| One dimensional (1D) nano-materials have driven much attention in catalyst and electronics due to their large specific surface area, large aspect ratio and electronic-transport confinement effect. 1D semiconductor nano-materials overcome the nanoparticles aggregation phenomenon and have important effect on enhancing response, shortening response and recovery time and improving selectivity of gas sensors. To date, researches are focused on binary and ternary-component solid solutions semiconductor materials, and the study on aligned nanofibers are still in the preparation of organic materials stage. The study on multi-compound-system and aligned sensitive nanofibers and their gas sensing properties is significative direction in 1 D sensitive meterials.This paper introduces the fabrication, characterization, gas sensing properties and sensing mechanism ofα-Fe2O3 nanobelts, ternary-component solid solution LaFeO3 nanobelts and nanofibers, quaternary-component solid solution LaxSr1-xFeO3 nanofibers and aligned In2O3 nanofibers, and lists some meaningful results.α-Fe2O3 nanobelts were fabricated by an electrospinning method followed by a calcination in air at 600℃process, the SEM photographs showed that the surface of belts are rough, the width and thickness of the belts are about 200 to 400 nm and 25 to 30 nm, respectively. Gas sensors based onα-Fe2O3 nanobelts have a response of 4.9, a response time less than 10 s and recovery time less than 24 s to 500 ppm ethanol at 285℃.LaFeO3 nanobelts and nanofibers were also fabricated by an electrospinning method followed by a calcination in air at 600℃process, the SEM photographs showed that the surface of belts are smooth and the width of the belts range from 200 to 300 nm; the diameters of LaFeO3 nanofibers are uniform in the range of 80 to 90 nm. LaFeO3 nanoparticles with diameters of around 30nm were prepared by a chemistry co-precipitation method. Contrastive experiment of gas sensing properties of these three morphologies LaFeO3 materials showed that LaFeO3 nanobelts and nanofibers have lower resistance compare with LaFeO3 nanoparticles and show lower optimum operating temperatures (170℃and 200℃, respectively). Under each optimum operating temperature, the response of LaFeO3 nanofibers material was 47 to 500 ppm ethanol, while that of LaFeO3 nanobelts material was only 8.6. When the operating temperature is 200℃and the concentration of ethanol is 200 ppm, the response and recovery time of LaFeO3 nanofibers were 11 s and 19 s, respectively, which were faster compared with LaFeO3 nanoparticles and nanobelts. The reason why LaFeO3 nanofibers showed higher response and faster response/recovery properties compared with LaFeO3 nanoparticles and nanobelts is closely allied to the geometric morphologies of the nanofibers. The high specific surface area property of nanofibers result in the rapid speed and large amounts of adsorption of gas molecules and this follows the enhancing of the response; the overlap of the surface space-charge layer along the fiber direction leads to the formation of a continuous electron transport tunnel, and this result in the improving of response/recovery property.Quaternary-component solid solution LaxSr1-xFeO3 (x=0.6,0.7,0.8) nanofibers were successfully prepared for the first time, the diameters of the gained nanofibers are uniform and in the range of 50 to 80 nm. When x takes different values,0.6,0.7 and 0.8, the contrastive experiment of gas sensing properties of LaxSr1-xFeO3 nanofibers showed that La0.7Sr0.3Fe03 nanofibers have higher response than the other ratios. At 185℃, to 500 ppm ethanol, the response of La0.7Sr0.3FeO3 nanofibers was 40.4, and the response and recovery time were 11 s and 10 s, respectively. Compared with commercial available product MQ-3 ethanol gas sensor, La0.7Sr0.3FeO3 nanofibers based sensors showed highest response at 170℃, while MQ-3 ethanol gas sensor showed highest response at 315℃, at the same time, La0.7Sr0.3FeO3 nanofibers based sensors completed a response and recovery period in 250 s, while MQ-3 ethanol gas sensor could not recover when break away ethanol. The above results show that the new one dimensional materials have low operating temperature, high response and fast response/recovery and are promising materials in gas sensor.Two conductive parallel-positioned magnets (8 cm×5 cmxl.5 cm) were used as collector in electro spinning process. During electro spinning, the electrostatic repulsion force and magnetic field which the charged jet experienced strech the fibers across the gap to form aligned arrays. The calcinated aligned In2O3 nanofibers had smooth surface, uniform diameter of 80 to 90 nm. The experiments results showed that at 275℃, the response and recovery time of aligned In2O3 nanofibers to 1 ppm NO2 are 0.6 s and 4 s, respectively, and at 245℃, the response and recovery time of aligned In2O3 nanofibers to 1 ppm Cl2 are both 0.7 s. While, the response and recovery time of randomly deposited In2O3 nanofibers to NO2 are 1.3 s and 13.1 s, respectively, and that to Cl2 are 1 s and 7 s, respectively. These results show that the aligned nanofibers have shorter response and recovery time. To aligned nanofibers, when oxygen molecules adsorption takes place, there are surface space-charge layers fonned at the surface of the nanofibers, these surface charge spaces overlap along the fibers, sometimes, even form flat band, in this continuous electron transport tunnel, due to the relatively lower potential barriers, the electron scattering probability decreases during transport process, and result in the fast response/recovery property of aligned nanofibers. Hollow ZnSnO3 microspheres were prepared by hydrothermal method, the diameter of the hollow ZnSnO3 microspheres was in the range of 400 nm to 600 nm. To 500 ppm butane, the reponse of the hollow ZnSnO3 microspheres materials was 5.79 at 380℃, and the response and recovery time were 0.3 s,0.65 s, respectively. The response and response/recovery properties of the gained hollow ZnSnO3 microspheres materials are sufficient better than that of solid ZnSnO3 microspheres materials, this can be explained as the surface of hollow ZnSnO3 microspheres are relatively loosen, and this is conducive to adsorption and desorption of gas molecules, so the hollow ZnSnO3 microspheres materials showed better response and response/recovery properties.In conclusion, in this paper, the experiments results showed the outstanding gas sensing properties of nanofibers, multi-component solid solutions with sensitive characteristics were successfully prepared for the first time, and applied aligned nanofibers to gas sensor, and demonstrated that aligned nanofibers can improve the response/recovery property.
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