| In various fields such as environmental monitoring,human health,food safety,and fire warning,gas sensors play a vital role in ensuring the safety of life and production.In the past ten years,social progress and development have improved higher requirements for gas sensors.Developing novel gas-sensing materials are considered to be one of the keys to fabricating high-performance gas sensors.With the development of nanotechnology,a strong driving force has been injected into the progress of novel semiconductor sensing materials.Nevertheless,the development of the gas-sensing area faces two major challenges that need to be broken through:1)Meet the higher requirements for sensor sensors:extremely high sensitivity,ultra-low detection of limit,excellent target gas selectivity,etc.;2)Explore and develop the gas-sensing mechanism based on the adsorption and desorption of gas on the surface of the material.In this dissertation,we summarized related literature in detail,adopted metal element doping and noble metal modification strategy,employed hydrothermal method and template method,and developed typical n-type metal oxide semiconductors,tin dioxide and zinc oxide,and a p-type metal oxide semiconductor,tricobalt tetroxide for the detection of ethanol,ammonia,nitrogen dioxide,and acetone gas.This paper mainly includes the following main contents:(1)A series of Ni-doped SnO2 hollow spheres were synthesized in one step by a template-free hydrothermal method.Gas-sensing results show that Ni-doped SnO2 sensors are most sensitive to ethanol gas.At the optimum working temperature,the response of the best sensor(NS-0.5)to 100 ppm ethanol is twice as that of the pure SnO2-based sensor.The response value of the sensor is linearly related to the concentration of ethanol gas.During the 30-day measurement period,the sensor's response to 100 ppm ethanol remained almost unchanged.In addition,the NS-0.5 sensor also shows excellent anti-interference ability against several common interfering gases.Material defects caused by Ni doping is the main reason for the improvement of its ethanol gas sensitivity,and the subsequent decrease in the specific surface area of the material has a significant negative impact on its ethanol sensitivity.(2)To avoid the negative impact of morphology changes on the gas-sensing performance during the material synthesis process and to control the consistency of the material morphology to further study the gas-sensing mechanism,Pt/ZnO composite ordered porous monolayer films were synthesized by polystyrene sphere monolayer colloidal crystal template method.NH3-sensing properties of the thin films were systematically examined.Results showed that pristine ZnO exhibited poor response and an unusual p-type like behavior to the reducing NH3 gas,while Pt-loaded ZnO was highly responsive to NH3 with typical n-type behavior.Pt loading led to significantly enhanced NH3 sensing performance,achieving 200-times larger response value,shorter response time,a high sensitivity of 10.5 ppm-1,and excellent selectivity under optimum conditions.The mechanism was discussed in terms of the porous microstructure and promoting effect of Pt nanoparticles.(3)To achieve uniform and non-agglomerated indium doping and avoid the complicated preparation process of hard templates,we adopted a one-pot encapsulation strategy for synthesizing indium-doped ZnO porous hollow cages.During calcination,metal ion species,composed of In(acac)3@ZIF-8,were oxidized,leading to the formation of In-doped ZnO porous hollow cages.In this case,ZIF-8 served as the host backbone for the uniform distribution of the indium source as well as the production of porous hollow structure.In doping led to significantly enhanced NO2-sensing performance,achieving a response of 3.7 to 10 ppb NO2 and a high sensitivity of 187.9 ppm-1.The mechanism was discussed in the terms of the intrinsic excellent gas accessibility of porous hollow structure and electronic sensitization by In doping.Moreover,our facile and effective synthetic strategy could be further extended to other doped ZnO materials.(4)ZIF-67 was used as a sacrificial template to synthesize pure and Au-loaded Co3O4 porous hollow nanocages.Through detailed material characterizations,not only the role of ZIF-67 as a sacrificial template but also the effects of the reactions between NaBH4 and KAuCl4 on the morphology change were clearly illustrated.Acetonesensing performance of the prepared pure Co3O4 and Au/Co3O4 composites was systematically examined.For the optimal sensor(Au/Co3O4-4),a large response of 14.5 to 100 ppm of acetone at the optimum working temperature of 190? were achieved.A sensor array composed of the pure Co3O4 and Au/Co3O4-4 sensor was assembled,in conjunction with principal component analysis(PCA)method,to distinguish acetone from other interfering gases including ethanol.Combining material characterizations with sensing performance,possible mechanisms were thoroughly discussed in gas accessibility of nanocages and catalytic promotion of Au nanoparticles. |
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