Selective detection of acetone and gasoline by temperature modulation in zinc oxide nanosheets sensors
Introduction
ZnO nanostructures are interesting to study not only because of the recent demonstrations of unique physical properties, but also because a wide variety of morphologies have been prepared. The size and morphology of ZnO nano-particles have great influences on their performances. Because the properties of nano-materials depend on their size and shape, new synthetic strategies in which the size and shape of nanostructures can be easily tailored are important. Some of the ZnO nanostructures exhibit nanowire, nanorod, nanoribbon, nanoplate, nanotube, tetrapod, cage-like and flower-like structures [1], [2], [3], [4], [5], [6], [7], [8], [9]. Among the various ZnO nanostructures, relatively few studies on the properties of two-dimensional ZnO nanosheets have been reported up to now. ZnO nanosheets have shown superior properties in nanoscale optoelectronics, solar cell electrode, catalysis and sensor devices [10], [11], [12]. The ZnO nanosheets have been prepared by various methods, such as, thermal oxidation of zinc powders, carbon-thermal redox of ZnO powders [13], [14] and chemical vapor deposition [15]. These methods need high temperature and are also limited by their low yields. However, the sovolthermal route is an important and simple low-temperature method for wet chemistry, and has been employed to fabricate ZnO nanopowders.
Gasoline is used as a fuel for automobiles. Normal human breath contains hundreds of volatile organic compounds (VOCs) in very low concentrations ranging from part-per-trillion to part-per-billion levels [16]. Some VOCs have been identified as biomarkers of specific diseases. For instance, acetone in human breath gas has been established as a biomarker for type-1diabetes (T1D). Hence, it will be very lucrative if a sensor can be developed to detect several gases. For a long time, metal oxide semiconductors gas sensors have played an important role in environment monitoring and chemical process controlling. Among the various solid-state sensors, zinc oxide (ZnO) is an interesting chemically and thermally stable n-type semiconductor with large exciton binding energy, large bandgap energy, and high sensitivity to toxic and combustible gases [17]. To date, various types of ZnO-based gas sensors, such as thick films [18], nanoparticles [19], [20], [21], [22], [23], have been demonstrated. Here, we report an interesting observation for ZnO gas sensors, where the same sensors can selectively detect acetone and gasoline through temperature modulation.
Section snippets
Experimental
ZnO nanosheets were synthesized by a simple mixed hydrothermal method. All reagents were 99.9% purity or better and purchased from Shanghai Chemical Reagent Co. and used without further purification. First, 0.004 mol zinc nitrate (Zn(NO3)2·6H2O) and 0.002 mol cetyltrimethyl ammonium bromide (CTAB, C19H42BrN) were dissolved in 46 mL 1, 2-propanediol and distilled water with the ratio of 1:1 under constant stirring. Then 0.002 mol urea was introduced into the above-mentioned solution. After 10 min
Results and discussion
To obtain structure and chemical composition evidence of ZnO nanosheets, X-ray powder diffraction was performed immediately after sample preparation. As shown in Fig. 2, all the reflection peaks of the products can be well indexed to pure hexagonal phase ZnO, which are in good agreement with the literature values (JCPDS card number 79-2205). No diffraction peaks from any other impurities are detected. The obtained particles composed of high crystalline ZnO with wurtzite crystal structure. The
Conclusions
ZnO nanosheets have been synthesized successfully by using a simple mixed hydrothermal method. The thickness of the ZnO nanosheets is in the range of 10–20 nm, and the width-to-thickness ratios of the ZnO sheets almost reach up to one thousand. The formation mechanism and effect of CTAB on the morphology of ZnO nanosheets have also been discussed. It has been found that the gas sensor made by these ZnO nanosheets can detect gasoline at 180 °C, and the same sensor can selectively detect acetone at
Acknowledgements
This work has been supported by the National Nature Science Foundation (50672075), the NCET and 111 Program (B08040) of MOE, and Xi'an Science & Technology Foundation (CXY08006, XA-AM-200905, and XA-AM-200906), and the Fundamental Research Foundation (NPU-FFR-200703) and Doctorate Foundation (CX200804) of NPU, and the SKLSP Research Fund (40-QZ-2009) of China.
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