Abstract
In this study, we demonstrated a highly selective chemiresistive-type NO2 gas sensor using facilely prepared carbon dot (CD)-decorated single-walled carbon nanotubes (SWCNTs). The CD-decorated SWCNT suspension was characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-visible spectroscopy, and then spread onto an SiO2/Si substrate by a simple and cost-effective spray-printing method. Interestingly, the resistance of our sensor increased upon exposure to NO2 gas, which was contrary to findings previously reported for SWCNT-based NO2 gas sensors. This is because SWCNTs are strongly doped by the electron-rich CDs to change the polarity from p-type to n-type. In addition, the CDs to SWCNTs ratio in the active suspension was critical in determining the response values of gas sensors; here, the 2:1 device showed the highest value of 42.0% in a sensing test using 4.5 ppm NO2 gas. Furthermore, the sensor selectively responded to NO2 gas (response ~15%), and to other gases very faintly (NO, response ~1%) or not at all (CO, C6H6, and C7H8). We propose a reasonable mechanism of the CD-decorated SWCNT-based sensor for NO2 sensing, and expect that our results can be combined with those of other researches to improve various device performances, as well as for NO2 sensor applications.
Highlights
As hazardous gases, nitrogen oxides are mainly generated by combustion processes of fossil fuels, such as vehicle exhausts, power plants, and various industrial processes, and are the main causes of acid rain and photochemical smog, having a significant influence on air, water, and soil pollution [1,2,3]
The carbon dot (CD) were further characterized by a wide-angle X-ray diffraction (XRD) pattern (Figure 2b)
Three kinds of CD-decorated single-walled carbon nanotubes (SWCNTs) suspensions were prepared with volume ratios of 1:1, 2:1, and 3:1, respectively, and characterized using transmission electron microscopy (TEM) and UV-visible spectroscopy
Summary
Nitrogen oxides (typically, NO and NO2) are mainly generated by combustion processes of fossil fuels, such as vehicle exhausts, power plants, and various industrial processes, and are the main causes of acid rain and photochemical smog, having a significant influence on air, water, and soil pollution [1,2,3]. Gas sensors using carbon-based nanomaterials (e.g., single-walled carbon nanotubes (SWCNTs) [5,15,16,17,18,19,20], multi-walled carbon nanotubes (MWCNTs) [3,21], graphene [22,23], graphene oxide (GO) [24], and reduced GO (R-GO)) show desirable properties, such as a high response, detectability of low concentrations, low temperature operations, etc., making them highly attractive as platform materials. Our new proposed mechanism of NO2 gas detection can provide researchers of sensor materials and/or devices with a promising solution to further enhance their sensor performances
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