This paper presents a flexible and reliable chemiresistor-type NO 2 gas sensor based on single-walled carbon nanotubes (SWNTs) on polytetrafluoroethylene (PTFE) membrane filter substrates. The sensor is realized by using a cost-effective spray coating in the preparation of SWNTs thin film, followed by the fabrication of metal contacts using a shadow mask and polyethyleneimine (PEI) noncovalent functionalization of the SWNTs. This showed a high sensitivity to NO 2 gas at room temperature in dry air; 21.58% to 167.7% for concentrations of 0.75 ppm to 5 ppm, and was almost nonsensitive to ammonia. Gas sensing characterization results, obtained for various substrate bending/wrapping over different cylinders with diameters of 75 mm, 12.5 mm, and 6 mm showed that bending does not significantly affect sensitivity for NO 2 concentrations of 0.75 ppm to 2 ppm, while in the case of 3 ppm to 5 ppm NO 2 , the bent samples indicate enhanced sensitivity. This is probably because of the porous nature of PTFE substrates; these sensors were 1.5 to 2.7 times more sensitive than those fabricated over silicon substrate for 1 ppm and 5 ppm, respectively. Moreover, the relative humidity of 10% and 30% significantly reduced the sensitivity of the sensors. The presented results could be useful for the future development of flexible electronics/sensors for monitoring outdoor air quality and for the detection of volatile organic compounds.
The development of a new type of hybrid material comprising naphthalene-based π-conjugated amine (NBA) and zinc oxide (ZnO) nanohybrid, grown in situ on polydimethylsiloxane (PDMS) flexible substrate, is explored. The morphology of the nanohybrids is controlled by optimizing growth time of the hydrothermal reaction. The CO 2 sensor utilizing NBA−ZnO nanohybrids shows outstanding sensing performance with a maximum response of ∼9% to 500 ppm of CO 2 at room temperature and a comparatively fast response/recovery time (∼3/6 min). The sensor has excellent mechanical flexibility with consistent sensing performance under bending/relaxing process. Hydrophobic nature of the NBA provides less humidity effect on the sensing performance of the NBA−ZnO nanohybrids, which make it suitable for room-temperature application. Also, the presence of layer-by-layer assembly in the NBA−ZnO nanohybrids provides a superior path for carrier transport, which reduces the response and recovery time. All these results indicate that NBA−ZnO nanohybrid is a promising material for room temperature CO 2 sensing application.
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