Design Of Tin-based Compounds And Their NO₂ Gas Sensing Properties At Room Temperature

With the development of modern information technology,low-powerconsumption,highly sensitive and wearable gas sensors are future development direction.At present,the research on the NO2 sensitivity of tin-based compounds at room temperature is still in the exploratory stage,and their operating temperature and response/recovery speed cannot meet the requirements of the development of modern gas sensor.For instance,tin-based oxides currently have problems such as high operating temperature and poor selectivity.Although tinbased sulfides,as a new type of two-dimensional layer material,have shown potential as room-temperature gas sensing materials,there are still problems of low response and long recovery time.Therefore,it is of great academic value and practical significance to realize excellent gas sensing performance at room temperature via structural modulation of a certain material system.In this thesis,tin-based compound gas-sensitive materials are taken as the research object,and their sensitivity to NO2 at room temperature is improved by means of structural regulation such as doping and heterostructure construction,and the mechanism of enhanced gas sensing is revealed by first-principles calculations.Finally,the adsorption behavior of NO2 on a new tin-based compound(SnGe2N4)was studied through first-principles calculations.(1)SnS nanosheets were prepared by a one-step hydrothermal method,and the sensitivity of SnS nanosheets to NO2 at different operating temperatures was studied.The results show that SnS nanosheets exhibit high gas sensing response(17.6),good selectivity,and fast response/recovery speed(16/35 s)to 50 ppm NO2 at 150℃.It shows that SnS has a potential application value for NO2 detection at low operating temperatures.To reduce the working temperature of SnS nanosheets,SnS/SnS2 heterojunction nanosheets were prepared by hydrothermal method,and their sensitivity to NO2 at room temperature was systematically tested.The results show that SnS/SnS2 nanosheets exhibit NO2 sensing performance at room temperature,and also have a low detection limit(50 ppb).Therefore,it can be determined that the construction of heterojunctions can significantly reduce the operating temperature of SnS-based gas sensors.(2)SnS2 nanoflowers were prepared by hydrothermal method,and SnS/Sn2S3 heterojunctions were prepared by annealing SnS2 nanoflowers in an inert atmosphere(Ar).The phase composition,morphology,and gas sensing properties of SnS/Sn2S3 heterojunctions were studied.The results show that the conductivity of SnS2 nanoflowers is realized after annealing in Ar,and the sensing performance of NO2 is shown at room temperature.The SnS/Sn2S3 heterojunction exhibits excellent NO2 sensitivity to 50 ppm NO2 at room temperature,including a high response(7.9),fast response/recovery rate(20/26 s),and excellent selectivity.The improved gas sensing performance of the SnS/Sn2S3 sensor is attributed to the synergistic effect of p-n heterojunction.(3)Sn6O4(OH)4 precursor was synthesized by hydrothermal method,and SnO/SnO2 heterojunction sensitive material was prepared by annealing at 400℃in air.The structure,morphology,and NO2 sensitivity at room temperature were studied.The results show that the SnO/SnO2 heterojunction exhibits fast response/recovery speed(53/34 s)and high response(38)to 50 ppm NO2 at room temperature.The formation of SnO/SnO2 heterojunction not only reduces the operating temperature of SnO2(145℃)but also improves the long response/recovery time of SnO(317/479 s)at room temperature.The excellent NO2 sensing performance of SnO/SnO2 heterojunction at room temperature is attributed to its layered structure,large specific surface area,and the formation of the space charge layer at the heterojunction interface.(4)S-doped SnO2 nanostructures were prepared by annealing the SnS nanosheet precursor in the air at different temperatures.The results show that SSnO2 annealed at 400℃ in air exhibits high sensitivity to NO2(63.7)at room temperature,and also has fast response/recovery characteristics(22/16 s).In addition,the adsorption behavior of NO2 on SnO2 and S-SnO2 surfaces was studied by first-principles calculations.By comparing the adsorption energy,the most stable adsorption configuration of NO2 on the surface of the sensitive material was determined,and the electronic structure of the most stable configuration was calculated.The calculation results show that S doping can increase the adsorption energy and charge transfer amount of NO2 molecules on the SnO2 surface.(5)To find potential room temperature NO2 sensitive materials,the adsorption behavior of several common gas molecules on a new layered tin-based compound(SnGe2N4)was studied by first-principles calculations.The adsorption energy,electronic structure,and work function of SnGe2N4 for H2,CO,CO2,H2O,NO2,H2S,NH3,and CH4 adsorption systems were systematically analyzed.The results show that the adsorption of NO2 on SnGe2N4 is better than other common gases.In addition,the electronic structure of monolayer SnGe2N4 adsorbed by different concentrations of NO2 molecules was analyzed.The results show that with the increase of NO2 concentration,the interaction between NO2 gas molecules and the SnGe2N4 surface is enhanced.This work confirms the potential application value of SnGe2N4 monolayer as a room-temperature NO2 sensing material.