Construction Of Micro-nanostructure Of Indium Oxide-based Composite Materials And Study Of Their Gas Sensing Propertie

Metal oxide semiconductor gas sensors are widely used in commercial fields due to their low cost and excellent gas sensing performance.However,the high working temperature,and poor selectivity and stability,limit their application in environmental monitoring of the Internet of things.Therefore,fabricating a highly efficient gas sensor with low power consumption,integrated and intelligent is of great important for monitoring various toxic,flammable and explosive gases,which can inject new vitality into the field of environmental monitoring in the era of Internet of Things.It is well known that the sensing performance mainly depend on the sensing materials.Therefore,the design and synthesis of sensing materials with unique architecture or interface would greatly improve the gas sensing performance of sensors.In this thesis,In₂O₃ was selected as sensing material and the effect of structures,morphologies and composition on the sensing performance was systematically investigated.The main research contents are as follows:（1）The CuO/In₂O₃ flower-like structures assembled by nanosheets were prepared by a simple one-step hydrothermal method,and their formaldehyde sensing performance were systematically investigated.The results showed that modifying CuO nanoparticles In₂O₃surface could significantly improve the formaldehyde sensing performance.Especially,when the molar ratio of Cu to In was 7%,the sensor exhibited the best sensing performance for detecting formaldehyde.The corresponding response value was 11.7 towards 10 ppm formaldehyde at a low working temperature of 100°C.Besides,it also exhibited good reproducibility and stability,sub-ppm-level detection limit（1.4-0.5 ppm）,high selectivity,and outstanding long-term stability.The enhancement sensing performance could be attribute:1)the unique CuO/In₂O₃ flower-like structures assembled by thin and porous nanosheets provide high special surface areas,large number of oxygen vacancies and strong oxygen adsorption capacity;2)the catalytic effect of CuO and the formation of CuO/In₂O₃p-n heterojunctions.（2）Ni O/In₂O₃ flower-like structures with different Ni/In molar ratios were prepared by a simple one-step hydrothermal method,and their trimethylamine（TMA）gas sensing performance were systematically investigated.The results demonstrated that decorating Ni O can effectively enhance the sensing performance of In₂O₃ gas sensor.Especially,the sensor fabricated from 0.05-Ni O/In₂O₃ composites with well-defined flower-like structures showed the highest response to TMA,giving a response of 20.5 to 10 ppm TMA at 200°C,which was 4.7 times higher than that of the pure In₂O₃ flower-like structures.Besides,this sensor showed good reproducibility and stability,and high selectivity to TMA.Moreover,this sensor also had ppb-level detection limit（0.5 ppm,1.5）.The likely reasons for improved sensing performance are attributed to:1)the formation of Ni O/In₂O₃ p-n heterojunctions at the interface;2)the catalytic activity of Ni O.（3）In₂O₃/In₂S₃ hydrangea-like structures were prepared by a simple hydrothermal method followed by calcination process,and their TMA sensing performance were systematically investigated.The constructed optimal In₂O₃/In₂S₃ structures exhibited superior TMA sensing performance.Specifically,the 0.5-In₂O₃/In₂S₃ hydrangea-like structures obtained at the calcination time of 0.5 hour processed highest response value（5.5）to 10 ppm TMA at 100°C,which was about 4.2 times higher than that of pure In₂S₃hydrangea-like structures.Besides,this sensor also exhibited good reproducibility,sub-ppm-level detection limit（1.3 to 0.1 ppm）,high selectivity and good long-term stability.The enhancement of sensing performance could be attributed to:1)the unique In₂O₃/In₂S₃hydrangea-like structures with high specific surface area and large number of active sites;2)the unique n-n heterojunctions at the interface of In₂S₃ and In₂O₃.