Detection of hazardous volatile organic compounds (VOCs) by metal oxide nanostructures-based gas sensors: A review

Quantum dots are a unique class of emitters with size-tunable emission wavelengths, saturated emission colors, near-unity luminance efficiency, inherent photo- and thermal- stability and excellent solution processability. Quantum dots have been used as down-converters for back-lighting in liquid-crystal displays to improve color gamut, leading to the booming of quantum-dot televisions in consumer market. In the past few years, efficiency and lifetime of electroluminescence devices based on quantum dots achieved tremendous progress. These encouraging facts foreshadow the commercialization of quantum-dot light-emitting diodes (QLEDs), which promises an unprecedented generation of cost-effective, large-area, energy-saving, wide-color-gamut, ultra-thin and flexible displays. Here we provide a Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays. We also identify a few key challenges facing the development of active-matrix QLED displays.

Quantum-Dot Light-Emitting Diodes for Large-Area Displays: Towards the Dawn of Commercialization.

Zinc oxide nanoparticles were synthesized using a simple precipitation method with zinc sulfate and sodium hydroxide as starting materials. The synthesized sample was calcined at different temperatures for 2 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and proton-induced X-ray emission (PIXE) analysis. SEM images show various morphological changes of ZnO obtained by the above method. The average crystallite sizes of the samples were calculated from the full width at half maximum of XRD peaks by using Debye-Scherrer's formula and were found to be in the nanorange. EDS shows that the above route produced highly pure ZnO nanostructures. PIXE technique was used for trace elemental analysis of ZnO. The optical band gaps of various ZnO powders were calculated from UV-visible diffuse reflectance spectroscopic studies.

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Synthesis, characterization and optical properties of zinc oxide nanoparticles

ZnO nanoparticles have been synthesized by precipitation method from Zinc nitrate. The powder was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, UV-vis optical absorption, and photoluminescence spectroscopy analyses. XRD patterns showed that ZnO nanoparticles have hexagonal unit cell structure. SEM and TEM pictures reveal the morphology and particle size of prepared ZnO nanoparticles. The UV-vis absorption spectrum shows an absorption band at 355 nm due to ZnO nanoparticles. The photoluminescence spectrum exhibits two emission peaks one at 392 nm corresponding to band gap excitonic emission and another located at 520 nm due to the presence of singly ionized oxygen vacancies. The synthesis method has potential for application in manufacturing units due to ease processing and more economical reagents.

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Synthesis, Characterization, and Spectroscopic Properties of ZnO Nanoparticles

Al-doped zinc oxide (ZnO) thin films were prepared by chemical spray pyrolysis technique. The dopant concentration (Al/Zn at%) varied from 0 to 1.5 at%. Structural analysis of the films reveals that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure with (0 0 2) preferred orientation. The lattice constants calculated from the most prominent peaks are found to be in good agreement with the ICDD reference pattern: zinc oxide, 01-080-0074 (a = 3.2535 A and c = 5.2151 A). The sensing properties of the films towards methanol vapour are investigated for various concentrations of methanol in air at different operating temperatures in the range 200–350 °C. It is observed that compared to the undoped ZnO film, Al-doped films show higher sensitivity to methanol vapour. Among all the Al-doped films studied, the 0.5 at% Al-doped ZnO film shows the maximum response (∼44%) at 275 °C to 500 ppm of methanol vapour in air. Further, the films show fast response and recovery to methanol vapour at higher operating temperatures. The methanol-sensing mechanism of the film has been explained.

Al-doped ZnO thin films as methanol sensors

ZnO thin films were prepared by sol–gel dip coating method using zinc acetate dihydrate and 2-ethanolamine as the starting materials. The powder and its thin film were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM) and IR spectra methods. The results indicated that the ZnO particles crystallized in the wurtzite phase, which were well-distributed in the films with the mean particle size of about 10 nm. The IR spectra of the gel and powders annealed at different temperatures were investigated. It showed that the vibration bands of NH and mono-acetate diminished and the stretching mode of ZnO at 471 cm−1 appeared after the dried gel annealed at 500 °C for 1 h. The diameter, D of ZnO particles in the monolayer was also calculated from the optical spectroscopy curve, which is close to that obtained from AFM observation. The gas-sensing properties of the multi-layers for alcohols with different chain lengths were measured at room temperature. The thin films exhibited high sensitivity and rapid response–recovery characteristics to these gases. The film can detect methanol, ethanol and propyl alcohol vapor as low concentration as 1, 10, and 0.5 ppm, respectively.

ZnO nanoparticulate thin film: preparation, characterization and gas-sensing property

https://hal.archives-ouvertes.fr/hal-00638336/document

Study on Sm1.8Ce0.2CuO4–Ce0.9Gd0.1O1.95 composite cathode materials for intermediate temperature solid oxide fuel cell

https://hal.archives-ouvertes.fr/hal-00957382/document

Li-Hua Huo

Papers

ZnO nanoparticulate thin film: preparation, characterization and gas-sensing property

Study on Sm1.8Ce0.2CuO4–Ce0.9Gd0.1O1.95 composite cathode materials for intermediate temperature solid oxide fuel cell

Study of oxygen reduction mechanism on Ag modified Sm1.8Ce0.2CuO4 cathode for solid oxide fuel cell

Effects of calcium doping to oxygen reduction activity on Pr2-xCaxNiMnO6 cathode

Preparation, characterization and gas sensitivity of copper naphthalocyanine derivatives LB films