Synthesis And Ethanol Sensing Properties Of Zinc Oxide Micro/nanostructures

In recent years, gas sensors based on metal oxide semiconductor materials have attracted special attentions due to their high sensitivity, fast response, convenient fabrication, ease of use. Studies have shown that gas sensing properties of the sensors can be improved by changing the sensitive material microstructure and defects, which provides an effective way for design the high performance gas sensors.Nanostructured zinc oxide(Zn O) has varied morphology, so in our work,nanostructures Zn O with different morphologies are prepared then made gas sensors.The effects of microstructure on the sensing properties are investigated systematically and its related mechanismis analyzed. The main results are as follows:Firstly, micro/nano structural Zn O with different morphologies were synthesized via different chemical methods. The Zn O nanostructure morphology can be tuned by changing synthesis method and parameters. The flower-like Zn O hierarchical structures composed of nanorods were synthesized via hydrothermal method; Zn O micro/nano spheres composed of nanosheets were prepared by the chemical solution growth method. Zn O nanorod arrays were synthesized on the ITO transparent conductive glass by a two-step solution growth method, and it is found that the ammonia amount could effected on the size and preferred orientation of the Zn O nanorod in course of synthesis.Secondly, we prepare four gas sensors based on commercial Zn O powders, Zn O flower-like nanorods, rod-like Zn O and micro/nano spheres Zn O respectively, by using the traditional indirectly heated gas sensor production process. The sensors based on the as-prepared Zn O structures show high response and good selectivity to ethanol except the commercial Zn O powder sensor. The micro/nano spheres Zn O gas sensor has the optimal ethanol sensing properties among them, which may be caused by the large specific surface area, the high proportion of exposed(0001) polar facets and the high surface oxygen vacancy concentration of the structure. The results show that the morphology of Zn O can be controlled by changing the growth conditions andpreparation methods, thus the gas-sensing properties of Zn O based sensor can be controlled.Finally, Zn O nanorod arrays and Zn O nanorod powders were synthesized by chemical solution growth method. The Zn O-based gas sensors are prepared in two ways via in-situ grown Zn O nanorod arrays and coated Zn O nanorod powder on the surface of alumina ceramic tubes. Test results show that the optimal working temperature of these two sensors are both about 300℃. In the range of 10-500 ppm ethanol concentration, the response time and recovery time are less than 10 s, and the response increased linearly with ethanol concentration. The ethanol sensing properties of the sensors prepared by powder coating is higher than that of in-situ growth. These indicate that the coating methods can effect on the gas sensing properties, which is important for the preparation of the Zn O gas sensor.