Fabrication Of Xylene Gas Sensor Based On Metal Oxide And Research On Its Gas-sensing Properties

The development of society has brought abundant materials for people,but none is perfect,and most of the materials have pros and cons.For example,as an important industrial chemical and organic solvent,xylene can be used in the production of dyes,paints,inks and resins.However,its toxicity also makes it become a kind of typical volatile organic compounds pollution,and at the same time,its flammability also determines the risk in the production process.Therefore,both in daily life and industrial production,the real time monitoring of xylene is related to people's health and life safety.There are many methods and tools for monitoring xylene,but in contrast,the semiconductor gas sensor has attracted more and more attention because of its advantages of small size,portability,quick response and low cost.As the key part of semiconductor gas sensor,the gas-sensing properties of semiconductor material play a decisive role in the performance of the sensor.From the previous SnO₂ and ZnO,next WO₃,Fe₂O₃,In2O₃,Co₃O₄,NiO,etc,later then LaFeO₃,Zn Co₂O₄,and some sulfides,at present,numerous types of materials was studied and applied to gas field is complex,but as the mainstream of gas sensitive materials,metal oxide is still a popular choice of gas sensitive rules.In this paper,for the purpose of detecting xylene,the metal oxide semiconductors are used as the substrate material,through the means of doping and compounding,to prepare the gas sensor with excellent performance.Experimental ideas and research contents are as follows:1.A method for the preparation of mesoporous Co₃O₄ rod-like materials has been found.Mesoporous can improve the specific surface area of the material and change the surface state.Meanwhile,the rod-like structure can keep the material stable better.In terms of gas sensing properties,mesoporous Co₃O₄ rod-like materials showed response to toluene,ethanol,formaldehyde,etc.Although the response to xylene was the highest one,the poor selectivity of the single materials remained to be a shortcoming.At the same time,the slow response and recovery to xylene also showed that the structure needed to be further improved,and therefore,next experiment was carried out.2.Co₃O₄ microspheres with hierarchical structure were prepared by hydrothermal method,and different proportions of Cr-doping were also carried out,and their gas-sensing properties to volatile organic compounds were studied,especially to xylene.Compared with pure Co₃O₄,Cr-doped Co₃O₄ materials showed similar responses to formaldehyde,ethanol,etc,but higher response to xylene,and the response reached to the highest one when the proportion of Cr-doping was 5 at%?the response was 6.38 in the atmosphere of 5 ppm xylene,increased nearly 4 times when compared with pure Co₃O₄?.The increase of response also made the selectivity of material better,and reduced the signal-to-noise ratio from the other gas in the detection process,and the response and recovery process completed fast,all in 30 seconds.However,for the effect of Cr-doping to the improvement of xylene-sensing properties,according to the theory of surface controlled resistance,it was considered that the doping near the surface maybe function better.Therefore,material was designed to be a appropriate heterojunction structure should exhibit better gas-sensing performance,so the third experiment was conducted.3.It was designed and prepared that with WO₃ as matrix material,on the surface of which Cr₂O₃ particles were developed to form gas –sensing material with heterojunction structure.The two-step water bath method was adopted.Flower-like WO₃ particles with hierarchical structure were synthesized,whose petals had a long width to provide attachment points for Cr₂O₃ growing on,and a thin thickness to benefit the effect of heterojunction structure.Compared the gas sensor based on Cr₂O₃@WO₃ with that on WO₃,heterojunction structure improved the response to xylene of material obviously,and the response and recovery speed were still fast,the processes of which completed in 5 s and 20 s,respectively.