallized, and the diffraction peaks can be indexed according to cubic In2O3. Gas sensors based on pure and Yb-doped In2O3 nanotubes have been fabricated and investigated for formaldehyde detection in detail. As shown in the experimental results, Yb-doped In2O3 nanotubes exhibit enhanced formaldehyde sensing properties compared with pure In2O3 nanotubes. At the optimum operating temperature of 230 ℃, the response of the gas sensors based on pure In2O3 nanotubes to 100 ppm formaldehyde is 18.4, while the response of gas sensors based on Yb-doped In2O3 nanotubes is 69.8 in the same working condition, which is 3.8 times larger than that of pure In2O3 nanotubes. The improvement of Yb-doped In2O3 nanotubes gas-sensing property may be due to the formation of the heterojunction structure at the interface between the two different semiconducting oxides. The response and recovery times of Yb-doped In2O3 nanotubes to 100 ppm formaldehyde are about 4 s and 84 s respectively, indicating the fast response speed of Yb-doped In2O3 nanotubes. Moreover, even at 100 ppb of formaldehyde a detectable response can be observed and the value is 2.5. The low limit of formaldehyde detection shows that the as-synthesized Yb-doped In2O3 nanotube gas sensors can be used for the detection of dilute formaldehyde. Furthermore, the Yb-doped In2O3 nanotube gas sensors have excellent selectivity towards formaldehyde. In this experiment, acetone has the highest sensitivity in a variety of common interfering gases and the response value is 22 to 100 ppm at 230 ℃, which is less than one-third of the sensitivity of formaldehyde. Carbon monoxide has the lowest response value of 1.7, which is much lower than that of formaldehyde. In addition, the responses of gas sensors to different concentrations of formaldehyde almost unchanged during the test (50 days), indicating that the Yb-doped In2O3 nanotubes possess good repeatability and long-term stability. The excellent formaldehyde gas-sensing properties of Yb-doped In2O3 nanotubes indicate that the as-synthesized nanomaterials can be used as a promising candidate to detect formaldehyde in practical applications.