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Proceedings ArticleDOI

Highly sensitive H2 gas sensor of Co doped ZnO nanostructures

10 Apr 2018-Vol. 1942, Iss: 1, pp 050059

AbstractIn this report, the hydrogen gas sensing properties based on Co doped ZnO nanostructures are explored. The undoped and Co doped nanostructures were grown by RF magnetron sputtering system, and its structural, morphological, and hydrogen sensing behavior are investigated. The maximum relative response was occurred by the 2.5% Co doped ZnO nanostructures among undoped and other doped sensors. The enhancement of relative response might be due to large chemisorbed sites formation on the ZnO surface for the reaction to hydrogen gas. more

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Abstract: Three-dimensionally ordered macro/mesoporous materials are known to possess a large accessible surface area with impressive permeability. In this work, we combine electrophoresis and electrodeposition to fabricate a hierarchical bi-layered inverse opaline film in which a ZnO sensing layer is stacked with an Au electrode for impressive H2 sensing activities. To enhance its responsiveness, both morphological and crystallographic properties of ZnO inverse opals are optimized using KCl as the porogen. The resulting ZnO inverse opals demonstrate a specific surface area that is three times larger over comparable ZnO inverse opals by the formation of nanoporous skeletons. In addition, the deposition bath was deliberately designed so the predominant crystallographic plane of ZnO is shifted from (10 1 - 0) to (0001) as the latter exhibits superior activity toward reducing gases. Through X-ray photoelectron spectroscopy, we show a significant increase of chemisorbed oxygen on the (0001) plane. Consequently, our hierarchical bi-layered inverse opals reveal a 500 % improvement in the sensitivity toward 15 ppm H2 under 200 °C. In short, this is the first demonstration of a vertically-arranged inverse opaline film incorporating both metal and oxide layers to function as an integrated three-dimensional gas sensor with low detection limit.

12 citations

Journal ArticleDOI
28 Jun 2021-Sensors
Abstract: Monitoring and detecting carbon monoxide (CO) are critical because this gas is toxic and harmful to the ecosystem. In this respect, designing high-performance gas sensors for CO detection is necessary. Zinc oxide-based materials are promising for use as CO sensors, owing to their good sensing response, electrical performance, cost-effectiveness, long-term stability, low power consumption, ease of manufacturing, chemical stability, and non-toxicity. Nevertheless, further progress in gas sensing requires improving the selectivity and sensitivity, and lowering the operating temperature. Recently, different strategies have been implemented to improve the sensitivity and selectivity of ZnO to CO, highlighting the doping of ZnO. Many studies concluded that doped ZnO demonstrates better sensing properties than those of undoped ZnO in detecting CO. Therefore, in this review, we analyze and discuss, in detail, the recent advances in doped ZnO for CO sensing applications. First, experimental studies on ZnO doped with transition metals, boron group elements, and alkaline earth metals as CO sensors are comprehensively reviewed. We then focused on analyzing theoretical and combined experimental-theoretical studies. Finally, we present the conclusions and some perspectives for future investigations in the context of advancements in CO sensing using doped ZnO, which include room-temperature gas sensing.

2 citations

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Journal ArticleDOI
Abstract: Hydrogen is a very important molecule with an enormous breadth and extent of application and use. It is currently being used in many industries, from chemical and refining to metallurgical, glass and electronics. Hydrogen is primarily used as a reactant. But it is also being used as a fuel in space applications, as an “O2 scavenger” in heat treating of metals and for its low viscosity and density. In this paper, current industrial uses of hydrogen in various industries in the industrial world will be summarized. Due to the increased use of heavier crude oils, containing higher amounts of sulfur and nitrogen and to meet stringent emission standards, need for hydrogen is experiencing a very rapid growth in the petroleum refining industry. Hence this application will be discussed in more detail.

462 citations

Journal ArticleDOI
Abstract: Aligned zinc oxide nanorods were synthesized directly via a two-step solution approach on an Al2O3 tube, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The zinc oxide nanorods prepared were uniform with diameters of 10–30 nm and lengths about 1.4 μm. The response Sr (= Ra/Rg) of the aligned zinc oxide nanorod sensor reached 18.29 and 10.41 to 100 ppm ethanol and hydrogen, respectively, which was a two-fold increase compared with that reported in literature, demonstrating the potential for developing stable and sensitive gas sensors.

299 citations

Journal ArticleDOI
Abstract: In this work, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique. The obtained La-doped ZnO products were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show that La doping changes the structures of ZnO nanofibers markedly. La-doped ZnO nanofibers have unique bead-like nanostructures, in which two phases of hexagonal La2O3 and wurtzite ZnO coexist along with partially incorporation of La into ZnO lattice. The gas sensing performances of the La-doped ZnO nanostructures to acetone were investigated via static gas sensor testing system. The sensing test results indicate that an appropriate amount of La doping greatly improves the gas sensing properties of ZnO nanofibers. The 1.0 wt% La-doped ZnO sensor has the highest selectivity and response (64, to 200 ppm acetone at 340 °C), in addition to its short response time and recovery time. The unique bead-like structure and the gas sensing mechanism of La-doped ZnO nanofibers are discussed. The La-doped ZnO nanostructures we have produced can be used as a promising material for acetone sensors.

93 citations

Journal ArticleDOI
Abstract: Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150 °C. The morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy. Gas-sensing testing results demonstrated that Ni-doped ZnO nanorods had enhanced gas-sensing performance. Furthermore, AC impedance spectroscopy and DC current–voltage curves were observed to investigate the gas-sensing mechanism. Current–voltage curves are approximately close to a linear function, indicating the potential barriers formed at the electron-depleted surface layer occupy a dominant when carriers transport in the gas sensor, and AC impedance spectra indicates the potential barriers height of the electron-depleted surface layer.

66 citations

Journal ArticleDOI
Abstract: In the present work, influence of terbium doping on structural, morphological, optical and gas sensing properties of zinc oxide has been studied. A chemical route was adopted for synthesis of pure and terbium (Tb) doped zinc oxide. X-ray diffraction study confirmed the formation of hexagonal wurtzite structure for synthesized materials. Raman analysis revealed the shifting and broadening of peaks with increase in Tb concentration. The presence of terbium in ZnO and its oxidation states was confirmed using X-ray photoelectron spectroscopy. Photoluminescence emissions indicated increase in concentration of oxygen vacancies with introduction of dopant. Gas sensors were fabricated out of synthesized samples and it was observed that doped samples have significantly high sensing response, temperature dependent selectivity toward ethanol and acetone, and sensors were able to detect even low concentration (∼10 ppm) of these vapors. The temperature dependent selectivity of terbium doped ZnO depends on target gas which may be ascribed to interaction of target gas molecules and doped metal oxide surface at optimum operating temperature. It was found that 4% Tb doped ZnO sensor exhibited maximum sensor response toward ethanol and acetone. The enhanced sensing response has been attributed to increase in oxygen vacancies, reduction in particle size, large structural disorders and high surface basicity.

55 citations