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Study On The Design And Application Of Ethanol Sensing Materials

Posted on:2014-01-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:H LiuFull Text:PDF
GTID:1228330395996357Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
As a common organic pollutant, ethanol is wide stay in our living environmentand has brought great convenience, but which brings tremendous harm to people.Particularly, during the past few years, numerous traffic accidents have beenoccurred, and most of them are attributed to driving after drinking. Up to now,ethanol sensors have been widely used in the fields of environmental protection, foodsafety, traffic safety etc. Therefore, it is very important to develop ethanol sensorswith high sensitivity, high selectivity, portable, and low power consumption.One-dimensional (1D) nanostructured materials based on metal oxides holdadvantages of high surface area, controllable morphology and good thermal stabilityunder various conditions. Additionally, the sensing performances of these1Dnanostructured materials can be enhanced by doping with noble metal or metal oxide,which ensure them as a hot topic in the field of gas sensing. Compared to othermethods toward preparation of1D nanomaterials, the electrospinning methodexhibits unique advantage due to its properties, such as simple structure of theequipment, easy to operate, controllable morphology of the1D nanomaterials byimproving spinning conditions. As a result, preparation ethanol sensors based on1Dmetal oxide nanomaterials using electrospinning technology has importantsignificance and application value.In this dissertation, three typical N-or P-type semiconductors1D nanofibersincluding SnO2, In2O3and LaxSr1-xFeO3were chosen as ethanol sensing materials,and the aim is to preparation of high performance ethanol sensors. For example,preparation of1D SnO2nanofibers with hollow structure using coaxial electrospinning technology; Preparation of uniaxially aligned In2O3nanofibers usingmagnetic-field-assisted electrospinning (MFAES) method; Preparation ofLaxSr1-xFeO3nanofibers doped with various amount of Sr element by tuning theratios of metal salts in the precursors. Then, the ethanol sensing performance of thesethree kinds of nanofibers and the relative sensing mechanism are also discussed.These results provide us some important methods and parameters for fabrication highperformance ethanol sensors. The innovative results obtained in this dissertationwere as following:1. Hollow SnO2nanofibers have been successfully prepared by coaxialelectrospinning using paraffins as inner fluid, and the ethanol sensing properties andsensing mechanism are also invested. By optimization the parameters such as thevoltage, the speeds of inner and outer fluids, hollow SnO2nanofibers with the poresizes about430nm have been successfully prepared under conditions of18kVvoltage and inner and outer fluids speeds with0.3and2.0mL/h. These hollow SnO2nanofibers exhibit faster response/recovery speeds, higher response and higherselectivity than those of SnO2nanofibers.2. Uniaxially aligned In2O3nanofibers have been successfully prepared byMFAES method. The relative work principle of MFAES, sensing properties andsensing mechanism of the ethanol sensor based on uniaxially aligned In2O3nanofibers have been also examined. By placing two magnets in parallel on thecollector, the stream of charged particles ejected spinning forces by the Lorentz forceand Coulomb electrostatic force during them moving to the collector, resulting information of uniaxially aligned In2O3nanofibers and randomly deposited In2O3nanofibers between the two magnets and on the surface of the magnets, respectively.The microstructure gas sensor is fabricated by spraying the In2O3nanofibers on thealumina substrate, which was previously covered with gold electrodes and ruthenium oxides as heater on frontal and back sides by screen printing technique. Interestingly,the ethanol sensing results indicate that response, response time and recovery time ofthe sensor for500ppm ethanol at operating temperature of120℃based onuniaxially aligned In2O3nanofibers are17,0.4s and3s, respectively, which is muchbetter than those of randomly deposited In2O3nanofibers. The charges adsorbed onthe surface of uniaxially aligned In2O3nanofibers would overlap along the fibers,forming continuous channels for electrons, which ensure the electrons move fasterthan that of randomly deposited In2O3nanofibers.3. By using electrospinning method, LaxSr1-xFeO3nanofibers doped withvarious content of Sr (where the value of x is0.6,0.7and0.8, respectively) havebeen successfully prepared by tuning the concentrations of precursors. The sensingperformances indicate that La0.7Sr0.3FeO3nanofibers show the biggest response valueof73.5among the three samples at the operating temperature of170℃.La0.7Sr0.3FeO3nanofibers also exhibit better sensing performance than that ofLa0.7Sr0.3FeO3nanoparticles at the same conditions. For example, the response timesof them are11s and98s, respectively. Furthermore, compared to the commercialMQ-3type ethanol sensor, the sensor based on La0.7Sr0.3FeO3nanofibers exhibitnumerous advantages of low operating temperature, high respeonse and fastresponse/recovery speeds, which is promising ethanol sensing material for potentialapplication.In summary, this dissertation reports the successful preparation of hollow SnO2nanofiber, uniaxially aligned In2O3nanofibers and LaxSr1-xFeO3nanofibers dopedwith various content of Sr by using electrospinning method. The characterizationsand ethanol sensing performance of these three kinds of1D nanofibers indicate that1D nanofibers are good candidates for fabrication of high performance gas sensors.The results further confirm the introduction of hollow structure, uniaxially aligned nanofibers and multiple metal oxides for1D nanofibers are the effective method forenhancing sensing performance of sensing materials.
Keywords/Search Tags:Ethanol sensing materials, gas sensor, hollow structure, uniaxially aligned, nanofibers, electrospinning
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