| Although gas sensors based on metal-oxide semiconductors (MOS) such as have been attracting heated interest due to their low cost, ease of use, and compact size, some MOS sensors usually show certain drawbacks such as low sensitivity, bad selectivity or stability. So the researchers regard improving these drawbacks as the object of gas sensors.As a simple, effective, low-cost and powerful approach to prepare1D nanostructure anomaterials, electrospinning was used to synthetize mesoporous InO3nanofibers.InO3nanofibers were characterized with differential thermal analysis (TG/DTA), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Then the gas-sensing properties of In2O3nanofibers doped with CdO or Cd in different methods were tested in a static state gas-sensing test system. The effect of the variety and concentration of the dopant were on he gas-sensing properties of In2O3was disscussed in further. Finally, the gas-sensing properties and sensitive mechanism of the composite In2O3/TiO2sensors were analyzed at two working conditions:heating and UV-LED irradiation, respectively.1. The In(NO3)3/PVP nanofibers precursors were synthesized by electrospinning and then were annealed at500℃,600℃,700℃to form In2O3nanofibers, respectively. XRD and SEM characterization showed that the as-prepared In2O3nanofibers annealed at500℃have the smallest average grain sizes (-28nm) and well mesoporous structure. The test showed that the sensor based on In2O3annealed at500℃has the highest response (-7) to10ppm formaldehyde (HCHO). Then CdO nanoparticles were prepared in the same method. The gas sensing properties of the sensors based on InO3mixed with CdO in molar ratio of1/0,1/1,10/1and20/1were investigated at each optimum temperature. The result showed that In2O3/CdO composite with molar ratio of10/1possessed excellent sensing properties:the response to10ppm HCHO is13.6and the response/recovery time is140s/32s when operating at lower temperature of200℃. In addition, the formaldehyde sensing mechanism of the sensors based on InO3/CdO composite was briefly analyzed. 2. Cd-loaded In2O3nanofibers with different Cd/In molar ratios (1/20,1/10,1/1) were synthesized by electrospinning and then annealed at500℃. The XRD, SEM and TEM characterizations showed that the average diameters and grain sizes of Cd-loaded In2O3were52nm,76nm,88nm and19nm,24nm,42nm, respectively. The formaldehyde sensing properties of the sensors based on pure In2O3, and Cd-loaded In2O3nanofibers with different Cd/In molar ratios were investigated at each optimum temperature. The result showed that Cd-loaded In2O3nanofibers with Cd/In molar ratio of1/10(In10Cd1) possessed the highest response and well selectivity at280℃. In addition, the formaldehyde sensing mechanism of the sensors based on Cd-loaded nanofibers was briefly analyzed.3. TiO2nanofibers were synthesized by electrospinning and then were characterized with XRD, FE-SEM, and TEM. The average grain sizes of TiO2were approximately32nm. As-prepared In2O3and TiO2nanofibers were mixed in1:1molar ratio to fabricate HCHO gas sensor. The gas-sensing properties of the composite In2O3/TiO2sensors were analyzed at two working conditions:heating and UV-LED irradiation, respectively. When working at the heating temperature of280℃, the HCHO gas sensor has excellent sensitivity to low concentration of formaldehyde (1-10ppm):the response to1ppm HCHO is6and the response/recovery time is60s/80s. When working under UV-LED irradiation, the response to100ppm HCHO is4.8and the response/recovery time is170s/320s, and the response of the sensor has a well linear relation with the variation of higher concentration formaldehyde (10～1000ppm). In addition, the sensor exhibited good selectivity to HCHO vapor at the two working conditions and the sensitivity of the sensors changed little with the variation of humidity under UV-LED irradiation. |
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