Abstract
Because of the interesting and multifunctional properties, recently, ZnO nanostructures are considered as excellent material for fabrication of highly sensitive and selective gas sensors. Thus, ZnO nanomaterials are widely used to fabricate efficient gas sensors for the detection of various hazardous and toxic gases. The presented review article is focusing on the recent developments of NO2 gas sensors based on ZnO nanomaterials. The review presents the general introduction of some metal oxide nanomaterials for gas sensing application and finally focusing on the structure of ZnO and its gas sensing mechanisms. Basic gas sensing characteristics such as gas response, response time, recovery time, selectivity, detection limit, stability and recyclability, etc are also discussed in this article. Further, the utilization of various ZnO nanomaterials such as nanorods, nanowires, nano-micro flowers, quantum dots, thin films and nanosheets, etc for the fabrication of NO2 gas sensors are also presented. Moreover, various factors such as NO2 concentrations, annealing temperature, ZnO morphologies and particle sizes, relative humidity, operating temperatures which are affecting the NO2 gas sensing properties are discussed in this review. Finally, the review article is concluded and future directions are presented.
Highlights
Tremendous increase in environmental pollution due to the fast industrialization, population growth, combustion of fuelsR
6.2 Indirect Deposition of Grown ZnO Nanostructures on Substrate. Another approach for the fabrication of porous ZnO-based nanostructured gas sensors is pre-synthesis followed by coating of the as-synthesized ZnO nanomaterials of various morphologies such as 1-D nanorods, nanotubes, nanofibres, nanotubes, nanolines, nanowires [35,36,37, 39, 49], micro/ nanoflowers [51, 52], quantum dots [53], nanoparticles [57, 59], hollow spheres [64], nanopyramids [65], and nanotetrapods [66] as thin/thick films/coatings [35,36,37, 39, 49, 51, 53, 57, 65, 66] on the transducer surface including alumina [35, 37, 39, 49, 51, 53, 57, 66] and SiO2 [65]
ZnO nanomaterials can be efficiently utilized as sensors for NO2 gas
Summary
Tremendous increase in environmental pollution due to the fast industrialization, population growth, combustion of fuels. A sensor is a component of an electronic circuit which senses and undergoes physical and chemical changes on its surface due to the adsorption of a chemical stimulant. Long ago in 1938, Wagner et al observed remarkable change in the electrical properties at high temperatures for semiconductor materials on exposure to reducing or oxidizing gases [6]. Based upon these facts, Seiyama et al for the first time developed semiconductor-based detector for gaseous components [7]. NO2 emitted by supersonic jets in atmosphere causes the destruction of ozone layer present in the stratosphere which absorbs the harmful damaging UV radiation coming from the sun
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