| At present,in many fields such as daily life,medical care and industrial production,it is necessary to monitor the type and concentration of some gases in the environment.For example,the concentration of air pollution gases such as sulfur dioxide in the atmosphere is monitored,and the special gases exhaled by human body are detected to diagnose diseases.And many kinds of gas sensors can realize the function of detecting gas.Compared with some sensors with complex operation and poor stability or expensive price,metal oxide semiconductor(MOS)based sensors are widely used due to their advantages such as good gas responsiveness,strong stability,long service life,low cost and portability.The sensitive material of the sensor determines the sensing performance of the gas sensor,so it is of great significance to study the influence of the preparation of the sensitive material and the modification and optimization of the sensitive material on the sensor performance,which is also the current research hotspot of the semiconductor sensor.Due to the low detection limit of metal oxide semiconductor materials,long or unrecoverable response time,poor repeatability,lack of selectivity,and high operating temperature,it is very limited in practical applications.In order to solve these problems and promote the use of semiconductor sensor performance,to solve more demanding higher gas sensor detection,need to optimize the semiconductor material itself and modification Therefore,in this paper,onedimensional oxide nanostructures with high specific surface area are used to improve the sensor performance and reduce the power consumption of the sensor.Zinc oxide,which is non-toxic and easy to obtain,is used as the research object.Electrospinning method is used to prepare one-dimensional nanofibers and noble metal modification is used to improve their sensing performance.The modification of the sensor is mainly through the regulation of the active site on the surface of the metal oxide semiconductor material,internal carrier concentration and the physical and chemical processes in the sensing process.The influence mechanism of the modified means on the sensing performance was also explored.The research work of this paper mainly includes the following parts:(1)Increasing the specific surface area of the base zinc oxide nanofibers,create defects in the material to increase the active site Zinc oxide nanorods with short length and smooth surface were prepared by hydrothermal method and zinc oxide nanowires with coarse surface were prepared by electrospinning method.In addition,gas sensitivity tests were performed on purchased commercial nanofibers and plasma treated nanofibers(prepared by electrospinning)for comparison.Gas sensitive test results show that all of the zinc oxide materials at around 275℃ test conditions for gas such as nitrogen dioxide has some response,but a higher response to ethanol.Compared with commercial and hydrothermal prepared smooth nanowires,spinning preparation of nanometer fiber because of its high specific surface area and has a better sensing response.In addition,the sensing performance of nanofibers prepared by electrospinning method will be further improved after plasma treatment of the material surface.By analyzing the gas sensitive responses of different Zn O nanofibers,it is found that for the same material,the enhancement of gas sensitive properties is strongly correlated with the specific surface area of the material and the defect of the material surface.(2)Decorating noble metal(i)In this experiment,gold nanoparticles were modified on the surface of Zn O nanofibers prepared by electrospinning using the method of photo-assisted immersion in water solution,and the nanofibers were annealed twice.The particle size of the modified gold particles was controlled by annealing temperature.Gas sensitivity test results show that the sensing performance of all Zn O nanofibers modified by gold particles has been greatly improved,and the optimal working temperature of all sensors has been reduced to different degrees.However,the sensor has different performance of modification when the gold content is the same and the gold particle size is different.When the gold particle size is small,the temperature modification of the sensor is more obvious and the response is faster.The best operating temperature of the sensor is reduced to 125℃ by the sample Zn O-Au 300,and the maximum response value is far better than that of the pure zinc oxide sensor.However,the sensing performance of the material with large gold particle size was not improved at low temperature.But the sensing performance improved rapidly after the test temperature increased to 175℃,and the response of Zn O-Au 600 to 50 ppm ethanol reached 151.8 at 200℃.(ii)In addition to exploring the influence of the particle size of gold particles used for modification on the gas sensitive performance of sensing materials,the experiment of this work also analyzed the influence of the same particle size of gold particles in different numbers on the sensing performance of zinc oxide materials.In the experiment,gold nanoparticles were modified on the surface of Zn O nanofibers by the method of photoassisted aqueous solution deposition.The difference lies in that different concentrations of gold ions in the solution were controlled,and secondary annealing treatment was not carried out in order to unify the particle size of the boundary Au particles.The results of sensor gas sensitivity test show that the modification of Au particles with small particle size can greatly reduce the working temperature of the sensor to 125 ℃,and it also has excellent sensing performance at a lower working temperature(50℃).However,the number of gold particles affects the sensor response and corresponding time,and a small amount or too much gold nanoparticles are not conducive to improving the performance of the sensor.The study on gold nanoparticles modified zinc oxide nanofibers shows that the modification of gold nanoparticles can effectively improve the gas sensitive properties of zinc oxide nanofibers,which is mainly due to the formation of schottky junction between materials,the catalytic effect of gold nanoparticles on the surface of metal oxide semiconductor and the electron spillover effect. |
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