Highly sensitive and selective formaldehyde gas sensor based on CdO–In₂O₃ beaded porous nanotubes at low temperature

Pure In₂O₃ nanowires (PINW) and CdO–In₂O₃ composited beaded porous nanotubes (CIBPNT) were successfully prepared by conventional electrospinning method and followed by calcination. The peculiar surface morphological images of as-synthesized nanomaterials were observed via scanning electron microscope (SEM) and transmission electron microscopy (TEM) from which we could observe a series of irregular holes distributed on the surface of beaded nanotubes. The inner structure of the samples was investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results reveal that the element composition of the samples are in conformity with the CdO–In₂O₃ materials. In addition, the average crystallite size of CIBPNT (17.5 nm) can be estimated from XRD which accords with the TEM images, and XPS analysis supports the oxygen vacancy principle by proving the oxygen vacancies concentration of CIBPNT is more than in PINW. The formaldehyde sensing performances of the samples were evaluated at different temperatures. The result shows that the sensor based on CIBPNT exhibits a excellent response (72–50 ppm formaldehyde) at a low operation temperature of 132 °C, and the value is eight times that of the response of PINW (9 to 50 ppm formaldehyde).The sensor based on CIBPNT could detect 0.1 ppm formaldehyde with a response of 2. In addition, good selectivity and a short response and recovery time (6 s, 12 s) are exhibited. The enhancement of gas sensitivity is attributed to not only the unique beaded shape of hollow and porous 1D nanostructures, but also the high catalytic activity of the CdO additive.