ZnO hollow spheres: Preparation, characterization, and gas sensing properties

ZnO hollow spheres were successfully prepared by using carbon microspheres as templates and characterized by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). A gas sensor was fabricated from the as-prepared ZnO hollow spheres and tested to different concentrations of NH3 and NO2 at different operating temperatures. The results showed that the ZnO hollow-sphere sensor exhibited extremely different sensing behaviors to NH3 and NO2. The optimum operating temperature of the sensor was 220 degrees C for NH3 and 240 degrees C for NO2, respectively. At 220 degrees C, the responses to 25, 50 and 75 ppm NH3 were 7.9, 11.1 and 20.4 and the response times were as long as several minutes. At 240 degrees C, the responses to 10, 50 and 100 ppm NO2 were 140.6, 172.8 and 286.8 and the corresponding response times were 31, 19 and 9s. In addition, it is also shown that the gas sensor exhibited much higher response to NO2 than to other gases at 240 degrees C, implying the good selectivity and potential application of the sensor for detecting NO2. (C) 2009 Elsevier B.V. All rights reserved