Preparation And Gas Sensing Properties Of Semiconductor Materials Based On Tin Oxide

Metal-oxide semiconductor gas sensors can change the resistance of the material through the redox reaction between the semiconductor material and the detected gas,thus realizing the applications in environmental monitoring,security alerts,disease diagnosis,and other fields.It provides an effective way to solve the air pollution issue and the detection of Volatile Organic Compounds(VOCs).However,there are still some disadvantages in metal-oxide semiconductor gas sensors.For example,due to the poor specific surface area and porosity of the pure sensor material,the stability of the sensor prepared and the inappropriate selectivity for the detected gas make the actual detection of pollutant gas more difficult.Secondly,the traditional metal oxide gas sensing materials have a short service life and there is higher working temperature requirement for it,which lead to the limitation of practical applications.Therefore,designing and developing a novel gas sensor with high sensitivity,high stability,good gas selectivity and lower operating temperature is a key problem to be solved in the field of semiconductor gas sensing.Tin dioxide(Sn O₂)as a rutile structure is a n-type metal-oxide semiconductor material with a stable physical and chemical properties,non-toxicity and simple preparation.It has been widely used in data storage,photoelectric detection,gas sensing detection and other fields.In this paper,the pure Sn O₂nanoflower was prepared by hydrothermal method,the morphology and gas sensing performance of three-dimensional(3D)Sn O₂nanoflower were regulated by adding different types of surfactants.On the basis of this work,the effects of double template method and the decoration of noble metal platinum(Pt)nanoparticles on the gas sensing performance of Sn O₂nanoflowers were studied.In addition,one-dimensional hollow Sn O₂nanofibers were prepared by combining electrospinning technology with hard template technology,and the effects of the functionalization of small-sized Pt nanoparticles on fiber structure,gas sensing performance and working temperature were investigated.The main contents are as follows:(1)The pure Sn O₂nanoflowers were prepared by hydrothermal method using tin chloride dihydrate(Sn Cl₂·2H₂O),trisodium citrate dihydrate(Na₃C₆H₅O₇·2H₂O)and sodium hydroxide(Na OH)as raw materials,and the microstructure of 3D Sn O₂nanoflowers was further regulated via using surfactant as soft template.The morphology,microstructure and porosity of samples were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscopy(TEM)and Brunauer-Emmett-Teller(BET).The gas sensing performance of as-prepared sensors were evaluated by H₂S as target detection gas,and the effect of surfactants on gas sensing performance of Sn O₂was preliminary studied.The results showed that the synthesized Sn O₂samples had a rutile structure,and no other paeks can be identified due to impurities.The morphology was 3D hierarchical Sn O₂nanoflowers with an average diameter of 2?4?m.Besides,the addition of surfactant plays an important role in the formation of nano flowers.As a cationic surfactant,the addition of PEI is conducive to the nucleation of Sn O₂nanocrystals as well as the orderly growth of Sn O₂nanosheets to form a relative larger specific surface area;As amphiphilic non-ionic surfactants,the addition of PVP and Triton X-100 can make the nanosheets grow more uniformly and separately.In comparison with Triton X-100,the Sn O₂nanomaterial fabricated with the help of PVP exhibits excellent gas sensing performance for H₂S due to its relatively higher porosity,including high response,fast response/recovery time and better selectivity.(2)A series of Pt-decorated Sn O₂nanoflowers were synthesized based on double template technique using small-sized Pt nanoparticles as decoration elements.The results show that the Sn O₂nanoflowers prepared by the double template technique exhibit larger specific surface area and higher porosity.In addition,the surface activity of Sn O₂nanoflowers is improved due to the decoration of Pt nanoparticles.When the content of Pt is 0.3wt.%,the sensor shows the best gas sensing performance.Even at room temperature,the sensor exhibits high sensitivity(Ra/Rg=64,1 ppm),low detection limit(100 ppb),short response/recovery time(50s/100s),good repeatability and stability to H₂S gas,which can be attributed to the functionalization of Pt nanoparticles.Pt nanoparticles become a new electronic capture center due to the decoration of Pt nanoparticles on the surface of the materials,which can accelerate the electron transfer and improve the gas sensing performance of sensors.At the same time,the small size effect of Pt nanoparticles can also facilitate the sensing performance of Sn O₂sensors.The average particle size of Pt nanoparticles(3 nm)is smaller than the thickness of the depletion layer of Sn O₂(2L_d=6nm).Therefore,the depletion layer can control the process of electron transit,leading to the prominent gas-sensing behavior.However,when the decoration amount of Pt nanoparticles is beyond its optimal content,the aggregation of Pt nanoparticles on the surface of Sn O₂nanoflowers is not conducive to the improvement of gas sensing performance.(3)A series of Pt-functionalized hollow Sn O₂nanofibers were prepared via a combination of electrospinning technology and subsequent high temperature heat treatment technology with polymer PVP as template,and the gas ensing performance of Pt-decorated hollow Sn O₂nanofibers were investigated using H₂S gas as tested gas.The results show that the one-dimensional hollow Sn O₂nanofibers are composed of many nanoparticles with small crystal size,exhibiting large surface area and pore diameter.Furthermore,the decoration of Pt nanoparticles is favorable for improvement of the surface activity of hollow Sn O₂nanofibers.When the content of Pt is 0.04%,Pt-decorated hollow Sn O₂nanofibers shows the best gas sensing performance to H₂S gas,and its response value to 5ppm H₂S gas is increased by one order of magnitude(?345)compared with the pure hollow Sn O₂nanofibers.In conclusion,a series of nanomaterials based on Sn O₂with different morphologies were synthesized by single template technique,double template technique as well as electrospinning technique,and the gas sensing properties of prepared nanomaterials were systematically studied.It has been found that the introduction of Pt nanoparticles can effectively improve the sensing response of Sn O₂sensor to H₂S gas,and greatly lower its operating temperature,realizing the effective detection of H₂S gas at room temperature.This thesis provides a novel idea for the preparation and application of metal-oxide gas sensors.