Preparation And Gas Sensing Properties Of Nano Composite SnO₂/CuO

In the past few decades,monobasic metal oxide semiconductors such as ZnO,Fe₂O₃ and SnO₂ have been widely studied as gas sensing materials.However,due to their inherent characteristics,they still have many disadvantages,such as poor gas selectivity,high optimal operating temperature,and can not effectively detect the low concentration gas.With the advent of the new era and the rapid development of new technology,people's demand for high-performance and high-quality materials is more and more urgent.Composite materials come into being at the right time.Through the synergistic effect between various components,it has excellent comprehensive properties that can't be compared with a single component,and has become one of the most active fields in nano materials science.In order to expand the research field of gas sensing materials,in this paper,nano composite SnO₂/CuO was used as the main material,and different morphologies of composite SnO₂/CuO samples were prepared by hydrothermal method and electrospinning method,respectively.The phase composition,microstructure and gas sensing properties were analyzed and discussed,and it was found that the gas selectivity was significantly improved.The detailed work of this paper is as follows.1.Nano composite SnO₂/CuO particles were prepared by hydrothermal method.Different composite samples were prepared by controlling the molar ratio of tin to copper and hydrothermal solvent.XRD,SEM,TEM and gas sensing test system were used to characterize and test the structure,morphology and gas sensing properties of the samples.The results show that the products prepared by hydrothermal method are two-phase composite materials composed of tetragonal tin oxide and monoclinic copper oxide.The morphology and structure are nanospheres self-assembled by nanoparticles,with nucleation the trend of shell structure.It is found that the sample prepared with deionized water as the hydrothermal solvent and Sn:Cu=1:1 has the best gas sensing performance.The results show that the response value of the sensor to 300 ppm ethanol reaches 12.6 at 320?,and it has good selectivity for ethanol.The results show that there is a good linear relationship between the response value and ethanol concentration in the range of 50?300 ppm,its response and recovery time are 13 s and 15 s respectively,the optimum working temperature is 320?,the saturated concentration of ethanol gas is 300 ppm,it has good stability.2.SnO₂/CuO nanotubes were prepared by electrospinning.A series of composite samples were prepared by controlling the molar ratio of tin to copper.The experimental results show that the prepared composite nanotubes are two-phase composite materials composed of tetragonal tin oxide and monoclinic copper oxide.The diameter of the nanotubes is larger,with an average of 650 nm.The inner and outer walls of the nanotubes are rough,and there are needle like spines.The results show that the composite SnO₂/CuO nanotubes have good selectivity for ethanol,and the response to ethanol at the same concentration and temperature is four times that of other gases.The saturated concentrations of ethanol are 250 ppm and 300 ppm,respectively,the optimal working temperature is 340?.When the concentration range is 25?300 ppm,the response value has a good linear relationship with the concentration of ethanol.It is found that the sample with Sn:Cu=1:1 has the best gas sensing performance,and its response value in the same concentration of ethanol gas is greater than other samples.The response value of the gas sensor with Sn:Cu=1:1 to 250 ppm ethanol at 340?is8.8,and its response and recovery time are 25 s and 40 s respectively.It has good stability and can be used in the preparation and development of gas sensors.3.Comparing the two preparation methods of materials,it is found that the samples prepared by hydrothermal method have greater sensitivity,because the samples prepared by hydrothermal method have smaller particle size and microporous structure,so they have greater surface activity.However,the gas selectivity of samples prepared by hydrothermal method is poor,which can be explained by the uneven distribution of nano SnO₂ and CuO.In this paper,the gas sensing mechanism of the material is explained by using the theory of electron depletion layer of semiconductor and the change of barrier height of grain boundary,which is the basis of our follow-up work.