Abstract
Hierarchical SnO2/ZnO nanofiber heterojunctions composed of SnO2 nanofiber matrix on top of which ZnO nanorods protruding 30- 90 nm long were assembled, were examined for chemiresistive-type gas sensors under UV activation at room temperature. The sensor demonstrated excellent sensitivity to different concentrations of formaldehyde and selectivity to several possible interferents such as alcohols, methanol, benzene, methylbeneze and acetone with UV LED at a wavelength of 365 nm. The fiber-like heterojunctions can facilitate the electron transfer from ZnO to SnO2 and this effect would be augmented further under UV light activation. Consequently it enhanced the oxygen adsorptions on the surface of the heterojunctions thus leading to the excellent sensing performance even at room temperature. The influence of the power density and wavelength of UV light used and ambient humidity on the sensor response was systematically investigated. Comparing to the conventional thermal activated one that instead showed preferred response to acetone at 375 oC, the enhanced sensitivity and selectivity of the same sensor at room temperature under LED UV light can be attributed to selective photo-catalytic effect induced by the UV light.
Highlights
It shows that the SnO2/ZnO heterojunction has both a tetragonal rutile structure of SnO2 and a hexagonal wurtzite structure of ZnO which are indexed according to JCPDS No.41-1445 and 36-1451, respectively
Since the ionized oxygen species with negative monovalence which usually has a lower photocatalytic properties to react to organic vapors, the reaction of O−2 according to equation (2) would prefer to react with more active polar gases such as formaldehyde and reluctant to react with the slight inertia gases such as benzene, acetone, ethanol, methanol and toluene significantly improving the selectivity of the sensor (Wu et al, 2012; Liu et al, 2013; Li et al, 2015; Chen et al, 2016)
The SnO2/ZnO nanofiber heterojunctions based sensor shows a good sensitivity to different concentrations of formaldehyde and an excellent selectivity compared to several possible interferents such as ethanol, methanol, acetone, benzene, and toluene under UV at room temperature
Summary
Semiconductor metal oxides (SMO) based chemical gas sensors have been used for detection of the harmful and toxic gases in many fields because of its fast response, high precision, small size, and low cost since it was introduced in 1962 (Seiyama and Kagawa, 1966; Shimizu and Egashira, 1999; Barsan and Weimar, 2001; Yamazoe, 2005; Tiemann, 2007; Lee, 2009; Miller et al, 2014; Liang et al, 2015; Walker et al, 2019).
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