| As a kind of detecting device, gas sensor can convert gas species or concentration to electrical signals, has been applied widely for environmental monitoring and industrial process control. The N-type wide band gap metal oxide semiconductor sensing material has been widely used in gas sensors, ZnO has been widely used to be gas sensor for its physical and chemical ability. However, due to the complicated application environment, diversity of the gas species and other factors, The ZnO gas sensor shows low response, high operating temperature and other problems in practical application. For its past research, we found surface morphology, grain size, specific surface area, etc, have closely relationship to ZnO gas sensing property. For this research, we prepared different morphologies ZnO materials by hydrothermal and precipitation methods, respectively. Systemic study the two different morphologies of ZnO gas-sensing properties, the following conclusions:The hierarchically assembled porous ZnO was synthesized through hydrothermal reaction by hydrothermal reaction for 2h, 6h and 16 h. the range of pore size were 16.6 to 18.3nm. From the SEM images we can see that the products were composed of flake shapes. The specific surface area of ZnO samples were in the range of 25.8 to 38.4m2/g. The highest sensitivity was 320.9 and 66.1, respectively. For the sensor based on hierarchical 3D porous ZnO, which prepared from 2h and 6h, for 100 ppm n-butyl alcohol and acetone at the operation temperature. The three ZnO samples sensors show highly sensitivity for n-butyl alcohol, when concentrations reached from 100-1000 ppm of ethanol, n-butyl alcohol, acetone, benezene. The response and recovery times of the sensor based on 3D hierarchical flower-like ZnO were less than 20 s to 100 ppm ethanol.The porous flower-like ZnO hierarchical nanostructures were fabricated by the method of precipitation, combining with annealing process. The powders before and after sintering were hexagonal system ZnO by X-ray diffraction. The porous flower-like ZnO hierarchical nanostructure was composed of micrometer spheres which assembled by nanoflakes and the microstructure of obtained ZnO powders were characterized by scanning electron microscope. The pore size was 24 nm and surface area was 82.78 m2/g. The sensor based on the porous flower-like ZnO hierarchical nanostructure show high response about 88.7 and 54 to 100 ppm ethanol and 100 ppm acetone at the operation temperature of 400℃, 420℃,respectively. The highest response to ethanol, acetone with the concentration range of 10-1000 ppm were estimated to be 322, 220, respectively. The response and recovery times of sensor to 100 ppm ethanol were 15 s and 20~30s. The good sensing performance of the hierarchical porous ZnO sensor indicated that the hierarchically assembled porous ZnO could be a promising candidate for highly sensitive gas sensor.Compared with gas-sensing performance of hierarchically porous ZnO synthesized by two methods, the hierarchically ZnO has the flower-like structure which was similar to flowers. Similarly, the hierarchical porous flower-like ZnO structure was better than porous microspheres ZnO in gas-sensing performance of sensitivity, optimum operating temperature and response and recovery times. But the precipitate method was more simply than the hydrothermal method, the macroporous structure was changed into mesoporous structure which provided gas molecules channel after sintering process. But the optimum operating temperature was high and very strict to control the concentration of sodium citrate. Therefore, the nano flower-like hierarchical structure ZnO prepared by hydrothermal method has more positive and far-reaching study significance. |
PDF Full Text Request