| Toxic and harmful gases in the environment are threatening human health and life safety.In order to monitor these toxic and harmful gases in real time and create a comfortable and safe living environment for human beings,gas sensitive sensor technology came into being.ZnO has been widely used in gas sensors due to its advantages of good physical and chemical stability,non-toxicity and harmlessness,low cost,easy preparation and more abundant nano-morphology.At present,gas sensors based on ZnO nanostructures have problems such as high operating temperature,low responsivity and slow response.Therefore,for the above problems of ZnO nanostructure gas sensor,the main contents of this thesis are as follows:(1)A certain amount of zinc acetate dihydrate and diethylene glycol was weighted and added to prepare a certain concentration of solution,ZnO nanospheres with a larger specific surface area,a smaller grain size and mesoporous were successfully synthesized by simple and inexpensive solventhermal method at different growth temperatures of 140,160,180,200,220,240,260 and 280? for 15 min or 30 min,respectively.Gas sensors based on all these NSs exhibit the same optimal working temperature of 235? and good selectivity to ethanol gas.The gas sensor based on ZnO NSs synthesized at 260? shows the best gas sensing performances: the response to 100 ppm ethanol gas is 61.2,the response time and recovery time are 15 s and 16 s respectively,the lowest detection limit is 100 ppb,and it has good repeatability and long-term stability.Finally,the ethanol gas sensing mechanism of the sensor is discussed.(2)A certain amount of ZnO nanospheres powder synthesized at 180°Cwas weighted and added into different concentrations of aqueous solution of chloroauric acid with a small amount of ammonia(25%)by simple solution immersion method at room temperature for 12 h.The surface modification of ZnO NSs with different concentration of Au nanoparticles were successfully synthesized.After modification,the optimal working temperature of Au@ZnO NSs sensor was reduced by 65 °C,and the most sensitive target gas was changed from ethanol gas to acetone gas.The Au@ZnO NSs sensor based on the amount of Aumodified is 1.63 at% sample exhibits the best gas sensing performances: the response to 100 ppm acetone gas is 192.4,the response time and recovery time are 27 s and 18 s respectively,the lowest detection limit is 500 ppb,and it has good repeatability and long-term stability.The performances of Au@ZnO NSs sensor were greatly improved,which was attributed to the Schottky barrier formed between Au and ZnO,as well as the overflow effect and catalytic activity of Au nanoparticles.(3)A certain amount of ZnO nanospheres powder synthesized at 180°C was weighted and added into a solution of anhydrous ethanol and diethylene glycol with different concentrations of nickel nitrate hexahydrate by mild hydrothermal method at 160°C for 12 h.The surface modification of ZnO NSs with different concentration of NiO nanoparticles were successfully synthesized,and a novel pn-type semiconductor gas sensor was designed.After modification,the optimal working temperature of NiO@ZnO NSs sensor was reduced by 25°C,and the most sensitive target gas was changed from ethanol gas to acetone gas.The NiO@ZnO NSs sensor based on the amount of Ni modified is 1.93 at% sample exhibits the best gas sensing performances: the response to 100 ppm acetone gas is 20.7,the lowest detection limit is 1 ppm,and it has good repeatability and long-term stability.The improvement of the above performances of NiO@ZnO NSs sensor was attributed to the formation of the heterojunction barriers between p-type NiO and n-type ZnO,as well as the generation of extra electron depletion layer on the surface of ZnO caused by smaller NiO nanoparticles. |
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