Study On The Structure Design Of Fe₂O₃Nanofibers And Its Sensing Properties

With the rapid development of the social economy, environmental problems havebecome more and more seriously. Especially the air quality problems, which hasaffected people’s lives seriously. In order to detect the inflammable and explosivegases and the common toxic and harmful gases, gas sensor has played an importantrole in our lives.Fe2O3is a kind of metal oxide materials, which is common and stable. It possessesthe excellent physical and chemical properties, which has been widely used inbatteries, pigment, photoelectrolysis reactors, magnetism, catalysts, drug delivery andgas sensors. In the field of gas sensor, Fe2O3has been used to detect various gases.However, the gas sensing properties of Fe2O3are relative low, which can hardly meetour needs. In order to improve the properties of gas sensitive materials, the mostfrequently used methods are doping, lowering dimension and forming pores. However,it has rarely been reported by using these methods at the same time, let alone combingthe synthesis of materials and the devices making, which is the vital aspect of theapplication of gas sensor. Earlier studies have shown that the gas sensor based on themetal oxide semiconductor nanomaterials exhibits the better gas sensing properties.In this thesis, we engage in the structure design of Fe2O3to improve its gassensing properties based on electrospinning technology by adjusting the ratio of rawmaterials of precursor solution and by the doping method. The details are exhibited asfollows.1. Design and synthesize one-dimensional metal oxide semiconductornanomaterials with different morphologies. By adjusting the ratio of raw materials ofprecursor solution, which are Fe(NO3)3·9H2O, PVP, DMF and ethanol, we electrospunthe PVP/Fe(NO3)3composite fiber. After calcined these composite fiber at a hightemperature, we obtained the α-Fe2O3nanotubes and the α-Fe2O3nanotube-in-nanotubes. The results of gas sensing tests show the responses of α-Fe2O3nanotubes and the α-Fe2O3nanotube-in-nanotubes to500ppm acetone are3.5and9.3 at the optimum operating temperature of240°C, respectively. At the meantime, theresponse/recovery times of them are3/5s and2/5s, respectively.2. Dope metal into the one-dimensional metal oxide semiconductor nanomaterials.We doped different proportions of La and Ce into α-Fe2O3, respectively, in order toverify the promotion of their gas sensing performances. The results show that the7wt%La doped-α-Fe2O3nanotubes show the best gas sensing properties among the4samples of doping La. The response of the gas sensor based on7wt%Ladoped-α-Fe2O3nanotubes to50ppm acetone is26.1at240°C, which is10timeslarger than that of the pure α-Fe2O3nanotubes. The response/recovery times of it are3/10s. The lowest detecting limit of it to acetone is1ppm (the response is2.64). The4at%Ce doped-α-Fe2O3nanotubes show the best gas sensing properties among the4samples of doping Ce. The response of the gas sensor based on4at%Cedoped-α-Fe2O3nanotubes to50ppm acetone is21.5at240°C, which is8.3timeslarger than that of the pure α-Fe2O3nanotubes. The response/recovery times of it are3/8s. The lowest detecting limit of it to acetone is1ppm (the response is3).Moreover, the gas sensor based on7wt%La doped-α-Fe2O3nanotubes and the gassensor based on4at%Ce doped-α-Fe2O3nanotubes all possess the excellentselectively and long-term stability.3. Synthesize the metal compound oxides. We doped a certain amount of SnO2and In2O3into α-Fe2O3, respectively, in order to verify the promotion of their gassensing performances. The results demonstrate that the gas sensor based onSnO2-Fe2O3possess excellent gas sensing properties to toluene and formaldehyde at260°C and220°C, respectively. At260°C, the response of the gas sensor to50ppmtoluene is25.3. the average response/recovery times to1ppm toluene are5/11s. Thelowest detecting limit of it to toluene is50ppb (the response is2.0). At220°C, theresponse of the gas sensor to50ppm formaldehyde is25.4. The lowest detecting limitof it to formaldehyde is1ppm (the response is3.2). The gas sensor based onIn2O3-Fe2O3possess excellent gas sensing properties to acetone and formaldehyde at 240°C and260°C, respectively. At240°C, the responses of the gas sensor to100ppmacetone is25, which is3.7times larger than that to100ppm ethanol. The averageresponse/recovery times to100ppm ethanol and100ppm acetone are2/4s and3/6s,respectively. The lowest detecting limit of it to acetone is1ppm (the response is3.5).At260°C, the response of the gas sensor to50ppm formaldehyde is9.8, which is6.5times larger than that of the pure α-Fe2O3nanotubes. The lowest detecting limit of itto formaldehyde is1ppm (the response is1.8). The response/recovery times to1,5,10,20,50and100ppm formaldehyde are2/3,3/3,4/5,4/5,4/7s, respectively.