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Preparation and Gas-sensing Propetries of Indium Oxide Based Nano-materials

Author: LiJiaJing
Tutor: WuFengQing
School: Jilin University
Course: Physical and chemical
Keywords: In2O3 sol-gel method nano-materials H2S gas sensing properties
CLC: X831
Type: Master's thesis
Year: 2012
Downloads: 84
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Abstract


With the development of material and spiritual culture level, the environmentalissues have attracted much attention of people. In recent years, industrial emissionsare common occurrences and have strong impact on the environmental pollution.Thus, gas sensors have been widely used for industrial process monitoring, for variouspolluting and toxic gases. Hydrogen sulphide （H2S） detection is a very importanttarget for the mining of gas and coal, and the production of petrochemicalmanufacturing. This gas can be very hazardous to human bodies when itsconcentration is higher than250ppm. For ensuring the safety of workers and theenvironment, the gas sensor with excellent performance for monitoring andcontrolling of H2S is crucial in laboratories and industrial areas.Semiconductor materials with unique optical, magnetic, gas and heat sensitivity,therefore, it have been widely used in many areas, with the field of gas sensorincluded. Indium oxide （In2O3） as a wide bandgap semiconductor material is featuredwith less resistivity and high catalytic performance, which attracts the majority ofresearchers. However, as a generally sensitive material, promoting the selectivity ofthe indium oxide has become the research priority.Since the nano-materials were reported in1984, its special structure, physical andchemical properties, has caused various areas of concern. Researchers in various areashave shown great enthusiasm on nano-materials. With the research to the depth,nano-materials have been widely used in various fields including biomedicine,mechanical electronics, environmental energy, aerospace, engineering constructionand optoelectronic information. The development of nanotechnology enables the control and the modification on the molecular scale, so it promotes the developmentof material modification, and greatly enhances the performance of functionalmaterials.In this paper, In2O3nano-materials are prepared. The efforts were made to improvethe sensitive property such as high selectivity by chemical modification. Preciousmetal doping is considered to be an effective mean for promoting the materialselectivity; therefore, the Pt doping is performed in the experiment. To furtherenhance the gas sensing property such as the response and recovery characteristicsand the stability, the material is doped with carbon nanotubes. Due to the droping ofcarbon nanotube, the material has a bigger pore diameter, which is beneficial to theadsorption and desorption of gas and increase the gas sensing property. Details are asfollows:1. The In2O3nano-materials are synthesized by a sol-gel method. The materialsare characterized by the X-ray diffraction （XRD）, transmission electron microscopy（TEM） and scanning electron microscopy （SEM）. The synthesized In2O3is a cubicstructure, the grain size is about20nm, and has partly aggregate phenomenon. Thematerial is calcined at different temperature, and prepared into an indirectly heatedsensor. For the problem of low sensitivity by testing the sensitivity of40ppm H2S gas,further doping is performed for promoting the sensitive property. The sensitivity ofthe material are better when calcined at500°C and600°C, so further experiment isneeded for determining the most favorable experimental calcined temperature.2. Different concentrations of Pt doped In2O3composite material are preparedand respectively calcined at500°C and600°C. The XRD characterization resultsshow that the doped In2O3crystal structure is still cubic crystal. The gas sensingperformance shows that the6mol%Pt doped In2O3gas sensor has best sensitivity onH2S at600°C. The optimal operating temperature is140°C. The sensitivity of thedoped sensor is17times that of the pure, which shows that the Pt doping enhances thesensitivity of gas sensors to H2S. At140°C, the gas sensitive properties are furthertested, and the response time is11seconds, the recovery time is about21seconds. So the selectivity is fine and the stability floats at a certain level. In summary, theresponse and recovery time and the stability need to be further improved.3. On the basis of6mol%Pt doped In2O3material, different concentrations ofcarbon nanotubes are doped, calcined at600°C for2hour. The characterized resultshows that the doped carbon nanotubes in the material at600°C are burnt, leaving alot of pore. Gas sensors are prepared, and the test results show that1wt%C,6mol%Pt doped In2O3gas sensor has best sensitivity on H2S at140°C. The response time isabout5seconds, and the recovery time is about14seconds. The sensor has betterselectivity and a certain increase of stability. In all, carbon nanotubes treated enhancesthe performance of the gas sensing properties in all aspects.

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