Synthesis And Gas Sensing Properties Of Tin Oxide Nanocomposite Structure

Recently,since the industrial leakage of the toxic,hazardous,flammable and explosive gas,it has contributed to a series of peril incidents like poisoning,explosion and fire hazard.These issues will be a serious threat to health and life safety,so the presence of these gases in the effective monitoring and timely treatment is particularly important.The use of gas sensors for quantitative and qualitative analysis of these dangerous gases can effectively prevent the occurrence of such incidents.So,research and development of gas sensor has become one of the most important subjects.Tin oxide?referred to as SnO₂?as the most widely used gas-sensitive materials has the advantage of heat resistance,corrosion resistance,lower material costs.But it also has many weak points because of its high work temperature and poor dispersion between particles.High temperature not only increase the energy consumption and decrease the stability.Also it will become a dangerous source of explosion if used in higher concentrations of explosive gases.Low dispersion of SnO₂ particles will be greatly reduced adsorption capacity of the gas which affects the sensitivity of the reaction.Thus,low-temperature semiconductor oxide sensor,especially the development of the room temperature sensor is of great significance.Gas-sensitive reaction is a gas-solid chemical reaction occurs on the surface of SnO₂ interface.So the morphology,structure and surface modification have a significant impact on gas sensing performance at low temperature.Via constructing SnO₂ thin film composite structure,reducing the size of SnO₂ nanostructures and the metal modification have great significance to improve the performance of the thin film gas sensor.In this thesis,we combine sol-gel with green-synthesis approach to get PMMA-SnO₂ composite films and porous SnO₂ nanospheres and then after annealing to obtain a low operating temperature of CH4 gas sensor.To further enhance the gas sensing performance under low temperature conditions,the porous SnO₂ nanospheres were decorated by Au nanoparticle and its gas sensing performance of CH4 and H2 were studied under low temperature.The following results were obtained:1.We use chloroform or acetone to dissolve PMMA as adhesion agent and the n-butylamine was used to modify SnO₂ nanoparticles to prevent agglomeration.PMMA-SnO₂ gas sensing thin film was get through spin-coating and different dissolvent of PIVMA were compared.It shows that use of chloroform-acetone mixture as PMMA-SnO₂ solvents increase the conductivity and sensitivity Ra/Rg significantly compared with pure chloroform as solvents.It is worth mentioning that,at the working temperature about 80 C Ra/Rg increased from ? 1.8 to ? 3.8,when the content of CH4 is about 770 ppm.What's more,the process is simple and suitable for large-area preparation and commercial applications.2.We develop a green synthesis approach to get porous SnO₂ nanospheres by the oxidation-reduction between D-glucose monohydrate and sodium stannate trihydrate.Use small-sized SnO₂ nanocrystals to improve the sensitivity of SnO₂ thin films and reduce the operating temperature of the device to improve its gas sensing properties.The results show that when the mass ratio of Na2SnO3·3H₂O and C6Hi2O6·H₂O is 1:2 the reaction product is porous SnO₂ nanospheres with diameter of 60nm.The nanospheres consist of SnO₂ nanocrystals with its diameter about 2nm.This structure exhibits good conductivity compared with other mass ratio but its gas sensing properties at low temperature is still not ideal.3.To improve SnO₂ nanoparticles gas-sensitive properties at low temperatures we use Au nanoparticles to modify porous SnO₂ nanospheres.Au nanoparticles is about 15 nm in diameter obtained through reducing chlorine acid by sodium citrate.After intensive mixing with SnO₂ nanoparticles the thin film was annealing at 550 C about 60 min under the atmosphere of argon to obtain Au nanoparticles modified porous SnO₂ nanoparticles.TEM results show that,it forms a good contact between the Au nanoparticles SnO₂ nanoparticles after annealing.During the reaction,measured gas regulates Schottky barrier between Au and SnO₂ to enhance the gas-sensitive properties under low temperature.In conclusion,Au modified SnO₂ nanospheres demonstrate a good gas-sensing response of H2 at a low temperature.