Modification And Gas Sensing Characteristics Of SnO₂ Nanomaterial

With the acceleration of my country's industria lization and urba nization,especially the rapid deve lopme nt of heavy chemical industry and transportation,the wanton disc harge of factory exhaust and automobile exhaust has caused serious air pollution and threatened our hea lth.Therefore,it is necessary to detect these toxic and harmful gases in time to reduce the harm of these gases to human health and the pollution to the environment.Gas sensors stand out among a variety of gas detection technologies.Among them,meta l oxide semiconductor gas sensors have become a hot research for scientists due to their ease of production and low cost.Tin dioxide(SnO₂)is an n-type semiconductor with a direct band gap of 3.2 e V.It not only has good chemical and therma l stability,but a lso has excelle nt electrica l,catalytic and sensing properties.In the fie ld of semiconductor gas sensor research,SnO₂ is one of the most widely used sensing materia ls,but a single SnO₂material has defects such as poor selectivity and high detection limit,so its application is limited.In order to improve the gas-sensing performance of SnO₂ sensors,the SnO₂ materia l is modified by metal ion doping and heterojunction construction.The specific research contents are as follows:SnO₂ materia l with flower-like structure was synthesized by hydrotherma l method.SnO₂ was modifie d by controlling the amount of Pd doping,and the morphology and structure were characterized.SEM results show that the prepared materia l has a flower-like structure with a size of about 4 microns.Based on the gas sensitivity test results of each sample,we found that the 5 mol%Pd-doped SnO₂sample has a higher response to NO₂ and H₂S at different te mperatures.Among them,the response to 10 ppm NO₂ gas is 380 at 80°C and the detection limit is 20 ppb.The response to 10 ppm H₂S gas at 180°C is 151,whic h is 50 times than that of the pure SnO₂.The detection limit is 500 ppb.At the same time,the device shows good repeatability in the test process.Therefore,the sensitive materia l of SnO₂ doped with Pd can detect H₂S and NO₂ by a djusting the temperature.The reduction of carrier concentration caused by Pd doping and the catalytic effect of Pd are the reasons for the improvement of sensor performance.The Sn O/SnO₂ composite materia l was successfully synthesized by solvotherma l method and controlled sintering temperature,and the materia l was subjected to a variety of characterization and sensing performance tests.The prepared materials include S1(unsintered),S2(300°C),S3(500°C)and S4(700°C).XRD results show that both S1 and S2 conta in two phases of Sn O and SnO₂.The TEM image shows that the interface of Sn O and SnO₂has a good lattice match,which confirms the existence of Sn O/SnO₂ heterojunction.While S3 and S4 are pure phases of SnO₂,indicating that Sn O is complete ly oxidized to SnO₂when the sintering temperature is higher than500°C.Among the four sensitive materia ls,when the sintering temperature is 300°C,the sensor has the best parameters.The sensor of this sample has a response of 33 to triethyla mine at 225°C,the detection limit is 500 ppb,and the response time is 2s.At the same time,the device is recoverable.The improvement of the triethyla mine sensing properties of Sn O/SnO₂ composites can be attributed to the following two main reasons:(1)Abundant active sites a llow more gases to partic ipate in the reaction;(2)P-N heterojunction for carriers In addition,the chemica l bonds related to the sensing reaction in the target gas molecules are easy to break and easily react with chemically adsorbed oxygen on the surface of the materia l.These factors improve the gas sensitivity of the device to triethylamine gas.