High Performance Gas Sensor Based On Modification Of SnO₂ Semiconducting Oxide

With the development of science and technology also the improvement of living standards,toxic and harmful gases produced in the production and life not only aggravate the environmental pollution,but also seriously threaten people's health and property safety.Some gases are an important component of resources and play a huge role in the resources utilization,such as methane.In the atmosphere of people oriented and energy crisis,it is necessary to monitor gases with detecting values.Compared with the analytical instruments,gas sensors have many unique advantages with miniaturization,intelligence and networking.In the development of high performance gas sensors,semiconductor oxide gas sensor have being a research hotspot.Although this type of sensor has been great and far-reaching development for gas detection,but still need further improvement in the following aspects: one is to further reduce the detection limit of the sensor and expand the detection range of the sensor;the two is to improve the stability of the sensor toward the surrounding environment such as temperature and humidity;the three is to increase the long term stability and the reliability of the sensor.In the development of sensor with the characteristics of high sensitivity,widely measuring range,fast response time,high selectivity,long life and reliability,we aim to make new progress in the sensing mechanism of the sensor for the benefit of mankind.In order to improve the performances of sensors,it is the key problem that preparing the semiconductor oxide sensitive materials with highperformance.In the development of high sensitivity,high selectivity,long life of semiconductor oxide sensitive materials,researchers have never stopped the pace.In addition to the noble metal loading,the semiconductor oxide composite methods,the nanosize and low dimensional are still the research hotspot of semiconductor oxide in the improvement of the gas sensor's sensitivity.In this paper,SnO₂ is the main object of study,through different methods to increase the sensitivity of SnO₂ and making a certain mechanism explanation.The main research contents include: loading the noble metal on the hierarchical structure to vary the reactive sites and adsorption sites of at the sensing material's surface reaction interface for improving the chemical reaction rate;constructing a surface reaction interface which is beneficial to the diffusion,adsorption of the target gas and the high reaction activity;preparing the semiconductor oxide composites with hierarchical structure and constructing oxide semiconductor heterojunction to change its energy band,electronic properties and chemical properties.The main results are summarized as follows:1.The hierarchical structure of Pd/SnO₂ and Pt/SnO₂ was successfully prepared by microwave hydrothermal synthesis method,and the carbon monoxide sensor was made by using this structure as sensitive material.By comparing the sensitivity of different sensors,the 3.0wt%Pd/SnO₂ and Pt/SnO₂ hierarchical structures have the best sensitivity to carbon monoxide.Compared with SnO₂,the sensor based on Pd/SnO₂ and Pt/SnO₂ has lower power consumption and detection limit to carbon monoxide.Among the two sensitive materials,Pd/SnO₂ has a lower optimal operating temperature?100°C?,while Pt/SnO₂ has a lower detection limit?1ppm?.The effect of antimony doping Pt/SnO₂ were study.2.The hollow structure of Pd doped SnO₂ was prepared by hydrothermal method,and the carbon monoxide sensor with high response value was fabricated by using this structure.The results of gas sensing characteristics show that the response of the sensor is 14.7 to the 100 ppm carbon monoxide.In addition,the carbon monoxide oxidation process on the surface of SnO₂?110?,Pd doped SnO₂?110?were calculated by DFT theory,showing that the reaction barrier of carbon monoxide on the Pd doped SnO₂?110?are lower,and it is a more easy and fast surface reaction consistent with the experimental phenomena.It provides theoretical guidance for the research of sensing mechanism.3.Indium-tin and cobalt-tin composite semiconductor oxides were prepared by one step hydrothermal method;Heterojunction semiconductor oxide of CoO/SnO₂ was prepared by two step hydrothermal method;three ethanol sensor were prepared.The gas sensing test results show that the response of the sensor based indium-tin composite semiconductor oxides is 59 to 100 ppm ethanol at 200°C.The response of the sensor?detection limit 1ppm?based cobalt-tin composite semiconductor oxides is 201 to 100 ppm ethanol at 200°C.The response of sensor based on CoO/SnO₂ is 145 to 100 ppm ethanol at 250°C.These three ethanol sensors are high performance with good selectivity and long-term stability,and the explanation of enhanced performances were given.