| With the rapid industrialization and fast increase of population, pollute the environment and harmful to health gases cause great threat to the industries and human’s day life. In the face of this problem, the research and development of gas sensor is very important.ZnO is a kind of n-type semiconductor material, has excellent gas sensitivity,optical and antibacterial characteristics, as well as low cost and environmental friendly. These advantages make the application of ZnO in the gas sensor is very common. However, the synthesis process and technology limited the development of the gas sensor, there are still some shortcomings such as complicated synthetic steps,difficult to modification, low sensitivity, bad stability, high working temperature and so on. Previous studies found that the morphology, grain size and composition of materials have a strong influence on their performance, and gas sensing properties.Therefore, we explore different synthesis methods to get various morphologies and excellent performance of ZnO. The photoluminescence, gas sensing and antimicrobial properties of material after doped with noble metals was discussed. In addition, a possible mechanism about gas sensing mechanism of ZnO was proposed in the paper,and the non-linear relation of response and gas concentrations also discussed. The main work of this paper includes the following five parts:(1) ZnO nanosheets were synthesized by hydrothermal method, and discuss the effect of egg white on crystal size and surface morphology. Sheet-like structure of ZnO is of large specific surface area and small size can great improve gas sensing properties of material. Meanwhile, ZnO reveal excellent antimicrobial activity against Staphylococcus aureus.(2) Ag/ZnO nanosheet was prepared using rape pollen grains as bio-template.After doping Ag, the grain size was obviously decreased and showed poriferous and lax structure. Ag(2 at%)/ZnO sensors has the maximum response to acetone gas atlow working temperature. The antimicrobial activity of Ag/ZnO in Escherichia coli and Staphylococcus aureus was positively correlated to Ag modifying molar ratio.(3) Nano-ZnO was successfully prepared by solution combustion method, using tartaric acid as fuel can greatly reduce the reaction temperature. Pure ZnO was sheet-like structure, which turn to six pyramid structure and grain size increase after doped Pd. The response of Pd/ZnO sensors to ethanol and acetone gas entirely different can significantly enhance selectivity of sensors to these two gases.Photoluminescence spectrum test showed that the UV emission peak of Pd doped samples is blue shifted and the peak intensity increased.(4) Au/ZnO nanoparticles were synthesized via a facile solution combustion method, NaCl as nucleation center can restrain the agglomeration of particles. Au doping leads to the decrease of crystallinity and particles size. At working temperature of 300 ℃, Au(4 at%)/ZnO sensors has the maximum response of 174 in500 ppm acetone gas, which shows excellent selectivity; and showed a good linear relationship between the logarithmic curve of sensitivity and acetone concentrations.(5) Au/ZnO nanospindles were synthesized through a precipitation and subsequent microwave irradiation procedure. Au nanoparticles in the amorphous state,lead to the destruction of nanospindle and grain size reduce. The Au(1 at%)/ZnO sensor showed a highly enhanced response(226.8) to 400 ppm acetone gas at a relatively low working temperature(270 oC), which is 8.4 times higher than that of pure ZnO sensor. The highly enhanced acetone gas sensitivity of Au/ZnO sensor could be attributed to its enhanced polarity owing to the peculiar morphology,catalytic effect of Au, as well as Schottcky barriers. |
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