The Research On Gas Sensors Based On Doped Mesoporous In₂O₃

With the rapid development in engineering in China in recent years,worse environment has brought us big troubles.Among them,air pollution always harms the health of mankind.NO₂,as a kind of toxic air pollutant,causes irreversible results in environment,such as acid rain and photochemical fog.Meanwhile,it has terrible effect on our health.For example,it can stimulate our membranes,eyes and lungs with toxicity.Gas sensors detecting NO₂ with low detection limit and high response is expected urgently.However,some gas sensors reported in recent papers always have the disadvantage of high detection limit.In order to solve this problem,our study focused on the sensing improvement of gas sensing materials on both structure and components so that gas sensors with high response and low detection limit can be obtained.We choose to make use of mesoporous materials providing large specific surface area to facilitate the adsorption and desorption of NO₂.Besides,we also changed the components of In₂O₃ by doping to produce more defects as active sites so that we can enhance the response to NO₂.In the introduction chapter of this thesis,semiconductor based gas sensors and their advantages were introduced.Also,the application and synthesis of mesoporous materials were introduced.At last,some characteristics of In₂O₃ were also mentioned.In Chapter 2,the proper method of nanocasting and etching template was explored.Besides,in order to characterize synthesized materials several characterization methods were used.The results show that the sample has a good long-range-order structure.In Chapter 3,we used nanocasting method which was mentioned before in Chapter 2 to synthesize the ordered mesoporous Ni-doped In₂O₃.Some methods were also used to characterize it.The results of characterization are shown that the Ni-doped In₂O₃ has long-range-order structure.We also measured the gas sensing properties of Ni-doped In₂O₃ and compared with that of undoped In₂O₃ mentioned in Chapter 2.It is found that the Ni doping can enhance the response of In₂O₃ to NO₂ in this case.In Chapter 4,enhancing synthesized temperature and Zr-doping were used to decrease the resistance of In₂O₃ mentioned in Chapter 2.Also,we characterized the sensing materials with various methods and the results showed that both samples have the ordered mesoporous structure.Besides,the gas sensing properties of Zr-doped In₂O₃ were measured and its detection limit is 20 ppb to NO₂.Meanwhile,the resistance is 23 K? and operating temperature is 75°C.It means that it has low loading so that it has great potential application in the nano and micro devices.In addition,we also compared the gas sensing properties of In₂O₃ and we found that the Zr-doping can enhance the response of In₂O₃ to NO₂.This thesis studied the gas sensors based on ordered mesoporous In₂O₃.Besides,different transition metals were doped in it to enhance the response to NO₂ and finally we obtained the gas sensor with excellent sensing properties.Specially,the resistance and operating temperature of gas sensor based on Zr-doped In₂O₃ is very low,which has great potential application in portable devices.