Construction Of Gas Sensor Based On One Dimensional Porous Indium Oxide And Their Properties Research

With the constant progress of life and production style,people pay more attention to the health threats caused by various toxic and harmful gases.Effective detection of toxic and harmful or volatile organic gases is very important for people’s production and life.Gas sensor,as a device for detecting gas composition or concentration,has been widely used in various scenarios.For metal oxide semiconductor（MOS）gas sensitive materials,due to its advantages of high sensitivity,low power consumption and fast response recovery,many researchers have been attracted to conduct in-depth and comprehensive exploration on the modification and application of the materials.As the most potential gas sensitive material in gas sensor equipment,it is necessary to further improve its gas sensitive performance.In this paper,In₂O₃ is taken as the research object,and a variety of material characterization instruments was used for in-depth comprehensive testing of the prepared materials,such as using differential thermogravimetric/differential thermal simultaneous thermal analyzer（TGA/DSC）to analyze calcined and decomposition process of material.The crystal structure and chemical composition of the material were examined by X-ray scanner（XRD）,energy spectrum（EDS）and X-ray photoelectron spectroscopy（XPS）.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to obtain the microstructure of the material.Finally,one-dimensional indium oxide nanomaterials with different morphologies and structures were successfully prepared by simple electrostatic spinning method,and gas sensors based on them were constructed.The results show that the improvement of the gas-sensitive properties of the materials is mainly explored from two aspects of material morphology regulation and heteroatom doping.The constructed sensor has excellent gas sensitivity performance.The specific research content is as follows:（1）Pure and Ho-doped In₂O₃ porous nanotubes with a diameter of about 100 nm were prepared by electrostatic spinning and calcination.The study found that the calcination temperature has a great influence on the material surface morphology.The formation mechanism hollow and porous structures can be reasonably explained by the Kirkendall effect and the change of grain size.The results of gas sensitivity test show that the sensor based on In₂O₃ porous nanotubes has a higher response value to 100ppm ethanol gas than the pure In₂O₃ nanotube sensor（from 17 to 20）.The response value of Ho-doped In₂O₃ porous nanotubes sensor shows the highest response value to ethanol,short response/recovery time（4 s/28 s）and good selectivity.The minimum detection limit was 200 ppb and the response value was 2.Combined with the characterization results of the samples,the excellent ethanol sensing performance of the 6 mol%Ho-doped In₂O₃ porous nanotubes was mainly due to the obvious increase in the number of oxygen vacancies and the porous structure of the nanotubes.In conclusion,the 6 mol%Ho-doped In₂O₃ porous nanotubes are gas-sensitive materials of great practical value.（2）In order to improve the stability of the material morphology and the extensiveness of the preparation conditions,liquid paraffin is directly introduced into the precursor as the morphology control agent for the first time in this part,and the beaded nanotubes were prepared by simple electrostatic spinning method.The phase separation between polar and non-polar liquids is the main reason for the peculiar morphology.Moreover,the liquid paraffin can be uniformly and continuously distributed in the fiber in the form of spherical droplets.This remarkable result shows that the liquid paraffin can occupy the inner space of the fiber and form the core-shell structure automatically even without the use of coaxial electrostatic spinning.The results of gas sensitivity study show that the structure of bead nanotubes has obvious influence on the gas sensitivity of materials.Compared with In₂O₃ nanofiber,the response value of In₂O₃ beaded nanotube sensor is significantly increased（from 227 to320）.Finally,the gas sensitivity mechanism of In₂O₃ sensor to H₂S is discussed.The In₂O₃ sensor has good selectivity,but has a slow recovery rate at room temperature,which is due to its special sensing mechanism（vulcanization and desulfurization reaction）.This gas sensor is a preferred choice for detecting H₂S.（3）This section further adjusts the calcination conditions to obtain the new material morphology.First of all,the calcined heating rate is increased from the original5℃/min to 10℃/min,finally a large number of holes was formed on the surface of beaded nanotubes.These holes can improve gas diffusion and increase the contact area.In the gas sensitivity test part,this part selects different device structures from the previous two parts.Previously,ceramic tubular devices were used,but this time,ceramic plate-type micro sensors with lower power consumption were used.In addition,Tb element was introduced into the crystal of In₂O₃.The gas sensitivity of the sensor to formaldehyde gas showed that proper amount of Tb element could significantly improve the gas sensitivity of the material to formaldehyde gas.Among all the doping concentrations,the 6 mol%Tb-doped In₂O₃ beaded porous nanotubes shows the highest response value,low operating temperature（160℃）,low LOD（100 ppb）,fast reaction/recovery time,good selectivity,and good long-term stability.Specifically,its response value to 50 ppm formaldehyde gas was 75,and the response and recovery time were 2 s and 10 s,respectively.The significant improvement of gas sensing performance is mainly due to the special beaded porous nanotubes structure and the doping of Tb,which lead to many defects in the material,such as the oxygen vacancy and crystal stress.This study will provide a simple new method and new structure for the study of porous structure,and provide a sensing material with excellent gas sensitivity performance for the detection of formaldehyde gas in actual production and life.