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 °C for NH3 and 240 °C for NO2, respectively. At 220 °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 °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 9 s. In addition, it is also shown that the gas sensor exhibited much higher response to NO2 than to other gases at 240 °C, implying the good selectivity and potential application of the sensor for detecting NO2.