| With the development of the world’s industrial technology and the continuous improvement of people’s living standard, environmental pollution is increasingly serious. Excess emission of variety of toxic, hazardous, fammable explosive gas were threatening to our survival environment and health. Semiconductor sensors are widely used because of low cost, easy to use, easy to acquire signals, and so on. Preparation of high sensitivity, fast response, good selectivity and good stability gas sensitive materials are the most important study for gas sensors. Selecting suitable preparation method, doping, compositing, modifing and catalytic technology were comment methods during semiconductor material preparation. The structure, morphology and element content of the sensing materials can be effectively controlled by above methods and then the gas-sensing properties of the materials can be improved. That provides a basic reserch for developing performance of gas sensors.A new bipolar electrospinning system of double jets with opposite electric field was designed and developed in our experiments. The repulsion problem came from the same polaritys have been solved in this new system. SnO2/In2O3composite nanofibers were prepared by using the modified electrospinning system. The factors influencing the spinning fiber morphology was studied, including the type of organic solvents, solution concentration, spinning voltage, and jets distance, etc. The structure and morphology of SnO2/In2O3composite nanofibers based on bipolar electrospinning were characterized and analyzed. Gas sensors were fabricated based on SnO2,In2O3, SnO2/InO3nanofibers, respectively. Gas sensing properties were tested in formaldehy concentration range of0.5-50ppm. The response value of SnO2/In2O3gas sensor was higher than both SnO2and InO3sensors, respectively. Gas sensing mechanism of SnO2/In2O3composite nanofibers was analyzed.The preparation process of bipolar electrospinning with double jets were modeled and simulated. Jet streams from double jets with bipolar were simulated to many discreted charged particles. Electric force form bipolar, coulomb force between defferent particles, surface tension and viscoelastic force of charged particles were analyzed in bipolar electric field of space. Motion locus model of jet stream was built. Motion locus of bipolar jet streams were numerical calculation based Runge-Kutta algorithm, respectively. And then, the motion locus of spinning fibers were simulated by MATLAB software. Many factors effected spinning fibers morphology was analyzed in electrospinning process. Using low temperature radio frequency plasma technology, SnO2nanofibers, SnO2/In2O3composite nanofibers and MWCNTs doped PANI were modified by O2plasma at low temperature. Combined with XRD, SEM, TEM, EDX, XPS, BET characterization methods, the morphology, structure and stoichiometric of three kinds gas sensitive meterials were analyzed. The mechanism of sensing material surface interacted with O2plasma were analyzed. Gas sensing properties test results of gas sensing materials modified by O2plasma show that O2plasma modification greatly improved the gas sensing properties of MWCNTs doped PANI to ammonia vapor. O2plasma modificationon greatly improved response sensitivity of gas sensor based on SnO2nanofibers and SnO2/In2O3composite nanofibers to formaldehyde. Both the operating temperature and the response times of the gas sensing materials were reduced. Gas sensing mechanisms of the sensitive materials modified by O2plasma were analyzed. |
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