Preparation Of In₂O₃-based Nanocomposites And Study On CO Sensitivity And Mechanism

Carbon monoxide（CO）is a colorless,odorless but toxic flammable gas produced by burning fossil fuels,car emissions and household fuels.Excessive inhalation can cause a range of symptoms such as headaches,palpitations and unconsciousness.Therefore,it is necessary to develop a real-time and efficient CO gas sensor.Among many metal oxide semiconductor materials,In₂O₃has been paid much attention due to its low resistivity and high catalytic activity.Therefore,in this paper,by using noble metal decoration and constructing a heterojunction method on the three-dimensional hollow spherical morphology,the gas-sensing properties of CO is improved.In addition,in order to make the CO gas sensor more practical,it is also crucial to improve the humidity resistance of the sensor.Finally,we discuss its gas-sensing mechanism in detail.1.CeO₂/In₂O₃composites with n-n heterojunction structure were prepared.CeO₂has good dispersion on In₂O₃hollow nanospheres,and the increase of specific surface area provides more active sites for oxygen adsorption.The gas sensitivity test results of CO show that the response recovery time of the 2 mol%CeO₂modified In₂O₃（CeIn-2）sensor is shortened,and the detection of CO can be completed under different concentrations.R²=0.96942 indicates that the CeIn-2 sensor has the potential to detect CO at the ppm level.Although it also responds to CO under high humidity,the sensitivity of the sensor is not as good as that under lower humidity conditions because the adsorption of water molecules on the surface of the material prevents the contact between the target gas and the sensor.2.Incorporation of noble metal Pd is an effective method to improve gas sensors.In the composite sample,the morphology still maintains the hollow spherical structure,which allows the target gas to have enough diffusion channels.The 2 mol%Pd modified In₂O₃（PdIn-2）composite response value at a concentration of 500 ppm CO is more than four times higher than that of pure phase In₂O₃,and the dynamic response curve shows that the PdIn-2 sensor has good repeatability,not only that at different humidity it still has the ability to detect CO even under humidity.The improvement of gas sensing properties is mainly attributed to the catalytic effect of Pd and the electron spillover effect.3.In order to prepare a sensor with both high-efficiency detection of target gas and short response recovery time,the combined effect of noble metals and heterojunctions is therefore investigated.The doping amount and order of Pd and CeO₂are optimally selected according to the performance of the first two parts,both of which are 2 wt%.It can be observed from the gas sensing performance test results that not only the response amplitude is significantly improved,but also the response time is slightly reduced.Among many gases,2 mol%Pd and 2 mol%CeO₂modified In₂O₃（PdCeIn-2）exhibited good selectivity for CO,and excellent repeatability and long-term stability.The PdCeIn-2 sensor can still realize the dynamic detection of CO at higher humidity,which is more meaningful for practical applications.