Preparation Of SnO₂-based Nanocomposites And Research On NO₂ Gas Sensing Properties

In recent years,with the rapid economic development,NO₂ and other gases emitted by automobiles and chemical plants have increased day by day.This has led to serious environmental pollution,and the harm to humans is becoming more and more serious.For example,when the concentration of NO₂ in the air reaches 53 ppb,it will have an impact on human health.Therefore,it is very necessary to develop a NO₂ gas sensor with low detection limit and fast response time at room temperature（RT）,which is also a key problem that needs to be solved in the current field of gas sensing.Metal oxide semiconductor gas sensors are widely used due to their high surface-to-volume ratio,fast response to high temperature,high sensitivity,and low price.However,they also have problems such as high working temperature,high energy consumption,and poor conductivity,which need to be modified.Therefore,this paper chooses SnO₂ as the basic material for detecting NO₂ gas.SnO₂ is used to compound with Co₃O₄ and Al₂O₃ respectively,or vertically controllable to construct a two-dimensional thin-layer MoS₂ gas-sensitive composite with high activity.Among them,the vertically grown active MoS₂ nanosheets and the porous semiconductor SnO₂ nanocrystals produce a synergistic effect,enhance the interaction of the compounded semiconductors,and build a high-speed electron transfer channel between the layered structure and the semiconductor.The assembled gas sensor can solve the problems of high detection limit and slow response speed of the current RT sensor.Simultaneously,SEM,TEM,XRD,BET and other characterization test methods were used to study the morphology,composition and structure of the prepared composite material.In addition,the mechanism of gas sensitivity is also studied in depth.Firstly,this paper uses Sn Cl₂·2H₂O as the raw material to synthesize one-dimensional SnO₂ nanotubes（NTs）by a simple electrospinning method,and prepare the SnO₂-Co Al-LDH composite material by hydrothermal method,and then the Co₃O₄-Al₂O₃/SnO₂（CASNTs）heterojunction nanocomposite was synthesized by high temperature calcination.The prepared Co₃O₄-Al₂O₃/SnO₂ has a high specific surface area and provides a large number of active sites,which is beneficial to the diffusion,adsorption and desorption of the target gas on its surface and inside.In CASNTs composite materials,thanks to the synergistic advantages of p-n（Co₃O₄-SnO₂）heterojunctions and n-n（SnO₂-SnO₂）homojunctions and the electron transport capacity is increased.As a result,the optimized CASNTs-2 assembled sensor an impressive sensitivity and selectivity for NO₂ gas detection at RT with the ultra-high response of 131.7 to 100 ppm,response time of 2.3s and the detection limit as low as 5 ppb.This synthesis method provides potential application prospects for detecting NO₂ gas in low concentration areas.Secondly,p-n heterojunction consisting of MoS₂ nanosheet vertically grown on one-dimensional（1D）SnO₂ NTs was fabricated via electrospinning and subsequent hydrothermal route.The sulfur edge active sites are fully exposed in the MoS₂@SnO₂ heterostructure due to the MoS₂ vertically oriented thin-layered morphology features.Moreover,the interface of p-n heterojunction provides an electronic transfer channel from SnO₂ to MoS₂,which enables MoS₂ act as the generous electron donor involved in NO₂gas senor detection.As a result,the optimized MoS₂@SnO₂-2 heterostructure composite material presents an impressive sensitivity and selectivity for NO₂ gas detection at RT.The response value is 34.67（R_a/R_g）to 100 ppm,which is 26.5 times to that of pure SnO₂.It also exhibits a fast response and recovery time（2.2 s,10.54 s）,as well as a low detection limit（10 ppb）and as long as 20 weeks of stability.This simple controllable preparation method of high-performance sensing materials will help mass production of RT NO₂ gas sensors.